OK, so on this non-HAMB friendly car, I've had the motor rebuilt and put back in....it's a 351 Cleveland 4V. Had a custom grind cam done for it, the engine builder spec'd it out to 272 or something like that. Stock compression, (11.2 to 1 or something like that stock) with the dual diaphragm dizzy. I've been burning premium in it, with an OTC octane booster, and I've backed the timing off to 6 Deg BTDC, and I'm still getting MAD dieseling when I shut it off. Any ideas???
May not be it, but when I bought my Falcon it had a 302 in it. It also ran on after shutting it off. It turns out that the previous owner hooked the electric cooling fan direct to the coil and as long as the fan was spinning the car would run.
Try different brands of gas. I have a tow rig that would diesel like a mofo all summer for the last 3 summers, chased my ass trying to figure it out and finally gave up and just shut it off in gear and tried to park away from embarassing situations. Moved to a different area (similar altitude) and no dieseling this summer. Gas is the only change to the equation.
This is most likely the correct answer. With a big cam, you have to set the idle higher, and with that much throttle opening it diesels. With a curb idle solenoid, you can close the throttle when the engine is shut off.
It might seem counterintuitive, but you may have your timing too slow. Kick it up to 14°-16° initial and limit your total (initial and centrifugal together) to 34°-36° by re-curving the distributor. If it kicks against the starter, back it of until it just starts clean, but i wouldn't run less than 10°-12°. Slow timing makes part of the mixture burn in the exhaust bowl and get the exhaust valves hot enough to glow. Good for emissions, but bad for longevity and power. Glowing valves and a little fuel causes dieseling. Over all the engine will run hotter and will heat soak. That is a small cam for a Cleveland with that much compression. Is it a solid or hydraulic? If its a solid, tighten the lash a little. It will help a little bit. It depends on what distributor you have, but you have to limit the initial and centrifugal timing together for the detonation limit of your fuel at WOT. Vaccum advance added to the two should never be over 52° at cruise, and drop out without pinging. Stock distributors have the weights under the points or pickup plate, you change it by flipping the cam around or swapping it for one close to your centrifugal timing goal. MSD has them on top like a GM and you use a bushing. Is yours a stock ignition? I can give you some advice on re-curving specific if you need it.
Sometimes, modified motor with big cams require the butterflies of the carb to open too much, just to idle. This gets the butterflies past the idling circuit and into the intermediate circuits. The cure was to drill two small holes in the front half of the butterflies to allow more air in. I found this tip in an old "How to Hot Rod a Small Block Chevy" book. I tried it on my roller cammed Nova and it did the trick.
sometimes sharp edges in the combustion chamber {resurfaced head/bad casting dags) etc become so hot they glow and act as an ignition point, hence, dieseling.But Id go with the idle speed to high........Bert
Yep, used to race a Cleveland in a roundy dirt car. Big cam, high compression, only recurved mechanical advance on the distributor, no vacuum advance. Never paid attention to initial advance, only total. Started easy, ran cool the entire race and never dieseled.
Thanks, guys. I now have HOMEWORK.... To give some more info, it has a Holley 650 w/vac secondaries and Ford kickdown. The stock Autolite 4300 would not tune with this cam. The ignition sytem is a Pertronix Ignitor with a Flame Thrower coil, and there is no mechanical advance, vacuum only. It does this only when the motor is hot, it shuts down like a champ when cool, even when the electric choke is still on and it is in high idle. I am running a very hot plug, I will try a cooler plug, and then work my way back through the other suggestions. I'll check on the limits of the ditributor, BillB. It has the crappy dual diaphragm dizzy that they put on California cars only, that has an advance side and another that actually retards the timing at idle. I tried the single diapragm type, but was having the same problem, so I'll give it another whack. The single diapragm type was also adjustable, so that might give me a little more to work with in initial timing, too.
Something with a Holley you can do too is lift the secondary throttle plates a little so you can lower the front ones. If too much of the off idle discharge slot is open it can let fuel by. If I can get away with it I would rather do that than drill the throttle plates. Sometimes you cant. I have a 750DP with the plates drilled., but that was on a 428 Ford with a 260@ .050 duration. A 272° probably is only 220° or so. I think 6° initial is slow for the swirl that closed chamber head generates, JMO.
The 400M(WORST engine to come out of Detroit) does the same thing. Similar head design. Thats why the factory mounted a solenoid actuated throttle shutoff. The damn thing is hard to start AND to stop. Tough motor though I've tried to blow mine up a many times! Its in a 78F-250. I leave it in drive and slowly turn the steering wheel as I shut it off. Unless its a real hot day, then I just walk away...
I think the 400-c, or M if you will, is one of the BEST designs to ever come out of detroit. Sure every engine from Detroit can use SOME kind of help. But I raced both 351-C and 400's back in the 70's and early 80's and the 400-c far out performed the 351-c. Torque like you wouldn't believe off the corners on a dirt track late model. I still have the single 4 barrel tunnel ram I designed and built for it, and it is going on my 53 F100 Hot Rod truck soon. Course I matched a set of heads to it too. I won't be running 12 to 1 compression like I did on the stock car, nor the hot Crane cam, but it should still fly. I also raced 390's and the 400 outperformed them too. I see this is a much maligned engine, but from my experience the distractors of this engine are misinformed, and/or didn't know what to do with it. And yes, they are very tough, even the so called "weak" early blocks. Just try to keep them below 6500 rpm's. Jim. ###
#19 I am both a detractor and distractor. Ford made many fine engines but the 400 is NOT one of them. It was a compromise motor poorly designed to meet pollution standards. They run hot, start hard, Diesel, all the while getting shitty mileage. They are durable though. Soon as mine blows up(and I try all the time) a 300 six is going in.
UPDATE------ Let me start by saying you guys ROCK! I dropped from an Autolite AP25 to AP24 (cooler heat range), then pulled the timing up to 16 deg BTDC with the retard diaphragm diconnected (connected it dropped to 14 deg) and was able to back WAY out on the idle screw......PROBLEM SOLVED!! Runs like a bat outta hell, starts easier, and NO MORE DIESELING! Thank you, gentlemen. Beer or beverage of your choice is on me.....
Now THAT is what I call a BAD engine, the 300 six. I have owned two vehicles with them and they lasted no time. I know some people like them, but I sure am not one of them. I would take a 289 or 302 any day of the week to a 300 six, or ANY inline six as far as that goes. They just don't hold up to my highway driving. The only good thing I can think of with the 300 is that it has the same tranny bolt pattern as the 302's. I never had trouble starting or running my high performance 400 engines. Mileage was about the same as my 351 Windsors. Which none were all that good. Jim. ###
Whatcha' say we take a chill pill. Any engine is a good engine if you build it right. Even a "gack " FE 390, which is what I am building right now with a solid roller, and a set of really good flowing heads and intake The 300 -6 is a legend, my son has one with 350,000 miles on it and it doesn't use any oil. I don't really think any bad mouthing is needed for any of the line up. The 400 with a set of CHI heads would be sweet, but for less money and not much more weight on the nose I can build a 595 ci 385 series with a set of Jon Kasse heads. Its all relative. And it isn't what this forum is about. There are guys running literally every kind of engine including inlines (babbit pounder stovebolts, Hudson flatheads anyone?) of every make in their rods, running peoples stuff down isn't good etiquette. My advice (meant in the most positive way) would be to lurk awhile and get what this site is about, instead of going down in flames. This for anyone who hasn't been here long, no one in particular. When someone starts cutting on someones stuff it doesn't do with what we are doing. Build a 400 or a 300-6 in a traditional rod and meet everyone at the HAMB drags and let the cars do the talking. It just works better that way and nobody gets a bloody nose out of it.
Glad to help, just be sure that when you rev it up with the vacuum line unplugged and blocked that when it stops advancing it isn't much over 36° and when you plug the line back in and rev it again that it isn't over 52° with the vacuum advance going. You don't want detonation. But I am glad to hear that the dieseling stopped, you are probably right on the money.
THIS from a rear-engined, air cooled motherfucker? With that Corvair, you're one "Sig Heil" away from being a VW driver, Englebert. Now go put yer carbs back together....
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