Running extra rich

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Joined
Aug 13, 2010
Messages
885
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Location
Conway, S.C.
My Car
1972 MACH 1
2019 F150
Was ruuning rich on old carb so bought new carb 600CFM. Now popping from tailpipe. Pulled plugs and all are black carbon covered. Should I go up one heat range on new plugs or could something else be wrong

 
not2old,

Have you checked your timing according to your cam selection. My chevelle needed to run richer due to the higher lift and seperation, If it's doing the same thing with 2 differnt carbs, you may want to take a look at it.

 
Did you pull the plugs and look at them before installing the new carb. The black carbon may be left over from the old carb, just a thought.

 
what type of ignition are you running if you are running pertronix make sure to bypass the resistance wire. You need a full twelve volts. I was burning spark plugs and getting backfires like crazy from the tailpipes. Now it's running great. If you are not running pertronix or you have bypassed the resistance wire. Check your wires and coil. If you are not getting good ignition putting in hotter spark plugs will probably not help you. giving the plugs a good cleaning wont hurt. Better yet get a brand new set.

 
Last edited by a moderator:
traditionally:

if your carb is too big, the engine will run lean.

if the carb is too small the engine will run rich.

you may have ignition wire issues as others have pointed out since your popping only from one bank.

you can check fire easy using a timing light, use it on all 8 wires and watch the strobe it can be easy to spot one of them not firing or misfiring. if you have a timing light with adjustable timing then you can really check to make sure all the plugs are firing. I had a situation with a bad Pertronix magnetic sleeve were 1 cylinder was no longer firing, i replaced the sleeve under the cap with a new one and the problem went away.

what carb CFM did you run before the new 600CFM?

----

When running right the extra carbon should burn off at highway speed. that is why the old way of checking a tune was to drive 55mph and shut the engine down pull a plug and check it this would give you uncontaminated results of how the Cruise mixture was set. idle always introduced extra carbon on the plugs and made reading them a pain.

if you have a lot of carbon built up then the engine timing will change as the carbon burns off. this can drive you nuts. the engine will retard timing as the build up burns off so you have to check the timing again after the first long drive.

I had a major rich condition in my engine due to bad ignition wires which fowled the plugs with heavy carbon,, when i changed the wires and the car ran decent, i had 18 degrees of initial timing i went on a 40 miles trip i came back the plugs were white and i had lost 8 degrees of timing and the car had settled at 10 degrees of initial timing, all from the carbon burning off and confirmed with my timing light.

----

If you rev the motor fast from idle is it popping also? you may need to play with the accelerator pump settings

 
Sounds like you could have a bad wire(hope).If not check for a loose rocker / valve lash too tight. I would determine which cylinder is missing/popping by removing individual plug wires one cylinder at a time. Restart the engine and see if the engine / sound changes . If it does move on to the next. Do one wire at a time until you isolate the bad cylinder. when you find the bad cylinder swap the plug wire with a known good wire and see if it clears up. It would be better if you could get another wire like a spare to see if you can get it to clear up.If the problem goes away you know you have a bad wire. If you know you have a good wire on the cylider that is missing you will have to dig a little deeper, pull a valve cover / run a compression check etc.....

If you still have a rich condition with two carbs you might want to check for a vacum leak.

 
traditionally:

if your carb is too big, the engine will run lean.

if the carb is too small the engine will run rich.

you may have ignition wire issues as others have pointed out since your popping only from one bank.

you can check fire easy using a timing light, use it on all 8 wires and watch the strobe it can be easy to spot one of them not firing or misfiring. if you have a timing light with adjustable timing then you can really check to make sure all the plugs are firing. I had a situation with a bad Pertronix magnetic sleeve were 1 cylinder was no longer firing, i replaced the sleeve under the cap with a new one and the problem went away.

what carb CFM did you run before the new 600CFM?

----

When running right the extra carbon should burn off at highway speed. that is why the old way of checking a tune was to drive 55mph and shut the engine down pull a plug and check it this would give you uncontaminated results of how the Cruise mixture was set. idle always introduced extra carbon on the plugs and made reading them a pain.

if you have a lot of carbon built up then the engine timing will change as the carbon burns off. this can drive you nuts. the engine will retard timing as the build up burns off so you have to check the timing again after the first long drive.

I had a major rich condition in my engine due to bad ignition wires which fowled the plugs with heavy carbon,, when i changed the wires and the car ran decent, i had 18 degrees of initial timing i went on a 40 miles trip i came back the plugs were white and i had lost 8 degrees of timing and the car had settled at 10 degrees of initial timing, all from the carbon burning off and confirmed with my timing light.

----

If you rev the motor fast from idle is it popping also? you may need to play with the accelerator pump settings
New carb is same Edlebrock 600CFM w/ manual choke. Engine won't idle without strong backfiring through tailpipe so waiting for wires before moving on to next step.

Alan L

 
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