I'm running a '62 distributor

Hm that's a thought about the carb plates not closing all the way. When it's idling it's at 1,000 rpms. Which is where it likes to be considering the cam I have. But maybe sometimes the carb plates don't close all the way and is allowing fuel to get in the cylinder walls and then ignites it since it's hot? Is that what you're thinking?

Yes, re check your timing.. Also what Distributor are you using? If by chance it's a 1957-58 distributor, John Mummert says they have too much centrifical advance built in, as the intention those years was to use only about 3* initial. He recommends using the later didtributors with a cammed engine, because of the need to run more initial..


Paul

there is one other  thing that could cause " dieseling" upon shutting the eng. off, and that is that the idle may be to high. what I mean by that is that the carb throttle plates may not be completely closed. this can cause the problem. Just another idea that I am sure you have not over looked, but I thought I would throw it out there.

I do have domed pistons, they are forged. I got everything from john mummert, he put the whole kit together and said all of those parts would be great and etc. I'm using a WC T-5. It deiseling is never a common problem. In the past when it had desieled, it's because my fuel mixture was off, added some of the Lucas Oil Octane booster, never did it again. Plugs aren't showing any signs of it being lean at all. I've been wanting to run some racing gas through it, but unfortunately it is a little difficult to get it around here. Have to travel atleast 20-25 miles to get some.

Thank you for the advice!

Bottle says "don't be fooled by misleading advertising. It takes 10 octane points to equal 1 octane number." It also says it treats up to 25 gallons. It doesn't say how many points it increases the octane. But I see where you are coming from. I've been buying cases of the booster, the big bottles from napa. My Napa guy gives me a great deal on it, $78 for 12 bottles. They sell the bottles $11.99 retail and its $143 for the case retail. I'm able to divide the bottles up each fill up so they last longer. Yeah it's kind of annoying I have to do that but it's not too bad. I always keep the bottles in my trunk and have plenty with me before I go on a trip. Do you think the booster is bad for the engine? This Lucas oil booster seems to work great, I've tried other boosters and it didn't do anything. Engine still continued to deisel. Never does it with the Lucas booster.

I have not checked to see if the carbs are jetted correctly, I can look into that though. They seem to be pretty good, engine is very responsive when I stab the throttle. Plugs are reading good as well, all of them are brown. But they could possibly still need some fine tuning. Cause we were told with my set up, all the engine parts I had and compression ratio that I should be able to get away with running high octane pump gas. But it doesn't want to run on just normal high octane pump gas.


I can't remember exactly all the timing specs, I was planning on going over to my grandfathers tomorrow and use his timing light to check all of that. I do remember that total advance is 36 degrees and it's at 16 degrees at idle. We talked to one of the techs at Clay Smith Cams where I got my cam from and he said that's where it should be. He knew exactly what cam I had in the engine and everything.

I'll never claim to be an expert, but contrary to popular belief most high performance parts are not ready to go out of the box. Domed Pistons are the worst. Guys and shops just don't seem to want to touch them. All sharp corners, edges, etc must be smoothed out. The edge around your cylinder head chamber also especially after a slight milling. I'll always knock it down with a die grinder and follow up with emory. The top of the bore too.
You don't say if your using an automatic trans and if you are shut off the engine in gear. DON'T let it diesel at all. Back in the day if I had an engine that did it I immediately turned it back on. You can always kill it with the clutch with a standard trans but that's no good either. Right now it sound like you have some hot spots making like "glow-plugs".
I would also look to the center carb as lean at idle. Jetting usually won't have much to do with that. 11-1 is tough on the street without aluminum heads or a computor controlled ignition system. As a thought some racing gas around doesn't hurt. I can buy Sonoco from our local circle track supplier in 5gallon cans and 1/2 gallon of leaded 112 octane can work wonders. Sure makes my old Harley come alive. . . . Good luck.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Re octane booster, there are a couple things I would call problems about using it.  First, read the bottle.  The front always has something flashy like "Increases octane 10 points!"  Read the back, and what you will see is that each of their "points" is a fraction of a point you see at the pump.  For this hypothetical, lets say 10 of the octane booster points is equal to 1 point of the number you see at the pump.  So assuming that 93 octane is premium in your area, the octane booster makes it 94, rather than the 103 you thought it was if you did not read the bottle.
Now the problems.  If that 1 point in octane is the difference between detonating and not, then you are on the ragged edge of what street gas can support.  If you ever need gas at a station that has 92 octane, then you will be in trouble.  A second problem is a reliance on octane booster.  What if for some reason none is available, or all that is available is not as good?  How about the increased cost of enjoying the vehicle?

RE the  carburetors, have you checked that they are jetted correctly?  A pro builder who knows what he is doing and has all pertinent information about the engine absolutely should be able to get them in the ball park.  But only once they are on the engine can it be determined if they are right or still need fine tuning.

RE timing, what is the initial timing, how much mechanical advance does it have and at which rpm does it get full mechanical advance?


Lawrenceville, GA

Well let me get your opinion about this, when I first got the engine running it started dieseling. So I started using a Lucas Oil Octane Booster, the diesling stopped, I've put over 3,000 miles on the car. The only time it's ever dieseled on me is when the fuel mixture is off or sometimes if I'm really low on gas but hardly ever. The carburetors (3X2 Fenton Intake, 2110's Holleys) are professionally built, specifically to my set up. Timing is correct, havent checked it in awhile but probably will again. If it was detonating since day one it probably would've already done the damage and hurt the car by now right? Do you think continueing to use the octane booster is the solution? It's been running fine and doesn't deisel when I run the booster

The engine does not shut off when detonation occurs.  It will detonate until it destroys itself, at which point it does shut off, for good.

Dieseling is detonation.  You need to fix that.  It could be as simple as a tuning issue.  It can also be a mechanical issue like too much compression, which is a more involved and expensive fix.  In your oil pressure drop thread, you stated that you have 11:1 compression.  This is usually far too much for pump gas and can very likely be the reason.

The only way you will achieve 11:1 with a 314ci Y Block and iron heads is with domed pistons, which is sort of good news, as you will only have to mill the domes to reduce compression and then have everything balanced again.  It should only be machining required, rather than new parts.

If you have not spent much time tuning, then you also need to do that.  Spark plugs which are too hot can also cause detonation.  Sharp edges can cause it; if cylinders or combustion chambers are not chamfered or beveled  after milling, it can be a source of hot spots.


Lawrenceville, GA