Engine stutter at full throttle

[buckshot1718]

I have an 81 gs850gl. The bike starts up and idles like a dream. When it is sitting in nuetral i can roll it on full throttle and it doesnt stutter at all. But when im on the road, 3rd gear and up, if i give it full throttle it has trouble getting to high rpms. Engine makes a muffled stutter. Runs perfect in 1st and 2nd, but after that if i give it any more than half throttle it seems to struggle. The bike also had free flowing exhaust pipes when i purchased it, ran like crap, so i beefed up the jets a bit and it helped. Then i was getting suspiciously good fuel mileage, so i figured it was still running lean. Moved the needles up one step and still no difference. Any thoughts?

 

[salty_monk]

Sounds like your jetting is still off... The easy solution might be to buy the Dynojet kit for it.

 

[buckshot1718]

Eh. Thats kind of the expensive route that im trying to avoid.

 

[hampshirehog]

Has the bike still got the original air box with filter or is it running with pods?

 

[Guest]

Well you could alway buy or borrow a set of micro bit and drill baby drill. I did that with my 1000G a few years ago. The PO put K&N pods on it abd it just bogged anything over three grand unless you took it really slow. I could have ordered multiple set of jets, but being that the jets are brass you can finger drill them out very easily. I just found which bit fit the jets size and kept drilling larger to it ran great. Just remember, you can't drill smaller.

 

[buckshot1718]

It has stock air box. Tried pod filters but i couldnt get them to cooperate, ended up just putting the stock filter back on.

 

[Guest]

Are you running an in line fuel filter? If so that may be restricting your fuel demand of the higher RPMs.

 

[buckshot1718]

I didn't think about that, but yes it does have an in line fuel filter

 

[buckshot1718]

Im not sure how i would fix that if thats the problem though, i wouldnt want to run it without a fuel filter.

 

[Guest]

Any thoughts?

Try pulling the choke the next time when it is stuttering under load at full throttle. If it clears out then you are lean, if it bogs just a little bit it is pretty close and if it bogs badly then you are rich.

Eh. Thats kind of the expensive route that im trying to avoid.

To be honest, compared to the damage running lean can do and the time you will invest in chasing the problem, a Dynojet kit looks pretty cheap to me.

It has stock air box. Tried pod filters but i couldnt get them to cooperate, ended up just putting the stock filter back on.

Stock airbox and a pipe shouldn't need more than 2-3 steps in main jet size and slight tweaking of the needle and mixture screws. What mixture screw, jetting and needle position are you are at right now?


Mark

 

[tom203]

Im not sure how i would fix that if thats the problem though, i wouldnt want to run it without a fuel filter.

The stock petcock has a filter,so you don't need another. Remove the petcock to check, or go crazy and buy a new petcock ($50) to eliminate it as possible problem. Make sure gas cap is venting properly or not enough fuel will make it to carbs under loading.

 

[steve murdoch]

As Tom suggests, an in-line filter can sometimes restrict the fuel flow enough to cause an engine stumble.

 

[JTGS850GL]

As Tom suggests, an in-line filter can sometimes restrict the fuel flow enough to cause an engine stumble.

This is especially true if the filter was not designed for gravity feed systems.

 

[buckshot1718]

I'll try and fiddle with the filter. And that choke idea is good too. Thanks all

 

[buckshot1718]

And the mixture screw is as it was. But like I said it is idling just fine. I went 2 steps bigger on the main jet and 1 step bigger on the pilot. Move the needle up one step as well.