Hi all,

Was having some trouble recently on my 66 Jetstar Eighty-Eight with dieseling and spark knocking. Suspected carbon buildup as the root cause, along with timing being out of whack.
Yesterday, I put a bottle of sea foam into the tank and filled it (well, nearly filled it) as well as sprayed some carb cleaner onto the actual carb. The dieseling got worse after my fifteen minute drive to work; it knocked for a good fifteen seconds before finally shutting off. After the drive home six hours later, it knocked only for about five seconds after shutoff.
Of course, I've noticed a ton of exhaust, presumably from the carbon burning off the cylinder heads/carb. Also, after the dieseling ends, lots of exhaust comes out through the carb itself (I realize this is probably because the engine is not running enough to push the exhaust through the rest of the system to the back).
I will not have access to a timing light until this weekend; however, the car will be minimally driven until then (20 miles or so, tops).
Having never dealt with this before, I'm of course a nervous wreck during the lengthy dieseling and accompanying cloud of exhaust from under my hood. I've been told that this is all something to expect and that you just have to rough it out.
Can anyone throw me some info on this type of problem? Tips? Words of advice? General encouragement? Am I doing everything right thus far?


As a side note, also was told by someone that a way to stop the dieseling with an automatic is to step on the gas after shutoff until it stops, but this seems counter-intuitive to me. Any truth to this?

 

Leave it in drive, with your foot on the brake, then shut off. Not the solution to the problem, but if should help stop the run on.
stetzie

 

x2
had a car a few years back that had bad vacume leaks, and so i had the idle up real high. Turning it off while in gear was the EASY solution to avoid the run-on diesling... much easier than pulling the intake was.

Likely your timing is too far advanced or your idle is set too high, or both.

 

I've heard this, too, along with the leave-it-in-drive idea, which I agree is much better. I think the point of stepping on the gas is to stall the engine by flooding it. With an overflow of fuel into the cylinders and no spark plug to ignite it, the fuel acts to cool the cylinder and stop the gas/air mixture from being ignited.

 

Sometimes this exercise results in an enormous backfire strong enough to blow your muffler/s apart - highly not recommended. I would stick with leaving it in gear!

On a side note, if your timing is advanced enough where you are getting an undesirable amount of pinging, you will destroy your engine in a very short period of time. I recommend not driving it until you get it under control.

 

Thanks everyone- the leaving it in gear move worked without a shudder. Going to mess with the timing and the idle (thanks @RAMBOW) this weekend when I get a light.

Car smells AWFUL while running, by the way. Normal?

 

P.S. Why does leaving it in gear stop the dieseling? Just curious.

 

By leaving it in gear when you shut off you are maintaining a load (the transmission) on the engine, making it harder for it to run-on.

Same can be done with a manual, just shut off in gear with the clutch in, if it diesels, let it out slow until it stops.

 

NO, not normal. You probably have the mixture set too rich and/or the timing to far retarded. A properly tuned car will not smell bad. One thing you should also do that no one else mentioned is check your fuel filter first. It might be dirty; this can also be the source of dieseling on occasion.

 

BUT it WILL smell unusually strong WHILE dieseling, as most gas is being pumped through unburned.
Enough to make your eyes water if you stand behind the car.

- Eric

 

Agreed. Not a pleasant smell either.

 

Definately check the timing. Also check the temperature rating of your plugs. Too hot will cause run on.

 

Perhaps you should fix the cause, not treat the symptoms.
If your pinging is caused by carbon build up you will only permanently cure it by removing the carbon.
A rather drastic cure I have used on old engines is to trickle a little water down the carburettor with the engine running at high idle speed. The cars popped and banged and spluttered while I was doing it, but lots of carbon bits came out of the exhaust and after 20 minutes of this treatment the engines ran a lot better.

Have you noticed after removing the head from an engine with a blown head gasket the piston crown on the cylinder(s) affected by the blown gasket is cleaner than the others?.
My guess is the superheated steam and cavitation break up the carbon deposits. I know it's a drastic treatment, but it has worked on a lot of old British engines. I see no reason why it shouldn't work on American engines (or engines made anywhere else for that matter).

Roger.

 

Trickle?

You can pour a whole glass of water down the carb over 20-30 seconds as log as you keep the revs up with your other hand.

It may work, too.

- Eric

 

Ahhhh, the old Cadilac cure!!

 

Just don't pour it down too quickly, hydrolock it, and bend a rod .

- Eric

 

I did say TRICKLE.
I wouldn't recommend it for cars with a cat or O2 sensor btw.
Or a diesel or 2 stroke engine either.

Roger.

 

I was having a wicked time getting my timing set.

It turned out that the outer portion of theharmonic dampner had started to rotate and thus to set the mark meant wicked retard and dieseling.

The balancer eventually separated and I had to get it replaced.

Maybe the dwell is off too?

 

The only time I've seen 'run-on' occur is when there was a vacuum leak - check all your vacuum hoses and the base gasket to the carb.
I've also had luck with running a tank of premium through it - gets rid of the carbon.
My Dad was a Ford mechanic and told me 45 years ago about the 'water trick'!
The dealer charged 2 hrs. for 'carbon removal'!

 

ALWAYS check your dwell.

Whenever you think of it.

If the idea enters your mind, "Gee, I wonder what my dwell is?" just go out and check it.

Modern points are mostly crap, with tiny rubbing blocks made of soft plastic, and dwell angles are constantly changing.

Recheck your dwell, and then re-recheck your timing.

- Eric

 

You retard your timing far enough you will get dieseling and it will do a nice blow back through the carbs before it eventually died.

This is exactly what happended when I retarded my timing quite far.

I also found that I was burining rich as well before I finally got it all worked out.

 

Dieseling:

My 71 Supreme 350/4bl stock has been running good for the past 1,000 miles. Recently I switched from 91 Octane to 87 Octane at a local food store. After using less than 1 / 8 th of a tank, my car developed chronic Dieseling every time I shut off the engine. This car has never dieseled before. The timing and all other values are within factory ranges. I suspect that this store has bad gas. I should be able to run my 8.5:1 engine on 87 Octane.
To temporally solve the issue I added 2.3 gallons ($8.70 per gallon) of Sunoco CAM2, 110 Octane (Leaded) fuel to my existing 16 gallons of liquid.

10 miles later, the Dieseling problem was gone.

I learned a few things.

#1 Now I know where to get 110 Octane Lead at $170 per tank.
#2 The next time I try 87 Octane, do not buy it from a place that sells food.

 

Don't all gas stations sell food now?

I wonder if he ever got it fixed??

 

Yes, you are absolutely right. 87octane should be just fine for your car. Your solution was interesting. I probably would have just used 94 octane. A lot less expensive than 110 leaded. I didn't even know you could get that stuff nowadays. 8.70/gallon? YIKES

Your assessment of 'bad gas' is very likely. You might also have filled up with gasohol without knowing it, a common formulation for 'winter' gas. Run the tank out and fill from a trusted source with 87. You might also want to double check your fuel filter to make sure it didn't get any crud blocking it from the bad gas. Cheap to replace. (around 2.00)

 

Yes, that is the Plan.
Gradually migrate a few full tanks at a time away from 91 Octane to 89.
I will use my trusted supplier, which has been providing me with reliable 91 Octane.
At least now I have a backup supply of good old 110 Octane lead.

PS, All fuel related rubber has been replaced with Ethanol approved hoses.

 

Bottle of dry gas or fuel line antifreeze works wonders too.

 

After a slew of problems, I solved my run on...

I went through and replaced every vacuum line I could find that was able to be replaced...

I have played and played and played with the old distributor, only to find out that the old one had grooves worn heavily into the posts for the weights, new distributor.

Had leaky fuel lines - replaced all the rubber lines I could find. Managed then to be able to get a decent look at where my timing was. Before that, the timing was showing like 36-40 degrees.

Adjusted the carb and moved vacuum lines around so that the vacuum advance wasn't instantly advancing. It was in the wrong place.

Although not the issue - replaced carb.

This isn't in the order that I did them, it was what I did over time to fix the problem. In the beginning, it would run on like a chugging freight train. Each step would make it go away. Every once in a while, I would get a slight cough. Now..... It runs like a top!

- Doing the same thing expecting different results will never fix anything -

 

That my friend is the definition of insanity.

 

My 64 88 has had the same problem since I rebuilt the carb. Starts great and runs fine.
A quick note..I PUT MY CAR IN GEAR AND SHUT OFF THE KEY IT KEPT RUNNING!! I could not believe it. Need to check to see if I have it too rich.