GS750 Struggles to get to 80 MPH...

[disstance]

Hello folks,

I took my 81 GS750L out for a romp on the back roads today, and normal riding and up to about 60 MPH the runs like a top. But winding her out above 6k feels dead, it's not a total power loss, but there's a noticeable decrease and I cant actually get the bike to redline. In 5th gear, the bike struggled to get to 80. I could get there, but it took a while. I'm not sure if it's related, but the bike also only gets to about 15 MPH in 1st gear before I have to shift (I've watched some youtube videos of this bike and that doesn't seem normal)

Couple things I noticed while under load above 5k.
1. the noise and the vibration urge me to shift. It's not a mechanical noise or vibration per se, it just doesn't "feel" right.
2. from 6-7k there is a definite flat spot
3 the bike actually seems to get better than normal riding fuel economy while riding harder, this was subjective test, but the results are there. I put exactly 1 gallon in the tank with some fuel system cleaner (berrymans B12) & stabil and went 46 miles before I started to get some starve issues. When tooling around town i get about 37-39 MPG.


Couple of notes:
- carbs just rebuilt & cleaned with K&L kit & new petcock w/ new filter
- prior to rebuild, the bike sat for 2 years.
- new oil & K&N oil filter (I'm told my oil isn't correct, but it's the oil the previous owner has used since he bought the bike 12 years ago - http://bit.ly/1E1DKGJ )
- new battery
- new tires

My thoughts are leaning towards timing/ignition since the carb was rebuilt. Or possible wheel bearings, they looked good to me when I replaced the tires though. I'm also suspect of a slight brake dragging issue however, it only really happens when cold and when I haven't ridden in more than 2 or 3 days. And it goes away at the first stop, like it gets stuck and then frees up after braking under load.

Anyway, thanks for taking a look. You guys have helped me bunches so far!

 

[chuck hahn]

My thoughts are leaning toward that k@L kits. Most aftermarket kits are full of inferior parts with incorrect needle tapers etc etc.

So why did you feel you had to use rebuild kits?? Go here and see the carb rebuild tutuorials right below the manual menu board on he right side. Scroll down and look at the right. Choose the CV tebuild.

http://members.dslextreme.com/users/bikecliff/

 

[chuck hahn]

And the conventional Valvoline is not the problem. Any conventional SAE 10W40 is ok. Most of us use Shell Rotella T Diesel oil but it isnt a must or bust deal. The Valvoline is fine.

 

[disstance]

So why did you feel you had to use rebuild kits??

http://members.dslextreme.com/users/bikecliff/

I will check out the rebuilt tutorial. But to answer your question, many of the parts inside were pretty chewed up. 2 main jets, all of the pilot jets, 3 emulsion tubes, 2 float needle seats and all of the rubber plugs had to be replaced. As well as all of the gaskets. I was able to clean the needles, so those are stock. The rest of the carbs looked pretty good, seemed to be common rebuild parts were too damaged. I do know the float bowl heights are a tad off, they're all within the tolerances but they aren't all equal.

I do have the stock float needles, and they were in decent shape, I could toss those in but to be honest, the K&L ones are definitely more springy.