Another dumb question.

Actually what causes it is not the compression or the timing. It is the octane of the gasoline.
Octane is actually the measure of resisitance to dieselling or self detonation by the fuel.
The higher the number the more pressure (without a spark) it will take for the fuel to explode.
The way you adjust for dieseling is to raise the octane of the fuel.
If you are running a '70 4v with a static compression ratio of 10.7:1 or a Boss with a static ratio of 11.7:1 then you need at leat 102 octane under the old system. 103 would be preferable.
The only place that you can get that now is at a racetrack.
103 on the current sytem would be about seven points lower, which is approximately a 96 octane.
Sunoco Ultra is the highest that I know of at 94.
There is a formula for racing the octane of pump gas by adding lead to it.
The simplest way would be with leaded aviation fuel. I believe that it would need to contain at least 1 gram of lead per gallon. 2 grams would be better.
Presuming that you can pull this off without being arrested, there are drawbacks.
Avi gas isn't formulated for cars. Avi gas will usually give you a lead build up in the chanber and on the plugs. This is a negative build up, not a positive one.
I don't remember the mixture formula. I don't remember what the correct quantity of lead is that you mix with premium unleaded and wind up with an octane that is actually higher then the one you started out with in either component.
Maybe someone here has the formula.
If you car is a '73 and the engine is stock, I believe that it is 8.0:1 or 8.5:1 cr.
You must be using 89 octane regular to be getting diesling with it. That engine has no compression to speak of.
If you go to KB-Silvolite Piston web site, they have a calculator for "effective compression ratio".
You need the camshaft timing events to use it.
Do I get more poits DT?

Gosh Doug, I used to have a 1970 engine but that was the one I blew up. SO I bought a brand new motor, and they said it was built to cobra jet spec so I assumed it was an 8 something to one. Maybe a should try a tank of gasohol??
And Mark, are you sure?????

Or you could have some carbon build up that keeps igniting the gas?

quote:

Originally posted by DeTom:
Gosh Doug, I used to have a 1970 engine but that was the one I blew up.

I would believe the high compression engines doing this but not the low.
Are you running hot? That could do it.

The carburetor's primaries are opened too far, because your ignition timing at idle is retarded too much, and your Holley secondaries are possibly set incorrectly.

Your friend on the DTBB

Jeff, it could be but the negine only has 1000 Kilometers on it, so if it gets carboned up in that short of a time, I got big troubles with it. Thank God it is still under warrenty.
Doug, the engine runs at 110 degrees celius.
George, so it could be the carburator? What would caus it to do that? Is it sticking? Should I try some of that carburator cleaner stuff you get at autozone?

Retarded timing will cause overheating that can cause running on.
I've had this on a few cars in the past.
Fix the timing and see if it still does it.

That's something like 235 F. You are right on the limit of boiling over.
I think that is much to hot.
It should run under 200F. That's about 90-95c.
You are overheating. Sounds like steam pockets are forming.
This is the argument about the thermostat that I have.
If you run a 180, the engine shouldn't go to 235 degrees. I will bet that you have a 193 in there.
You need to run a 160. In the Pantera I don't care what anyone says, by the time the radiator even gets hot the engine is borderline overheating. This is also where you are going to get baked on deposits in the engine as well.
Here we go again folks.

Yeap, get that timing dialed in. Too retarded or advanced will cause the engine to run hot or ping creating other less desirable damage. Simple and cheap solution to the problem.

Ignition run-on due to fans, happens when you use a spark box (like an MSD). The radiator fans continue to spin after the engine is off creating enough power to keep the engine running. Believe it or not, the fans spining do become a generator creating 12V to continue to power some circuits. "Your own portable windmill". I diode is placed into the wiring to prevent his feedback. If you do not have a MSD or MSD like unit, it is not a problem for you to worry about.

quote:

Originally posted by DeTom:
...George, so it could be the carburator? What would caus it to do that? Is it sticking? ...

Here's the situation my friend. If the ignition is retarded at idle, the primary butterflies must be adjusted further open than would otherwise be necessary to enable the motor to idle at the proper RPM. If the secondary butterflies are not adjusted properly (i.e. fully closed), this will result in the primary butterflies being open even further yet. The idle circuit is jetted richer than the intermediate cuircuit, so as the primary butterflies are opened further, the idle mixture leans out.

The increased opening of the primary butterflies allows the cylinders to fill with more air at idle (lower intake manifold vacuum). The increased volume of air in the cylinders, combined with the lean mixture, creates a situation whereby the air/fuel mixture ignites by the act of compression, without the need for a spark from the spark plug. In other words, the motor is dieseling.

Advancing the timing at idle will allow the primary butterflies to be set in a more closed position, raise the intake manifold vacuum at idle, create a richer idle mixture, and thereby eliminate the conditions causing your motor to diesel. Running a higher octane fuel will sometimes alleviate the problem, as the anti-knock components of the higher octane fuel will prevent dieseling.

To prevent this "idle run on" condition, carbureted motors with smog tuning came from the manufacturers with an "idle solenoid" that held the primary butterflies open the proper amount to achieve the correct idle rpm. When the ignition was switched off, the solenoid retracted allowing the butterflies to go fully closed.

I have explained a few times on the DTBB how to properly set the ignition advance at idle & will gladly do so again if you need me to.

your friend on the DTBB

AHHHHHHHHHHHHHHHH HAAAAAAAAAAAAAAAAAAAAAAA!!! That is why. I knew something bad was gonna happen. I told the guy that put the engine in that the plaque right on the car says 16 and he said that the book said 8. Now to be honest when I first got it back it did not run as hot as it has been so I imagine the distrbuter has slipped a little bit. But when you are starting off at only half the advance recommended, when something like this happens, it has no where else to go. That guy shoulda listened to me.
Just shows to go ya, if you want something done right, you gotta do it yourself.
Thanks gentlemen. Now everything makes sense to me. I knew the new motor was going to be a dog relative to the old one, but nothing explained it untill now. That is why it was a real stone above 5000 RPM. This all makes sense now.

I can vouch for the run on effect from the fans, although I have to admit until reading this I hadn't realized...but it all makes sense now.

I installed a Fluidyne rad and flexalite fans a week or so ago......my run on problem disappeared

Julian

It could be that, but I am going to take it a step at a time. This is something that slowly has become more pronounced. I think my timing has slipped. Since it is a brand new engine with less than a yhousand miles on it, It would make sense that the timing nut has loosened. Anyway I will check that first Sunday night, and if it is on the money, I will know I have to get new fans.

Wow, this stuff is strange. In my car unless I shut off the DVD player thw engine won't stop.