SmokinBBC
Well-known member
Need some help guys with a run on issue.
I have about 1600 miles on the rebuild. 454 +.030, 224/234, .569/.569. Timing is 34 all in at 2800. Initial is 10. There is no vac. advance at idle due to the TCS(cuts advance off in first and second MT). It has the original Q-jet rebuilt with the stock jets and rods. It runs great, but I have a couple of tuning issues to handle.
The AFR at idle is 14.5 to 15. Idle is 700.
AFR at cruise is 13.0 to 13.2.
AFR at WOT is initially 10-11 (pump shot effect?) and then climbs to about 12 to 12.5.
The spark plugs look good, perhaps a little dark/rich.
Here is what I am trying to remedy:
The engine has run on. Sometimes a couple of rotations, sometimes more. There isn't an idle soleniod. The good ole dashpot is still there and working. It idles around 700. The run on is probably due to running lean at idle. The choke blade is strait up and down when warm. It has about 1/8 inch to 1/4 inch of play. If I close it up with my finger by that play, the AFR goes down to about 13.5 to 13.7 and the idle picks up a little bit. This puts the idle AFR a little more in line with the cruise AFR. If I cup it slightly with my palm, I get the same effect which basically verifies a lean idle. Vacuum at idle climbs to 11-12 from 10 when I cup the carb.
Starting the car cold is a little bit of a problem. Needs to run about 15 to 30 seconds before it starts to climb to fast idle. Another minute or 2 before it hits fast idle. Perhaps the choke is set up wrong? I verifed that it has 1/4 inch play from full close before starting the car. Choke pulloff is functional.
I want to get above 13 AFR at cruise and increase the AFR slightly at WOT. I have figured that going up one size in rod will take care of the cruise. If I drop a jet size, I can accomplish increasing both the cruise and WOT AFR.
If I drop the cruise AFR, I'm afraid that my idle will lean even more causing more run on. I don't want to go into the idle circuits if possible. The idle mixture screws are out at 3 1/4 turns. The carb will pop out the carb on light throttle at about 2 1/4 turns. Richening it up more than 3 1/4 has no effect.
So, after a long winded explanation, to get back to the question, before I start tuning for better AFR, what can I do about the run on?
Thanks.
I have about 1600 miles on the rebuild. 454 +.030, 224/234, .569/.569. Timing is 34 all in at 2800. Initial is 10. There is no vac. advance at idle due to the TCS(cuts advance off in first and second MT). It has the original Q-jet rebuilt with the stock jets and rods. It runs great, but I have a couple of tuning issues to handle.
The AFR at idle is 14.5 to 15. Idle is 700.
AFR at cruise is 13.0 to 13.2.
AFR at WOT is initially 10-11 (pump shot effect?) and then climbs to about 12 to 12.5.
The spark plugs look good, perhaps a little dark/rich.
Here is what I am trying to remedy:
The engine has run on. Sometimes a couple of rotations, sometimes more. There isn't an idle soleniod. The good ole dashpot is still there and working. It idles around 700. The run on is probably due to running lean at idle. The choke blade is strait up and down when warm. It has about 1/8 inch to 1/4 inch of play. If I close it up with my finger by that play, the AFR goes down to about 13.5 to 13.7 and the idle picks up a little bit. This puts the idle AFR a little more in line with the cruise AFR. If I cup it slightly with my palm, I get the same effect which basically verifies a lean idle. Vacuum at idle climbs to 11-12 from 10 when I cup the carb.
Starting the car cold is a little bit of a problem. Needs to run about 15 to 30 seconds before it starts to climb to fast idle. Another minute or 2 before it hits fast idle. Perhaps the choke is set up wrong? I verifed that it has 1/4 inch play from full close before starting the car. Choke pulloff is functional.
I want to get above 13 AFR at cruise and increase the AFR slightly at WOT. I have figured that going up one size in rod will take care of the cruise. If I drop a jet size, I can accomplish increasing both the cruise and WOT AFR.
If I drop the cruise AFR, I'm afraid that my idle will lean even more causing more run on. I don't want to go into the idle circuits if possible. The idle mixture screws are out at 3 1/4 turns. The carb will pop out the carb on light throttle at about 2 1/4 turns. Richening it up more than 3 1/4 has no effect.
So, after a long winded explanation, to get back to the question, before I start tuning for better AFR, what can I do about the run on?
Thanks.
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