Dammakins

Hi Fellas,

Apologies for all the posts about this new car I bought - I'm still in the "Discovery phase" and have lots of questions.

I bought a 69 427 a month or so ago and am having trouble with Dieseling. I ran a can of seafoam through the car and had a shop work on the carburetor and have been told it's still an issue. I was told that the previous owner rebuilt the engine and apparently put a high performance cam in it as many knowledgeable Vette people have told me it sounds way more "lumpier" than the L36 originally did. The shop where it's at right now just ran a compression test and told me it is now at 10.9:1 which is definitely higher than the original ratio. I just wanted to pick your brains to see if you guys have any opinions as to why the engine would ping OR diesel after having all the plugs changed and carb dialed in. The shop told me I may need to go out and snag some aluminum heads as the original iron ones may not be able to handle the new compression ratio. Car's currently running 91 octane gas with no additive. I have a friend who has a 66 L72 and never runs octane booster/additive and has zero problems with his car.


Really appreciate all the help!



Alex

sullyman56

Sounds like a timing issue.

MelWff

which is it pinging or dieseling. Pinging sounds like marbles rattling while accerlerating. Dieseling is when you turn the car off and it continues to run on for a few seconds.
You will have to supply more information.
1. You dont have access to 93 octane gasoline?
2. What is the idle rpm, in neutral if a manual in gear if an automatic?
3. Compression tests doent give you compression ratio, the L-36 had 10.25 to start with.
4. What is the initial timing with the vacuum line disconnected?
5. What is the total mechanical advance?
6. How much additional advance is the vacuum advance providing?
7. What does having the carb "dialed in" actually mean? what did they do?
8. does this shop do a lot of corvette or vintage 60's car work?

gkull

For a motor to diesel it has to have a hotspot. My dieseling vette was caused by the spark plugs protruding tips and wrong heat range


I would not trust a mechanic that told me my compression ratio from a compression test


The symptoms caused by excessive compression. Is rattle or ping cruising down the road or lightly applying the throttle

Dammakins

Car does both - Diesel's when shutoff and has pinging noises when you get the RPM's higher.

1). Most gas stations in southern California are 91 octane. I do have access to one station that sells 101 for an arm and a leg though.
2). The car was around 1,100-1,200 at idle when I took it to the shop
3). All I was told was that they did a test and found that it's now 10.9:1
4) - 6). Not sure - Will ask
7). I was told that were adjusting the idle and mixture screws as the car was running very rich when I brought it in
8). Yes - Lots of old cars. They did a frame off resto on my family's 49 3100 pickup. No - they're not Corvette specific

69427

Why is the idle speed so high? That's the fast road to dieseling.

I agree with Sully and Mel above. Sounds like your timing curve at multiple points needs attention.

Dammakins

Thanks.

Shop told me they got the idle down to 800. Curious to ask them about the timing - All I know is that the car has a "newer looking" HEI distributor which sits high and doesn't allow you to fit the chrome shielding over it.

MelWff

1. The 1969 L36 specs call for 800 rpm in neutral for a manual and 600 rpm in drive for an automatic. So which transmission do you have?
2. Try to find out the manufacturer and part number of the HEI distributor which will help.
3. Find out what the shop set the timing for?
4. Are there any other modifications you havent mentioned, such as you no longer have the original Rochester Quadrajet carburetor?

Skybolt

It sounds like you also have a vacuum leak somewhere if you can't get the idle below 800 rpm. Someone probably compensated by manually timing the engine and now your "dieseling". As stated above, running after the car is off? If so,the timing is to retarded, most likely cause by vacuum leaks.

When I first got my car, it ran pretty well, then I dove in to poor performance, and found many little vacuum leaks causing the car to be timed wrong. Now at least I have my slow car back, but it runs fine. I would possibly get another mechanic to look at this, if you can't this yourself.

Good luck with this, as this car is all vacuum. Willcox corvetts has a great help section on there web site, one of which has a vacuum diagram pointing to where and how the lines are run. This may help.

Edit: also make sure the distributor vacuum line is off and plugged when they set the timing, but more importantly is coming off of a port BELOW the butterflys of directly to the intake manifold itself.

roscobbc

Perhaps the car was running 'rich' when you took it in to the garage due to the 'hi-po' cam fitted causing insufficient vacuum at idle and accordingly not activating idle circuits correctly. Opening out the idle screws and richening-up the idle mixture to try compensate for the correspondingly inability to idle would be a 'Bubba' fix. Seems that you also need to find out what cam was fitted to the engine too!
If it does have a 'cam' and still uses the stock ignition timing 'curve' it will be unlikely to help the engine to idle properly.

Dammakins

Hi Mel,

1). I have a 4-speed. So it sounds like they got the idle to where it should be at 800
2). Pretty sure the manufacturer is Pertronix but I'm not 100%. I know car has the "Flame Thrower II" ignition coil
3). Will ask today
4). I know the Rochester Carb on it is a repop and not the original numbers matching one (I have the original in a box). Car also has an electric choke - not sure if that may be the culprit of the problems.

Thanks,


Alex

Dammakins

Yeah - I would love to know the answer as to what cam the former owner put in this car. All I know is that it's definitely not the stock one that went in the L36 and creates that "lumpy" sound when it sits at idle.

530planeman

Alex
Is there a idle selnoid on the side of carb?My 70 has one so as to prevent dieseling.I don't know if 69 used one.
What is total timeing at 2500 rpm? Should be 28 to32 degree
Wes

Dammakins

I don't recall one being added on. My understanding is that the solenoid is hooked to the A/C which my car does not have. I'll ask the shop. Thanks for the suggestion!

Dammakins

I've been told that they checked the timing of the engine and everything is correct and set to where it should be. The shop is convinced that the Rochester Q-Jet is totally dead and beyond a total rebuild. They told me they spent hours yesterday working to dial it in and set it properly. However, they said within 10 mins of getting it to stay at 800 RPM idle, the RPMs would begin to jump to 1,200 and move very inconsistently. I'm going to try and tear the thing off and work with a co-worker of mine who's had lots of experience rebuilding these things and go to town on it. I'm just curious to know if there truly is a point where a carburetor is dead and beyond the point of rebuilding...

Tim Ware

My 454 would "ping" under load regardless of the brand or octane of the fuel. Completely eliminated by installing an MSD distributor, 6AL box & blaster coil. Your problem, as others have suggested, is probably more associated with overall out-dated ignition issues .

Dammakins

Thanks Tim - I was told today that after the shop added additive/octane booster and it eliminated the pinging and dieseling. I guess the engine has problems with the crappy, over-regulated gasoline we have here in CA.

ddawson

Trust but verify. I had no issues with CA 91 on my stock L36.

Base timing was 18 degrees. Q-jet was rebuild by Oley's carburetor. Yes bushings can be bad as well as seals, but it's doesn't mean the whole carb is bad. They can be rebuilt.

forman

send the original carb out to get rebuilt

69427

Detonation (ping) occurs well after the ignition point. Unless that MSD distributor has a timing curve that's retarded compared to your previous distributor, how do you explain the detonation going away?