Mtr stumbling, you tell me?
04-19-2009, 11:45 PM
#1
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Mtr stumbling, you tell me? Carb'd 346" LS1, cam-only internally.
239/247 @ .050 comp cam
QFT 750 Mech carb
-4.5Hg PV
-jetted 74's fr and 84's rr
MSD 6LS
-MAP reads 14.7 psi dead, 10.5 psi idling
Air/Fuel while idling is 12.0-12.2
Vac modulated 4l60 MVB
Vig 4400 converter
Idling at 900 rpm
When I put it in gear(1st or rev) the mtr stumbles and tries to die. You can give it some throttle to keep it from dying, or if you do nothing> it dies.
Other things that happen going into gear:
-A/F goes from 12.0 to 10.0(bottoms out)
-MAP goes from 10.5 psi to 12.5 psi(needle jump around)
-RPMs fall from 900 to 500.
I did some fooling around with timing and idle adjustment on the carb. It seems to do best with 22deg of idle timing and 2 turns out on the idle screws, all four corners.
Things I've already done:
-Checked for vac leaks>none
-Checked power valve>good
-Cleaned metering blocks, jets, the hole carb>no trash found
-Fuel PSI set at 6.5psi as per QFT tech
-Fuel bowls set 1/2 way up on sight glasses per QFT tech
-Endless adjusting of idle screws
I took the car out on the road and it pulls good, runs out without issue. Just have this idling problem when going into gear... I can increase the idle rpm to 2000 and it won't go dead but it sounds like a 'tater truck.
I'm at a loss of what to do next. I'm tempted to fool around with the air bleeds to lean the idle mixture up a bit as it seems like it's loading up. I've had some locals tell me to plug the front PV and square up the jets.
Any suggestions??
239/247 @ .050 comp cam
QFT 750 Mech carb
-4.5Hg PV
-jetted 74's fr and 84's rr
MSD 6LS
-MAP reads 14.7 psi dead, 10.5 psi idling
Air/Fuel while idling is 12.0-12.2
Vac modulated 4l60 MVB
Vig 4400 converter
Idling at 900 rpm
When I put it in gear(1st or rev) the mtr stumbles and tries to die. You can give it some throttle to keep it from dying, or if you do nothing> it dies.
Other things that happen going into gear:
-A/F goes from 12.0 to 10.0(bottoms out)
-MAP goes from 10.5 psi to 12.5 psi(needle jump around)
-RPMs fall from 900 to 500.
I did some fooling around with timing and idle adjustment on the carb. It seems to do best with 22deg of idle timing and 2 turns out on the idle screws, all four corners.
Things I've already done:
-Checked for vac leaks>none
-Checked power valve>good
-Cleaned metering blocks, jets, the hole carb>no trash found
-Fuel PSI set at 6.5psi as per QFT tech
-Fuel bowls set 1/2 way up on sight glasses per QFT tech
-Endless adjusting of idle screws
I took the car out on the road and it pulls good, runs out without issue. Just have this idling problem when going into gear... I can increase the idle rpm to 2000 and it won't go dead but it sounds like a 'tater truck.
I'm at a loss of what to do next. I'm tempted to fool around with the air bleeds to lean the idle mixture up a bit as it seems like it's loading up. I've had some locals tell me to plug the front PV and square up the jets.
Any suggestions??
04-20-2009, 12:07 AM
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I've adjusted the screws in on all four corners to 1/4 turn out and that only brings the ratio up .2~. I'm guessing the next step would be go up with the air bleeds. It's got 33's in it now... so, up to 35's?
