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Need diagnosis...bike surging

  • Thread starter Thread starter Gary_t200
  • Start date Start date
G

Gary_t200

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Ok. I have done quite a bit to the bike in the last couple months. . Rebuild carbs. Synchd. Did valves. New plugs. New petcock. New stator and RR. New ground wires. Changed oil and shaft oil. Airbox pretty well sealed but i havent oiled the air cleaner yet. Bike has 9700 miles. GS 850 GLZ.

So I got new stator and RR in and took it for only its second ride. It is surging a bit. It idles nice at 1200. But riding it, it will surge...sometimes pulling hard, sometimes not. So acceleration is inconsistent.

What can be causing this ? Would appreciate all ideas.

Thanks.
 
Gary_t200 said:
Ok. I have done quite a bit to the bike in the last couple months. . Rebuild carbs. Synchd. Did valves. New plugs. New petcock. New stator and RR. New ground wires. Changed oil and shaft oil. Airbox pretty well sealed but i havent oiled the air cleaner yet. Bike has 9700 miles. GS 850 GLZ.

So I got new stator and RR in and took it for only its second ride. It is surging a bit. It idles nice at 1200. But riding it, it will surge...sometimes pulling hard, sometimes not. So acceleration is inconsistent.

What can be causing this ? Would appreciate all ideas.

Thanks.
Click to expand...

Could be running too lean on the needle, or just not getting enough fuel when the demand is high.

Did you fit an inline filter to your fuel line? If so, they can cause a flow restriction if the wrong type is used, or if they are positioned with a loop in the line.
 
Yes I did put one on. It may be the culprit. I will remove it. Don't really need it w my new petcock.

Also, it does actually kind of bog down a bit if I hit throttle fast. I think I actually may be rich, not lean. Definitely no sign of rising or hanging idle. But it's also not stumbling and dieing at idle.
 
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ok - I took off the filter and its still doing it...It's almost like one cyclinder is cutting out...not sure. But I would have suspected more substantial loss of power if one was cutting out.

I notice one pipe with a blue tint now and three with a yellow tint. Not sure what that means...
 
Where are your carbs' vent hoses? They need to terminate in still air. Behind the airbox is stock, just below the little loop on the back of box that keeps them in place and tidy.
 
Thank you guys for weighing in...Stock pipes.

Bike is entirely stock and in great cosmetic condition... I dont think it has run in many years though as it was a mechical mess when I got it and would barely run fully choked and nothing at all otherwise. Also didnt charge.

I will check where vent hoses are...
 
Check your float levels, and make sure float valves work properly.
 
OK the stock pipes are double walled, they don't blue easily. For them to turn blue it is REALLY lean and REALLY HOT in there.
 
I'd oil the air filter. Surging is lean and oiling the filter will richen the mixture. Plus, not oiling the filter lets dirt get though to the engine which does no good.
 
Ok. Some good thoughts there. Filter is dry. I will oil it and also redo pilot screws...making sure to open the blue pipe more. When I redid the carbs I was really careful with floats. I set them perfectly. But I could replace the float needles...

I also plan to snip a 1/4" off the spark wires and reseat the caps.
 
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Please check and reset your points. Make sure that easy item is accounted for before you go tearing into your fuel system.
 
mattfeet said:
Please check and reset your points. Make sure that easy item is accounted for before you go tearing into your fuel system.
Click to expand...

Good suggestion but the bike in question doesn't have points.
 
Timing may be an issue...not sure I did that right. I did a chk and thought it was ok but I may not have been thorough enough. Its on my list to dig back into...
 
ok - Update...I took out inline fuel filter, replaced fuel and vacuum hose, snipped 1/4" off plug wires and reseated caps.

Bike starts and idles easily. Bike has sort of flat/lower power spots as RPMs rise on acceleration...especially noticible around 5000 rpms...and then will pull hard and then drop off and pull hard.

I have an 82 850 so no points...but I guess my only timing issue is to turn the backplate to the right spot. I had checked it once and it seemed right on but I can check again Sat. Does this symptom sound like timing?

I would be amazed if the carbs were clogged because I really went through them carefully (and replaced orings)...but I can redip them this fall and clean again.

Maybe gas cap vent? I havent done this before...
 
Give it choke when you hit the flat spot and see how it responds. How do your plugs look?
 
If it responds and doesnt float out with a little choke applied as suggested youll know its lean..which will mean you urn the mixture screws out. Just do 1/8 turns..run it..and readjust as needed. Better a tad rich than any lean.

To clean the cap vent, just dip it in vinegar over night and rinse well with warm water. Then blow everything dry with an air hose. should be nice after that.Also look just at the lower rim of the filer neck for a small hole..its a air vent that allows the tank to expand and retract drawing or pushing air out the gas cap venting. Be sure its open.
 
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Wow. This is crazy. But I decided to clean, oil, and reseal the air filter. The air filter was totally dry. No sign of any oil on it now or ever. I put nice rubber door/window gasket on top edge. Oiled it so it would slide in place nice.

Cleaned foam element with simple green. Oiled it with 20w/50. Rubbed it in good. Carefully squeezed it out. It felt much heavier. Prob had 4-8 oz of oil remaining in it. Put all back together.

I took it out. It felt very nice and responsive. Hit entrance ramp and opened it up hard. It took off. Never pulled harder. Redline in second, redline in third, approaching redline in 4th...needle buried(freakin 85mph speedo). Holy cow. It's fixed !!!! I ran 70 to 80 for the next thirty minutes. Then turned around.

Wow this bike sounds nice when its accelerating hard. Nice music from those pipes.

As strange as it seems....I think my final problem was the air filter oil and top edge seal.

Bike is like new. Time for cleanup and time to submit pictures !

Since I bought this bike and joined the site I have done following using this site, and bikecliff site:

New Plugs, recapped wires
Timed.
Valve shim adjustments
Tore carbs down, dipped, new orings, set floats, reassembled
Re-synced carbs
New petcock, new fuel hose, new vacuum hose
New stator, new gasket, new REgulator, new ground wire, extra ground wire to frame.
New AGM battery. Cleaned wire connections.
Sealed airbox, oiled filter
Changed oil and filter, changed shaft oil (rear drive had no oil and loose drain plug from some dumb PO) doesn't seem to have been driven wo oil)
Air in front fork ( seems to be holding pressure)

Had close to 500 bucks in parts. Prob 80-100 hours in labor. I am slow.

Bike runs like new. Thanks !!!
 
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