Engine Diesels terribly
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From: Down by da beach.... boy
Engine Diesels terribly
I'm getting sick of shutting off my truck, and hearing it go, put, vroom, put, vroom, shooosh, vroom, put, etc, etc. New carb was put on the 351w last year. Truck seems to run rich at times, and sometimes feels like it's just dumping gas when i step on it. Truck still to this day doesn't idle right, post ignitions, and two different mechanics haven't been able to fix my problem, including the mysterious cold weather shut downs (thats another story that I don't want to get into). Could this be a timing problem, or could the carburater just be no good? Or maybe the mechanics (two previous turned out to be terrible mechanics who charged an arm and a leg to fix anything and everything) have to take a better look. This carb cost me 650 dollars, it shouldn't perform like crap, and I'm losing patience. Any suggestions?
Lead Driver
Joined: Feb 2003
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From: Oak Harbor, OH
Engine Diesels terribly
Check the adjustment of the carb, set your timing according to the emissions sticker as well. Make sure you disconect the vacuum advance before you adjust the timing. What are the specs on the motor and carb? Is the engine stock? What CFM is the carb? If you have put too big of a carb on the motor it may make it run really rich.
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From: western pa,zelienople
Engine Diesels terribly
my 351m dose not run on cheep gass. i would run good high octine gass for a couple of tanks befor i make major adjustments or changes. i can not run any of sheets gass.
bob
bob
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From: Down by da beach.... boy
Engine Diesels terribly
The motor is stock, just bored 30 over. And the truck always ran on regular unleaded from the day the family bought it. And the truck will backfire whether I use Amoco or sunoco or wawa gas. I'm gonna give it a good look when I get the time. I can't afford much downtime on it either since its my worktruck as well as daily driver. Thanks for the replies
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Joined: Aug 2002
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From: Minneapolis, MN
Engine Diesels terribly
Dieselling or run-on is usually caused by the idle speed being set too high, usually from trying to cover some other problem. The air/fuel coming through the carb is being ignited by hot spots in the cylinder. With the idle set low, there's not enough coming through to keep the engine running. If the choke doesn't open fully, it could still be on the fast idle cam. If you have an idle stop solenoid, use that to set the idle speed and set the curb idle to around 500 RPM. If everything is in good tune and you don't have an idle stop solenoid, you can add one.
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From: Down by da beach.... boy
Engine Diesels terribly
That does make a lot of sense about idle air mixture to cover up "other problems" since in the winter the truck would never idle, and has a bad habit of starting, and then turning off and flooding. Do you guys think that the Carb could just be a bad unit? I mean, I've had it looked at numerous times over teh past year and it still doesn't run right.
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Engine Diesels terribly
is the carb a 4 barrel holley? If it is the repacement square bore throw it out and get another. Almost everybody I know who has one threw it out including me. I now run an autolite 4100 and it runs fine. Swap out the carb.
Have your checked the vaccum using a guage. It is a must to help diagnos these problems.
Have your checked the vaccum using a guage. It is a must to help diagnos these problems.
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From: CA
Engine Diesels terribly
Too big a carburetor will not cause a rich condition, rather just the opposite. Too big a carb causes a slower passage of air past the venturies resulting in a weaker signal to the gas (too little vacuum) usually resulting in a lean condition.
Also, while often caused by poor timing, backfiring can have several causes. Backfiring through the tailpipe can often be caused by a rich mixture in combo with a burned exhaust valve-or very late timing. Backfiring through the carb can be cause by a lean mixture, advanced cam timing, burned or sticking intake valve, or way advanced timing. If it's a timing problem it will usually be associated with a poor running engine, but this is also true of burnt or sticking valves as well as bad mixtures.
I've owned many square bore Holley's with no problems. Maybe I'm just lucky!
Also, while often caused by poor timing, backfiring can have several causes. Backfiring through the tailpipe can often be caused by a rich mixture in combo with a burned exhaust valve-or very late timing. Backfiring through the carb can be cause by a lean mixture, advanced cam timing, burned or sticking intake valve, or way advanced timing. If it's a timing problem it will usually be associated with a poor running engine, but this is also true of burnt or sticking valves as well as bad mixtures.
I've owned many square bore Holley's with no problems. Maybe I'm just lucky!
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Joined: Oct 2001
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From: Crosby TX
Engine Diesels terribly
The other thing that can cause dieseling is carbon deposits on the tops of the pistons. The carbon gets real hot and continues the ignition process.
Run a couple of tanks of 91 or higher octane and see if that stops the problem.
Run a couple of tanks of 91 or higher octane and see if that stops the problem.
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Apr 7, 2003 09:07 AM