I have been experience some run on as of late. It does not occur all the time, but some. Motor has 10 to 1 comnpression and I use 93 octane fuel. My timing is set at 19 initial and 36 total. I believe have a good tune on the carb.

Any tips as to what to look at?

The usual culprits are too little advance and/or high idle speed. With 19º initial I doubt that advance is your problem. Other possible causes are a hot spot in the combustion chamber. A rough edge, carbon build-up, etc..

yes...... did you buy gas at a different station by any chance ??? if it is a Bad gas problem .... it will pass .... ROFLMAO :thumbsup:

yes, I think I may have bought some fuel at BP instead of Shell.

Also,depending on where you live some fuel has already started the change over to the winter formula which could also make a difference too.

As mentioned above your timing looks to be about right so make sure your idle speed is not set too high and also turn the motor off with trans still in drive which usually enough additional load to stop the motor from desieling/run on.

Do you run a vacuum advance? If not your only running 36 deg total and most street perf motors like a vac advance to increase timing to approx 50 deg (+-) for part throttle cruise. If you dont have a vac adv then the motor is running approx 14 deg retarded at part throttle cruise which can also cause the motor to run hotter then it should,waste fuel,and feel a little soggy at lower rpms too.

Also,as mentioned above there could be hot spots due to carbon build up esp if your motor uses a little oil . So try running a good fuel system/intake valve/fuel injector cleaner like Chevron sells in the black bottle and run a that in a couple tanks of fuel to knock out any carbon in the combustion chambers that could possibly be adding to the problem.

I would stay away from the old timers trick of dumping lrg amounts of cold water down the carb/intake while reving the motor up to shock/break the carbon loose. It does work but it sounds horrible when it's done and could possibly crack a psiton so dont try it if anyone suggests it.

Lastly,a motor running a little hot,carb fuel calibration set too lean,a vacuum leak leaning things out,or too hot a spark plug heat range can all single handedly or in combination cause/ lead to run on/desieling or detonation.

Scott

SWHeaton

I live in Fla. and I have no idea if the gas formulation has changed yet.

I have run some 110 in it at the track.

I can't turn it off in gear. Its a 4 speed. I guess I could let out the clutch and let it hop.


I don't run a vacuum advance. The GMPP can adds 20* of advance. I have been meaning to re-curve the dizzy or back off the timing for cruising. If I ran the can it would give me 56* total.


I try some of the additive. How about Marval Mystery oil?

I run it pretty hard, so I hope the carbon is not built up to bad. The motor has around 8000 miles on it.

Motor does not run hot. Stays at around 195*. Now if it idles for a few minutes the fan will kick on to cool it.

My mxture screws I tune for the highest vacuum. I DON'T screw it back in until the vacuum starts to fall like some do. Probably would help.

I could try a colder plug.

Here is my combo:

350 OEM roller block
Forged Crank
PM rods
-6 Flat Top pistons (hypers)
10 to 1 compression
.035 for quench (.015 gasket and .025 in hole piston)
Cam is 290/300 and 232/242 @.050 for .510/525 lift.
AFR rev kit
Trick Flow 195 heads, 2.02/1.6 valves
Edelbrock Air Gap RPM
Holley 750 DP with stock jets and orange cams and #35 squirters
GMPP dizzy
1 5/8 hedders


Thanks

I have backed off the timing to 34* and re tuned the carb for the highest vacuum level and still get dang run on.

Could be carbon, but motor has less than 10,000 miles on it.

Car does not run hot (195*) and no vacuum leaks that I know of.

Maybe I will try some that fuel cleaner.

It is darn aggrevating.

Be sure to retorque all your intake manifold bolts, and carb bolts.

I just fought with this exact problem for a month, turns out two of my carb stud shoulders were taller than the other two- causing it not to torque down right, and a major vacume leak. Had major dieseling & violent backfires out the carb.

Thanks, I will check those. I have a inch spacer. I did notice that the nuts do not go down equally all the way around. I always have a fear of overtorquing the carb nuts.