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First of all, love this site there are lots of super helpful people on here. Hopefully someone can help me pin point this problem...
Im fairly new to carbs and this one is driving me nuts. Its a Carter AFB 625cfm
I got it running, set the timing, idle speed and adjusted everything until i got a good reading on a wideband oxygen sensor. I took the truck around the block for the first time last weekend and after going for about 1/2 mile I would push the clutch in and the air/fuel ratio would shoot to 18-19:1 (super lean). As soon as i stepped on the gas it would drop back down to a normal range, but every time i had to come to a stop it would shoot back to lean (I could also smell it in the exhaust).
So what do i need to adjust/fix/inspect to stop this from happening?
I took it out this weekend and it did the same thing. I would like to actually take this thing out for a drive soon.
for the short time that i have driven it, it runs well. no bogging, hesitation or anything.
It still holds idle when its leaned out, and accelerates off the line fine. I just panic when it gets too lean and drive it straight back to the house.
When I was starting the truck in weeks prior (and even today), i can let it idle in the driveway without driving it and the A/F ratio wont change but as soon as i take it around the block it leans out...
I was doing some research and want to see if its maybe the fuel pump? I have a clear filter and can see fuel moving, but maybe the pressure isnt where it needs to be? Its a brand new mechanical pump so i wouldnt think it would be that but you never know....
Idling in the driveway it's "loaded up" and hot. Small amounts of fuel stick to the inside of the manifold and little airflow keeps the carb hot making more fuel flow. This isn't an unusual phenomenon. Stock many fords had a heated spacer.
A little lean at idle though is just fine and in many ways good, it keeps the plugs clean. As long as it doesn't miss, backfire, stumble, or slow it isn't too lean at idle.
Basically you want as lean as it will run well at idle, as rich as isn't wasteful or fouling at WOT, and a curve in between. A 14.7 stoichiometric is a guide line not a rule.
Idling in the driveway it's "loaded up" and hot. Small amounts of fuel stick to the inside of the manifold and little airflow keeps the carb hot making more fuel flow. This isn't an unusual phenomenon. Stock many fords had a heated spacer.
A little lean at idle though is just fine and in many ways good, it keeps the plugs clean. As long as it doesn't miss, backfire, stumble, or slow it isn't too lean at idle.
Basically you want as lean as it will run well at idle, as rich as isn't wasteful or fouling at WOT, and a curve in between. A 14.7 stoichiometric is a guide line not a rule.
Im ok with it being a little lean, but 18-19:1 i think is a little too lean; the same way that 3-4 points the other way (11-12:1) is too rich and will foul the plugs/cause carbon build-up. the motor only has 19k miles on it so i'd rather not cause any damage to it.
Whats throwing me off is that I can let it sit in the driveway and idle for 45 mins and it wont lean out, it just hangs around a normal range. It literally only happens after i drive it.
Im ok with it being a little lean, but 18-19:1 i think is a little too lean; the same way that 3-4 points the other way (11-12:1) is too rich and will foul the plugs/cause carbon build-up. the motor only has 19k miles on it so i'd rather not cause any damage to it.
Whats throwing me off is that I can let it sit in the driveway and idle for 45 mins and it wont lean out, it just hangs around a normal range. It literally only happens after i drive it.
Two simple truths here, lean at idle isn't going to damage anything, and there's only so much you can do with one of those carbs.
06-28-2014, 03:05 PM
