Choke, fouling plugs, and spitting

[Anonymous]

I have a 1981 GS850GL with 14K miles on it.

The bike starts without choking and sounds good for a few minutes. I'll take off on her, just to keep wind flowing across the engine, and after a couple of minutes the RPMs are sticking high -- about 2000 rpm -- as I try to shift. Sitting in the drive the rpms will stick too, for 5 seconds or so. They always drop to idle.

And speaking of idle, when the high RPM problem occurs, the bike is idling more erratically and will try to die.

I took the carbs off, again, last night and checked the rod connecting the choke plungers. I noticed that one of the plungers was sticking and thought I'd found the problem. I took the plunger apart and cleaned and lubed it. It then moved freely. All the other plungers looked OK.

The bike is also fouling plugs. In the past couple of weeks I've replaced them all -- one at a time -- at least twice. (Everytime I start the bike and run it for any length of time I have to replace a plug).

The carbs were pulled and dipped a few months ago. I replaced all the O-rings in the carbs. I replaced the O-rings under the intake boots the carbs slip into. I checked the diaphrams for tears when I had the carbs apart. I just rebuilt the petcock and fuel is being deliverd as expected (fuel is dispensed when the engine is running). I have an air filter with 22 miles on it in the airbox and it has been lightly oiled. The throttle cable is not too loose or too tight. I've disconnected the choke cable just to make sure it isn't sticking. I cleaned the throttle mechanism to make sure it was returning to position when the throttle is closed. Screws on the carbs are 2 1/2 turns out and adjusting them seems to make no difference. I've balanced the carbs and rechecked balance multiple times. Plugs are black and sometimes wet.

I have not reset the float level in 8 weeks but was certain I'd set it correclty then. I'll gladly check them again if this comes back as a possible problem.

The exhaust system is rotted at the tailpipe and leaks at the premuffler.

Oh. I get a little bit of 'spitting' (very small backfire) on either 3 or 4.

The filter for the airbox sits in a metal frame. The top portion of the frame butts against the plastic airbox top. I can't believe this makes an airtight connection. It doesn't sound like I have a too-much-air problem, but I thought I'd mention it.

As I've demonstrated in the past, I am mechanically disinclined. I'm not sure what to look at next.

Aside from selling the bike and getting into a hobby that follows my skill level a little more closely, does anyone have any suggestions.

One more thing -- I've started this post several times and midway through each time I've thought of something else to check so I'd not post and check that thing only to have it not fix the problem at all. As I was getting ready to press send this time, it occurred to me that maybe the bike is running well when I start her up as she's firing on all 4 ... as I test drive her she fouls a plug and the idle goes to he**. Would this cause the RPMs to stick high. Typically when I encouter this problem I've been in an 'out of time' situation and don't check the plugs. Normally, when I fire her up the next time, I have to replace a plug or two. [See, right now I don't want to send this because I'm sure this is the problem. Odds are, based on my history, that not sending it and trying to fix the problem myself would be fruitless ... and I'd find myself here in a day or two typing in a War And Peace length help request.]

As always, thank you all for your help.

 

[daveo]

are the carbs synced?

 

[robinjo]

Do you have the correct jets fitted? Like the main, idle and airjet. Do you have a manual for the bike to check the correct sizes? Can't think of anything else that you haven't already checked...

 

[nert]

you may want to look at the ignition. Poor spark will foul plugs.
Have you checked compression, orbetter yet, leak down test with each cylinder at top dead center. MAybe you have 3-4 intake valves too tight.
GENERALLY, backfire through carb is a lean mixture. Does not seem like you have a lean condition. But a weak or random spark could be igniting at an improper time causing backfire through the carb. Or if a intake valve is too tight, (even less clearance with hot engine) the cylinder can't contain the combustion because the valve is not completly closing resulting in a backfire (spitting) through the carb.
Backfire through exhaust is generally a rich mixture. The wet and unburned fuel finds additional air after leaving the cylinder and entering the exhaust than ignites and results in an exhaust backfire.
GUT tells me ignition problem.
Maybe try. Fill the carbs on prime. Disconnect and plug the vacuum line at the petcock. Switch the petcock to run. (u will now have NO fuel flow to the carbs) Start the engine and see if everything clears out and runs good as you begin to run the carburetors out of gas. eliminating an over rich fuel mixture.

 

[Anonymous]

This topic is related to the following item -- I've listed that topic here should someone with a similar problem have an interest in seeing all the symptoms and how the problem presented itself over the course of time.
http://www.thegsresources.com/_forum/viewtopic.php?t=19303

Anyway, the solution was: Recheck the float height.

In the process of creating this problem I had adjusted my floats. I was certain I'd adjusted them correctly and, being bullheaded, refused check them again. I'd much rather spend hour after hour twiddling with mixture screws, rebalancing carbs, changing plugs, etc. than go through the 10-minute process of removing the airbox and carbs.

In my defense, well, the picture in my book is very dark and hard to see. I had set the float height by the highest part of the carb -- closest to the hinge end -- the bit that has the metal bracket mounted to it; you know, just before the stair step down. The picture in my book ... the very very dark -- so dark a person almost needs night vision goggles to see it picture ... upon closer examination shows the measurement being taken from the end furthest from the bracket. Past the stair step.

So, things are much better. Sorry about the bad clues and thank you to all that had suggestions.

I am curious about how I was able to tool around for 30 miles one day without too much trouble. Would misset floats be more trouble idling than riding at 30 mph?

 

[Philly_Chris]

Glad you got it running better.

One thing that occurred while reading the initial post was that it sounds like you are missing the foam on top of the air filter element. This seals up the gap between the wire filter housing and the roof of the air box. You may be sucking junk in through this gap.

People have replaced it with weatherstripping as well as cut up mouse pads. Try a site search.

I am assuming that it belongs on your bike, without having much familiarity with your model. But I think I'm correct

Edit: Or to put it another way: I have a lot of familiarity with your model as I have an 82 850. For some reason i had it in my head you had a 450.... Don't mind me....