bike spluttering. and sometimes running on 2 cylinders?

[xivlia]

hmmm. okay so my bike was running perfectly fine for the last month id say. until recently the bike sometimes runs on 2cylinders. while riding it sometimes jumps back to 4 cylinders, and then goes back to 2....im getting flames coming out of my exhaust when im giving little throttle while going slow...it could be running rich from the jets i got.. 118/120.....used to have stock...i think it was 110/110? Jap specs K plate...and sometimes when i give full throttle to accelerate the bike wont rev past from 4k-6k...it stays there for about 3 seconds and then it just boosts up again...could this be because of too big jets? and about the issue with running on 2 cylinders, can it be ECU? coils, plugs, HT leads?

i hope this wont turn into a 50 page topic with 400+ replies

[magg]

If the problem is consistently occurring at 5000 rpm you might want to check the speedo sensor or bypass, whichever is fitted. Might be intermittent which will limit rpm to 5000 whenever the cdi things the sensor is missing.

Are the flames from the exhaust occurring after running on only two cylinders? If you run on two cylinders for a time and then it goes onto four, the unburnt fuel vapor in the exhaust pipes associated with the two cylinders that had stopped firing can then be ignited and cause exhaust flames.

Main jet sizes only affect the high rpm running. Low speed and mid range should not be affected. 118/120 mains are not particularly rich, they were fitted standard to my grey import to oz and I have had no reason to change them.

[xivlia]

but the weird thing is. its not dead on 5k rpm...and it doesnt ALWAYS happen...it also feels like there is abit of fuel starvation when i give full throttle. and it splutters and struggles to go to higher revs, it does go up in the end.. it just takes some time.

[magg]

Maybe my poor choice of words, the speed sensor cutoff at 5000 rpm does not stop the engine from exceeding 5000 rpm, it just makes it loose a lot of power and thereby the performance falls away dramatically. I also said it might be intermittent. You could use the resistor bypass to eliminate the speedo sensor as a potential source of the problem.

If you think there is a fuel starvation problem, have you checked the vacuum operated fuel tap.

[CMSMJ1]

LOL Ersan..come on mate!

one thing at a time..

You need to try and pinpoint the problem - it might seem random, but something is causing it.

I'd put money on it not being HT or coils..though knowing you have had issues with plugs I would not rule them out.

Carbs..well, yes, can easily be running badly - did you set them up? Are you confident they are right?

What air filter have you got?

[xivlia]

yes i set the carbs right.. well im sure i have. i had adjusted the screw to 2.25 turns for my TSR half system. but they may still not be set right, i cant tell for sure.. i may also need carbs balanced, my idle is fluctuating + - 500rpms.... i didnt have any problems with the bike today. been riding it from college to home and its been fine. it was very cold yesterday.. maybe that could be the problem. i will see...if it doesnt do it again for a while. then im gonna assume it was the cold.

[phil x]

If its a k plate (reg) won't that make it an rvf?
If it is don't they run smaller jets anyway?
Just a thought, Phil

[Cammo]

i didnt have any problems with the bike today. been riding it from college to home and its been fine. it was very cold yesterday.. maybe that could be the problem. i will see...if it doesnt do it again for a while. then im gonna assume it was the cold.

I think that's the wrong way to look at the issue. You have a problem and it's intermittent.

Best to do some diagnosis and go from there, rather than guessing via vague symptoms.

I hate to say it but it sounds typical of an electrical problem.

[xivlia]

nope im pretty sure its a vfr ...if it IS an rvf then i ripped off the guy who i bought it from.. haha !

[xivlia]

hmmm okay. il try and do what i can.