Lean At Idle

[38932]

I have a 7040263 which seems to be lean at idle. The engine starts and runs on choke but idles very low. Once choke is open engines wants to stall. I tried the TIP In procedure at 2000 rpm and also at idle using the choke flap. The engine idles up. It appears to be hunting as well. Idle screw is turned in as far as it will go just to keep it at idle. It eventually will stall.

I rebuilt the carb with one of Cliff's kits using the #2 recipe. Cliff recommended 74 mains with 42b primary rods.

Engine is 400 .30 with ported 48 heads, cast intake, HO exhaust, Summit 2802, Pertronix. Engine sounds and runs great. Plugs are very light tan color.

Any ideas?

[38932]

Some additional info:

I adjusted the carb using a vacum gauge. Mixture screws approx 5 turns out, has 15"vacum at idle. Nice steady idle when it decides to idle.

Also, compression has been lowered to 9.5. Rebuilt distributor with new vacum advance and properly working curve. Initial set at 10.

[Cliff Ruggles]

What size idle tubes, and DCR's?.....Cliff

[38932]

Idle tubes are 37, DCR could not get accurate measurement but they are over 55. I know this answer does not help.

The jets are 73 with 42b rods, not 74. Inlet seat is .135.

The idle mixture screw adjustments make a slight difference but not as dramatic as I am used too.

[38932]

I guess I need to remove the idles restriction tubes to measure them.

[autonaut]

Try and find out if it is taking in false air through the baseplate or booster. Use a non lit acetylene torch for the baseplate. Check the booster to by turning off the vehicle and wait 30 secs before pushing the brake pedal.. If the booster is tight, it will still have vacuum to help you press down the pedal. If not, there is a leak somewhere from the line going to the booster or the booster itself.

Also, have you checked to see where the float level is at? If the float level is too low this could be the problem.
Check for fuel delivery. Clogged filter, bad pump, too low pressure.

[38932]

Problem solved......When I rebuilt and modified the carb I put the new idle tubes in and did not drill them. For some odd reason I thought they were pre-drilled . I removed the tubes, drilled .038 and problem solved. Engine is very happy now, idles and sounds great.

[Cliff Ruggles]

Good news!....Cliff