ironhead backfire

[ironhead rocco]

I just bought my first harley a 1984 sportster with a keihin butterfly carb i rebuilt the carb because of a backfiring condition but it still sometime happens .My first question is does the idle air screw on the carb come out because the head is all messed up ans is hard to set and second do you have any ideas what else it might be its driving me nuts

[L.Linkert]

Do a compression test and replace the maifold to head seals?

[ironhead rocco]

Thanks for you help ill do a compression test what should the number be also do you know if the idle air screw on the keinhin carb can be replaced?

[Ironhead1977]

Yes, you can replace the Idle mixture screw can be replaced, not sure the part number. Iam sure someone here might know the part number. Is the timing correct? I had this same problem when I rebuilt my 77' Ironhead, and finially it came down to the timing, Not sure what else it could be I am kinda new to this Harley world also. Good luck, post some pics..

[ironhead rocco]

tHE SCREW ONLY TURNS OUT SO FAR I NEED TO DRILL IT OUT I JUST WANT TO BE SURE BEFORE I MESS UP THE CARB

[ToddM]

Originally Posted by ironhead rocco

Thanks for you help ill do a compression test what should the number be also do you know if the idle air screw on the keinhin carb can be replaced?

The factory service manual should have the cranking pressure listed, as well as the procedures to check it. MAKE SURE YOU HAVE THE PROPER MANUAL BEFORE WORKING ON IT!!!!! I can't remember what it is off-hand. My 1976 was over 190, but then again, I had 12.5:1 compresssion pistons in it. Make sure both cylinders have similiar pressure, at least within 10% of each other.

Check for intake and exhaust leaks, too. They can cause backfiring. So could worn ignition parts, including the coil, wires, plugs, points, advance unit, weak battery, etc.

Only after checking these things would I worry about tuning the carb. A small leak could have you fiddling with the carb adjustments for weeks! Follow the book for adjustment procedures.

Another bit of advice... if you can afford it, scrap the carb and get an S&S Super E. They work best on those engines.