Rich running condition/other problems
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8th Gear
Joined: Mar 2024
Posts: 8
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Rich running condition/other problems
Hey guys, I have a 351w with factory dish pistons and some unknown aftermarket aluminum heads. I am having an unfixable rich running condition. At least I think it’s rich.
I have an edelbrock avs2 800 cfm at the leanest jetting and metering package on the tuning chart and still have spark plugs that are trying to foul. There is a slight bit of oil on the outside ring of the plugs, nothing too crazy tho IMO.
I have heard that aluminum heads use longer reach spark plugs than factory, I am using factory plugs; could this be causing fuel to pool up on the plug?
Additionally I am running a 160 thermostat, could I need a hotter plug to burn off the fouling? Or should I try to run a higher thermostat to maybe mitigate the blow by?
sorry I know it’s a lot of info, but I am at an impasse! Thanks for any help you guys can give me!
I have an edelbrock avs2 800 cfm at the leanest jetting and metering package on the tuning chart and still have spark plugs that are trying to foul. There is a slight bit of oil on the outside ring of the plugs, nothing too crazy tho IMO.
I have heard that aluminum heads use longer reach spark plugs than factory, I am using factory plugs; could this be causing fuel to pool up on the plug?
Additionally I am running a 160 thermostat, could I need a hotter plug to burn off the fouling? Or should I try to run a higher thermostat to maybe mitigate the blow by?
sorry I know it’s a lot of info, but I am at an impasse! Thanks for any help you guys can give me!
Lead Driver
Joined: Jan 2019
Posts: 5,086
Likes: 869
From: N.W. Alabama
Need to figure out what heads, to get correct plug, stock cam?, how much timing before you get pinging, what made you think you need a 800cfm carb? prolly need to step down a few 100cfm's with a stock cam.
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8th Gear
Joined: Mar 2024
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comp xe 274h flat tappet, 230 ish duration at .050 if I remember correctly. Lopes pretty good. Can’t find a thing on the heads. I used a mic to find the length to the end of the threads for the spark plug hole and it came out to 3/4 inch. Nervous to move to the longer plug because I’ve heard those consequences are much worse than running one too short. At wot I can run upwards of 40 degrees if I really wanted to without pinging, at part throttle however I was running into pinging around 2000 rpm. Hooked up vacuum advance and bump total timing down and that problem is not near as bad
Thread Starter
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8th Gear
Joined: Mar 2024
Posts: 8
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comp xe 274h flat tappet, 230 ish duration at .050 if I remember correctly. Lopes pretty good. Can’t find a thing on the heads. I used a mic to find the length to the end of the threads for the spark plug hole and it came out to 3/4 inch. Nervous to move to the longer plug because I’ve heard those consequences are much worse than running one too short. At wot I can run upwards of 40 degrees if I really wanted to without pinging, at part throttle however I was running into pinging around 2000 rpm. Hooked up vacuum advance and bump total timing down and that problem is not near as bad
Laughing Gas
Joined: Jul 2009
Posts: 1,032
Likes: 424
From: NE Ohio
800cfm is waaaaay too big for a stock-ish 351W. Heck, I was running a 670cfm Holley Street Avenger on my mildly cammed (X4262H) 9.4:1 393W - That's another 13% bigger than the stock 351!- and it passed Ohio's emissions testing leaned out a bit (emissions tested at idle, and 2500rpm)! Oh, the headers were glowing red, but it passed. I daily-drove that car/engine for years, but stepped up to a 750cfm carb for racing with a self-imposed 5400rpm limit. Street manners were better with the 670.
Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
An 800 cfm carb is WAY to big. As for the plugs, if they're not protruding into the chambers, then that will cause them to look as if the mixture is too rich. And your cam is much too big for your comp ratio. Post pictures of the heads. There should be at least a part number on them somewhere. Your engine would be happier with a smaller cam (like an EFI grind) and a smaller carb. Or just disconnect the secondaries on that carb and run it as a 2 bbl. It will flow a little more like that than a Holley 500 cfm 2 bbl does. A Holley 500 2 bbl is half of a 750 CFM 4 bbl.
Cargo Master
Joined: Oct 2020
Posts: 2,705
Likes: 800
Most aftermarket aluminum heads use gasketed plugs with a 3/4 thread like an Autolite 3924. If you're using the 3/8 thread plug then that puts it up inside of a hole and it will run poorly. Check that first.
I don't think I'd worry about the carburetor size very much. Carter carburetors are not rated at the same depression as a Holley so for the same cfm rating they are smaller by about 15% or so.
I don't think I'd worry about the carburetor size very much. Carter carburetors are not rated at the same depression as a Holley so for the same cfm rating they are smaller by about 15% or so.
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