Bike starts randomly bucking when I am riding

[rblankenba01]

Hey guys,


I have a 2003 monster 620 that I just bought a few months ago so I'm still really learning about it. Everything's been going great until tonight. I was riding for about an hour and on the way home my bike started bucking randomly. It did it in almost every gear and I'm not really sure what's going on and if it is safe to ride or not. Any thoughts?

[RUFKM]

More info needed.  Speed, RPM, Shifting or Cruising, Wet, any other observations.

All gasoline engines run on the same four requirements - Fuel, Air, Ignition & Momentum.  Since it was running Air & Momentum are pretty much a given.  Check fuel system for pinched lines/clogged filter.  Ignition can be a little more tricky with a lot of variables.  Never hurts to pull the plugs to get a peek.

Good Luck.

[rblankenba01]

It happens at just about any speed, doesn't doesn't matter what gear I'm in, and it happens when I'm in gear, not during a shift. Thanks for the help.

[erkishhorde]

This is what most people call surging. Perhaps that can help you search for a result. Other than that, I've got nothin.

[Slide Panda]

It happens at just about any speed, doesn't doesn't matter what gear I'm in, and it happens when I'm in gear, not during a shift. Thanks for the help.

Does it happen at a specific engine RPM, or across the band?
It it present while rolling on the throttle, or just when it's held constant?

Are there any modification like an open air box or powercommander?

Miles on it?
Is it up to date on the service?
What grade of Gas?

You've got to give us more to go on.

[chisel]

Does the engine surge if the bike is parked in neutral and run at a constant RPM?

[rblankenba01]

It happens across the band and is present both when I'm rolling he throttle and just holding it constant. I don't have any mods at all, completely stock. Miles are right at 7600, been using 93 octane, and I"m not positive on it being serviced. I just bought it two months ago so I'm not sure when the last owner serviced it.

[Slide Panda]

been using 93 octane, and I"m not positive on it being serviced. I just bought it two months ago so I'm not sure when the last owner serviced it.

Well 1 problem and 1 issue.

Stop with the 93. There's no need for it, and and it may be detrimental to the smooth running of the bike. Basically none of the air cooled monsters right high enough compression to require higher octane levels. Octane actually slows the burn. In a high compression engine this retardation is offset by the compression.. but in low compression engines it can result in poor running, power loss and extra tail pipe emissions.  Fill up with 87.

Speaking of gas - did start shortly after you filled up, or a big rain?

IF you don't know the service records, I'd try to find out.  You are WAY over due for new Cam belts if they have not been replaced in the last 2 years (which is not part of the standard 6k service). And if the bike has not had a 6 k service, it's quite possible the valve need adjustment which can be contributing to this issue.


AND... have you looked at your plugs at all?

[64duc]

  Try keeping your engine rpm at 4000 and above. If this cures it, it's normal.

[rblankenba01]

Thanks for the advice on the gas and yes, it did start happening right after I filled up. BUT I have been running 93 in it for a while and it never did this before. I'll be sure and go with 87 next time though. I havn't looked at my plugs, what should I be looking for?

[Slide Panda]

Well, it's not un heard of get a dose of bad gas. If possible, drain out you current tank full, as much as possible and fill up from a different station and see if that improves the situation.  It's more noticeable in bikes since they don't compensate near as much as modern cars can for problems during combustion

I didn't mean to imply that 93 was the root of the problem - just that it might compound any running issues since it's over-octane'd for our bikes. 87 will work just fine, perhaps a little better and think of the savings!

IF you look at the plugs, they should be a golden to medium brown in color.  Black means the bike is runnig rich, white is lean. Oily.. is oily.

And don't gloss over my comment about the belts - that's serious if one lets loose.

[EEL]

Check you chain tension.

[booger]

I had some mild surging below 4k and just did my valves. Now it's gone. I had some loose closers. YMMV [moto]