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ZX750 carb problem


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aaronmillar
User

Apr 25, 2014, 5:46 PM

Post #1 of 29 (2951 views)
  post locked   ZX750 carb problem  

I have a 1987 ZX750. I bought it and it wasn't going. I took the carbs off to clean them and now I am trying to get it running. It starts when I have full choke on. When I take the choke off or even just take it off the full position it stalls. When I give it a little throttle it stalls. Do u have any idea why it is doing that? Is it too rich or lean? Do I need to adjust fuel mixture? I set the mixture screw to what it was before I took it apart - 1 3/4 turn from bottom. Thanks


nickwarner
Veteran / Moderator
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Apr 25, 2014, 9:48 PM

Post #2 of 29 (2936 views)
  post locked   Re: ZX750 carb problem  

You have clogged main jets and are running lean. Full choke richens the mix and thats why you can't run without it.

You not only need to get those jets soaking in some good carb cleaner (the stuff with the basket you dip it in and leave for a while) but may need you to run a tip cleaner through it. An alternative is to get new jets in the factory size and install them.

If you have kept this bike stock, that should work. You will still need to synch your carbs and will need the right tool to do it. If you have an altered intake or exhaust you are into custom tuning and may be better off sending this to a cycle shop used to doing this kind of work.


aaronmillar
User

Apr 25, 2014, 10:50 PM

Post #3 of 29 (2933 views)
  post locked   Re: ZX750 carb problem  

Hi nick. Thanks for ur post but I totally cleaned the jets when I took carbs apart so I doubt that is the problem. Every part got cleaned thoroughly with carb cleaner anf q-tips where possible. Any other ideas?


nickwarner
Veteran / Moderator
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Apr 26, 2014, 7:08 PM

Post #4 of 29 (2911 views)
  post locked   Re: ZX750 carb problem  

Qtips? That isn't going to get inside of a jet. Sometimes you can get some crap in a jet that just soaking in carbcleaner will not get out. That's where torch tip cleaners or a tip drill set come in real handy. You also want to look closely for vacuum leaks.


aaronmillar
User

Apr 26, 2014, 7:38 PM

Post #5 of 29 (2907 views)
  post locked   Re: ZX750 carb problem  

I also used pins to clean jet holes. Held them up to the light to make sure there was no blockages. I replaced the fuel hoses as well as the fuel filter... but... the fuel line from the tap to the fuel rail is a bit longer than the one I replaced so it is a bit bent and part of the hose is higher than the tap which means that some of the fuel has to go up hill a bit and the filter is not completely full. Would that make a difference?


nickwarner
Veteran / Moderator
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Apr 26, 2014, 8:45 PM

Post #6 of 29 (2903 views)
  post locked   Re: ZX750 carb problem  

Your fuel should be gravity feed, so that might make some difference. Are your idle mixture screws set correctly? All the way in then 1 1/4 turns out is a good starting point if memory serves correctly. Have you synched the carbs or at least put a synch gauge on them to see how much vacuum each cylinder is pulling?


aaronmillar
User

Apr 26, 2014, 10:01 PM

Post #7 of 29 (2897 views)
  post locked   Re: ZX750 carb problem  

The tap is vacuum opened from one of the carbs which seems to be working fine. It doesn't have an on/off switch but has a primer button which also works fine . Idle mixtures were set at 1 3/4 turns from bottom when I took then out and put them back the same way. To adjust them while carbs are kn seems impossible with a standard screw driver as there isn't enough room I haven't tested vacuum but two mechanics saw carbs when they were out and pushed the plunger diaphrams and commented on the good suction on them


Tom Greenleaf
Ultimate Carjunky / Moderator
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Apr 27, 2014, 1:41 AM

Post #8 of 29 (2891 views)
  post locked   Re: ZX750 carb problem  

#1 - Not a bike tech at all. Just that I noticed that you see a fuel filter not full on a gravity feed set up. Alone could be normal but maybe the trouble is the flow from the gas tank?


Can you remove a hose and watch it flow, thru filter into a container and is it a fair amount? It's just a note but have a mean machine for a lawn mower* (1987 also) and have to blow air backwards thru line to clear it as obviously there's some debris in tank that I've just been too lazy to take off and wash out. It has a non motor bike fuel shut of that quit also so put one in line so I can run it dry of fuel which works great. Yours should be more of the turn to on and a reserve, right? I've owned my share of bikes, almost all brand new and rid of them before warranty expired on most. Not the point but not much goes wrong right away with things but likes to be properly stored for off seasons like the mower as well.


* By that I mean this mower is commercial duty wildly expensive thing that would now sell for about $7,000 bucks so no ordinary thing and needs lots of routine this and that maintenance to keep it running perfectly. Use now of ethanol has been trouble for any machines that old mostly on anything to do with fuel stuff.


They sell a product and IDK if it really works that is stated to defeat the harmful effects of fuel with ethanol and so far so good with that. No problems with anything used all the time it's more of problem with seasonal stuff.......


T



nickwarner
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Apr 28, 2014, 9:42 PM

Post #9 of 29 (2864 views)
  post locked   Re: ZX750 carb problem  

 You are going to need vacuum readings. After teardown of carbs they need to be synched. The screws aren't the easiest to reach. They make a special tool just for getting at them because of it, and they use a test tank to feed fuel while the gas tank is off to give you access. Summit Racing has them in the Pit Posse brand name.

I wonder about vacuum especially with the type of fuel petcocks you use. They are the same as my Yamaha in design. No off position, just run, reserve and prime. Vacuum line from the engine opens the valve so if it isn't running you can unhook the fuel line in the run position and nothing will come out. Works good but only if you have a strong enough vacuum to open it. If the vac line is leaking or there is low engine vacuum, closing the choke would increase it somewhat which might account for this.

Before you tore down the carbs, was this bike running right? Have you done the timing chain tension adjustment and valve adjustments? Have you tested the coils for spark strength? Have you checked the strainer/filter in the fuel petcock assembly to see if it has any crap on it?


aaronmillar
User

Apr 28, 2014, 10:42 PM

Post #10 of 29 (2860 views)
  post locked   Re: ZX750 carb problem  

When I got the bike it wasn't going but the guy I bought it off said he had it running but I am doubting that now.
One other issue is that the ducts between the air filter box and the carbs were so perished that I had to use a bicycle tyre inner tube and cable ties to connect them. In theory this should work well enough to get the engine started just to make sure the engine works before I buy new ducts and clamps (at about $60 each).. Problem is that there may be leak on one of them (one of the centre ones which was harder to reach and caused some problems getting it on). But I thought it shouldn't matter if air is sneaking in a little here as it is still before the carbs.
On another note I dont remember actually checking to see if there is a hole in the end of the main jet. I assume there is to let the fuel into theair bleed pipe/needle jet jolder. I remember I couldn't get one of them apart as it was siezed up a bit.
So I am going to take the carbs out and dismantle them again and check the jets out which people in previos posts have mentioned could be the problem. I really didn't understand how a carb works when I first cleaned them. Since then I have read a bit more and understand them a bit more. While in do that I will order the ducts.

Thanks everyone so far for the advice. I will keep u posted as to how I get on.


nickwarner
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Apr 30, 2014, 7:39 AM

Post #11 of 29 (2844 views)
  post locked   Re: ZX750 carb problem  

https://www.youtube.com/watch?v=exa467_eoXw

Try watching this guy's vid series.

These engines need to have no vac leaks to work right. You've never heard it run so you are at square one. Clymer makes a pretty complete manual for bikes. I like the detail in the one I have for my Yamaha. You should have one on hand if you are working on your own bike.

Those boots need to be in good shape and properly sealed up. With vac leaks this will never run right. Bike engines seem even pickier than car engines on this one.

Seized parts are a challenge. Soak it in penetrating oil for a while and try holding it in a vise. Pad the jaws with cardboard and rags. Remember, this is an aluminum case so don't crank too hard on the vise or go caveman with a hammer. You'll wreck the carb if you do. Put your screwdriver in the jet, hold slight pressure to loosen and rap a little on the handle with a mallet. Can help get that out.

I've seen new intake boots for less than $60 apiece on e-bay. Might look around there for parts.

I would recommend you check engine compression and valve lash on this too. You've never heard it run and don't know for sure how it was maintained. The manual will have details on how to do that. You will need a compression tester for the c-test and a set of metric feeler gauges for the valve lash.Both available for reasonable prices at parts stores. When you go to synch it, there are a few industrious people on youtube who thought up a neat way to do it without blowing $300 on a synch tool. Check this one out.

https://www.youtube.com/watch?v=Qj3nUjW6Yck


aaronmillar
User

May 21, 2014, 6:10 AM

Post #12 of 29 (2802 views)
  post locked   Re: ZX750 carb problem  

hi Nick. Thanks for your comments. Here is where I am at now...
I took carbs out and checked the air bleed pipe and main jet for blockages (this was just double checking as i thorougly cleaned out each carb and all their internal parts previously). I also checked that all idle mixture screws were set at 1 3/4 turns from bottom (which is how they were set when I took carbs off bike but as you pointed out, I don't know if it was running properly before hand but I will assume it was set correctly).

I bought new air filter to carb ducts and springs.I re-installed the carbs with the new parts and am almost certain there are no leaks now around the boots (ducts). I fired it up and found that after all that work it is still only running on full choke. There were moments when I was able to use the throttle a little to get revs up but then it started to die until i released the throttle.

I haven't synced them as i don't have the tools for this but i am thinking that maybe i need to invest in them as per your advice as taking it to a mechanic will cost $100 an hour and I would rather spend less, end up with tools, experience and knowledge as this is my project and i would rather not pay someone else to work on it.

I have a manual which will be helpful doing this... but... my main first issue is to get it running better first as i don't think a sync problem would be causing it to run this way. i will look into getting the tool to adjust the idle mixture. any chance you could send me a link to one online? as well as a sync tool. i looked for Pit Posse on sumit racing but couldn't find anything.

I wondered if the problem could be with the air filter. I replaced the old filter foam with a thinner piece which I got from the local kawasaki dealer (not genuine - just a piece of thin foam cos i figured it was overpriced for what it is). i thought maybe it is too thin so i have put another layer of foam in there. i will give that a go tomorrow as well as putting back the old piece of foam to test my theory. i am doubtful but hopeful that this will fix it. the cover for the battery area and main vent in to the air filter box has a small gap where it joins up as the new battery is slightly higher than the old one and preventing it from sealing 100%. it is only a small gap and i wouldn't think this could be a problem...?? i also put the side guards on and seat to see if adjusting a few small things makes any difference. i am getting stuck for ideas of what is causing this engine to run so lean. it could be a very simple problem or a major problem. it could be something i could fix or it could be something i can't fix. i wouldn't know. i am not experienced enough to work this out so any advice would be greatly appreciated.
i hope you enjoyed my short essay here on my problems :)


nickwarner
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May 21, 2014, 8:43 PM

Post #13 of 29 (2789 views)
  post locked   Re: ZX750 carb problem  

I had a whole bunch typed up and just when I went to post it the computer spazzed out on me. Ugh. Here I go again.

Your air filter not being stock can and will make it run lean. Had an old Honda 400 years ago that got running bad because I changed the stock filter to a K&N. It was jetted for a certain amount of airflow at a certain level of vacuum. When you open up the air intake you drop the vacuum, so unless the carbs are re-jetted to compensate for it you run lean. Here is a link to a factory air cleaner.
http://www.bikebandit.com/houseofmotorcycles/1987-kawasaki-ninja-750r-zx750f/o/m150349#sch43588

You should also check your coil output just so we know we aren't chasing our own tails here. Just take off the spark plug wires one by one and have a 12v test light hooked up to battery ground. While the engine is cranking you should be able to get a nice blueish white spark to jump about 3/4 to one inch of air gap. If it can't, and the spark is more of a yellow-orange you have a weak coil or plug wire. If your wires are removable from the coil you can retest there to see which one it is.

Also check for vacuum leaks where the carbs mount to the intake of the engine. With the engine running, spray some carb cleaner a squirt at a time around intake areas. If you hear the engine suddenly change pitch or RPM you found a vacuum leak.

Here are your tool links. Showing 3 different ones for the synch tool. When you go to Summit's site look toward the top center for something that says power sports place. Thats where I found this.

idle mixture screw tool
http://www.powersportsplace.com/search/product-line/pit-posse-carburetor-adjusting-sets?autoview=SKU&keyword=ptmpp2590&sortby=BestKeywordMatch&sortorder=Ascending

this one was a bit cheaper
http://www.powersportsplace.com/search/product-line/pit-posse-pilot-screw-adjusting-tools?autoview=SKU&keyword=ptmpp2751&sortby=BestKeywordMatch&sortorder=Ascending

carb synch, basic model
http://www.powersportsplace.com/search/product-line/tecmate-carbmate-carburetor-calibration-tools?autoview=SKU&keyword=tmtts111&sortby=BestKeywordMatch&sortorder=Ascending

better model
http://www.powersportsplace.com/search/product-line/tecmate-synchromate-carburetor-calibration-tools?autoview=SKU&keyword=tmtts101&sortby=BestKeywordMatch&sortorder=Ascending

really cool model that costs a lot
http://www.powersportsplace.com/search/product-line/tecmate-vacuummate-me-carburetor-calibration-tools?autoview=SKU&keyword=tmtts71&sortby=BestKeywordMatch&sortorder=Ascending


nickwarner
Veteran / Moderator
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May 21, 2014, 8:52 PM

Post #14 of 29 (2786 views)
  post locked   Re: ZX750 carb problem  

Here are a few vids you should look over as well.

This one was pretty cool
http://www.youtube.com/watch?v=GaTRyHxvneY

this guy has a synch tool that basically is just 4 vacuum gauges tied to a board next to each other. you could make one yourself for less than a hundred bucks
http://www.youtube.com/watch?v=t0qf11BOx6o

this one I threw in just because its the same bike I have
http://www.youtube.com/watch?v=ijAM9skj0S4

a little explanation of idle air screws
http://www.youtube.com/watch?v=zm5mB3R8Ucw

Check that all out and see what you can come up with


aaronmillar
User

May 21, 2014, 9:17 PM

Post #15 of 29 (2782 views)
  post locked   Re: ZX750 carb problem  

So I started up my bike again today and managed to finally run it without the choke and could use the throttle so maybe it has something to do with the air filter after all? It still runs pretty rough and sometimes it revs very high by itself and then dies off again. There now is another issue I have found... it seems someone at some stage has done some patch work on the exhaust system and it is leaking smoke out of the patches. Not sure if that would contribute to it not running well. I think I also need to adjust the throttle cables as they dont seem to be set correctly. The idle screw also seems to be not working that great either. So I might buy a stock filter for it and work out a way to get the filter box to close properly by propping up the box a little so it clears the battery. I will do as u suggest and spray some carb cleaner around all the carb connections to check for vacuum leaks. Not sure what u mean about testing the coils. I have a multimeter. Could I use that to test them? I will post more once I get a chance to work on it again. At least I am making some progress.


nickwarner
Veteran / Moderator
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May 22, 2014, 8:28 PM

Post #16 of 29 (2774 views)
  post locked   Re: ZX750 carb problem  

So you have an exhaust with lower backpressure than stock and also an air filter that is just foam? That is for sure going to make it run lean as all hell.

I would think you battery interference is pretty much only going to be fixed by putting the correct sized battery in there. Bike batteries aren't that terribly high-priced for a decent one.

What I mean about testing the coils is to see how much of an open air gap your spark is able to jump. A test light won't light up when the spark hits it but will allow the spark a path to ground. You hold the end of a test light in front of the coil tower or plug wire and crank the engine. You want to see how far it will jump the air gap. I tried to find a youtube vid on it and didn't find one. If one of my friends that has a smartphone comes by this weekend I'll do a test and upload a video for you so you can see what I mean. No guarantees, my weekend is pretty busy.

You are indeed making progress. A little more progress and you will be riding this thing instead of tinkering on it and listening to everyone else ride their bikes past your house. I always hate that.


aaronmillar
User

Jun 2, 2014, 11:29 PM

Post #17 of 29 (2725 views)
  post locked   Re: ZX750 carb problem  

so i have installed the new filter and fired it up. it is still running lean. i have uploaded a video of it onto youtube. can you have a look and see what you think please? it stalls when i release the choke even just a little bit. as you can hear the idle speed increases and decreases by itself. i am not giving it any throttle. in fact, when i do give it any throttle it still dies. looks like i will have to buy a pilot jet screw driver tool and adjust that. i have carb cleaner in a can which i plan on using on my next day off to see if there is any leaks in the vaccuum. i am a little hesitant to use the stuff i have as it doesn't say what the ingredients are - just that it is flammable... anyway here is the link to the youtube vide...
https://www.youtube.com/watch?v=j3-iUR3kWRo

link working properly now...


(This post was edited by aaronmillar on Jun 4, 2014, 7:39 PM)


aaronmillar
User

Jun 4, 2014, 7:40 PM

Post #18 of 29 (2712 views)
  post locked   Re: ZX750 carb problem  

It seems like my bike has just been sitting in the shed for ages with no real progress but last night I wrote up what has been done so far and what needs to be done to get it safe and operational. I thought I would share it with you.

I managed to find a manual online in pdf format which I printed out. Only problem is that it is a manual for the 600 as well as 750cc bikes so has a lot of content not relevant for me. There is also slight variations on US vs UK models. With all my research online I still have not been able to find a bike like mine with the gold wheels, rocker cover, foot pegs etc. So I have not been able to work out exactly where this bike has come from. I am sure it is probably not from America as it does not have the Ninja markings on it which in the States it did. And it is definitely not from California as it does not have the extra fuel emission control parts on it that Californian bikes require. It doesn't really matter too much where it is from (as most of the specs are the same) but it is more a puzzle I wish to solve. Was the gold trimmings done after market? Or is it a special edition? As it was made in 1987 before the internet there is little information online about this bike.

So when I bought this bike it was not running but the guy who sold it to me swore he had got it running recently and taken it for a ride and checked all the electrics out. The more I worked on it, the more I came to realise he was probably full of it and I highly doubt that in its condition when I bought it that he managed to get it running or have a ride on it. You will see this from my following list of what I have done to it and what still needs doing.

First thing I needed to do before spending a lot of time and money on parts and repairs was to make sure that the engine runs and that there was no major issues with rings, pistons, crank, etc. So I inspected the engine and found that there was a bunch or mice/rat poo everywhere along with dust and dirt. So I started cleaning and polishing. The story I was told was that the bike has spent most of its life in peoples garages which accounts for why the speedo only has 9000km on the clock... which I am questioning... most of the plastic parts seem to have perished which would make sense if it has sat in hot sheds for years. But the engine doesn't leak oil and the oil appears to be pretty clean... so maybe...

When I inspected the carbs closer I found that there was some inner tube wrapped around each carb where it joins the air filter box. This was all perished so I removed the tube to see that the air filter ducts were warped and not connecting to the carbs properly. So I decided to take the carbs out and clean them as who knows how much gunk was inside them and I needed to inspect the air filter ducts a little more. I went into a few bike shops for advice on these ducts, asking, if I make the same home job connections for the ducts if my bike would run ok. I was advised that just to get the engine going it would be an ok temporary solution but not a good permanent one. So I went online to find these parts and found they would cost about $50 each plus $10 for the spring to hold them onto the carbs (not a clamp, but a spring). So I set about fabricating myself some temporary ducts fasteners similar to those that were on it before – using an inner tube and some cable ties.

I totally stripped the carbs down and cleaned the whole assembly inside and out until it was all shiny (well as shiny as it would get). I inspected all the internal parts and used carb cleaner, toothbrushes, toothpicks, needles and pins to ensure everything was clean and grim free. Everything seemed to look good with little wear – pilot jets, main jet needle, etc(which supports the theory it has done low kms). I then reinstalled the carbs and wrapped the ducts with my makeshift seals. This sounds easy but it is totally not easy and it took hours – there is bugger all room to move when jamming the carbs between the air box and engine intake manifolds. Which is why I don't want to take them out again to adjust the idle mixture (I will talk about this later). Then trying to attach the duct seals was a mission too.

Next things I did were...
Buy a new battery and fill with acid. Buy a battery charger (the recommendation is to have a trickle charger but I bought a fast charger from K-mart as it was less than a third the price of a trickle charger)
Fabricate a new air filter out of a piece of foam I got from Kawasaki (before spending $50 on a genuine part in case it did have major engine problems). Cost $10
continue cleaning and polishing bike – good therapy after the hard work of doing the carbs
Replace fuel lines and clamps as well as fuel filter
Add carb breather hoses as it had none. I had to buy some hosing that was slightly smaller than what I needed so had to soften them with boiling water then clamp them on. It also took a while to work out what all the hoses coming off the carbs, air filter box and fuel tank are for. The vacuum hose from the carbs to the fuel tap is on carb 1 but in the manual it was coming off carb 2 but I figure it doesn't matter.
Take apart and clean the fuel tap as it was leaking. Reassemble and test. Works fine now
Drain the fuel tank and add fresh fuel (check that the fuel gauge works)
Remove and inspect old spark plugs (may have been running lean). Install new plugs. This should have been simple but I needed to use a thin walled long tube socket to get inside the head to remove the plugs – went to about seven different stores. Noone had the size I needed so had to order one in.
Put a clamp around the engine breather hose that connects to the air filter box - this seems to not be sealed 100% as I think the box is slightly out of shape as it is made of plastic and as I have mentioned, most of the plastic is slightly perished or warped. The air filter box is not quite sealed on the top as the battery prevents it from sealing so I used some double sided tape to complete the seal (as it is on the air intake side of the filter this shouldn't matter too much.
Drain, flush, inspect and refill radiator with coolant
Buy a few bolts, screws, washers for things like the rear handle, windscreen and sourced some cool decals for it – two NINJA decals for the knee guards and one large decal for the windscreen which is Japanese Kanji symbol for Warrior.
Remove throttle assembly on handle bars as it was slipping – the pin that holds it onto the handlebars needed to be pushed out a little. Reassemble throttle.
Check electrics – Indicators not working properly – needed to replace relay. Number plate bulb needed replacing. Both front indicators needed to be replaced as they were broken and not repairable. Foot brake spring was a couple of cable ties so ordered a new spring and replaced that. Powered up the radiator fan and that works.
Inspected clutch and found it wasn't working (how did the guy ride it with no clutch?). The seal was blown in the slave cylinder and the piston seized. Took it to Kawasaki about a month ago. The mechanic got it apart and they ordered a new seal. Still waiting for the seal. Those guys are pretty useless. I could have ordered the part myself and got it quicker.

After all that work I managed to get the bike started but to my dismay it is not running right. It only runs on full choke and stalls if i give it any gas. From what I have researched on youtube and some advice from this forum it is running too lean. When I took pilot screw (mixture screw) out I took note of how many turns from the bottom it was – 1 & ¾ turns from bottom (didn't check specs but now I realise I should have as the specs call for 2 turns from bottom which explains why it is running lean – I will talk about this soon). It is also revving high and low on its own. Not sure why. Maybe a vaccuum leak or due to the exhaust, or the air filter not thick enough. So I ordered a new air filter as well as brand new air filter ducts with springs. Now I know the engine is ok I can spend some more money and time on proper parts. This meant taking the carbs out once again to be able to remove the air filter box and fit the new ducts. While I had the carbs out I checked the pilot jet and main jet for blockages which I knew it didn't have but wanted to be totally sure. Carbs went back into the bike and installed the ducts and springs – pretty sure they are seated properly but not 100% sure and not 100% sure that the carb to engine seals are sealed correctly. Need to get it running and spray some carb cleaner around the seals and see if the revs increase which would indicate a vacuum leak (but as the revs are going up and down by themselves anyway this will be hard to work out).

When the bike was running and getting up to a warm temp I checked to make sure that the radiator hoses were hot both side of the thermostat so that is working ok. Topped up the coolant a little. (took me ages to work out that the overflow reservoir doesn't attach to the bike but actually sits inside the ferrings. The fan came on temporarily so that seems to be working ok but won't know until I can actually take it for a ride. Not sure if the temp gauge is working 100% but will work that out later.

So... here is where I am at now...
Still waiting for clutch parts to be able to put that back together.
Need to adjust the fuel mixture which means either taking the carbs out again and adjusting and put back in and hope I got it right or buy a specialist tool – pilot jet screwdriver which has a long handle and a 110 degree bend on the end to get to the screws which are impossible to get to with any standard tool. I have only been able to find this tool online and the freight cost is more than the tool. Think I will try to get one from a local tool shop maybe. Need to investigate this more. I have found a place in the US who can ship me one and they also have carb sync tools which I will probably need to tune the carbs so I could buy both of these tools and save some postage costs. But I am hesitating as I am not sure I need to sync the carbs. Wouldn't hurt to have that tool though so I don't know why I am procrastinating getting these tools. I sort of hoped I could fix it without them or without having to pay someone else to do it. Mechanics charge $100/hr. But they have the right tools and experience to do the job. But I would have to hire a trailer as well to take it in and bring it back so I might as well spend the money on the tools and learn how to do this myself.

A few other things I need to buy/do is get a new tail light - it might pass inspection as most of the lense is intact but there is a large chip missing on the edge which was covered with a sticker when I got it (and I have put a new sticker over it). I also need to make sure the chain and sprockets are ok – on initial inspection they look ok but I don't really know for sure. I also need to make sure the brakes are ok as well as the suspension. It does have pretty new battleaxe tyres so that is good. Oh, I almost forgot... when I got the bike going I noticed smoke coming out of the exhaust under the bike. I got on the ground and noticed that where the two pipes join up underneath it is all rusted out and had a crap patch job done using thin sheet metal patches held on with clamps. I can't get a new exhaust system – none in stock anywhere but luckily it is only a section that needs replacing so I am hoping I can get that fabricated by an exhaust specialist. Another major job that could cost a bit. There is also a small leak in one of the tail pipes.... baffles look ok though but I am not sure.

I also need to adjust the throttle and throttle release cables as they are not set right yet. I am also going to test the coils and HT leads to make sure they are ok.

Once I get it all sorted out I need to go and take it for an inspection and get it legal with a new number plate. After that is done I will get some of the ferrings repaired (there are a few cracks) and then paint it. I have a lead on a surfboard and plastics welder who should be able to repair it for me.

So this afternoon I am going to go have a talk with a local bike mechanic and pick his brain and pop in to a tools shop to see if I can get the tools I need without having to import from the states. Wish me luck and I will keep you posted.


(This post was edited by aaronmillar on Jun 4, 2014, 7:45 PM)


nickwarner
Veteran / Moderator
nickwarner profile image

Jun 4, 2014, 8:57 PM

Post #19 of 29 (2707 views)
  post locked   Re: ZX750 carb problem  

Your video is set to private. Couldn't watch it. Didn't realize you weren't in the states, the shipping would get pricey from here to get to you.

Do all the vacuum hose nipples for each cylinder have a line coming from them or are some empty? If so, do you have vacuum caps on them so as not to leak vacuum?

After tearing carbs apart it is necessary to synch them. Won't run right without that.

Best of luck with this and let me know what you come up with. I don't know what wheels or decals were offered on these, but the internet has a lot of info about pretty much everything on it so you could probably find the answer if you took the time to search for a while.


aaronmillar
User

Jun 4, 2014, 9:37 PM

Post #20 of 29 (2703 views)
  post locked   Re: ZX750 carb problem  

I changed the settings on youtube. The other three carbs have caps on the vaccuum hose nipples. I am going to test for vacuum leaks next and insert some extra foam into the air inlet channels that go to the airbox. This should hopefully solve my issues. Here's hoping...


aaronmillar
User

Jun 5, 2014, 6:48 PM

Post #21 of 29 (2692 views)
  post locked   Re: ZX750 carb problem  

I sprayed some soapy water around the inlet manifold ducts and found a major vacuum leak. Took the tank off and loosened the clamps and pushed carbs further into the ducts to make a proper seal. Am now able to take choke off and use throttle. .. but I have to work the throttle up and down to find a sweet spot where it runs ok when its past 3000 rmps. If it drops below that rpm with no choke on it stalls. I have not had much luck adjusting the throttle idle level. When I turn the idle screw to the right I can lower the idle speed but turning it left doesn't turn it up. Weird. Anyway when I had the tank off I tested the coils. Specs say primary resistance should be 1.2 - 3.19 ohms. Mine measured 5.8 ohms. I tested secondary resistance but think I did that wrong. I disconnected the ht lead from the coil and measured to where the spark plug connects and number 1 cylinder had 4.07 (on 20k setting) and the number 4 cylinder ht lead had 3.86. Specs say should be 10-16k ohms. Could this explain poor performance at low rpm and stalling whe at low rpm?


nickwarner
Veteran / Moderator
nickwarner profile image

Jun 6, 2014, 10:46 AM

Post #22 of 29 (2686 views)
  post locked   Re: ZX750 carb problem  

Weak coils will explain a lot. This is a high performance engine with high compression. As the cylinder pressure increases, the amount of voltage to jump the same distance increases. So rev it up and you get even more pressure, right? Less time to bleed off pressure. So a coil that is marginal at idle is going to fall on its face at higher revs where the pressure increases.

Told you that you had vac leaks. You might have more that are smaller. A bunch of small ones add up to a big one. You can use carb cleaner, and yes it is flammable. That is why ti works. If a leak sucks it in, it burns and increases your engine pitch. Using it in small amounts is ok to find leaks, and used properly a great diagnostic tool. Used improperly in a vehicle with leaking secondary voltage could result in a loss of eyebrows (ask me how I know. I was in my teens then).

I think your coils are drawing too many amps without giving enough KV of spark. Its like a teasing prom date. All noise in the city, won't put out in the country.


aaronmillar
User

Jun 23, 2014, 10:04 PM

Post #23 of 29 (2572 views)
  post locked   Re: ZX750 carb problem  

so i did some tests on my coils and ht leads. here are my results. both primary resistance are around 6 ohms (i tested twice under different temperatures - got 6.3 when it was a cold day and 5.8 when it was a bit warmer). the manual says the ideal ohms should be 1.8 - 2.8 ohms. secondary resistance on a cold day was 21.1k for coil 1&4 and 22.4k for coil 2&3. the warmer day test was 20.7k and 22.3k. the manual says ideal ohms is 10-16k. so based on this data you would expect that the resistance is too high. the fact that each coil and both primary and secondary resistance are very similar shows that it is not just one thing that is defective - just that the whole system is a bit old and worn out.
the spark plug caps measured 4.37, 4.27, 4.97 and 4.20 (when set at 20k on the multi meter).
the ht leads measured 1.2, 1.5, 1.5, 1.7 (when the multimeter was set at 200)

so i did another test that my manual describes which is cutting a hole in a piece of wood and putting a couple of nails into the hole with a 7mm gap, attaching the spark plug wire to one nail and attaching an alligator clip to the wood and earthed to the bike. it shows a nice strong white spark which would indicate healthy coils. i have some pics of the spark but i haven't worked out how to upload them onto this site...
so i am a bit confused. i would ideally like to replace the coils and leads and caps but it is going to cost over $500 to get them and i only paid $700 for the bike.... so i have taken the tank off again and have made a makeshift fuel tank out of a coke bottle so i can get a good look at the engine and carbs to see if i can find any other leaks or problems... and then i will take it into a shop to do some troubleshooting once i have done all i can do...


aaronmillar
User

Jun 23, 2014, 10:20 PM

Post #24 of 29 (2569 views)
  post locked   Re: ZX750 carb problem  




aaronmillar
User

Jun 23, 2014, 10:21 PM

Post #25 of 29 (2566 views)
  post locked   Re: ZX750 carb problem  








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