Running out of ideas on getting a GS850G running right

[jboyce]

Hey guys,

Having an issue with my GS850G. It will idle without a problem, but I cannot get it to rev above 3,000-4,000 rpm's. My first thought was that the carbs were dirty, so I pulled them off, disassembled and cleaned them (dip, air, carb cleaner), but the issue persisted. I then tested the coils, thinking that it had to be a spark issue at this point. Both coils were reading 5 ohms across the primary and 32k ohms across secondary. I then tested the plug ends, and most were sitting in the kilo-ohms, but one was in the mega-ohms, so I replaced all the spark plug boots. I also replaced the plugs, since they are pretty cheap (B8ES plugs), and the rpm stutter still persists. If I fully choke it, it goes up to its normal 5,000 rpms without bogging, and I can crack the throttle to get it up to about 6,000 or maybe even 7,000 before it bogs down. I then ran a compression test on the bike, the numbers were low (didn't do it right), but I did a valve adjustment anyways, got them all in spec, and then redid the compression test (dry and wet, properly). They dry compression test numbers were 120, 118, 95, 115, for 1,2,3,4 respectively. The wet compression test turned out about the same, except for cylinder 3 came up to 120 psi with the rest of them (I have previously replaced all the piston rings about 2 years ago, my guess is that cylinder 3 may have not sealed properly?) I then redid the timing to make sure it was 100% on point, and it seems to be. My next steps are going to be a carb sync, and then pray to the almighty suzuki god that this bike will start running properly.

The point of this rant is to see if anyone else may be able to give me some ideas of things to try, because I'm running out of ideas on what could possibly be causing the problem. The intake manifolds are less than 2 years old, and has the port screws still in them. Plz halp

Pics of the bike included for suffering through the rant!

 

[jboyce]

Another photo (most recent photo of my friend riding it)

 

[Nessism]

The spark advance circuits built into the ignitor may be malfunctioning. I've not investigated how to check this but maybe the service manual has some instructions? Getting your hands on a known good ignitor would be another way to investigate the issue.

 

[bwringer]

You can check whether it's advancing easily with a timing light. This will also uncover any spark issues at high RPM -- you can see the light cutting out. Move the timing light's pickup to all the wires to make sure they're all at least trying to spark reliably.

What's your voltage at the coils?

One thing you didn't mention was the airbox -- these bikes are EXTREMELY touchy about the airbox. Is it properly sealed, with a good air filter element in place and sealed, not too much oil on the filter, and is the airbox still wearing the snorkel? Are the airbox-to-carb boots in good shape and properly seated on all four carbs? It's VERY easy to end up with the inner two boots folded up, and this is VERY difficult to spot.

I wouldn't worry too much about the compression numbers right now. You've got enough to run fine, and it's very difficult to get reliable compression readings on these things with the carbs mounted.

What do the plugs look like?

 

[eil]

A carb sync won't help, that only has an effect on idle and very low throttle openings.

An issue with the advance is plausible. Does this year have electronic or mechanical advance? Mechanical is easy to check, just take the cover off the signal generator cover (right side of the case) and check that it moves smoothly. The one on my 850GL was a little sticky this spring so I took it out, cleaned it up, applied plenty of oil, and now it works great.

But more likely (to me), your description of the problem speaks to an air leak somewhere on the intake side. See bwringer's suggestions above and also check the carb-to-head boots. Take them off and verify that the o-rings underneath them are sealing.

Was it running fine before or is this bike new to you?

 

[Guest]

It sounds like my 1000G did when the PO put pods on it, but didn't increase the mains. It would idle fine, but it would bogg at around 3K. Too much air and not enough fuel. No filter in the air box may do the same thing.

 

[SepiS]

Have you checked the timing chain? I had "clang" caused by starter motor turning too slowly. And this was caused by ellipse shaped worn end bearing. When starting my Suzuki kicked back and timing jumped one tooth. This was enough to limit the revs to 4-5k. After having renewed starter clutch, cabs checked, starter repaired the bike runs ok. So check the timing chain!

 

[rcook52459]

had a kz few years ago doing the same thing turned out to be the carb boots leaking.