Help !!!

[nightfly]

Bought a '81 gs850 several months back, ran fine for a few weeks and started to bog down on occassion until finally it would not even idle. I have had it to two mechanics so far, they adjusted the valves, been through the carbs, and I had the tank kreamed ( it did have some rust in it ). The bike seems to be running rich, and I am still having the same problem. I have changed the plugs several times, it runs great for about 200 miles, and the plugs foul out it will bog down again. The first mech thinks it could be the coils going bad, the other says no because they work or they don't. Hmmm..
What do you think guys ?

[Schweisshund]

My Honda Nighthawk is doing that, does it have a slight popping backfire at all?

[nightfly]

Yes , with a fresh set of plugs it will run just great for a while, then it will start backfiring slightly when I blip the throttle or downshift. Soon after it will start to bog down very suddenly. It happend to me today, and fortunatly I had a set of the previous plugs with me, changed them and it got me home.

[Schweisshund]

Its either one of these two things - you need to do a valve clearance or check your timing chain. I don't know how to do either but will keep an eye on this thread so I can learn how to do my nighthawk.

[nightfly]

The first guy I brought it to adjusted the valves and said my timing chain looked fine, the other guy checked the valves again and said they were right on. He thinks that I may have a broken valve or something , but wanted me to have another guy check it out before he takes it appart again. Does this sound like a possiblity ?

[Schweisshund]

yes - it explains the backfiring and bogging down.

[chef1366]

To test for a broken valve do a compression test. If you had trouble with rust you probably still have some swimming around in your float bowls.

[txironhead]

To test for valves, wouldn't he need to do a wet compression test? I'm leaning toward carb problems or coils myself.

And no, coils do not "work or not work". The most common problem with the coils is corrosion in the wiring not allowing the coils to get a full 12V. Many people solve this with a relay hooked up to a "hot when key on" wire that connects the coils directly to the battery. If your coils aren't getting enough juice, they don't provide a hot enough spark. Also, your manual (if you don't have one, get one) should show a resistance test for the coils to test if they're up to par.

[nightfly]

What I don't understand is that if it is a broken valve, how can it run so good when I put new plugs in it? I would think it would run like crap all the time, but I don't have too much experiance with these things.

[longgreensilverado]

check the fan belt. or maybe the cdi box

[nightfly]

Thanks for all your help guys. I am new here, and kind of a new rider. This is my second bike, my first last summer being a Ducati 748s, but I sold that one in the fall before having to do any maintenance or having any real problems with it. Not having the funds to buy something in that condition this summer, I picked up this gs850 for $900. I did'nt have it checked out by a mechanic before buying it, and not knowing what to look for, I am now learning the hard way. I am really becoming attached to the bike when it is running good, I just hope it will all work out without dumping a fortune into it.
Again, thanks for your all your advice

[BentRod]

have you tried using smaller jets?
if you pull the float bowls off, you can access the main jets. find their size and then go to a parts shop and ask for the next couple of sizes down. keep going down till you get a good spark plug reading.

it sounds as simple as you are running rich, your plugs are getting fouled, and that is spoiling the plug and thus the spark.

[Nessism]

Lots of conflicting advice in this thread because there are lots of unknowns. Basic advice for all new GS owners is to go through the bike completely and do all the basic maintaince and tests. Complete carb rebuild, by diping the carbs and replacing all the rubber O-rings, new plugs, filters, valve adjust, compression test, etc. Only after all these basics are complete can you be on good footing to understand what direction to move in to fix problems like you describe. Sorry to lecture but we see many threads like this with too many unknows. And many people that claim the carbs are "rebuilt" (even if performed at a shop) have to go back and do the job a second time, or third time, if the job was not done right the first time.

All this said, if you have one particular spark plug that keep fouling you might want to look at the spark plug caps. They are cheap to replace. Go to Z1 Enterprise and search for NGK.

Good luck.

[bwringer]

That broken valve theory is the product of a diseased mind... yeesh. :roll:

Don't go back to that mechanic, mmkay?

Anyway, the most likely explanation is that someone "rebuilt" the carbs with crappy kit parts. It could be as simple as an incorrect float level or jets that were hogged out or replaced with poorly calibrated aftermarket stuff.

Pull the carbs, drain the bowls, take the float bowls off, and tell us what you see. The stock main jet on an 850 should be a 115, and it MUST be a Mikuni brand jet. If your bike has an aftermarket pipe and/or pods, the main might be a 120, 122.5 or 125, but anything bigger would be waaaaaaaaay too big.

[pvtschultz]

If it runs good with new plugs, but then bogs out after a couple HUNDRED miles, I would have to suggest going to a hotter spark plug. Are you using the BR8ES?