what causes this??

[hilljob26]

well,my dad put a new holley on his truck,he messed with it alittle bit,seems to run great,but now when he shuts it off,it deisels a little,how can he fix that,any ideas,its a new holley 600 that does not have adjustable floats,its called a next generation needle/seat,just doesn't look right without that nut and screw on the top,but seems to work okay,just this little problem.....mike

[northcountry67]

It sounds to me like your timing is too advanced. It could be a combination of a number of things like the timing along with the idle too high. Check your timing with a light.

[Billla]

Originally Posted by northcountry67

It sounds to me like your timing is too advanced. It could be a combination of a number of things like the timing along with the idle too high. Check your timing with a light.

[Novaguy73]

Ill third that...

[crazy longhorn]

Call me #4 on that! Try setting the idle speed down, & see if that helps(assuming the timing was not changed, & there was no prob before) L

[Longhorn Man]

third choice, it may be a little lean.
If timing is good, and idle speed is good, fatten up the mixture a bit.

[cduster]

I'm going with mixture also.

Dan

[cypress TX 72]

Timing !! (I'm with the other guys -I guess #5)
Try retarding it a little

[krue]

Check idle first.

[mike nutt]

good call everyone!

[hilljob26]

right on,thats what i needed to know,we never touched the timing,but will look into it.......mike

[Longhorn Man]

If the timing was never touched... then it should be fine... or good enough anyways.
Idle speed... it would be noticeable IMO... 850 RPM isn't going to do it, we're talking like 1000 RPM.
So that leaves mixture.

[68/72parts]

Check your idle speed first and set it to spec. And see what happens. Then check your timing just like the last few replies. Generally it will run on if your idle is to high, when its set at a higher than norm idle the throttle doesnt close enough to stop the air and fuel flow and the truck will continue to run. Make sure that your throttle linkage is set properly as well especially if you changed from a different style carb!! Just my 2bits..

[boundstaffpress]

If you just replaced the carb. It is very likely a linkage problem. I went two barrel to quadrajet. The linkage hung up and kept the throttle from closing. It took 6 months of messing with throttle and timing adjustment before I solved it by adjusting my thottle linkage bracket.

[Sweet72]

Stock carb more than likely had a idle stop solenoid to close the throttle plate completely with the key off. If your holley throttle isn't closing as somebody already mentioned it will deisel with the key off.

[rkarr]

Originally Posted by Longhorn Man

third choice, it may be a little lean.
If timing is good, and idle speed is good, fatten up the mixture a bit.

I agree.
if she's lean, she'll do that...