Gs850 bogging down

[ninjadave7]

Hey all,
I've got an '80 GS850 that I've been refurbing a bit. When I got it the carbs were almost hanging off and the air box was missing the element and the snorkel. Since then I've completely dissassembled/cleaned/reassembled the carbs according to the guide on cliff's page, including new gaskets, o-rings, etc. but with the oem jets. Everything dipped, carefully-reassembled, the works. I ordered a new air box with the snorkel and element and installed a Uni filter, and redid the carb boot o-rings. The boots themselves are still pliable and good. It has a brand new petcock from Z1, and I synced the carbs and set my air/fuel screws on top back 2 1/2 turns.

My problems are these:
It's a tad sluggish taking off, but runs well until throttle is around 1/2 open. From there out, and especially if I open it up wide, it bogs down until it almost dies. I also hit a flat spot between 4-6k, for instance if I run up the rpms in first to around 6 and then shift to 2nd it lands right there and seriously bogs. I've looked at the plugs and they look normal, no gas on them, no black, no white, just... normal (to me and the test pics online).

This am I pulled the carbs and sprayed out the main jets, all jets actually, and ran wire through just to see if something was impeding, but nothing seems to help...

I know this is a long description, wanted to show I'd covered my bases (I think) before asking for help.

Anyone?

[850GT_Rider]

Did you check the valve clearances?

[Steve]

Have you cleaned the carbs?

Yeah, I know you said you ran a wire through the jets, but that's not all that needs to be cleaned.

You really need to dip them to clean all the passages between the jets.

When they come out of the dip, they need to be treated to new o-rings from cycleorings.com, then installed and synchronized.

.

[ninjadave7]

The one thing I haven't done (didn't have the tools) is check valve clearances. Steve, thanks for the reply, but in my OP I described that I did do a complete, by-the-book cleaning/dipping/new o-rings/sync/everything. The quick spray and double check jets was just this morning quickly before work, because I was still having problems. I also resealed the airbox per cliff's guide on his page.

would the valve clearances effect everything that much? If I recall from the maintenance papers I saw, they were adjusted a few years ago.

[koolaid_kid]

Dave, one of the reasons Steve mentions the valves is that you must remove all other variables from the equation when attacking the jetting. A valve clearance check is critical in this equation.

[ninjadave7]

Hey guys,

I'm ordering the shim tool now, I didn't have one before to adjust the valves.

Is there anything else I can try in the meantime?

Wisgolfer, thanks for the reply, I knew valve clearances were important, but didn't realize how important maybe. Every post I've read regarding the types of trouble I've been having were responded to by suggestions to fully clean carbs, seal air box and boots, check petcock, etc. I've done those things (except valves) and so I'm looking for further insight!

My response to Steve (who wasn't the one suggesting valve check) meant no disrespect, on the contrary I have a lot of respect for everyone on here for helping each other all the time. But he didn't read my post, just saw the end and scolded a little for not doing the carbs right. Sorry if I somehow got off on the wrong foot, just want to get this sorted out and hopefully the answers will help everyone else too!

[Steve]

Sorry about that, you are right. I missed the first part about the complete cleaning and only saw the "wire through the jets" part.

Don't worry, I didn't take it as a "scolding", but your symptoms sound like it's running a bit lean and dirty carbs (usually due to failed attempts at cleaning) are the usual culprit.

Valve adjustments are extremely important. The clearances tend to tighten up with age/use, and are frighteningly small to start with. The manual calls for inspection at 3,000 or 4,000 mile intervals, depending on the bike. How many miles have been traveled since the "few years ago" indicated in the service records?

By the way, you don't really need the special shim tool to adjust the valves. If you have seen the valve adjustment tutorial on BassCliff's site, you should have also seen the very next item, The Zip-Tie Method. Many of us prefer this method to hold the valve open for shim removal. I have "the tool" and have yet to use it successfully, so zip-ties are the only way for me.

By the way, feel free to take advantage of the invite in my sig.

.

[Mattias44]

Try running it with the choke on to see if the flat spot gets better or worse. If it gets better, you probably have a lean condition. If it gets worse, you probably have a rich condition. The plugs wont tell you much unless you do proper plug chops (search for the procedure on this site).

Have you double-checked your jet sizes?

Also the valves are important, but the carb sync you do after doing the valves will probably have a greater effect on your current symptoms.

Good luck and keep at it!

[DanTheMan]

One more avenue to check, (if it's running lean) is the carb boots themselves. Mine on my 850 look fine, but #1 and #2 have hairline cracks in the rubber that isn't visible to the eye. I sprayed a vacuum leak sealant (can't remember the name offhand, got it at Auto Value) on the boots while it was running, the RPM jumped as it sucked into the carbs, so that's how I discovered it. I sprayed the sealant on all my carb boots, and it alleviated the vacuum leak for awhile. This winter I plan on rebuilding the carbs again, and replacing all the boots. I've replaced the airbox boots twice now due to the first replacement set hardening up and leaking after two years (desert heat running through Nevada and CA deserts may have been a contributing factor).

[ninjadave7]

Great, I'll try all this stuff. I didn't see the zip-tie method but that sounds way better than buying tools

The jets are the original ones, so I haven't checked, but I'm pretty sure they're right.

How would I adjust the lean/rich situation? the air/fuel mix screw?

thanks!

[DanTheMan]

Great, I'll try all this stuff. I didn't see the zip-tie method but that sounds way better than buying tools

The jets are the original ones, so I haven't checked, but I'm pretty sure they're right.

How would I adjust the lean/rich situation? the air/fuel mix screw?

thanks!

On the top side of your carbs (ref BikeCliff site for a good photo) you'll see a plug in each one. If you didn't remove the mixture screws during your carb dip, you missed a vital step (bad, bad, bad). By missing that step, the little tiny o-rings under the mixture needle valves are now gooey (they needed replacing anyway). Anywhoo, you need to drill a small hole in the pot metal EPA mandated cap, screw in a drywall screw (or similar), pull up gently, and the cap pulls out. Throw the cap away. Now, down in the bottom of the hole is a small slotted screw. When you unscrew it, there will be 4 items: the screw, a small spring, a tiny washer and a tiny o-ring. These must be removed and cleaned up, and you should also spray carb cleaner through the hole to make sure they're cleaned out.

On edit: Now, that I re-read your post, you've probably already found the screws, my bad! Anyway, yes, that's the spot to adjust the mix for low speed.

[Counter]

Check your jets, needles, etc. When I was rebuilding mine (81 850GX) with the help of the good people on this board, I found that some of the parts weren't original (one jet was very slightly different than the others and a needle valve was from another bike.

While you have the carbs apart, check everything because you never know what the PO might have done.

[ninjadave7]

Dan the Man, you mentioned "that's the spot to adjust the mix for low speed," but my trouble seems to be more at anything past 50% throttle. Would that adjustment be the same?

[DanTheMan]

Mid throttle problems would be jetting. I've had the same problem occur, and it's always been dirty jets or air leaks that cause it.

[MisterCinders]

Since you are running into the bad patch at 1/2 throttle, your jet needle setting is the most likely culprit. But you also seem to have a less than stellar (but not terrible) idle.

Not sure if your needles are adjustable, but if they are, you can do a plug chop or try the choke trick mentioned above to see whether to adjust the needle for lean or richness.

HTH