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Discussion Starter #1
Hey y'all.....

I have posted this before and never really got a solution to the "running on" after the ignition is turned off!! This is the 408W stroker with 9.5:1 CR, Windsor Sr. heads, Comp 274H cam, Edelbrock RPM with 750 cfm on top.

I have the base timing at 8-10* with total mechanical of 24*. It idles OK at about 900 RPM at 10*, but seems to want to kick back and wind down backwards(??) when the ignition is shut off......Hissing out of carb while winding down?? The guy that built it says too much base timing will cause this but if I drop it back it idles so rough it damn near shakes the car apart!! Also, I can't tell anything about timing changes with respect to power, but it seems smoother and accelerates smoother with about 10* base timing!!

Any Ideas??
Cobrajack
 

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Sounds like your engine is "dieseling" because the plugs are getting to hot for some reason. If that's what is happening I'd change to a different type of spark plug first.

Seems like I read somewhere that going to a better grade of gas might help too.

Good luck
 

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Running on/dieseling can be caused by, low octane gas, excessive heat or hot spots in the cylinders due to carbon deposits or too high heat range plugs. Also high idle or high compression can be the cause. Assuming you are already using premium fuel, have you tried any of the octane boosters to see if they helped?
 

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Discussion Starter #4
Thanks Guys...

I felt like gas might be the problem and have seen really no appreciable difference between brands!! I am using 93 octane and the run-on only happens about 10% of the time...Other times it stops OK??

BTW...It isn't the old "Dieseling" where it clunks, bangs, shakes, and chugs until it stops....It simply appears to clunk and shudder while "Wheezing" back through the carb for a second or so??

I wondered about "Winter Gas" blends.....maybe that is the problem since it didn't seem to do it in the Summer!!??

Also, compression may be more than 9.5:1?? I'll try some octane boost and see if that helps.....It doesn't seem to hurt anything, just sux when in a parking lot and it does it!!!

Cobrajack
 

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Air is thinner in the summer when it's hot and it lowers your effective cylinder pressures so it would make sense that you wouldn't have any trouble then.

The wheezing, etc. sounds like you still might have a light case of detonation from some hot spots (hopefully just plugs).

With your heads and cam 93 octane should be more than enough. Unless your CR is more than 9.5:1...

I'd still consider a cooler plug or at least a different brand.

This is interesting,
keep us updated on what you find out!
 

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Interesting point about the winter gas. I have noticed that the winter oxygenated gas performs poorly and knocks in my work truck under a load, and stepping up to the next grade makes it go away. I've been told that octane boosters don't actually do much to increase the octane. Have you considered running a few gallons of sunoco 100 octane per tank to bring up the octane? I know its expensive, but if it appears as though there is detonation during shut-off, i would be concerned that it is happening under power as well. As far as the timing, isn't 24 degrees awful light? My experience has been stuff runs great with at least 32 degrees total, so maybe that is another indication of detonation problems. I'd suspect high compression ratio. Anyone else think so?
 

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Discussion Starter #7
musthave302...

The base timing is 8-10 degrees and the mechanical advance adds another 24 degrees all in by 3000 RPM's.....Total is 32-34 degrees and no evidence of detonation!! I pulled a couple of plugs and they are light grey and clean!!

I think the real problem is the "Winter" gas and 900 RPM idle??!! If I idle it down to 700-800 RPM's it shuts down OK, but the cam lope damn near shakes the car apart!!!

I guess I'll have to install a solenoid to hold the idle up while the ignition is on but shuts the carb butterflies as soon as the ignition is turned off??

Cobrajack
 

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Mine does it too. Jack seems like it might be the same as yours...It wont run on when I am by myself, but as soon as there is people around, sure as ****, it will run on. I have an auto, so I just leave it in Gear when I shut it off, and it is fine now. Then put it in park, then walk off. Works so far =)

Jeff Given
 

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Discussion Starter #9
Well.......I was looking for a solenoid arrangement to hold the idle up to around 900-1000 RPM's (smooth and not too lumpy) but would let the throttle close completely when the ignition is turned off.

Martel Bros. carries an air conditioner idle advance solenoid kit from Edelbrock that should do the job if wired to the ignition switch instead of air conditioning (which I don't have)?? I ordered one and will post how it works out....makes sense though!!

Cobrajack
 

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Ford used anti-dieseling solenoids on a lot of carbed engines and they do work very well. You could probably find one at the wreckers to try if you wanted. Basically with the power to the solenoid off, the idle speed should be just high enough that it runs and then with power to it the idle speed should be set where you want it to idle at normally. The solenoid is adjustable to acheive this.
 

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Discussion Starter #11
BTW....

I have noticed it is worse with Union 76(93 octane), a little better with Texaco and Enmark (old Crown), and almost non-existant with Hess gas??? May be related to added low volitiles added to gas for winter starting and cold weather drivability???

Like I said before, it didn't do it in Summer!!

The solenoid is on the way....I'll let you know how it works!!

Thanks,
Cobrajack
 

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Discussion Starter #12
Got the solenoid kit yesterday and installed it last night and wired it directly to the ignition.

I will start it up today and adjust the idle to be about 900 RPM's with it on and completely closed butterfly with it off....The engine should die as soon as the ignition is switched off.....I hope??

I'll let you know how it works.

Cobrajack
 

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Discussion Starter #13
SOLENOID KIT WORKS G-R-E-A-T!!!!!

Set idle at 950 RPM's with solenoid and backed off completely on idle stop screw. Now when I turn off the ignition, it dies without hardly making another revolution!!

BTW, with the idle at 950 it is fairly smooth and doesn't shake the HELL out of the car!!

Thanks to all.....
Cobrajack
 
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