86 XJ700S (Hitachi's) Sputters Between 4k to 6.5K RPM'S

My 86 XJ700S sputters between 4K to 6.5K RPM'S. It idles just fine and runs good up to 4K, and after 6.5K it seem to clear up some. On the freeway it seems to require a little extra throttle to go faster.

The carbs were soaked and cleaned very well using compressed air,
with all the orfices and jets being probed and cleaned.

The carbs were synced using a morgan carb tool.

I sprayed gumout carb cleaner on the carbs and intake manifolds while running and that did not change the way it ran.

I had an experienced motorcycle mechanic adjust the mixture screws.

A new O.E.M. air filter was installed.

The engine has excellent compression and does not smoke at all.



My first guess is that there is some dirt in the carbs. Any ideas as to what is wrong or what to do next???
:?

 

mine was similar until i replaced plugs and plug caps, also poor connection where plug caps screw onto leads.

 

Thanks for replying.

I replaced the spark plugs and the spark plug end caps. The spark plug end caps are NGK 5K. It runs the same so I will keep trying to figure out what is wrong.

 

i have the exact same problem.
Any help guys??

 

i had the same problem but it was everything UNDER 4K RPMS. 4 to 6 ran like a champ to me.

the ignitor box wasn't retarding the spark timing for lower rpms. it was running advanced timing.

since you have the problem ABOVE 4k. it might not be advancing the timing.

 

It sounds like you've done it all right except for one.
Do not trust any one to work on your bike.
Before I learned the right way a yamaha mech told
me to "just turn the pilots lean unill it backfires, then
1/2 a turn rich after that.
Read RickOMatics guides on tuning the carbs-A dime or nickle width of
a turn makes a huge diff in performance.

Did you polish the throttle body slides? you may have one or more
"sticking". And yes, even after a cleaning something can get by and
cause a prob.