[Theresa Shank]

We have a SBC 350 in our street rod. It is pre-electronic ignition, so it is probably a mid 70's version. Problem is that when you shut engine off it wants to run on and jump around. We pulled plugs and they do not appear to have a lot of carbon build up, timing is set at about 12 degrees. Problem seems worse when engine is hot, if you shut it off in gear it will act normal? Any suggestions would be appreciated.... THANKS... THERESA

[1969NovaSS]

I recently had this problem with my friends engine i boult for him with a demon carb. The transition slot was open to far and just closed it up some. Other then that i would say retard/advance the timing some to see if ti gets better or worse.

[DHMag]

advancing the timing will only worsen the dieseling, try retarding it a few degrees.

Dale

[57 Chevy]

Dbl post, sorry

[57 Chevy]

In my limited knowledge, The throttle stop screw is open too far. Turn it down and readjust the idle speed with the idle screws.

If your dist still has points in it, take a look at Pertronix or some other electronic replacement. I did and saw a big difference in low end torque and idle.

[jimfulco]

Try the cheap stuff first. Lower your idle speed a bit & see if it doesn't stop.

[docvette]

Doc here,

Lower the Idle speed if you still have adjustment left..First.

You want about 750 Manual, and 950 Automatic for curb idle..Ballpark

After you achieve that, toss a timing light on it and check your Static timing with the Vacuum advance pulled and plugged..It will probably be retarded if it was set up at a high idle..Reset it to about 12 degrees.

Other sources of High Idle are major Vacuum leaks..so take a little time to inspect all your Vacuum Hoses for cracked , rotted or just plain fallen off conditions.Don't forget the power brake booster, Modulator Valve and PCV valve..

If those are good, spray the induction system down with Carb cleaner, anywhere it speeds up you have a leak..repair as needed.

Doc

[budthespud]

I found the best way to check for vac leaks is with propane. If you have a standard propane tank (hand held) take the end off the valve and put a 2 foot hose on the end. Start your vehicle and turn the propane on and run the hose all over the vac lines and the carb. If the RPM's pick-up then you have a leak. This is much better than spraying carb cleaner all over your engine. I agree with the timing issue but also too I had the same problem with a 350 motor and it ran best on high octane from Sunoco/Shell etc...Good luck!!

[Dave E Shank]

It sounds like we need to work on idle setting and maybe use a octane booster. I will also check for vacuum leaks..... THANKS.... DAVE & THERESA

[pmeisel]

May not be your problem, but I had one on the Jeep that I attributed to carbon buildup... got it cleaned up good and the problem was still there.... checked all the vacuum lines and found that I had the distributor advance running to manifold vacuum rather than ported vacuum from the carb, which meant that some advance stayed in when the throttle went closed... changed the line and the problem went away.

Coincidence? maybe -- 24 beers in a case, 24 hours in a day....