GS850GL plea for help - bike won't pull past 5000 rpm

[Reckhard]

Why can't you go all the way to redline? Don't have a first gear?

I don't have sufficiently sized testicles to keep the throttle pinned when the bike is begging for a shift...

[tom203]

I don’t like the consistency of not pulling past 5k…..can you find a safe long downhill and see what happens when it’s lightly loaded under full throttle?
in my opinion, the main jet is doing most of the mixture delivery by 5k…..I’m assuming you got the rubber plugs over the pilot circuit.
I asked before if you had the mechanical advancer setup…..apparently some 82’s had the electronic gizmo ignitor.

[rphillips]

Thinking the pilots won't have any noticeable effect at 5K.

[Reckhard]

I don’t like the consistency of not pulling past 5k…..can you find a safe long downhill and see what happens when it’s lightly loaded under full throttle?
in my opinion, the main jet is doing most of the mixture delivery by 5k…..I’m assuming you got the rubber plugs over the pilot circuit.
I asked before if you had the mechanical advancer setup…..apparently some 82’s had the electronic gizmo ignitor.

I can get it to rev over 5K under light load - like down a hill. It caps at around 5 only while accelerating. My bike has the electronic ignitor - no points. Plugs are over the pilot circuit.
As I mentioned the bike pulls strong without the air filter so timing should not be an issue.

[tom203]

Yes, all the 82’s had ignitors, but earlier models had separate mechanical advancers. Later versions had the advance curve built into ignitor itself. In any event, advance would be complete by 4K for both types. When you’re going down this hill lightly loaded, what happens at 5k …..any sense of misfire? ….no throttle response?

[Reckhard]

When the engine goes above 5k under light throttle it sounds reasonably normal but giving it more throttle does little but cause the stumble.

I've nearly convinced myself that the issue is with the main jets. I may have messed them up when I cleaned the carbs. I'm ordering a new set so will be giving that a shot and posting after they arrive and I have a chance to try them out.

[pdqford]

-fuel system was a disaster - tank was thick with rust, cleaned everything. New petcock. replaced all the fuel lines and fuel filter.
-bought a new foam air filter, all the old foam bits had turned to dust.
...

Just wondering what type of fuel filter you installed.
(I assume that stock 850s didn't have an in-line filter?)
Could it be plugged after the fuel system disaster?

Anyone know if there is a spec for the amount of fuel that should flow for a given amount of time?

Heavy throttle at higher RPMs requires "a lot more" (technical term) fuel flow than a lightly loaded system.

[Grimly]

Anyone know if there is a spec for the amount of fuel that should flow for a given amount of time?

0.5lb / HP / Hour

[rphillips]

Now that's confusing. 0.5lb per HP = 40lb, from a gravity flow system. Not sure about the HR either.

[pdqford]

0.5lb / HP / Hour

Technical terms?

Okay, thanks dave.

If my math is correct,
that's about 0.008lb per HP minute.

And when it's putting out say ~60HP,
that would be about 0.5lb fuel per minute.

Say fuel weighs about 7.5lb per gallon
so 0.5lb would be about 1/15th of a gallon a minute.

At 128 oz/gal, that would be about 8.5 oz/minute,
or 2/3 of a soda pop can in a minute,
while laying down 60 HP.

So can O.P. (Reckhard)'s gravity fuel system come close to filling a soda pop can in a minute?

[tom203]

”I've nearly convinced myself that the issue is with the main jets. I may have messed them up when I cleaned the carbs“

while you’re having carb fun, check the vacuum diaphragms for integrity and for correct orientation

[Reckhard]

I came with an inline K&N fuel filter. I swapped it for a much larger one with no change.

Vacuum diaphragms all look good and are in the right way.

As for handling the fuel flow - Suzuki designed the bike this way - I presume they knew what they were doing and the bike as designed was able to get to the 78hp it was rated at.

New jets arrive next week - carbs are sitting on my bench waiting...

[rphillips]

No doubt, hope this fixes the problem, but got to be skeptical. I wondered since reading post # 21, How can you mess up a main jet other than the screwdriver slot or threads? Thinking it'd be hard to accidently make the tiny hole that meters the fuel smaller or larger... Do hope this fixes the problem.

[Rich82GS750TZ]

I came with an inline K&N fuel filter. I swapped it for a much larger one with no change.

As for handling the fuel flow - Suzuki designed the bike this way - .

No, they didn't. Your bike may have come to you with a fuel filter, But Suzuki didn't put it there. There's a filter screen on the petcock, and on the the float needle valves inside the carbs. But your bike did not come from the factory with an in-line fuel filter.

[pdqford]

I came with an inline K&N fuel filter. I swapped it for a much larger one with no change.

Vacuum diaphragms all look good and are in the right way.

As for handling the fuel flow - Suzuki designed the bike this way - I presume they knew what they were doing..

I agree, Suzuki knew what they were doing, but your fuel system is now 42 years old and has had a fuel system disaster.
If it was me, I'd pull the fuel line, stick it in a beer can, put the petcock on prime and see how long it takes to fill the can. If fuel flows well, go for the mains. If it doesn't, see Rich's post #29 above.
But that's what I'd do.