Sputter at Certain RPMs

[rough n ugly]

I've done some searching, but haven't found anything that describes my problem. The bike is an '81 GS550L. The problem is that the engine sputters at a certain rpm in each gear. It runs strong up until it reaches that certain rpm. In first, it gets to about 7k, and each gear after it the magic number gets less and less until 6th it gets to about 3500. It doesn't matter if it's mild acceleration or wide open throttle. It ran great until a few months ago when a coil went out. It sat for a couple months, I replaced the coil, then this happened. I've swapped in some other coils too, but to no avail. Any thoughts? Thanks in advance!

[spyug]

Welcome.

Well sputtering points to carbs. When were they last cleaned? With the fuels we have today, it doesn't take long for it to go off and or you may have particles in your tank that are plugging a jet or passage.

If you don't know when they were last cleaned I'd say you should strip, dip and rebuild with fresh O-rings. There is a really good tutorial on it that our official unofficial greeter Cliff will provide you with shortly.

Good luck with it and show us some pics of your ride.

cheers,
spyug

[rough n ugly]

Welcome.

Well sputtering points to carbs. When were they last cleaned? With the fuels we have today, it doesn't take long for it to go off and or you may have particles in your tank that are plugging a jet or passage.

If you don't know when they were last cleaned I'd say you should strip, dip and rebuild with fresh O-rings. There is a really good tutorial on it that our official unofficial greeter Cliff will provide you with shortly.

Good luck with it and show us some pics of your ride.

cheers,
spyug

I cleaned the carbs last spring, using the tutorial I found through this site. The fact that it doesn't matter whether it is gentle acceleration, or WOT leads me to believe it's ignition related, but then again, I have no idea what I'm doing. And as for pics, well my user name is "rough n ugly" for a reason.

[mike10]

Sputtering

I have to agree about sputtering.
Most of the time is fuel delivery, Bad fuel. Electrical problems tend to be live or dead engine quits as if the key is being turned off and on. Or just stops dead. I would check for Air leaks also, they can screw with the mixture too much air. CV carbs? I guess.

[rough n ugly]

I have to agree about sputtering.
Most of the time is fuel delivery, Bad fuel. Electrical problems tend to be live or dead engine quits as if the key is being turned off and on. Or just stops dead. I would check for Air leaks also, they can screw with the mixture too much air. CV carbs? I guess.

Yes, CV carbs. That's 2 votes for carbs, so I guess I'll start with a good carb cleaning, and see where that gets me.

[spyug]

As I mentioned gas goes off very quickly these days and your tank can flow things like this:



I have cleaned and rebuilt carbs, put them on and after firing up and running for 10 minutes they ran like crap again with junk like that in the bowls and passages so its not at all uncommon for carbs to go "off" quickly.

Give em another going over. As mike says electrical problems appear differently and are usually more catastrophic as in the bike suddenly dies.

Good luck with it and let us know what you find.