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Motor Troubles: Rough Idle

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Old 07-01-2002, 11:33 AM
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Unhappy Motor Troubles: Rough Idle

Any input on this matter would be great seeing I am not to mechanically inclined when it comes to things like this.
OK here is the problem i am having. I have a 1990 / 454 / 330 that has been giving me trouble since I bought it last summer. It's problem is that at any thing bellow 2000 rpm it runs rough and you can smell fuel when you have a back draft. I had the stock Rochester 4 barrel carburetor rebuilt and it did not make much difference. Changed the plugs and the wires and from what people told me the plugs looked normal. I also fresh water cooled the engine this year seeing the boat was a fresh water boat since new and was now going to be used in the salt water. The last few weeks i have noticed some antifreeze loss but have not had milky oil nor any smoke in my exhaust when watching at an idle. I could have a loose hose some where but have not checked this out as of yet. I do not know what more information you will need to try to assist me, but I will be happy to add what ever I can if asked. Some one said it could be the electronic pick up under the cap and rotor but would it work half-way or would it work or not work? Well let see what you guys can add for input.

Thanks Jason
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Old 07-01-2002, 03:18 PM
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check your ign coil. It may be on its way out! I had a problem like this last year. The engine ran fine till i engauged the drive then it would stall. Pissed me off bigtime!!! Had to rev the engine a split second before engaugement to get it to run! Finnaly conked out on me in Millwaukee leaving the breakwall area out to lake MI!!! had to idle back on one engine to Racine harbor where i promptly ran out of gas not more then 1000ft from the launch!!! What a day that was!! ANYWAY!! my advice would be to check that. Also you may want to double check that you are getting enough voltage to the coil its self! My MSD system acts funny if it gets below 11volts!
You may also want to check that you dont have any floats stuck or adjusted wrong on the carb.....may be drowing the engine at idle speeds........
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Old 07-01-2002, 03:26 PM
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Those carbs have some internal leaks around small like freeze plugs if they leak they run ruff and suck down your fuel smoke.. most rebuilders wont fix this unless they know whats going on or they dont know.
 
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Old 07-01-2002, 03:57 PM
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turbo2256 is right. The Q-jets have a welch plug between the base plate and the carb body. The welch plug leaks. You will notice a foam rubber piece that Rochester put there to absorb the fuel, but if it gets really bad, the foam can't do it. All you have to do is pull off the base plate, (make sure the carb is empty), clean the welch plug under the float bowl, and epoxy this little baby up so it won't leak again. I've do this every time I rebuild a Q-jet now.

ps. This may or may not be your problem.
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Old 07-01-2002, 06:33 PM
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CHANGE THE FLOAT! I rebuilt many of these carbs,the float picks up a few grams of weight over a period of time and the needle doesn't put enough pressure on the seat.
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Old 07-01-2002, 09:20 PM
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Had to ask the basic"s.Is the choke opening all the way?Was the carb re-adjusted after engine warmed?
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Old 07-02-2002, 10:01 AM
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In regaurd to the cab float it was replaced when i had it rebuilt. And the Welch plug where is that? I have seen my carb apart but do not recall seeing that part? If i take off the base plate it will be there? Also everyone seems to be leaning towards the carb so i thought i would throw in the fact i tried some one elses carb from the same type of engine and it ran worse with a lot off back firing when under a load and it was a "good carb" from what i was told. The engine also does backfire once and a while esp when under a load or quick exceleration, but it has noit been doing it too much lately.
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Old 07-02-2002, 10:02 AM
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Quote:
Originally posted by DONZI
Had to ask the basic"s.Is the choke opening all the way?Was the carb re-adjusted after engine warmed?

Hey a local guy!
Hi Donzi,
I tried adjusting the carb a few times but the two screws in the front of the carb do not seem to do very much, but i do not recall i i gave it time to warm up or not. Also i was told it was about a turn and a half for each screw and that was all that needed to be done.
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Old 07-02-2002, 11:28 PM
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HI,JASON Where are you located at ? I have another carb. you can try. If nothing changes when you turn the adj. screws it sounds like there is a problem with the idle circuit or other items mentioned. E-MAIL ME AT [email protected]
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Old 07-02-2002, 11:37 PM
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I'd replace the coil like Wally said. If you need one, I have one that might as well be brandy new. You're welcome to it for the cost of shipping. Or, just go pick one up, they're cheep.

How many hours on your motor?? Could also be your ignition going bad....I just happen to have one of those also. And I KNOW it works.
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