New to the GS - carb problems

[madfrog]

Hi all,
I have been reading on the FAQ and so have already a few ideas, but let me describe my problem and try to crowd-source the solution:

I bought a 2004 GS500F for my wife to learn on. She has her MSF course completed and license, now she needs some practice.
The bike I found is OK, but didn't run. So I cleaned out the carbs, dumped the old fuel for some fresh one and finally got it started and the carbs synced. It now runs "ok". While cold, anyway. As soon as the engine gets hot, it goes in super lean idle and races to 4000rpm. I played with the mixture screws, but couldn't find the factory specs. I have them at 2.5 turns out for now, but have tried 3 turns, no difference.
So here are my questions:

- the intake pipes' rubber is cracked where it meets the flange, but the crack doesn't seem to to all the way through: could that be a problem anyway? (I ordered "good used" ones from ebay and some new crush rings from BikeBandit, waiting on them to come in)
- the solenoid under the carb: I have tested that it clicks on and off with test voltage, but I noticed that there is a cap on it (with the Mitsubishi logo) - is that supposed to be a vacuum cap, or a bleed? I ask because when I blow in the lines, air escapes from where that cap is.
- what is a good starting point for the mixture screws?

I have checked the vacuum lines, and otherwise I am fresh out of ideas, except to maybe run a guitar string through the pilot jet passageway in case the compressed air I ran through wasn't enough? Any suggestions are welcome!

Thanks in advance.

[craigs449]

Probably air leaking at the intake manifolds....sound like they are in bad shape. Fire the bike up and let it idle....spray some carb cleaner/electrical contact cleaner in that area wher the crack is...if the idle changes when you direct the spary there, the air is leaking at that point.

[madfrog]

I replaced the intake pipes and o-rings. Still doesn't run right. I sprayed WD-40 all around the carbs, but no dice.

It actually behaves as if it's running both rich and lean:
- the idle hangs high: lean
- it bogs on part throttle: rich, and I have to get it wide open in order to take off, otherwise it will stall.

It also makes a pretty loud metallic clunk if the idle is around 1000rpm, at higher RPMs, it goes away.

Also: at idle, only one slide jumps around, the other one doesn't. If I open up the throttle, they both go up and come back down.

I've cleaned the carbs, blown air through all the orifices, it's stock jetting, and I have about 3.5 turns out on the mixture screws.

Any ideas? At this point, all I can think of is that I need to check the valve clearance and maybe I have an exhaust valve that doesn't close all the way?

After that, I'm ready to pitch the piece of crap out.

Any help greatly appreciated.

[00sanchez]

Valves usually don't make a "clunk" sound, that I know of... it's more like a thin chatter. I'd look at them anyway. This could definitely cause similar problems. Have you cleaned the carbs and checked the float levels? Do you notice any gas in the air filter housing or leakage anyhere?

[madfrog]

I've cleaned the carbs several times, no leakage anywhere, no fuel in the air filter housing.

I need to go buy another set of feeler gauges, mine only go down to 0.05x mm. That and a new valve cover gasket, the previous owner dumped a ton of gasket sealer all over the place, it's gonna take a while to clean it all up...

[Nick89]

Sounds like the previous owned messed something up. Get the Shop manual.

I'm getting ready to rebuild the heads and carbs on my brothers GS500F.

[madfrog]

So I think I found the problem. Neither exhaust valve had ANY clearance. I got one shim .1 smaller and that gives me about .06 clearance. On the other side, I tried .2 smaller and there is still no clearance. If you don't have a test shim, is  my only option to keep trying until I get the right one? That's a lot of potential trip to the dealer for swaps...

TIA

[craigs449]

So I think I found the problem. Neither exhaust valve had ANY clearance. I got one shim .1 smaller and that gives me about .06 clearance. On the other side, I tried .2 smaller and there is still no clearance. If you don't have a test shim, is  my only option to keep trying until I get the right one? That's a lot of potential trip to the dealer for swaps...

TIA

Pull the shim out of the ultra tight one, go get one that is a size smaller (they come in .05mm increments).....fit that one, spin the crank around a few times, and recheck clearance.

[madfrog]

yeah, I did that. I pulled out the 2.6 shim and traded it for a 2.5 shim. Still too tight. I then took out the 2.4 shim out of the other side exhaust and put it in - still 0 clearance... I ordered a 2.3 today so we'll see if that does the trick.

[madfrog]

All right. so the 2.3mm shim came in, and I dropped it in. several engine revolutions later, I can get a 0.03mm feeler gauge in there. So, it ***just*** within tolerance. Problem is, I didn't see any shims smaller than 2.3 on the site I ordered from. Oh well. I buttoned it back up with a new valve cover gasket and thar she goes.
Now the bike idles and runs pretty well, finally!!! So, one side exhaust valve needed a 0.1mm smaller shim, the other side 0.3mm ( ) smaller shim.

Incidentally, it was pretty easy to push down on the bucket with just a screwdriver instead of a special tool to swap the shims. YMMV.

The only spot of trouble now is that you really need to rev it to about 3k rpm on take off - otherwise the engine tends to "lug" and make unpleasant noises. And especially if you have a passenger on the bike. Is that a common thing, or is my engine just getting tired? (the bike has about 22k miles on it, and doesn't look like it was maintained very well - if at all) - maybe I'm spoiled by my usual daily rider, the VFR750?

I replace the black crap some might call oil and the bike even shifts pretty smoothly now. Now I just need to get the wife to start riding the thing!

[craigs449]

just be careful not to damage anything using the screwdriver method, or break the tip off.

[BaltimoreGS]

All right. so the 2.3mm shim came in, and I dropped it in. several engine revolutions later, I can get a 0.03mm feeler gauge in there. So, it ***just*** within tolerance. Problem is, I didn't see any shims smaller than 2.3 on the site I ordered from. Oh well. I buttoned it back up with a new valve cover gasket and thar she goes.
Now the bike idles and runs pretty well, finally!!! So, one side exhaust valve needed a 0.1mm smaller shim, the other side 0.3mm ( ) smaller shim.

Did you do a compression test before messing with the valves?  I'm thinking with that lack of clearance the valve may have been hanging open.  The valve or the head itself may be damaged.

-Jessie

[madfrog]

That is certainly something that crossed my mind. I don't have a compression gauge. Before I fixed the valve clearance, the bike would make clunking noises at low RPMs (I think I mention this in some of my earlier posts) but the noise would go away beyond idle speed.
I am hoping the clunking was detonation because the exhaust valve was hanging open - worst case, it was the valve and the piston getting intimate, although I would have expected the noise to continue at all RPMs if that were the case. 

I am thinking that as soon as my wife gets more comfortable riding (or decides she hates it) I am going to sell the bike for whatever money I have in it and move on.

This bike was not taken care of my its previous owner(s) at all. When I changed the oil - well, let's say I put oil in. What came out was black, stinky, and watery and didn't do much lubrication I'm afraid. I think this bike is a bit of a basket case, and I don't want to spend even more time polishing a turd...

[craigs449]

Try adjusting/replacing the chain.  Most of the slow riding clunking noises are from a "too loose" or badly worn chain with ridgid sections in it.  You can only hear/feel it at low speeds...it goes away once you get going.

[madfrog]

Thanks for the suggestion. However, (sorry that I wasn't clear) the clunking noises coming from the left cylinder were happening with the bike stopped, on the center stand, in neutral. I don't think that could have been the chain.

While rolling, the bike does make some other noise that sound like a front wheel bearing may be going out (womp-womp-womp kind of noise, if you know what I mean)