Jetting issue

My 75 Z1b has the stock carbs and it bogs down when the throttle is cracked more than half way. It was previously jetted to run in Denver Co. and is now at an elevation of roughly 900 feet. What main jets should I change too if 110s are in now? By the way their is a bunch of backfire during warm up and then some afterfire when I am engine braking.

Thanks for the help.

I would say 115s. If you have an after market exhaust 117.5. You may also want to raise the needle by one grove and put larger pilot jets in. your pilot jet should be at least a 20. you may also have to change your air jets.

How can you tell if the pilot is a 20? When I did the carb tear down and cleaning I could not find a number on them. Where should the number be located?

The # is right on the side of the pilot jet. You will see the distinct Mikuni Square and the # is right behind it.

ok. I installed 117.5 main jets and it does not bog down in gear any more but my pilot jet is a 17.5. My maintenance manual says it should use 17's while you guys say 20's. What should I do?

If it runs good and the plug color is good, run it. For the record, I think most of these bikes had pilots a shade lean to reduce emissions. My California 750 twin came with 40 pilots, the standard set for that year for all the other state's models was 45, and it runs best with a 47.5 or 50 pilot. The jets are cheap if you want to buy a few sets and try them.

I used to run the stock jetting on my new 74 Z1 in Miami Fl with an RC pipe on it. Ran 12.19 @ 108.95 which wasnt bad back then with a fatboy riding

I have the 83 750f model 4cyl. I belive the pipes are MAC's. What should I run for mains and pilots?

Well the 20 pilot jets and 117.5 mains are in and what a big difference. There is a lot less popping on decel and it doesn't bog down no more!! I also replaced the vacuum caps and it idols so much better. The bike also starts very quick now too. Thanks for the help.