Running lean at WOT
Thread Starter
Racer
Joined: Jun 2014
Posts: 431
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From: Las Vegas Nevada
Running lean at WOT
Hey guys, so I've got an AFR gauge and I've been seeing that my ratio drops as low as 17:1 under full throttle. I'm really not sure why this is happening, I don't seem to have any issues holding 6.5 psi fuel pressure and have a pump with plenty of gph.
So I have this carburetor (It's a Quick-Fuel style 650 vac secondary). I have 67 Primary jets (little rich at cruise so probably should be 65), 76 secondary, a 5.5 PV. According to the spec sheet that came with the carb it has a 33 pump nozzle, 31 high speed air bleed primary and 31 secondary, 63 idle air bleed primary and 63 secondary, a 46 primary power valve restriction (and a plate.. thing in the secondary side), and a 97 needle seat on both primary and secondary.
Engine is a mild/performance 350. This engine build from Hotrod is very similar to mine but I have better heads, according to them it should be capable of 440hp/440ftlbs at the crank.
So.. any idea what's wrong with my tuning? I feel like my secondary jets are large enough to not cause a lean condition, but I'm not really too sure.
Edit: The lean condition gets worse as my engine warms up. Cold WOT gets 15:1. Warm WOT gets 17:1.
So I have this carburetor (It's a Quick-Fuel style 650 vac secondary). I have 67 Primary jets (little rich at cruise so probably should be 65), 76 secondary, a 5.5 PV. According to the spec sheet that came with the carb it has a 33 pump nozzle, 31 high speed air bleed primary and 31 secondary, 63 idle air bleed primary and 63 secondary, a 46 primary power valve restriction (and a plate.. thing in the secondary side), and a 97 needle seat on both primary and secondary.
Engine is a mild/performance 350. This engine build from Hotrod is very similar to mine but I have better heads, according to them it should be capable of 440hp/440ftlbs at the crank.
So.. any idea what's wrong with my tuning? I feel like my secondary jets are large enough to not cause a lean condition, but I'm not really too sure.
Edit: The lean condition gets worse as my engine warms up. Cold WOT gets 15:1. Warm WOT gets 17:1.
Last edited by Shdggsdv; Apr 15, 2020 at 04:11 PM.
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Ck fuel pressure at WOT. Bowls could be running dry or low. CK fuel level in carb.
JIM
JIM
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Are you sure you're getting the secondairies to fully open with the pedal?
Thread Starter
Racer
Joined: Jun 2014
Posts: 431
Likes: 15
From: Las Vegas Nevada
Nah it's an adjustable just like this one, but if my secondary isn't opening enough would that really cause a lean condition? If I understand correctly the secondary adjustment effects both fuel and air on the secondaries, no?
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Thread Starter
Racer
Joined: Jun 2014
Posts: 431
Likes: 15
From: Las Vegas Nevada
Also! I found out my lean condition at WOT is more significant when the engine is warm vs cold.
Cold: WOT gets 15:1
Warm: WOT gets 17:1
And this only applies to WOT, my part throttle and cruise are totally fine
Last edited by Shdggsdv; Apr 15, 2020 at 02:34 PM.
Racer
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From: Millbrae California
try either leaving the gas cap off or loose to see if that effects the lean at WOT problem, we have seen quite a few lean at heavy throttle condition problems that were caused by a fuel tank venting problem. Henry @ olescarb
Is my vette stock?? HAHA
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Whats your fuel pressure, when my carter was failing it would do this. It would pump enough fuel to run and keep up under normal low power driving, but was only putting out about 3 psi. Not enough for W.O.T
Thread Starter
Racer
Joined: Jun 2014
Posts: 431
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From: Las Vegas Nevada
Thread Starter
Racer
Joined: Jun 2014
Posts: 431
Likes: 15
From: Las Vegas Nevada
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From: At my Bar drinking and wrenching in Lafayette Colorado
Remove the secondary jets and see if it goes pig-rich at WOT. If it's still lean at WOT, the carb has a secondary fuel feed problem - maybe a passage or two not drilled in the metering block or the carb body.
Lars
Lars
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You could try blocking the secondary's closed and just go WOT on primaries to see if it does better. If you can get a longer line for fuel pressure gauge you can route out from under hood and use wiper blade to hold it for a quick blast. Some tape will hold it steady.
JIM
JIM
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You could try blocking the secondary's closed and just go WOT on primaries to see if it does better. If you can get a longer line for fuel pressure gauge you can route out from under hood and use wiper blade to hold it for a quick blast. Some tape will hold it steady.
JIM
JIM
Last edited by Rescue Rogers; Apr 22, 2020 at 05:27 AM.
Thread Starter
Racer
Joined: Jun 2014
Posts: 431
Likes: 15
From: Las Vegas Nevada
You could try blocking the secondary's closed and just go WOT on primaries to see if it does better. If you can get a longer line for fuel pressure gauge you can route out from under hood and use wiper blade to hold it for a quick blast. Some tape will hold it steady.
JIM
JIM
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You've verified the float levels are high enough right?
JIM
JIM
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From: Crossville TN
And you are sure that pushing the accelerator pedal to the floor (NOT working the carb linkage by hand) actuates the secondary vacuum system AND the vacuum signal will pull them completely open?