8ba chugging after ignition shut off

R

Rollingmenace

Member
Oh here goes my 51 is running an 8ba with a new bubba's distributor. After running a while and the motor is good and hot.. I go to shut the car off turn ignition switch off and the motor chugs a bit before finally shutting down... I know the ignition is powered off ... The timing pointer is set at 0 deg or pointer lined up with dot on crank pulley... I'm at a loss here, any suggestions??
 
After run is caused by :

1=High Idle Speed and throttle plates not closed allowing air and fuel to enter the engine...

2=Timing too advanced , remove distributor cap and make sure advance is springing back when turned against spring tension.

Very rare for a flathead to after-run or diesel on shut down.....
 
^^^ I agree weird.... No I do not have an electric fan though .. I'm running an bubba's dizzy and a gm single wire alt, car is 12 v converted otherwise everything iS basicly stock under hood
 
Rollingmenace said:
Oh here goes my 51 is running an 8ba with a new bubba's distributor. After running a while and the motor is good and hot.. I go to shut the car off turn ignition switch off and the motor chugs a bit before finally shutting down... I know the ignition is powered off ... The timing pointer is set at 0 deg or pointer lined up with dot on crank pulley... I'm at a loss here, any suggestions??
Click to expand...

When you say "chugs a bit" do you mean that preignition dieseling sound or that the engine simply keeps running?

The first thing has to do with fuel mixtures and combustion chamber temperatures causing the engine to "fire" even without ignition spark.

The second thing has to do with your ignition system continuing to be powered. Sometimes a wiring error will cause an electrical feedback loop that continues to power your coil even after you turn the key off.

I'd put a test lamp or meter on the power side of the coil. Cycle ignition switch on and off. The power should drop immediately. Start engine and shut it down while watching test lamp. Power should again go out immediately.
 
Last edited:
It's a dieseling effect.. Shut key of engine diesels and eventually stops... I'm thinking along the lines of fuel issue idle was set kinda high I lowered the idle a bunch I'll know more in a bit... It doesn't do it in driveway only after driving it a bit and heating engine up... I tested ignition circuit key on coil power key off no power I'll look at it from running as well... I'll test it here in a hour or so...
 
i have 2 suggestions but they are both terrible. One of to floor the throttle when turning the engine off, the extra air adds compression that the engine finds hard to overcome. The other was leave the car in gear and stall it, not much help with an automatic transmission.
 
Gotta agree with Bubba.

"1=High Idle Speed and throttle plates not closed allowing air and fuel to enter the engine..."
This was very common on 70's and 80's cars, on a flathead, maybe.
 
My vote is for the ide speed to high. this leaves the throttle plates open and the vac. from the eng. keeps pulling fuel into the combustion chamber. if there are any hot spots, such as carbon build up, and it does not take much , or the fact that the eng. is just good and warm it will " diesel" and try to keep running. the back yard fix, if you don't want to find the real problem is to shut the ignition switch to the eng. off in gear, foot firmly on the brake and let the clutch out.
 
Also, if it shuts down good when it isn't very hot, and only diesels when it is
warmed up really good, then It sounds like it is all carboned up.

The carbon can stay red-hot when it is warmed up good, and tries to ignite
the fuel comming in, when shutting engine down while hot.

Run some good carbon cleaner through the engine.


Edit, I type slower than Jim, so I didn't get to read his post first.







.
 
Lanny said:
Also, if it shuts down good when it isn't very hot, and only diesels when it is
warmed up really good, then It sounds like it is all carboned up.

The carbon can stay red-hot when it is warmed up good, and tries to ignite
the fuel comming in, when shutting engine down while hot.

Run some good carbon cleaner through the engine.
.
Click to expand...

Yes, what he said. Plus, check your timing with a vacuum gauge instead of the stock timing marks.
 
Carbon is a good call, had that one. Also to hot a sparking plug, and other stuff. Pull the plugs and have a nose about in there, see lots of carbon, time to tug the heads and give him a decoke.
Had the leky fan thing in the past, it needs a diode in circuit to stop the whizzing round fan becoming a generator when you turn off.
Martin.
 
ok guys It seemed to me when driving it the idle was way to fast... so I turned down the idle screw yesterday and set the idle to a more normal setting... I drove the car in 70 degree weather so it got nice and warm and it shut right down when I turned off the key.... Im happy about that im going to run car tonight and pull in some atf through vac line to clean any small amounts of carbon build up... but it seems no more dieseling
 
You must log in or register to reply here.
Back
Top