New crate motor dieseling

[green81]

I went through this last year after I put my AFR heads, cam and an Edelbrock 650 carb on my car. It would diesel almost every time that I shut it off. I always ran ported vacuum to the distributor. I now run manifold vacuum to the distributor. it never diesels and the idle is much stronger and smoother.
Timing the engine:
Warm the engine
Disconnect vacuum line and plug.
Set timing to desired setting (I am running about 15 degrees initial)
Plug the vacuum line into the distributor to manifold vacuum. (RPM will increase)
Turn your idle down to where you want it.
This worked for me.

 

[Nitrousmaster]

So I was installing a remanufactured 350 VC111P crate motor on my 1979 Camaro and I use to have a 305 with a edelbrock intake 2701 and 1405 carburetor and I reused alot of the stuff because it was all a little over a year old parts well come to my suprise the engine is dieseling I'm about 160 miles on the engine and I've been trying to figure this out the car drives really nicely so I feel like the timing is good but it still has this issue every so often it doesn't happen all the time after I changed out the ignition coil old coil it happened all the time on shut off now it only happens maybe 1 in every 4 shut offs of course input would be nice these forms never let me down on good info.

It happens when you turn the ignition off. That means timing doesn’t matter, the plugs aren’t firing. Diesling is a function of octane and combustion chamber temperature. It probably doesn’t happen when your engine isn’t hot. The factory used to put a solenoid on the throttle that let it almost completely close when the key was turned off. So lower idle speed and definately better octane for the compression your engine has will get you there.

 

[rocket dawg]

Yup, factory installed throttle solenoid on 70's sbc's and even big blocks. You set idle with key turned to ON/running and turned the small hex ended plunger on the solenoid. Car shuts off, throttle plates close as much as the idle screw was turned in/out on the carb. Dieseling is caused by low octane gas mostly, but timing/vacuum leaks are a big part of it. The simple fix was to shut car off in drive ( automatic ) basically a lower idle speed. Clark W. Griswald's family truckster did that and Clark said, " all new cars do that honey" My 406 did that once in a blue moon after a hard run. The 750 Holley would take a little time to idle down and it did the dieseling. My new Sniper 2 efi system does not do this at all. Distributor weights free? vacuum leaks all taken car of? Idle as low as you can get away with? If everything is in order, a throttle solenoid will help.

 

[Sbcking]

It happens when you turn the ignition off. That means timing doesn’t matter, the plugs aren’t firing. Diesling is a function of octane and combustion chamber temperature. It probably doesn’t happen when your engine isn’t hot. The factory used to put a solenoid on the throttle that let it almost completely close when the key was turned off. So lower idle speed and definately better octane for the compression your engine has will get you there.

Residual current coming from the alternator will keep the power in to the ignition system for a time

 

[Steemo]

Yep. Timing first. 1 degree more of initial advance solved my run-on.

 

[kdsracing]

So I was installing a remanufactured 350 VC111P crate motor on my 1979 Camaro and I use to have a 305 with a edelbrock intake 2701 and 1405 carburetor and I reused alot of the stuff because it was all a little over a year old parts well come to my suprise the engine is dieseling I'm about 160 miles on the engine and I've been trying to figure this out the car drives really nicely so I feel like the timing is good but it still has this issue every so often it doesn't happen all the time after I changed out the ignition coil old coil it happened all the time on shut off now it only happens maybe 1 in every 4 shut offs of course input would be nice these forms never let me down on good info.

Dieseling was a common issue in the ‘70’s. GM solved the problem with a solenoid that was used to set idle speed when energized by “key on” power. The idle screw on the carb was set to about 400 RPM in park. Timing curve has nothing to do with it as long as timing doesn’t come in until at 1000-1800 RPM. I set up everything for the timing to start at 1000-1200 RPM and be all-in by 1800. Small blocks like timing. This setting allows for best fuel efficiency at normal highway speeds. Set total timing where the car likes it (34-38 degrees all-in) and set curb idle as low as the engine will allow. Also use venturi vacuum, not manifold vacuum for vacuum advance. This should solve the problem. Another trick to prevent “run-on” is shut the engine down with the trans in “drive”. If you want to use the solenoid method, they are available at parts stores.

 

[kdsracing]

De

87 octane will do it. Set idle to 800 rpm. Timing 14* initial.

Depending upon what cam the engine is equipped with, 800 RPM may be a bit high, and initial timing depends upon timing curve.

 

[kdsracing]

Residual current coming from the alternator will keep the power in to the ignition system for a time

If this is happening, you have other problems to deal with before addressing timing.

"A lot" if the time, what you're experiencing is due to the timing being too low...which will make the idle very low. Instead of correcting the lpw idle by adjusting the timing, some folks will simply turn the idle screw up on the carb....which basically dumps more gas. So when the engine gets cut off, the carburetor is still sending gas down the hole and as it enters the combustion chambers, the heat keeps igniting it causing run-on or "dieseling". Start with your timing 1st and foremost.

you don’t set idle speed with timing. You set the timing based on what the engine wants to run well, then set idle speed at the carburetor. Run-on is corrected with idle speed, not timing, not spark plugs.

 

[G72Zed]

I have found that many engines that show up for "issues" like that of the OP is mainly a lack of initial timing, improper timing curve/ignition parts and not to mention a lack of SCR in most cases for the cam chosen from the owner/buddy, as it's usually "too" much cam for the actual CR.

I say to them "does the car run hotter than it should cruising, headers discoloured, floor boards hot, lack of throttle response/crispness down low, bad fuel milage given the power, run-on most times" yep.......

Most carb problems are traced to ignition issues in many cases.

 

[need-for-speed]

I have found that many engines that show up for "issues" like that of the OP is mainly a lack of initial timing, improper timing curve/ignition parts and not to mention a lack of SCR in most cases for the cam chosen from the owner/buddy, as it's usually "too" much cam for the actual CR.

I say to them "does the car run hotter than it should cruising, headers discoloured, floor boards hot, lack of throttle response/crispness down low, bad fuel milage given the power, run-on most times" yep.......

Most carb problems are traced to ignition issues in many cases.

“90% of all carburetor problems are in the distributor”

In my younger days, I rebuilt the Quadra jet on my Monte Carlo three times before I finally figured out the mechanical advance had failed. $25 junkyard HEI and all good!