440 dieseling

[pmschmitt]

I have a 69 300 with a 440/727, with 130,000 miles (I believe it has been rebuilt but unsure of when). I have had the car for several months and only use it occasionally. When the car was bought it was running sluggish so I set timing based on harmonic balancer to fsm specs (retarded the timing to 8 degrees advanced , it was set at 19 degrees advanced, and I repaired a vacuum leak)The cars mixture was adjusted to get 21 with a vacuum gauge. And the curb idle was set at about 600rpm. I have been using regular unleaded pump gas. Have run about 4 tanks through the car since purchase.

Car are has been running good, very smooth, starts right up when warm, good acceleration etc. recently I have noticed when I turn off the ignition the car wants to sputter and or spit for approx 30 sec before dying. I understand this to be called dieseling. This has gotten worse over the last week. I understand dieseling can be due to 1) Carbon build up in intake 2) improper timing 3) cheap gas or too low octane fuel 4) too high curb idle

Anybody have experience with this? What can I do to prevent this and or fix it. The car does have a lot of carbon buildup on the tail pipe but what big block doesn't. All help And comments are appreciated.

 

[polara66hardtop]

Eight is a tad advanced, but it sounds like your vacuum advance is sticking, weak springs, I would Unplug the vacuum, and drive it on mechanicals, and try it again. if you have 21 at idle, that is high, 15-21 is normal range, depending on options, like power brakes.

 

[saforwardlook]

Typically dieseling is caused mainly by high idle speed. Generally 750 idle neutral speed is about right, maybe as much as 800, but that should be enough. But if you are using only 87 octane rather than 91, that too would likely contribute to dieseling - in fact I can hardly believe it would not knock like crazy on the 87 rotgut.

 

[440Sled]

Get those RPM's up manually and slowly dump some SeaFoam down the carb to help clean out all the gunk in the intake and carb. Then dump a can in a full tank. Be sure you do this outside or have the tailpipes facing out of the garage! Good luck!

 

[pmschmitt]

How much sea foam down the carb ? At like 2500 rpm??That sounds like it could cause some problems if done incorrectly. Sorry just never heard of this. How often do you gave to sea foam a 440?


I will also also try using an increased octane ( or an octane booster to the tank of 87 I have currently) and will check if it does it with the vacuum advance disconnected.

 

[rush]

My old 69 charger with the 375hp 440 would diesel everytime I'd shut it off. The timing was a 0 and I ran premium every tank. My NYB will diesel and I pulled the timing from 16 to 10 degrees and I do run 91 in it. My idle is at 750. They do make a electric solenoid that you can use the set the idle and when you shut the car off it shuts the throttle. I used one on my Ramcharger. I did read that I can put 1 gallon of e85 for every 6 gallons of 91 and that will give me 93 octane so you might give it a try.

 

[polara66hardtop]

my 71' 440 did it until I put stronger springs in the distributer. higher rpm tends to advance the timing, and it sounds like it is slow to come back. I blew a muffler once driving through dallas about 70 mph, and let the gas off too fast in order to avoid a truck. The engine backfires, and blew a hole in the muffler, because the advance wasn't retarding quickly enough. that was a long drive back to Nebraska without a muffler.

 

[moper]

I'll add check the float level and also make sure the secondaries actually shut all the way. It's getting fuel and air from somewhere it shouldn't be.

 

[440Sled]

I add Seafoam to the tank every Spring and pour about half a can in the carb. Never had any issues. Have one hand on the carb linkage and the other pouring. Keep the RPM's up so it dont stall.