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post #1 of (permalink) Old 06-23-2003, 09:29 AM Thread Starter
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Weber Carb Dieseling

I am reposting this question after a weekend of no cure.
Briefly, 84 CJ7 w/258, minimal emmissions (no EGR, ECU, etc), TFI upgrade and Weber carb. Good vacuum, good gas, good fuel filter, good spark, good choke, correct idle speed, etc. Can't seem to get it timed where it will perform at top end and NOT diesel on shut-off. I removed the fuel pressure regulator because it was fuel starving the carb in 3 and 4 gear.
I have no vacuum leaks. Have timed it per engine specs (9 @ 1600) and many points in between. I have timed it advancing the ignition to to pull the most vacuum at 1600 rpm. All idles @ 650. No mater what it diesels on shut off.
I know the regulator should be in line. This may be part of the problem. The other clue I believe has something to do with the air fuel mixture. I can turn it in and cause the engine to stumble but can turn it all the way out with no change. The correct mix should be in between the two stumbles, right?
The CJ was running fine with a slight top end ping prior to the addition of the regulator and the adjustment to the timing. Any ideas?

Scott
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post #2 of (permalink) Old 06-23-2003, 10:36 AM
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Re: Weber Carb Dieseling

On other engines I've cured it by putting on a idle stepper sol. so when you shut it off it closes the venturi.
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post #3 of (permalink) Old 06-23-2003, 11:36 AM Thread Starter
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Re: Weber Carb Dieseling

Any particular type or brand to look for? Feel free to talk to me like I'm stupid so I understand the application.

Scott
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post #4 of (permalink) Old 06-23-2003, 12:46 PM
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Re: Weber Carb Dieseling

Back your idle screw way back so it won't idle. If you then start your engine and turn it off and doesn't continue to "diesel" then that should solve your problem. All the stepper would do is bring your Idle settings back to normal when the key is switched on. Cars with air used these to compensate for the additional drag on the engine. Make sense?
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post #5 of (permalink) Old 06-23-2003, 01:20 PM Thread Starter
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Re: Weber Carb Dieseling

This may sound stupid but if I back the idle screw off so it won't idle I won't be able to start it to turn it off. Am I missing your point?
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post #6 of (permalink) Old 06-23-2003, 03:11 PM Thread Starter
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Re: Weber Carb Dieseling

Weber suggested putting the regulator back in-line and opening it up to 4 or more psi. Good chance the regulator isn't "regulated" properly. Also to adjust the idle down as far as it would go without shutting down and then backing out the mixture screw. Makes sense. If these don't work may have a bad needle seat. Wish me luck.

Scott
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post #7 of (permalink) Old 06-23-2003, 06:16 PM
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Re: Weber Carb Dieseling

Can't you start it by applying a little throttle? If not place a shim under the adj screw, start it and then remove the shim and see how it shuts down.
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post #8 of (permalink) Old 06-23-2003, 06:44 PM Thread Starter
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Re: Weber Carb Dieseling

So far no dieseling after advancing the timing. I have no idea where it is - just moved it till it started pinging in 2nd gear and retarded from there. No top end power. Floored I'm at 57 mph. I am going to regap the plugs from the TFI recommended .045 to .042 and work from there.
Two more problems. My second fuel pressure regulator in a week has failed (Mr Gasket inline 1-5lbs) CJ shut down on me like it was out of gas, put a piece of hose in place of the regulator and all was well. The second problem is the air/fuel mixture. Still won't stumble engine when screwing the needle out. Might have a bad seat. I can't understand how or why. Too many little things at once!
Engine has cooled enough to pull the plugs - hope it helps.

Scott
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post #9 of (permalink) Old 06-23-2003, 07:34 PM
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Re: Weber Carb Dieseling

First off. Running out of gas in 3rd and 4th. Float is set just a tad too low. Raise it up to cure that problem. Next, do the Nutter bypass and get that computer completely out of the loop. Plug the vacuum line and retime at about 800 RPMs at about 6 to 8 degress before top dead center. Remember to use port vacuum after the bypass. I think my Jeep idles at 700 RPMs. When I raise it to 1000 for off-road use it will diesel pretty bad. Also remember that you should not have more than 2 turns on the idle speed screw. Try these tips and see if it helps. Check back if it does not.
post #10 of (permalink) Old 06-24-2003, 05:46 AM Thread Starter
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Re: Weber Carb Dieseling

The float setting was not the problem. Had my second fuel pressure regulator in a week go bad - can't even blow air through it! Replaced it with fuel line and it runs fine - but I still need to get that regulator issue worked out.
I am already running bare bones. No EGR, ECU, etc. Only vacuum line is for the dist.
I think my problem lies in the air/fuel mixture. Can't get he engine to stumble on turning the screw open. Must have a bad needle or seat. What else could it be? Pulled the plugs and regapped them to .040 - had them at .045 for the TFI. Very carbon fouled but hat could be due to a week of tuning up and dieseling.
So far no dieseling on shut off but the top end power is missing. I can get up to 65 mph but if I hit an incline power and speed start waning.
I am hoping the cure is in the air/fuel mix. Calling Weber today to see if they concur. It may not be the cure but that mix control is NOT working properly.

Scott
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