I've been having problems with my motor continuing to run after I shut it down. I have never done anything about it. The motor is a 327 SBC with a mild cam, power pack heads with the intake valves opened up to 1.82, and split ration rockers, with 1.6 on the exhaust side and 1.5 on the intake. OK, so last time I filled up I sprang for the good stuff, premium gas, and the run on is gone. I mean totally gone. So I suspect the compression may be a tad to high to run on pump gas but only because I have a basic understanding that higher octane means a more stable fuel. I'm not a mechanic and have a low skill level, although I am learning. With that tidbit can you advise me what should be done to run on the cheep stuff?
I'll just tell you what worked for me. Check your timing & advance curve. Mine was too far advanced & way too slow- like all in a 4800 rpm. Pulled it out, had a shop recurve it in the Sun dissy machine. Installed a limit on the vacuum advance 4 degrees, starts at 900 rpm, all in by 2800 & the run-on was gone. It was 37 total w/ vacuum plugged, it's 34 now & like a different motor.
Check the above. Also you may have carbon deposits that are staying hot and igniting the mixture after shut off. A 327 with early PP heads is gonna have a fairly high CR for el cheapo gas. Run it on Premium as the engine has been probably designed to do so. To minimise engine damage in the short term, shut off the enigne with it in gear NOT Park, this will kill the engine asap. Then Put it in Park Rat
If you are giong to run a high conpression engine on regular, you might want to think about warer injection.
I think with those heads and flat top pistons, you have something like 9.7 compression ratio, which means you need to run on Premium. Steves32 experience sounds just like what I've seen on lots of SBCs. I always shoot for about 34 total timing with the vac. advance disconnected to come all in by around 2800 to 3000 RPM. Getting the timing right really seems to "wake up" an SBC and make it more fun to drive. You can "recurve" a stock distributor yourself pretty easily by playing around with different mechanical advance springs and weights from a cheap "recurve kit". Mallory Unilites seem to be pretty close right out of the box. The stock distributors advance too slowly. Just putting in the lighter springs from a recurve kit on a stock distributor seems to get it about right. There are other things that could be causing your problems, like carbon build up or carb problems. But it sounds like you should stick with premium. Premium now is about like what the crappy gas was like back in the '60s. I wouldn't think about using crappy gas in an engine with that compression ratio. After you get the timing right, you may find that you can lower your idle RPMs down lower than it is now, and that will also help keep it from running on.
Lower the idle.... alot!! thats why they put those drop off solinoids on cars in the 70's. See what its suppose to be & set it there.probably around 650 or so jimV
And remember the goldenrule of pump gas, with cast iron heads, max cranking compression is 180PSI and wirh alum. 200 PSI, this can be altered by retarding the cam to lower cranking PSI or a longer duration cam is another fix in effort to bleed off too much compression. I have heard of guys bolting a starter on the engine while on the stand just to test this before buttoning up the cam area.
My 9.0/1 CR 462" Buick has just about the same timing curve that Steves32 noted. All-in is 32* BTDC and it sounds like I have a little more advance on the vacuum advance than he does - can't remember for sure. Initial is 8* BTDC. Cam is advanced 4*. I've heard of the big Buicks running as little as 28* all-in and 427 & up Rat Motors running 32* all-in with good results in both cases. The Buick engine has a mild cam, 260* and 266* advertised duration intake and exhaust. Idles at 600 RPM. No run on probs with the mild cam or either of a couple bigger cams with dual quads that also idled at 600 RPM. Approx 284* & 292* advertised duration on those. Only real difference was the 112* and 118* lobe separation angles. The car runs fine on 87 octane summer or winter with no run-on probs. For the most part all the higher octane gasolines do is burn slower which helps to resist knock. I'd try backing off the max advance on the mechanical side. You can unhook and block off your vacuum advance and run some part throttle tests looking for knock at half throttle, but you do want to run vacuum advance sourced to manifold vacuum to avoid overheating at idle and slow speeds. Another one that can help is to install a bigger cam which lowers the dynamic compression ratio due to it bleeds off some of the intake charge due to its later intake valve closing event. Something along the lines of a 270* or 280* advertised duration.
try playing with the advance curve and total advance. make sure the little plastic bushing is on the advance limit. try swapping the rockers around and taking a comp test afterwards to get the lowest cranking pressure. try an msd or some kind of programmable ign. put 75 cc heads on it. all of the above...good luck
Run-on with the ignition turned off has nothing to do with ignition timing or advance (It's turned off, no ignition) unless you are so very far off you are ready to fry something. That is not very likely. That is called "dieseling" when it ignites by itself and runs on without the spark-ignition. If it didn't do that long ago in the past, and now it does, it usually means carbon buildup that is making the compression ratio higher. Sometimes it means a sharp hot-spot inside the combustion chamber. Yes a glowing spark plug could be the hot spot, but that would be due to a bad heat range choice. There are a number of old remedies such as certain gas additives that are supposed to remove carbon, or by slowly drizzling something down the carb with the engine running at very fast idle, or ... ? (some say water, some say solvent) I have never tried them so I don't know which one to recommend you try or avoid. Now might be a good time to check the local gas stations in your area to see which ones are the crooked ones and which are honest. When I gas up my Stude with Premium gas at Kroger, Casey's, or Phillips 66, the dieseling stops. When I gas up my Studebaker at MOTOMART, and pay extra for Premium gas, it still diesels badly. MOTOMART STEALS FROM YOU. They sell the junk Regular and call it Premium with Premium prices. Now is a good time to see who can be trusted and who's crooked. When I get a batch of low octane gas that won't let the engine die, and turning it off while in-gear isn't quite enough to get it to stop, I sometimes put it in neutral, then back in gear. Right about the time the trans is about to hit into gear I turn off the key. Usually that is enough to kill the engine. Dieseling is a very bad thing in that, very often, the engine can counter-rotate (run backwards for a moment). That can play havoc with timing chain (Studes have gears), or even spit vaporized gas and start a fire in the air filter, or hammer the engine just like detonation. Don't try to "live with it" if you can cure it. You probably have an engine that just needs Premium, and that's all. Water-injection units used to be sort-of common in the 1970's when this problem was much more widespread. In addition to helping the low octane gas, they were also known for keeping combustion chambers clean. There was a concern for a while that the water steam could have an effect on engine life, but when it was pointed out that burning gasoline produced gallons of steam already, the concern about engine longevity seemed to go away. Long ago there were several articles written about adding small amounts of detergent or alcohol or other things to the water mix. It might be interesting reading for anyone who wants to do the research.
Actually- run-on w/ the key off has alot to do with timing. Yes- key is off but incorrect timing & sluggish advance curve will raise combustion temps & will make things hot enough to run on after the key is turned off- especially when combined w/ a too-fast idle (in my case).
I see as usual that the focus is in how to misunderstand and misdiagnose the problem, rather than simply fix the problem. I just said how to fix the problem. It worked on a few MILLION cars.
I do remember all the problems back in the 70's and that was because we had high compression engines trying to run them on low octane fuel ! You have a high compression engine . It is around 9.5 to 1 or better . You can do all the adjustments you want but then the timming will be so retarded it will run like shit . Always buy your gas from the same place too ! Use the good gas and don't be so cheap ! It will ruin all the money you have invested in your engine if you keep running the cheap gas ! If 15 to 20 cents a gallon is going to kill you then you shouldn't have built the engine !
We're not all dumb shits here. Contrary to what you think. Perhaps your rather abrasive personality would be better accepted on a different board....
I agree... dad had a station wagon back in the day that did this from time to time. The only thing that fixed it was what he called "flushing the toilet"... running the engine at 2000rpm or so, and gradually pouring about a quart of water down the carb. It basically steam-cleans the carbon from the combustion chambers.
Shut it off in gear or rig up a idle shutoff solenoid. Retarding the timing will help get the combustion chamber a little cooler, but you've gotta get that idle down after the key is turned off. That'll pretty much shut off the fuel supply. But yeah, shuttin' in off in gear will also work, or if it's a stick, just pop the clutch out in gear when you turn the ignition off.
I view the curb idle solenoid as a bandaid fix in the early '70s after they started adding all kinds of lame smog controls that messed with the timing, killing vacuum advance in certain gears, lean mixtures, running too hot, etc. Lucky Strike has a 327, which was before all that crap, and it is possible to make a 327 run well without a curb idle solenoid. But even all tuned up, it'll still probably need premium gas due to the higher compression. We were just giving him tips on getting it tuned up better so that it ran cooler, not "misdiagnosing" or "misunderstanding" the problem. We understand the problem very well. I have tuned up lots of small block Chevys and got them to all run like champs WITHOUT a curb idle solenoid. A curb idle solenoid sure wouldn't look good on a 327 in a traditional hot rod anyway. An engine that's running way too hot is way more likely to have run-on than one that's running cool. The carb can get so hot that fuel starts percolating out of the overflow vents and glowing gobs of carbon in the combustion chamber can ignite that fuel and keep it running after you turn off the key. That's how the crappy early '70s cars would get, and they added that solenoid as a bandaid to try to stop that crap. Even with that solenoid, I remember some of those '70s cars gasping and coughing for ten seconds after turning off the key. 327s never needed them though, especially back when the fuel quality didn't suck. I'd keep putting Premium fuel in it, but tuning it up better will sure help out. The fact that he gets run on just by using cheap fuel, tells me his engine is running probably a little too hot, and working on the tuning will probably make it run better and make it more fun to drive. Another thing that helps on those older engines is to just take it out and floor it once in a while to blow the carbon out. The combustion chambers back then were more likely to get caked up with carbon if you didn't drive it hard once in a while.
my 355 runs 10.5 to 1, premium gas only. luckily here that means 93, so it runs pretty well. and i only get it from chevron stations. that part might be OCD tho, lol. octane booster may help, not sure, every time ive added some something acts up. it deisels every once in a while, not bad.
Well- excuse the shit outta me. A idle solonoid? Are you serious? All that does is reduce idle RPM below the idle screw point & closes off all air & fuel & stall the motor. That doesn't fix squat. It's a bandaid fix. Might as well just ignore it & stall the thing in gear. Just as effective.
One thing I should have mentioned, but forgot, is that I have a Pertronix unit in the dizzy. My plan is to just run premium for now, but it did not always diesel so there should be some fix for it. I'll try the water flushing thing, and adjust the idle down...it is kinda high.
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