okay so i picked up a 99 900 that need some work.the bike will start and run but idles rough,sometime it will rev up in neutral but it hesitates and bogs.i took the carbs off and cleaned the main jet and the slow jet.everything works as it should inside the carbs.im kinda at a loss as what to check next.i dont think i have a misfire but may try to pull a plug while its running to see if theirs a difference.i feel like the bikes not getting enough gas.sometimes the bike will rev up out of nowhere and run at 4k if i try to adjust the idle back to 1k she sputters.the plugs where replaced by the previous owner a good friend but they may have gotten fouled. any help!!

 

Leaking inlet rubbers? Carbs properly clean inside? That is, have you tried at least blowing them through with an air hose, at best you should get them ultrasonically cleaned.

Dave

 

yea i cleaned the carbs. i didnt separate them but i took out all the jets and ran a copper wire through then.gonna try a compression tester before going any further the bike was wrecked about two years ago the guy who wrecked it is a friend and as far as i know the engine is still good.the number 4 header is not gettting hot!!i am getting spark at number 4, i have swapped plugs.after the comp test imma clean that carb again now 4th time having it off.my hope is clogged jets or something on 4.hopefully the motor is still good it only has 12k thanks for the help

 

Sounds like an intermittent spark issue on the #4. If that header is not getting hot - you're not getting combustion (at least not consistently). When it spastically revs and then bogs - that sounds like an intermittent spark - intermittent combustion. You're idling the bike high to keep it running on 3 cylinders, the 4th kicks in and the revs shoot up. You should be able to easily hear that there is a misfire.

Is it coil-on-plug with the 900's?

 

there is no fuel filter on the bike either so it seems possible that the carbs are really gummed up.gonna get a compression tester before i go any further.will report back

 

I could be off here but have you checked your battery voltage. I had very similar symtoms to this and did just as you did, carbs plugs all the usual and then.....why would I suspect the battery if she fired up easily ?......just took my meter and did the measurements. One foooked battery !!!. Replaced. New it was sorted as soon as she fired up, crisp. Been right ever since. Not exactly sure what was going on as it would always fire up easily. Worth a check though mate
Best of luck

 

actually there might be a filter attached to the peacock leading into the tank itself.. depends if its a original part.. i'd take a look and pull it apart..

 

I wouldn't do the compression test first. I'd add an in-line fuel filter, clean the carbs, and then concentrate on the electrical side of it. Coils, plugs, etc - and wes has a good point. I've seen bad batteries do some weird things.

Remember, it's most likely something simple and is most likely not something internally with the motor like fried rings or bent valves.

 

i cant imagine it being a compression issue,i know the guy who i got the bike from i know this bike ran good 2 years ago when he wrecked it.i have cleaned the carbs,but they may need a deep clean.the plugs and spark are good.i have moved the plugs and coils and still have the issue on #4 so i wanna check the compression just to make my mind feel better.i have cleaned out the jets on the carbs again as well.the battery is new and i have a battery tender on the battery.thanks for all the help i will report back after christmas.hope everyone has a good holiday.

 

Oh, if you've swapped coils and plugs and it's still #4, I bet it is in the carbs then. There are some good threads about deep cleaning the carbs. Good luck! Merry Christmas.