fresh engine

[hotcoupe]

hello all, i have a completely re-built 239 c.i. engine in my `37 1/2 ton, i`m just trying to get a point of reference on a couple of items. some pertinent facts about the motor, owner re-built single 94 carb, #49 jets,4.5 power valve, max-1 cam,piston to head clearance .045", Bubba rebuilt crab, timing is 4 degrees B.T.D.C., Innovate wide band A/F meter. question is the idle speed, seems like the motor "likes" 850 R.P.M., anything lower and it sounds like it`s "laboring", is this idle speed normal or high? the A/F ratio at idle is 13.2 - 14.0, 16.5" vacuum. if i idle the motor in the 600 R.P.M. range the A/F ratio is 18 -20 and the vacuum reads 13". interested in your comments.
tom

[Ross6860]

I'm not a flattie expert, and don't pretend to be.

How do you know you are at 4° BTDC? Did you or someone install a pointer?

I take it you adjusted the idle mixture screws to see if that helps? You may be opening the butterfly enough with the idle screw to get into the main fuel circuit, and it likes it.

Stochiometric A/F ratio is around 15:1, so you are lean at 600 rpm and rich at 850 rpm.

Try setting you r idle at 500 rpm and open up the idle mixture until it stumbles, then back it off until it stumbles again, then go a turn or so back open. Should be close. Use your A/F meter for dialing it in.

Then adjust timing for max vacuum and back it off 0.5" Hg or so.

Tuned by ear...

The cam may require higher idle speed. Hopefully someone with more flathead knowledge will chime in.

[Ross F-1]

Stock jets are #51 for the 8BA's with a 94. I tried #50's for my altitude (5300 ft) and it was too lean. I can't believe with your cam you need a leaner jet.

Have you checked for vacuum leaks?

[Walt Dupont--Me.]

The Max-1 cam is a good street cam but with those tight heads and that cam it will never idle good at 500rpm. With one carb I'd use the 51 jets. Probably 700rpm would be about right with that setup. Walt

[hotcoupe]

thanx for taking the time to respond.
ross6860, i fabbed a timing pointer, when i first tried to tune this carb i had the throttle plates open too much and i`m sure the carb was operating in the high speed circuit. i have since dialed the carb in and i believe it is running on the idle circuit. the motor will not run at 500 R.P.M.
rossf-1, when the motor was idling at 850 R.P.M. the A/F was 13.2 - 14, so it is running a little rich. i don`t understand why the carb runs so lean [A/F 18 -20] at 600 R.P.M. i was hoping on of the carb Guru`s would chime in on this

[Ross F-1]

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High A/F, low vacuum at lower idle could be a vacuum leak or plugged circuits in the carb. Where is your A/F sensor? If it's in the tailpipe there may be outside air at very low exhaust flow rates (low idle).

[hotcoupe]

walt, the carb is running a little fat at idle now with #49 jets and one thing i didn`t mention before, if you rev the motor at 2000 R.P.M. the A/F ratio is about 11.5. i believe this is a carb based problem, i just don`t have the experience to fix it. sorry for the HUGE photo, i don`t know much about computers either.
tom

[hotcoupe]

ross, i welded a bung in the head pipe, about 16" from the exhaust port. i will check for vacuum leaks this A.M.
tom