Guest Anonymous Posted August 31, 2003 Share Posted August 31, 2003 I have searched through the archives and noticed that dieseling seems to be a problem with SU's also. My problem is that I am not very experienced with carbs. I have a Bob Sharp intake, stock Holley 390 4 Barrel, Zx Distributor. The engine has a mild cam, and flat tops. I got discouraged with the car when built the engine in 95. Now I have the money to resume the restoration. I installed a new carb on the car, but it still has the dieseling problem. Does anyone have any experience with these carbs, or is my problem else where? The car idles great but takes forever to kill. Thanks for any help Travis Quote Link to comment Share on other sites More sharing options...
Guest zbot43 Posted September 1, 2003 Share Posted September 1, 2003 Hello, ok I work on cars all day just about everyday. I use to work at a carburetor shop, so I've got some idea about what you are talking about. Ok, the usual reason for the big "D" is airflow. You have the throttle cracked to far open at the base idle. Usually with small primaries on a good breathing engine. What happens is that there is still enough airflow through the carburetor to draw fuel with it. There are three ways to deal with it, that I can think of right off the top of my head. 1. (a method used in many cars with smaller engines, and many v8's too) Use an idle solinoid. When the key is in the run postion power is applied to this solinoid to raise the base idle speed to what suits you. When the key is turned off the solinoid is shut off, and the setting on the carburetor is low enough to not allow dieseling to occur. You adjust the carburetor's idle setting to a setting low enough for no dieseling. And the solinoid to set the idle speed, which the vehicle runs well at. This is probably the easiest method. 2. Drill a couple metered holes in the secondary throttle plates to allow greater airflow. This will let you close the throttle on the primary venturis. It is a lot harder to get fuel to flow on the secondary venturis (the larger ones towards the rear), so this airflow with not carry fuel with it. If you choose this method, I would buy a book on holleys so you get it right. Not sure how to add pictures here, so will leave this one up to you. It is very easy and requires no more parts, and yes it does work. The only drawback is it is hard to go back if you go to far. Experience is everything here. 3. If you can handle a little more base timing. You can shorten your spark curve, and raise your base timing setting. Now when you do this you will need to close the throttle further, and effectively stop the flow of air through the primary venturis. I hope this is some help. If you have any questions. I will try and answer them for you. Sincerely, Marcello Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 2, 2003 Share Posted September 2, 2003 I like the sound of option one. Where can I get a idle solinoid from? Would Summit or Jegs have these? I read some previous post regarding dieseling and if I understood what I read, I assume this would help with the vacuum that is causing the dieseling? Thanks Travis Quote Link to comment Share on other sites More sharing options...
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