Idle issues

[willaim]

I have a 89 4.3l v6 with a 2 barrell carb. I have had the carb rebuit, installed new fuel pump and replaced the fuel lines, filters and anti siphon valve. It still will not idle under 2000 RPM. Could there be an electrical issue, thanks.

 

[Kainon]

Re: Idle issues

wont idle under 2k also says possible vacuum leak at the carb or intake.. what is the idle mixture screws set to?

so how do you start this ? you cant go from 300-400rpms @ start to 2000..

 

[willaim]

Re: Idle issues

The mixture screws are backed out 2and a half turns. When i go to start it i pump the throttle three or four times wile turning the switch, it fires and you have to keep the throttle up. When you try to back down on the throttle it dies instantly, just like turning it off.

 

[Kainon]

Re: Idle issues

you "should" only have to do 1 pump to set the choke and get some gas into the engine, 3 or more and you can flood it with too much gas

things i'd checkw

1. Choke: take the flame arrestor off and when the engine is COLD and you pump the throttle once, does the choke set?
2. Choke pt2: while the engine is warming up, does the choke ever open up? there by releasing the Idle Increase Cam ?
3. That carb uses a slightly thicker carb base gasket, is there a THICK Gasket under the carb? about 3/8" as apposed to about 1/32"
4. In the Distributor there are 2 springs and 2 weights these make up the mechanical ignition timing advance, if 1 of the springs is broken or very weak this can cause the advance to not return properly and cause a high idle
5. Loose intake manifold bolts or loose carb can cause a vacuum leak ( and leaving washers under the base gasket but not typically on your carb, I did that on a 4bbl 350ci )
6. Idle set properly? you need to set the idle with the choke open and engine warm, I also disconnect the throttle cable so that doesnt SET my idle, I then will attach and adjust that after to make sure the idle is right and the throttle is being slightly forced closed.
7. Need to make sure the timing is set right but you cant check it @ 2000 RPMS. ( well you can but you'd have to look at a chart somewhere about 25-30 degrees I think )

So the idle circuit operates at about 1200-1500 rpms so below at that rough number the idle mixtures come into play above that and your using the main circuit of the carb, if the carb isnt cleaned and setup properly It could be dumping too much gas into the carb causing it to not idle

If the choke is not opening and the engine draws more air through the main circuit in the carb, which will draw more fuel in causing a high idle and run rough.

to test for a vacuum leak with the engine running you can spray around the carb and intake manifold, IF the engine is already getting alot of fuel spraying with Carb CLeaner will cause it to die down and run rough (flooding it out)

If the engine is lean, spraying with carb cleaner will cause RPMS to increase and should smoothen out the engine

 

[willaim]

Re: Idle issues

I have not tried any of your sugestions because i just got home, but before i went to work this morning i put a rag over the carb and it fired right up and idled real rough, when i took the rag off it shut off. With it ideling i sprayed wd 40 around the carb and manifold and no change. Another piece of the puzzle. I am going to get to work.