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454 losing power after 30 seconds
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wizzard6767
New User
Dec 10, 2012, 3:53 PM
Post #1 of 3
(1469 views)
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454 losing power after 30 seconds
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Hi there guys ... I would appreciate help here as I am close to tearing my hair out.
I have been working on 2 airboats for the last week (swamp boats with the huge propeller at the rear)
They are both running 454 chevy motors and holley double pumper carburetors.
Since the problem has occurred the fuel filters have been changed, new electric fuel pumps have been brought for both. Carburetors have been stripped down and rebuilt, new spark plugs installed. New distributor caps and coils have been installed and I still have the same problem.
Which is this - On startup the motors run fine, dropping the accelerator is fine to begin with, the motors run fine, then ... after about 20 seconds, they start to splutter and cough and the engine looses power.
When this occurs if you keep your foot on the accelerator it picks up and dies intermittently until it dies altogether. If you back off the accelerator to about half or a little less it runs smoothly and you get more acceleration after about 15 seconds then it starts the same problem again.
For an airboat (swamp boat) you need to run at full throttle for most of the time to skim over the swamp and marsh. Half throttle is no good as you can get stuck pretty good in some places, and of course we do not want this happening!! lol.
I am at sea level if that makes any difference. The carburetors are both adjusted on the fuel mix to a standard on both bowls. Screws turned all the way in till they seat, then backed off 1 1/2 turns.
Do I need to run the secondary bowls on a richer mix maybe?? I am not a professional mechanic, though I have one working with me and he is just as perplexed.
Please help guys, we need these boats running for a commercial operation!!
Thanking you in advance :)
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 10, 2012, 3:59 PM
Post #2 of 3
(1464 views)
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Re: 454 losing power after 30 seconds
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I assume they share a common fuel tank. I suspect a problem with the feed line. Many marine applications have a screen inside of the pick up tibe inside the fuel tank. Maybe you could try running it on a 5 gallon can for testing.
edit
OK, I just realized we were talking about 2 different boats. I was thinking one boat, twin engines but it could still be the same issue
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Dec 10, 2012, 4:00 PM)
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Sidom
Veteran
/ Moderator
Dec 10, 2012, 8:00 PM
Post #3 of 3
(1420 views)
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Re: 454 losing power after 30 seconds
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Might not be a bad idea to run off a 5 gal can.
2 different boats develope the exact same problem at the same time? You would have to think it was something put into both or done to both at the same time....
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