1982 GS 850 G Surging at speed, poor performance CURED

[CCMcC]

1982 GS850G with 29K miles

Symptoms:

Surging at highway speeds
Poor performance; especially midrange
Rough idle

The 7 steps I took to find The Cure:

1. Replaced air filter (soaked with filter oil, squeezed out and allowed to dry);
2. Replaced spark plugs;
3. Installed NOS petcock and a new fuel line;
4. Had carburetors synchronized and air screws adjusted by a mechanic;
5. Adjusted choke lever to make sure choke rail fully closes;
6. Sealed air box side ?doors? with weather stripping; reinstalled rubber ?snorkel? at rear of the air box that had come loose.
7. Adjusted and lubricated throttle cable

The Long Version

As my other posts attest, it all began when I decided to change the air filter on my recently acquired 1982 GS850G. I bought a UNI air filter, over-sprayed it with filter gunk, and then The Troubles began.

The bike began to run very poorly. I washed and dried the filter and replaced all of the horribly fouled spark plugs. The engine then began to surge at highway speeds and to have hesitant performance.

I read posts on the GS Forum related to similar symptoms and posted messages asking for advice. I was impressed with the helpful advice folks on the Forum quickly offered in response. I ran carburetor cleaner in my gas to clean out any blockage from the air filter gunk. That didn?t seem to help all that much.

Then, based on another post, I installed a NOS petcock and a new fuel line. This solved the surging at highway speeds. Still, the engine was hesitant, especially in the midrange. The idle was erratic, rising and dropping at least 500 rpms.

Reading more posts, I took the bike to have the carburetors synchronized and the air screws adjusted by a mechanic. The mechanic used a mercury gauge for the synchronization. But, he adjusted the air screws by ear. He tightened all four air screws and then turned each air screw out, counterclockwise, until the point where the engine ran faster. He then lowered the main idle screw and did the same thing successively with each air screw, lowering the main idle after each air screw was adjusted. The mechanic said that rather than a certain number of turns, he set the screws ?to where each cylinder wants to be.?

The mechanic also discovered that the choke lever was improperly adjusted. The choke did not fully close which contributed to the erratic idle. There is a screw that holds the choke lever that can be loosened and retightened to make sure the lever's ?off? position fully pushes in and closes the choke rail on the carburetor.

The idle was very smooth and the acceleration was considerably smoother after the carburetor adjustments. But the midrange was still hesitant and mushy.

These engines were apparently set very lean at the factory to meet anti-pollution standards. Another GS Forum post suggested that any air leakage in the air box would, therefore, cause the bike to run too lean and perform poorly.

I used weather stripping to seal the ?doors? at either end of the air box. Looking into the air box, I saw light coming in from the bottom and back of the air box. There is a rubber ?snorkel? that fits the back and bottom of the air box. This had come loose and left a significant gap. I had to remove the air box to refit the ?snorkel.? I reinstalled the air box, making sure that no light could be seen that would indicate an air leak.

I cleaned and oiled the UNI air filter using filter oil (not spray). I gently squeezing out the excess filter oil and let the oiled filter dry for 30 minutes before reinstalling the air filter and refitting the weather-stripping-sealed air box ?door.?

Finally, I adjusted the throttle and lubricated the throttle cable (which was sticking) inside the throttle housing (where the start and kill switches are located).

The bike RUNS FANTASTIC now. Better than before, I believe. Smooth idle. Good choke control. Clean, crisp acceleration from off idle, through the midrange, up to redline.

The maddening dull, mushy drone at midrange had been replaced by a very pleasing almost turbine-like whir.

I am, again, a happy man.

[KEITH KRAUSE]

I'm glad this site helped lead you to getting your bike fixed.

[bwringer]

This is really a good checklist to go through every few years or upon acquiring a GS850G. It's remarkable how sensitive they are to excess air. They really LIKE to breathe through that silly little snorkel.

The only part I would disagree with is letting some grease monkey with only a vague idea of what he's doing sync your carbs. Carb sync is critical, and if that goofball got them anywhere near correct, you're very lucky.

I recently corrected an annoying, very slight midrange hesitation with a good thorough sync. Last time, I forgot to have the engine running at about 2,000 rpm. I was trying to sync while the bike was idling at about 1,000 rpm, which is impossible with the mercury jumping around like mad. This time, I turned up the idle to about 2K, and brought it right into sync within two minutes.

Some excellent carb sync instructions from CRC2:

http://www.crc2onlinecatalog.com/carb_synk.htm

Now, can anyone explain in small words exactly how normal mortals can set the idle screws? The best I could get was by trial and error. Starting at 1 1/2 turns out, I had to put the tank on and ride around to detect any differences at all. After about six iterations, I finally settled on 2 1/2 turns out for the two middle carbs and 2 turns out for the outside two.

[KEITH KRAUSE]

With the motor warmed up and on the centerstand, set your mixture screws to achieve the highest rpm's. Turn each screw until you hear the rpm's max'. After all four are set, re-set the idle to 1,100 rpm's with the idle adjuster knob.