I have a 1978 ironhead sportster that I spent 2 years building in my garage. I have it all back together and have it fired up. It has a bendix with adjustable main jet and points. I built this bike on a tight budget and will upgrade to electronic ign. and a CV carb down the road but for now I have set the low speed 2 turns from seat and the main 4 turns from seat. It idles ok and low speed is ok but has soon has i give it some throttle it pops, spits, wants to die. Any ideas?

Thanks for any help you can give
T-Ron

 

It is too lean. Richen it up, likely by backing out the main jet, but possibly both of them. And of course, make sure there are no air leaks, the circuits/jets inside aren't gummed up, etc.

Make very, very sure that all the screws are tight on that Bendixcarb. It also would not hurt to carry a small fire extinguisher in your saddle bag. They were known for leaking gas and bursting into flames. I've seen it happen and put one out at a gas stop once.

 

For the guys saying to change your jets, specifically idle and low-speed jets ignore them. The bendix/zenith has one fixed jet, or the adjustable main jet if you got that version or installed your own. Considering you mention it, you've got the adjustable jet. If your idle and low-speed is working fine your air fuel screw is set right at the moment. The tuning instructions mention getting your bike up in rpm(4500) thru to second gear and seeing how it rides. If it sputters or has a hard time you need to adjust your main jet screw till it doesn't and then adjust the air fuel mix screw as needed followed by the throttle side idle screw.(the one that pushes your throttle open as it tightens on the carb end of the throttle cable.)
stock setting for this carb is dial the jet down till the spring is coil bound, dont crank it then back it out 4 full turns. Adjsut from there. The air fuel mixture screw is stock setting once screwed till coil bound and backed out 1 full turn. On the fixed main jet version I've read it stock setting at 1 and 3/4 full turn out.

For both of these adjustments, the air fuel mixture richens at it closes towards the carb body. The main jet richens as it backs away from the carb body.
Got the zenith instruction paper in front of me.

​​​​​​​I realize it's been a few years, I hope you got it running. For others looking for the answer I got some instructions here.