New bike = new thing to tinker with.

[AceFrehley03]

Hey everyone. First time here, and since it seems like everyone knows what they're talking about I thought I'd go ahead and give this a shot.

I just bought a 1980 GS850G (well, GS850GT according to the title. It has the full fairing, saddle bags, et cetera.) Anyway, I picked the bike up for cheap because it had what the previous owner thought was a "carbuetor issue."

He said that they could get the bike to run and idle, but it was rough, and any effort to give it throttle would kill the bike. Sure, I've heard of this on carbs before, but I've also heard as it being a cam timing issue.

I'm not sure just how reliable the cam chains are on these things, but I have the carbs off and the bike reasonably pulled apart right now so I can work on things. Is the only way to check cam timing to pull the valve cover off? I don't really want to but if need be, I'll pull the cover off. Also, since I'm here, how well do the automatic tensioners work? Do they keep everything pretty quiet? (Problem on an old '74 KZ400 I had, that's why I ask.)

Anyway, I'm heading out to tear into the carbs and just give them a thorough cleaning and see what I can get out of that, and see where that gets me. I might start piecing the bike together in the mean time and I'd like to hear it run by tomorrow night!

Thanks for any help you can offer everyone, and I look forward to learning from you all!

[bwringer]

Here's a cam chain tensioner rebuild series in pictures and words. The tensioners normally function quite well -- the rebuild is mainly needed to replace two o-rings and a small seal that aren't listed on most parts diagrams. The seal seems to start leaking after 20 years or so.

http://bwringer.com/gs/camchaintens.html

Also things worth checking/replacing on any "new" to you GS850:

http://bwringer.com/gs/intakeorings.html

http://bwringer.com/gs/tachcableseals.html

There's a good chance that your problem with the carburetion is actually related to the airbox. You're likely getting too much air.

Make sure the airbox is installed, that the rubber boots between the airbox and carbs are in reasonable condition (they're pretty inexpensive if not), and make sure the airbox is sealed -- you have to seal the airbox side covers and the top of the air filter cage with foam weather stripping. Basically, air should only be able to enter the airbox via the snorkel at the back and via the circle of vent holes on the bottom. Plus, air should anly be able to get to the carbs by passing through the air filter.

It's also very common with an 850 to find that the foam air filter element contains far too much oil, which can cause the engine to run rich. Wash it out thoroughly with dish detergent, dry well with compressed air, and reinstall. The slight film of oil left after washing will be plenty.

[bwringer]

You do need to pull the valve cover to check the cam timing, but more importantly, you should check the valve clearances. These tend to tighten over time, and since they are very small clearances, you can quickly end up with an engine that runs very poorly.

The proper clearances for all the valves (in all 8 valve GS engines with shim adjustment) are very small -- only .03mm - .08mm -- and they are critical. You'll want to get a metric feeler gauge -- they're about $5 at any good auto parts store. Don't get confused and try to measure thousandths of inches.

Valve clearances are supposed to be checked every 4,000 miles, but are commonly neglected. The bike will never run worth anything unless these are correct, so it's worth checking them ASAP when you buy a bike. The procedure is clearly outlined in all the manuals.

[AceFrehley03]

Sorry it's been so long since I've posted, I've been spending a good amount of time cleaning this thing.

Well, I popped the valve cover off and found a small tear in the gasket (repaired) and the chain is in excellent condition. The clearances are in spec for the camshaft according to what I can find.

I took the carburetors off and cleaned them thoroughly, just did no readjusting or anything of that nature. I left it all where I found it and I cleaned everything as well as I could. All needle valves and jets are clean now and haven't been bored out, etc. etc. Cleaned out the fuel tank, fuel lines and the petcock.

It has an original airbox (I believe it's all hooked up properly, and it is very well sealed, lol) but has a K&N air filter. I started the bike and I noticed a few things right off the bat.

One, it won't idle without full choke and when it does, it's around 3,000 RPM or so. Eesh. Two, there is no throttle response whatsoever. Turning the throttle kills the bike quickly, no matter how much or little. Three, and this is a big one, number two is a dead hole. 1, 3 and 4 are running as the pipes are hot. All plugs have been replaced (B8ES and have been gapped to .026" if I remember right) and the plug wires APPEAR to be in "ok" shape but they are beginning to get worn. The cylinder has equal spark to the three that run. I know the firing order is 1-2-4-3 but I'm not sure how to check that as my coil isn't labeled, nor is there anything in my crappy Clymer's manual that states.

I'm running out of ideas. I'm wondering if this is a coil issue, or if it's something else? One problem I found was that the throttle diaphragm on number three was completely screwed but I fixed that without a problem.

I can't think of anything else worth noting, so if anyone has any ideas I'd like to hear them? Thanks all.

[chef1366]

If #2 isn't firing chances are your petcock is leaking through the vacuum line into #2 cylinder. Are you getting spark through #2? One coil fires 1&4 and the other 2&3. If you're getting spark to three cylinders it isn't a coil. Check the petcock and make sure the spark plug cap has a good connection on the wire. You can screw the cap off and snipe a bit of wire off till you see a good copper wire and srew the cap back on.
Hope this helps.

[AceFrehley03]

I am getting spark through to #2. I'm getting spark to all four plugs. The petcock doesn't appear to be leaking any fuel into number two from what I can see. The plug cap has a good connection, I gave it some new wire just for good measure with no improvement.

Edit: While I'm at it - I'm assuming that I have the carbuetor hooked up right. I have the valve cover breather hooked up to the airbox. The large fuel line from the carbuetor (between 2 and 3) going to the primary outlet on the petcock and the smaller one going to the rear part of the petcock (the vacuum line.) There are two hoses between carbs 1 and 2 as well as 3 and 4, which I believe are overflows. There is also a hose on the gastank from what appears to be the fuel sending unit, which I have routed to be an overflow.

That's all I can think of at the moment.

[AceFrehley03]

Could this be the dreaded ignitor by any chance?

[chef1366]

Actually those two lines between your carbs are vent lines for the float bowls.
Make sure the fuel line isn't kinked when you put down the fuel tank.

[Nessism]

When you had the carbs apart did you remove the pilot jets next to the mains? Don't mean to question you but many people don't go far enough when "rebuilding" the carbs and have to do it a second time. The pilot jet circuit had a very small orifice and almost always clogs up if the bike has sat.

Only other thing I'd suggest is a compression test.

[DimitriT]

When you cleaned the carbs did you take out the idle mixture screws and clean that passage? If this passage is gummed up it won't idle right.

[Steve]

When you did your "thorough cleaning" on the carbs, did you take them completely apart and dip them overnight in cleaner? Remove all the non-metallic pieces (gaskets, o-rings, etc.) and dip each carb body overnight in Berryman's carb cleaner. Re-assemble that carb, do the next one overnight. Really does wonders for cleanliness. Also be sure to use new o-rings when you put it all together.


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[AceFrehley03]

Chef - The fuel line isn't kinked, and good, I have those two lines routed as fuel overflows.

Nessism - Yes, I removed the pilot jets next to the main jets and cleaned them as well. I was pretty thorough in these, I've been doing old dirt bikes for years upon years so I'm good at cleaning them.

DimitriT - Yes, I took out the idle mixture screws and also cleaned out that passage with carb cleaner.

Steve - I separated the carbs as per the instructions on here and I didn't use Berryman's, I use one called "Chemdip." I don't know what the experience of others is with that stuff but it works pretty well for me. All o-rings are new.

I'm really running out of ideas on this one. I'm going to start trying to play with the idle mixture on that cylinder and see if I can get it to start firing. I believe right now it is backed out 2 1/2 turns, with everything else being 2 3/4. I'll see where that gets me and I'll report in. Thanks everyone.

[AceFrehley03]

Alright, I've gotten somewhere. I got the bike back apart and RE-cleaned everything, the tank, petcock, everything. I repaired the plug wire on number two and voila, it runs on all four now! I can give it gas and it actually revs!

Now it gets weird. First of all, she runs hot on the right back, #3 and #4. Or at least it seems that it does to me. Two, I can't get it to idle down no matter what I do, the screw has a very small effect, if any whatsoever. Not choked, it's idling around 2200-2300 it seems like. I'm going to go fill the tank up and make sure that it isn't being starved and go from there.

Is the ignition timing adjustable on the 80 models? If so, how do I go about that? My Clymer's manual doesn't cover it. Thanks all.

[nabrams]

High idle is very commonly due to air leaks - do a search.
Also, are you sure that choke is fully releasing. Many have found that the choke is still partially "engaged" even though they have it in the fully "off" position.

[AceFrehley03]

The choke is fully releasing, and I'll check on air leaks. I couldn't find any, but I went really quick? Thanks.