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82 GS850 Issues

  • Thread starter Thread starter Damien
  • Start date Start date
D

Damien

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Hey all. This site is incredible. Purchased an 850 from a friend in somewhat ill-repair and have been working on getting it in good condition with a friend of mine who's much more mechanically inclined. We've ended up replacing the stator, the starter motor (which had shorted and burned up), cleaned carbs thoroughly as per the guides, new petcock, changed spark plugs and just recently replaced spark plug caps.

As of the now the bike starts, maintains a charge on the battery, and idles just fine. In idle though it doesn't seem to want to push past 5k or so revs. In attempting to diagnose this we noticed that when we removed the spark plug cap from the farthest right cylinder (fourth), there was no change to RPMs or to the way the bike ran at all...as if it's not firing. But it has gas, and there is definitely spark to the plug. We tried swapping coil wires to make sure it wasn't a faulty coil and it still didn't fire. He had noticed there was low voltage coming from one of the coils so we had rigged a relay as per the " Coil Relay Modification " on Bikecliff's site. The coils are now getting full voltage.

Other than this cylinder not really seeming to fire I can tell that the right exhaust pipe that comes from cylinder 4 has less pressure coming through the pipe than the other side. I'm assuming that's BECAUSE the cylinder isn't acting as it should, but perhaps there's something obstructing the path of the exhaust?

The odd thing is when the airbox comes off, it runs like a dream. That would then point to a carb/mixture problem but after fiddling with all the carb's mixtures, and putting the airbox back on, it fails to maintain that fourth cylinder firing.

We're kinda stumped. I appreciate any help you guys can give.
 
Valve adjustment done?

Airbox sealed up?

Air filter not over oiled?

Running better with the airbox off indicates a rich mixture-really rich. What jet sizes did you find when you cleaned the carbs?
 
Haven't touched the valves, yet. We haven't sealed the airbox but I do have the stripping necessary for it...and I know for a fact I overoiled the air filter. When I got new K&N filter I knew I should be oiling it with the little plug of oil it came with. Except I didn't read their directions fully, as I used the whole plug and they said you should only use half.

We figured the jet sizes could be interfering somewhere so we swapped the ones that were in the bike before (180) to 170. Nothing seemed to change. I ran it a bit today and it seems like it's fine till about 3k - after which there's a dead zone where the throttle won't produce any change in the bike...it sags there, until I bottom throttle out and it picks up and goes from 3k to like 6.5k+.
Could those things involving the airbox/air intake cause this?
 
Damien said:
Haven't touched the valves, yet. We haven't sealed the airbox but I do have the stripping necessary for it...and I know for a fact I overoiled the air filter. When I got new K&N filter I knew I should be oiling it with the little plug of oil it came with. Except I didn't read their directions fully, as I used the whole plug and they said you should only use half.

We figured the jet sizes could be interfering somewhere so we swapped the ones that were in the bike before (180) to 170. Nothing seemed to change. I ran it a bit today and it seems like it's fine till about 3k - after which there's a dead zone where the throttle won't produce any change in the bike...it sags there, until I bottom throttle out and it picks up and goes from 3k to like 6.5k+.
Could those things involving the airbox/air intake cause this?
Click to expand...
170-180 main jets :eek::eek::eek::eek: I believe this bike should have like 115's maybe someone will chime in , but if it runs better with out the air box the big jets make since:eek:
 
Those 170 and 180 jets are the PILOT AIR JETS, not the main jets.
In fact, changing them from 180 to 170 will richen the pilot (idle) mixture, probably making your problem just a bit worse.

To see what the main jets are, you will need to remove the float bowls and read the numbers on the jets.

There are obviously no jets in this picture, but the main jet would live in the larger hole near the top of the picture.
IMG_2801.jpg


Another suspect item would be float level. A common problem is reading the distance to the wrong part of the float. You measure to the BOTTOM of the step, not the top.
IMG_2161.jpg


.
 
Ill crack them open at some point and take a look. The suggestions made earlier about the airbox/air filter being sealed...im still curious to know if those would stop the bike from breaking 3.5k rpms until full throttle?
 
Yes, this.

#4 could be not firing because of a valve not closing fully (no clearance with the cam), causing decreased or no compression. This will in turn make the other cylinders run worse. You cannot diagnose jetting until air is moving through the carbs correctly. Valves must be opening and closing correctly, and the intake system must be sealed.
 
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