Carburator Rejet Fail!

[Bartolucci]

Well, I rejetted my carbs on the XS400 and got nowhere. Runs just as bad as before. Plugs are sooty now, but I could only run it with the choke on so I don't know how much of an indication that is.

Here's the skinny:
1) Went from 135 mains to 142.5
2) Went from 42.5 pilots to 45.0
3) New needle valves and seats
4) Carb was cleaned thoroughly
5) Floats were reset

The bike starts cold and races with full choke. Backfires out the carbs and eventually won't run at all when warm.

It was running really lean as I had opened up the exhaust and air intake.

Any suggestions on what to try next?

[Montreux_Blue]

Did you sync the carbs too?

[Bartolucci]

That I didn't think to do. It's only a twin and I don't have a sync. tool. Do you think it would possibly make that much of a difference?

[Montreux_Blue]

It needs to be synced in to run good. Did you try adjusting the pilot screws at least? Here are two good threads that you can do to get it running somewhat until you can buy or borrow some sync gauges.

http://www.xs11.com/forum/showthread.php?t=88
http://www.xs11.com/forum/showthread.php?t=13124

[randy]

That I didn't think to do. It's only a twin

Twins are even MORE sensitive to synch 'cause there are only two cyl. Had an XS400, and they're not easy to get right with out a good synch. Also seems you may have gone too big on the pilots and the mains, a float adjustment would have done the job.

Obviously, it's running too rich. While you're trying to get it running, keep a spare set of plugs clean. Clean and replace the plugs as you go.

[Bartolucci]

Back at it

I see I have much to learn on these. I'll be back at it today and will report later. Meanwhile THANKS for the help!

Tony B.

[Bartolucci]

Progress today

I found one BIG reason why the bike ran so badly. The rubber cap on the vacuum nipple at the intake books was torn off. Major vacuum leak!

I tried to sync the carbs with a vacuum gauge. The needle on the gauge bounced around at low idle so I tried to get the carbs in the ballpark at 4k rpm. I found a 'recipe' for a homemade vacuum gauge and will try that tomorrow.

There are small adjustment screws at the top of each carb that I trust are the pilot screws. I messed with those, but also need to fine tune.

All in all the bike is running and starting much better that it has been. No gas leaks out the air boxes like I had before either.

I pulled the exhaust off and cleaned / prepped it. Then put on exhaust wraps and black paint.

Cheers,

Tony B.