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1970 GM 350 engine with ignition problems, I think??


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rsrandle
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Jun 28, 2012, 11:14 PM

Post #1 of 9 (2265 views)
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1970 GM 350 engine with ignition problems, I think?? Sign In

I have an old truck that has a 1970 350 engine in it. It has a 2GV Rochester carb. At first it ran good. Then it started to miss randomly. I put a timing light on the tower wire and watch it at idle. It will be on constant for a while then it will start to flicker then it goes out and the engine dies.

The timing is at 4B, the dwell is at 30. The battery is at 12+ when it is stopped and 14 when it is running.

What I have done so far:

Jumpered out the ignition switch
Jumpered out the ballast resister
Replaced the cap, rotor and wires
Replaced the coil
Replaced the points and condenser
Replaced the distributor

I think I’m going insane!!!!

Any ideas will be greatly appreciated!!!

(edit to target year and make of engine only in subject)


(This post was edited by Tom Greenleaf on Jul 9, 2012, 3:10 AM)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jun 29, 2012, 4:20 AM

Post #2 of 9 (2219 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

Specs seem right. Can't verify timing spec, but dwell is right.

What is with "jumpering out ballast resistor" as you stated? Yes it's been a while but the concept is to reduce voltage to save points + probably condenser but allow full battery voltage for cranking only time. That higher operating voltage will not work in 12V systems or for long if only minutes?

Probably not the issue but what "tower wire" are you using to time this? Best to use an inductive type that goes over #1 cyl. wire, vacuum advance usually required to be disconnected and plugged at distributor.

Back: Jumping the resistor may have ruined the condenser? If you did your own points did you check the alignment that they touch each other square on? If messed up.

Just a note to add: Timing spec for 1970 should work however the fuel ratings may require using premium or definitely not 87 octane rating currently called regular which in pre unleaded days was at least 89 octane. You can time these by knock point under load and guess by intake manifold actual vacuum too when fuel and engine don't match up to the OE specs,

T
_________________________________________
Long retired now


rsrandle
Novice

Jun 30, 2012, 3:51 AM

Post #3 of 9 (2190 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

I did replace the condenser. I had originally tried putting 12v directly to the + on the coil with no difference.

For timing I used cylinder #1. But for checking the spark going to all of the cylinders I put the timing light on the tower wire. The result was a very fast flickering light, it flashed each time a cylinder was supposed to have spark. So I could see if I had spark or not.

I even verified a good ground to the distributor just in case it was not making good enough contact.

Something I am looking at now is whether the carb is causing the symptoms by flooding the engine out and shorting out the plugs. Now that I've written this it sounds silly but I am at the point of trying anything.

I think when I gassed up earlier I put in the middle grade of fuel. I'll have to be more aware of what rating I use in the future. I forgot how critical it is to use the correct octane on older engines.

Thanks for your reply, I appreciate it.

Rod


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jun 30, 2012, 5:21 AM

Post #4 of 9 (2182 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

Do you get spark at the plug wires and if so is it strong using a tester that can show the gap it can do? Get one if you don't - cheaper tool as things go.

Gasoline's octane isn't preventing it from just running but all proper will want the higher octane. IMO it might just knock under load too easily.

If (some can) flooded out enough, plugs can get wet and take spark and get to ground without making a spark. They need to be hot to about glowing to shed that if the problem or new again even if not too old.

IMO - carb not the issue yet. Alcohols in current fuel in wide use does raise hell with gaskets and rubber items not tolerant of it. This engine would fire (don't) with the carb missing and some prime put in the manifold!

Begin with seeing spark getting to plugs. Rotor in cap may have a problem making contact with cap's center post carbon contact new or not.

Avoid jumper wiring things. Rather test for power by test light or volt/multimeter,

T
_________________________________________
Long retired now


rsrandle
Novice

Jul 5, 2012, 12:49 AM

Post #5 of 9 (2135 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

I have rebuilt my carb to no avail. Tonight I gave in and removed the intake manifold. I found the sealant I used had failed at both the front & back. I’m going to get new sealant and a new set of gaskets for it and try again. I have a feeling it might just run fine after this.

I feel kind of dumb about this. At least I found it.

Rod


rsrandle
Novice

Jul 5, 2012, 11:37 PM

Post #6 of 9 (2111 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

I just picked up a new intake gasket set with new sealer. I found out I caused the gasket failure. I put a thin coat of sealer on the silicon end gaskets which let them both slip out of position. Duh!

I even know better. Oh well. Proof I'm only human!

Rod


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 6, 2012, 6:30 AM

Post #7 of 9 (2102 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

Thanks for the follow up and posting the fix. I'll lock this for now as a case closed and can be unlocked at your request or by any moderator.

Good luck with the redo fix,

Tom
_________________________________________
Long retired now


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 9, 2012, 3:07 AM

Post #8 of 9 (2071 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

Unlocked by request. More coming,

Tom
_________________________________________
Long retired now


rsrandle
Novice

Jul 15, 2012, 3:35 AM

Post #9 of 9 (2032 views)
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Re: 350 engine with ignition problems, I think?? [In reply to] Sign In

I finally got it running. I had a number of problems. I had installed the intake incorrectly and both end gaskets had blown out.

I replaced the intake gasket. It started then quit and wouldn’t restart. I pulled the top off the carb and found the accelerator pump had come apart. I rebuilt the carb including a new blue accelerator cup. The cup came off again! I replaced the cup one more time with the same results.

I finally gave up trying to restore the old carb. I sprung for a new manifold and carb. It runs good now. I put a Edelbrock Performer intake and a 1406 carb on it.

I am finally content with how it is running.

Thanks for all your comments and help.

Rod


(This post was edited by rsrandle on Jul 15, 2012, 3:44 AM)




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