hot 4 and 6 cyl's

[airplanemech]

I had a new 350 crate eng put in a 84 chevy silverado about 2 yrs ago. I had recently pulled the plugs out and noticed that 4 and 6 was running hot. The insulation on the plugs was chipped and cracked, i also at the same time had some hesistation when i try to get on it. I took the truck in and they had found that my primary coil lead was shorting to the coil itself-i never thot of chkg that. Anyways, i had put new plugs in and ran it for bout 3 weeks or so and fig that i get some carb cleaner and spray around the intake manifold and listen for a change in RPM. I never noticed a change when I sprayed all around it, i used bout 1/2 can. So I am kinda stumped as to what is causing it. It does have the Rochester carb on it that I had on the 305. Should I try and mess w/ the mixture screws--even those adjustments are adjusting for curb idle. If i remember right reading somewhere if the spark plugs look like I mentioned it means its happens at hard accel. I would think that the jets from a 305 to a 350 would make that much of a difference. well hope that someone can help me out.

u can also email at rpapmech@aol.com

[bowtie355]

You might want to try using a propane torch with a piece of rubber hose on it instead of the carb cleaner. I've had better luck with that setup to detect leaks.

Have you run a compression test?

Jim

[raceman6135]

It sounds to me like it's running lean. What do the other plugs look like? They all should be a nice tan/light chocolate brown colour. If they are bone white, it's running lean.

Numbers 4 and 6 are not typically the problem on small block Chevrolets; it is usually numbers 5 and 7 that experience ignition problems as they are side-by-side at the back of the driver's side of the block and they are also sequential in firing order.

Depending on the exact tag number off the carburetor, it's a very real possibility that it is your problem. Which crate engine do you have? What year/model/etc. is the carb from?

Adjusting just the idle mixture screws on the Quadrajet will not eliminate all your problems, unless all that damage is getting done just when you're driving around with the carb still on the idle circuits. Once the carb tips over into the intermediate circuit, the problem will either get worse or it will get better. Same with the high speed (aka main) circuit.

I would not haphazardly change jets in the Q-jet. They really should be matched to the metering rods that ride in them. Also, a late model, emissions-laden 350 might actually have LEANER jets in it than an early '80s, non-emissions carb might have!

[airplanemech]

the other plugs look normal on the other ones. so u think that i shold consider gettin a carb that is jetted to a 350 instead of a 305? AS IN THE PREVIOUS POST --- 5-7 FIRE AFTER EACH OTHER SHOULD BE MY PROBLEM AS IN HOT--NOT! AND I HAVE A FEW FRIENDS THAT RUN DRAG CARS AND(OR) BLD THEM. THEY R ALSO STUMPED ON Y 4 AND 6 IS RUNNING HOT ON A 2 YEAR OLD CRATE 350. I AM TALKIN FRIENDS THAT RUN LOW 9S ON 383, THIS IS A TIME IS A SIMULATED DYNO--THEY ARE STILL DOIN MINOR WORK TO IT--THE COMPANY IS - MUSCIAL CARS OF OKLAHOMA) AND THE 502 ENG( THIS IS A HOME BLT)!

ANY HELP ??

[airplanemech]

come to find out it was 4 a 6 rocker arms that had major lash in them. being a crate they set them cold.

[Gearhead52]

I wouldn't put all my eggs in the lash basket......I'd have to agree that the problem sounds like a lean condition. Many things that can cause it. Vacuum leak, fuel starving, EGR malfunction, etc.

I've seen this a few times before and will get servere enough to burn a valve. Most cases a vacuum leak was found. One was the EGR gasket.

Never known a lash problem to cause a lean condition.

[airplanemech]

yeah luckily i didnt burn a valve did a comp test on it 108-120 on all cyl w/ about 55k miles on it.
it really got worse when the truck blew a hose and ran too hot till it just died. also melted the temp sensor. lol its a chevy and its runnin fine.