Another dieseling thread

[Ronno6]

Maybe this has been flogged to death...........
Just built my 355.
Compression 10.1:1
initial timing 10° BTDC, but not sure what idle speed.........
87 octane fuel non-ethanol.
I can idle the critter for 5 minutes and get some dieseling when I shut 'er down.
No pinging when I rev it up, but have not driven on the street.

Spark plugs are Accel shorty's, heat range 4 which is as cold as the shorty's go in my configuration.

Might this be new engine-itis?
If not, where should I begin??

 

[legopnuematic]

Maybe this has been flogged to death...........
Just built my 355.
Compression 10.1:1
initial timing 10° BTDC, but not sure what idle speed.........
87 octane fuel non-ethanol.
I can idle the critter for 5 minutes and get some dieseling when I shut 'er down.
No pinging when I rev it up, but have not driven on the street.

Spark plugs are Accel shorty's, heat range 4 which is as cold as the shorty's go in my configuration.

Might this be new engine-itis?
If not, where should I begin??

What's the idle speed in park? My 76 was idling too high and would diesel upon shutoff, also check to make sure the dizzy mechanical advance is free and moving correctly

Sent from my Moto Z (2) using Tapatalk

 

[Ronno6]

What's the idle speed in park? My 76 was idling too high and would diesel upon shutoff, also check to make sure the dizzy mechanical advance is free and moving correctly

Sent from my Moto Z (2) using Tapatalk

I do not have a tach as of yet, but I would gestimate the idle speed in neutral (manual tranny? to be 750-800rpms.
The distributor is a new MSD, and the timing at shutdown is 12°.

Is there something equivalent to the old dwell tack for HEI !!

 

[Frankenchevy]

The $100 timing digital timing light from Napa has tach readout and advance functions. Kind of nice for non indexed crank pulleys and seeing rpms from the engine bay.

Sorry, can’t be much help other than that. Sounds like timing though. Good luck.

 

[MrMarty51]

Install a kick down idle solenoid on the throttle, set the idle speed with the kicker down, turn the idle plate stop screw to about 550 to 600 RPM, when the key is turned off, the kick down will drop the throttle plates to what the curb idle screws is set at, then, no more diesel run on.

 

[Ronno6]

Install a kick down idle solenoid on the throttle, set the idle speed with the kicker down, turn the idle plate stop screw to about 550 to 600 RPM, when the key is turned off, the kick down will drop the throttle plates to what the curb idle screws is set at, then, no more diesel run on.

There's a thought............

I'm gonna try premium gas first...........

 

[Matt69olds]

Could you add a couple degrees of initial timing to raise idle speed, then turn the idle speed setscrew to a lower setting? That would allow closing the throttle blades a little. If you add initial, you will probably need to take some centrifugal advance out. Since you have a MSD distributor, all that is made easy. Do you have a vacuum advance canister? Is it on manifold vacuum? Once again, vacuum advance would raise idle speed, and allow setting the idle setscrew lower.

 

[legopnuematic]

Could you add a couple degrees of initial timing to raise idle speed, then turn the idle speed setscrew to a lower setting? That would allow closing the throttle blades a little. If you add initial, you will probably need to take some centrifugal advance out. Since you have a MSD distributor, all that is made easy. Do you have a vacuum advance canister? Is it on manifold vacuum? Once again, vacuum advance would raise idle speed, and allow setting the idle setscrew lower.

That's how my 76 likes it with vac advance at idle, the idle speed screw is all the way backed off. 900 in park and around 600 in drive.

Sent from my Moto Z (2) using Tapatalk

 

[Frankenchevy]

That's how my 76 likes it with vac advance at idle, the idle speed screw is all the way backed off. 900 in park and around 600 in drive.

Sent from my Moto Z (2) using Tapatalk

is a 300 rpm split normal for a carbed auto? I never had a tach when I had a carb. my split is 100 (750 in park, 650 in drive) now with a really tight low stall converter.

 

[roundhouse]

Just shut off the ignition while it’s in drive , the drag of the trans being in drive will usually stop it from dieseling

I used to have a 69 thunderbird with the 429 thunder jet / cobra jet engine and it always did it and that was the only cure

 

[Ronno6]

Could you add a couple degrees of initial timing to raise idle speed, then turn the idle speed setscrew to a lower setting? That would allow closing the throttle blades a little. If you add initial, you will probably need to take some centrifugal advance out. Since you have a MSD distributor, all that is made easy. Do you have a vacuum advance canister? Is it on manifold vacuum? Once again, vacuum advance would raise idle speed, and allow setting the idle setscrew lower.

As I pondered things tonite, that thought occurred to me. I had taken 2° out of the initial, and the increased throttle at idle did make things worse. I rationalized as you suggested.....
Distributor vacuum off the port on the Holley carb

Actually, the kick up idle solenoid is an intriguing idea..........if premium gas doesn't do the trick.

Just shut off the ignition while it’s in drive , the drag of the trans being in drive will usually stop it from dieseling

I used to have a 69 thunderbird with the 429 thunder jet / cobra jet engine and it always did it and that was the only cure

No automatic.....Muncie M20 4-speed/Hurst shifter.......old school........

 

[legopnuematic]

is a 300 rpm split normal for a carbed auto? I never had a tach when I had a carb. my split is 100 (750 in park, 650 in drive) now with a really tight low stall converter.

I'm not sure, I think I need to retune the carb to dial it in more, but it idles at 900 with 21 pounds of vacuum and at 600 with 19 pounds of vacuum. I think I'd like it to be more around 800/700 (a split of 100) or so. Just can't seem to get any good weather in Missouri, rain, tornadoes, or stupid hot to get out and play with it.

 

[roundhouse]

As I pondered things tonite, that thought occurred to me. I had taken 2° out of the initial, and the increased throttle at idle did make things worse. I rationalized as you suggested.....
Distributor vacuum off the port on the Holley carb

Actually, the kick up idle solenoid is an intriguing idea..........if premium gas doesn't do the trick.




No automatic.....Muncie M20 4-speed/Hurst shifter.......old school........

Then just put it in third and ease the clutch out

Dieseling is because of today’s crappy gasoline

With all the ethanol garbage in it

 

[MrMarty51]

Timing has got not one thing to do with the engine running on. Once the key is turned to the off position spark and timing is removed from the equation and bad fuel has nothing to do with runon. It is the idle speed being set too high that causes the engine to run on. A lot of the carbed engines had that step up solenoid incorporated into the throttle lever just for that reason. If You look around a salvage yard you just might be able to find one with the mounting plate included. bad fuel can cause an engine to ping when load is applied and timing can be adjusted for that too.

 

[Ronno6]

Timing has got not one thing to do with the engine running on. Once the key is turned to the off position spark and timing is removed from the equation and bad fuel has nothing to do with runon. It is the idle speed being set too high that causes the engine to run on. A lot of the carbed engines had that step up solenoid incorporated into the throttle lever just for that reason. If You look around a salvage yard you just might be able to find one with the mounting plate included. bad fuel can cause an engine to ping when load is applied and timing can be adjusted for that too.

Ahh, but the beauty of advancing the timing is that you close the butterfly plates a bit to reduce the idle RPM.............less throttle opening means less run on..............
Again, as I have a manual tranny, idle is set pretty low.
The only objection to the kick up solenoid is that I would have to rig something to further kick the idle up when the A/C is turned on.....

Check my video in the "Which 350" thread and see if you think it is idling too fast.....