Carb tuning question

[iceman]

My engine runs rich at low RPM - above idle, but runs great at higher RPMs. During long cautions the headers will start glowing red and the engine will start misfiring. When we go back to green, the engine will bog down in the turns. My carb is a Quick Fuel 750 CT and my ignition timing is set at 36 degrees. I run a Falcon transmission, so I can't down shift or step on the clutch and rev up the motor to try to keep the exhaust temps down. I'm looking to fix the problem, not find a work-around. I bought a book on Holley Carbs would be great for explaining the basic principles of how carbs work, but actual tuning or repair - Nope! Thanks!

[dirtrace09]

What size engine? What is the jetting now? What fuel? I would check and double check your timing. Is your distributor locked out?

[iceman]

355 sbc 9.5 to 1 compression (rules), jets are 74, 91 octane pump gas (rules), 4.5 power valves, HEI distributer not locked - 36 degree at full advance. Have checked the timing several times, even tried different timing lights. Had a 25 lap feature go caution free - no problems. Next 20 lap feature, one long caution - engine stumbles on the restart and is flat coming off the turns.

[dirtrace09]

How about fuel pressure? Are you running a regulator? How do the plugs look?

[iceman]

6.5 psi fuel pressure - regulated. The plugs were black the last time I checked/replaced them. I haven't pulled them since the last race.

[perfconn]

Take 2 numbers of jets out and lock the distributor timing.Probably need to adjust the 4 corner idle screws in some.They need to be 1 1/2 turns out from bottom.

[hogracer3d]

Idle bleeds plugged?

[let-r-eat]

How much cam?

[iceman]

Cam Duration 282/286, Lift .531/.542

[29 avenger]

does regulator have a bypass if not maybe vapor locking

[perfconn]

Vapor locking won't cause the plugs to be black.

[7uptruckracer]

Lock Distrubutor, set correct timing.

[Lizardracing]

I'd be checking the idle restrictions and air bleeds for dirt and debris. Glowing headers tell me there's is fuel still burning as the exhaust valve opens and the black plugs tells me there is too much of it. I'd surmise the excess fuel is still burning when it leave the valve so figuring out why there is too much near idle and tip in is where I'd start looking beside the timing is where is should be. Just my thoughts.

[jmarkaudio]

A few things need to be done. First, the transition slots in the Quick Fuel baseplates are too large, to fix this you need transition slot restrictors in the metering block face of the main body. 8-32 brass set screws, drilled to .082. And second is lower the idle feed restrictions, it will make idle and transition fuel more stable. For a lowered idle feed I would start with a #66 drill, .033" start with a .070 idle air bleed, tweak as needed. Timing should be locked out. And then take the main air bleeds to .030. Instructions for the idle jet relocation at the link below.

http://racingfuelsystems.myfunforum.org/viewtopic.php?f=31&t=18

[95shaw]

A few things need to be done. First, the transition slots in the Quick Fuel baseplates are too large, to fix this you need transition slot restrictors in the metering block face of the main body. 8-32 brass set screws, drilled to .082. And second is lower the idle feed restrictions, it will make idle and transition fuel more stable. For a lowered idle feed I would start with a #66 drill, .033" start with a .070 idle air bleed, tweak as needed. Timing should be locked out. And then take the main air bleeds to .030. Instructions for the idle jet relocation at the link below.

http://racingfuelsystems.myfunforum.....php?f=31&t=18

makes you wonder what you are buying with namebrand carburetor. seems should be closer out of the box than that no matter what engine combo.