xj550 cuts out and cracks high rpm accelerate

Hi. I have 81 xj550 and carbs are cleaned and synced, battery is new, starter is good and solenoid new. Bike runs and starts good but accelerating full throttle it cuts out like no spark in second and sputters also exhaust pops sometime and always when decelerate from high rpm. Is this ignition coil problem ? RPM goes up 10k with clutch on and neutral then on load full throttle and coughing snap cracle popping. Does new coils solve problem ? Thanks in advance for gurus. Awesome site full of information.

 

You may have float level is off ...at full throttle if float level is too low then it is starving for fuel it may appear to be ignition related , but to me sounds like floats are off. Did you replace butterfly seals ? Adding in vacuum leak is also a problem ...are you running PODS ? and has your jetting been altered ? All can cause problems popping in the exhaust indicates sync is off ...how did you set it (the 4 vacuum gauges my preference ) ?

 

Floats i set to 220mm. Synced them with 2 drill bits, saw someone using this method in youtube and it was ok. No air through butterflies when throttle off. What you mean butterfly seals ? I took old throttle shaft seals away from outer carbs #1 and #4 cyl carbs and put 2 o-rings to both ends. Better than old cracking shaft seals. Yes pods and open exhaust. Bike started this only little time ago and like the cutting is going more bad week after week. I check tomorrow how the coils measure multimeter. I also suspected carb thing first when this started but carbs are now been so many times different settings and tuned that I think they are not the problem now. Yes I changed bigger main jets and intake manifold rubber cracks i sealed from outside good with rtv sealant. Also idle is constant maybe 30 sec then it does little cut also then constant then does that cut again. Tomorrow see how in specs those coils are.

 

I think this is referred to as circular logic.
I suspect carbs.

 

i don't know what that is

drill bits make good holes, that's about it

do o-rings work on 550's?

never mind

 

If the outer seals are bad then the inner ones are bad as well. And the other problem may be fuel flow that is poor from tank. Rust and clogged vent in gas cap may also be a problem.

 

^^^
This, if you did not break the rack (sounds like a no) then your carbs are not right

 

You have to break the rack and separate the carb bodies and remove butterfly plate and pull shaft out to replace inner seals . I suspect you did a bench synch only ...not going to cut it you HAVE to do a running synch ( 4 vacuum gauge hooked to intake boot nipple with bike running to synch all 4 carbs ) .... How big of jets did you go up with the PODS ? You have several issues going against you ...and what did you measure float height at 220 mm? ....with floats looking down 17mm measured from flange to tip of float is good starting point , did you wet set floats?

 

Yes inner seals needs replace certainly also. Have to do that when have time for it. Rust is out from tank with good old acid treatment so no clogged petcock any more.

There were 110 mains and tested 120 those was not good no good power higher rpm. 115 are good mains, power all throttle position rpm goes high only this cutting is interfering my driving pleasure. The floats is set by what I found from this site mikuni bs28 float height measures. 21.5mm -0.5+mm. Dry height.

 

IN THE CHURCH OF CLEAN

Cleaning your Mikuni carbs

Replacing your Hitachi throttle shaft seals (works for Mikiuni too)

Setting the fuel levels

 

Thanks for the links. Will read them.

I checked the coils. #1 and #4 coil high tension wires show 22.8k ohms. #2 and #3 show nothing. Multimeter does not get anything to other coil reading. This coil has little crack on outer shelf. Guess its time to replace it.

 

I replaced the coil with used not even perfect coil and bike runs perfect again with whole throttle position. Was riding almost 3 hours with 3000-11000 rpm and not even one cutting out or cracks in low or middle or high rpm. Smooth sound and torque with all gears.

 

I set those floats exactly like in that link. From carb body to highest float point to 22mm. Many thing motorcycle tweaking succees with common sense.

 

Did you follow up with a wet-set?
Setting by the float height measuremnt gets you in the ballpark, but it is not the final step.

 

No thats in my to do list same time next when i do vacuum sync to carbs. Bike runs nice now but vacuum sync still not bad add.