Possible fried exhaust valve?

[Wagoneer]

Need some insight on the possible tell-tale signs of a cracked exhaust valve.

So I was riding into work tonight and the bike was running great. Literally a block away from work I just hear a very slight "pop" and I lose all power and the bike immediately starts stuttering and running on one cylinder. Almost feels like the same scenario as when you start running out of gas before you switch to reserve. Problem is, I have plenty of gas in the tank.

Nothing visually wrong with the engine other than the tiny oil leak by the speedo cable, same place it's always been. Problem is, I have zero tools at work so I can't pull the plugs or check the fuel filter or anything like that. I'm just planning on calling CAA and getting it towed home after my shift and start troubleshooting.

I'm thinking best case scenario one carb is gummed up. Worst case scenario I have a cracked exhaust valve. Any way to quickly check if it's fuel related to make sure that's not the problem? Will checking the plugs be a good indication? If the plug is dry can I assume it's fuel related and start cleaning out the jets in the carb?

To give some background, I checked valve clearances before putting the bike away last winter (it was all safely in check) and I haven't put more than 2,000km on it this summer, so I figured it was fine. Bike was showing no signs of running improperly at all, fuel economy was right around 50mpg like usual. She fires up every morning like a charm.

I'm open to any suggestions on where to begin.

[Wagoneer]

So I just thought I'd give it another try before setting up the tow for when I finally get off work and she fired right up on both cylinders and idled, rev'd and ran perfectly fine.

Is this a characteristic of a tight exhaust valve then? I can't imagine if it was a blocked jet or fuel line it would just magically unclog itself from sitting there? I can't imagine an exhaust valve being out of clearance in under 2,000km. Both were well within clearance at ~.08, and I didn't even have to switch shims, both were still within clearance. I guess I'll drive it home and see if the problem comes back up again, but the ambient temp is now almost 10deg celcius colder then when I drove in. I have no idea if that'll make a difference or not. I would think if it was overheating wouldn't there be some above normal heat radiating off of the engine? I didn't notice any more than usual when I parked the bike after it acted up on the way in.

I guess I'll drive it home, park it in the garage and do another valve clearance job on my day off.  Should I aim for .1 next time for the exhaust valves?

[Wagoneer]

Could it possibly be the vent hose clogged for the gas tank? When enough vacuum builds up in the tank it starves itself? It was really behaving like it was being starved of gasoline like when you run out of gas and runs super lean.

[gsJack]

Check for a loose plug wire in a coil, would leave you running on one cylinder and could come and go off and on like that.  Reach up in there and see if you can turn one.  The plug wires are screwed in and then bonded tight in place and if OK they can't be turned. 

[Wagoneer]

Plug wires are in nice and tight.

So I made it home, but as I turned down my street the exact same thing happened. All of a sudden zero power and extreme lean situation.

I'm almost certain now it's a fuel flow issue. I'm going to have to take off the tank and check the filters and lines. I think after time the fuel flows and fills the carbs and then when it runs it slowly runs out of fuel and it can't supply enough.

Sound like I'm on the right track?

[gsJack]

Could still be a bad ignition coil or pick-up coil, they can cut out when hot and come back when cold.  But when you mention filters that could be the problem.  Assuming you mean aftemarket inline fuel filters I'd get rid of those first, the GS doesn't need more than the one inside the tank on the tank petcock.  By the way there isn't a gas tank vent hose, it's vented thru the cap and if it's the problem leaving it loose could check it out.  If it's a carb problem I'll let the carb experts speculate on that, my 02 originally identical to your 01 has gone 100k happy miles with untouched carbs.

[twocool]

A "burnt" valve can be diagnosed by using a compression test or leak down test.

If the cylinder in question has a burnt valve, the compression test will show very low...like say, 30 PSI.

If you use a leak down test...it will also show low...but you can also isolate what /where it is leaking....if it is exhaust valve...you'll hear the leak in the exhaust pipe...

You can rent a compression tester, (and maybe a leak down tester) at most auto stores, like Advance Auto...for free!  You put down aq deposit, which is refunded in full when you return the tool...

I really don't think you have a burnt valve...but if you want to be sure...use above diagnostics..

Cookie

[Big Rich]

If it is an electical issue like Jack mentioned, try and inspect the plugs the next time it happens. Losing spark on a cylinder will cause the plugs to look extremely rich (since the engine is still suckling gas from the carb and not burning it off efficiently).

[Bluesmudge]

I think Jack is correct, this sounds like an electrical issue to me as well. I had a similar thing happen with a bad pickup, it would run fine when cold and then die once warmed up. Something must be wrong with the electronics/wires for the plugs if it keeps running on one cylinder.

[Wagoneer]

So those are my plugs. Can you say lean much? I'm back to thinking its a fueling problem. Time to pull the tank and start cleaning things.

[Wagoneer]

But when you mention filters that could be the problem.  Assuming you mean aftemarket inline fuel filters I'd get rid of those first, the GS doesn't need more than the one inside the tank on the tank petcock.  By the way there isn't a gas tank vent hose, it's vented thru the cap and if it's the problem leaving it loose could check it out.

For some reason I thought there was a filter but I may be thinking of one of my other toys. There are no filters my system. And the vent hose I'm talking about is the hose that's attached to the bottom side of the tank, right beside the petcock, and it goes through the tank tank with a hard line up to the cap. I found that hose with a nasty kink right at the connection to the tank. It's a real stupid spot, it butts up against the top of the carb so it has no option but to kink. I'm going to buy a plastic 90deg cap for the end of it so I don't have a problem with kinking any more. I have no doubt that's my issue right there. After a lot of searching I finally found a thread on here about another person with the exact issue and tank venting was also the problem. The bike would use up all the gas from the system and run dry. He'd let it sit for a couple hours and after the pressure equalized it would allow gas to flow again and after running the same thing would happen.

You can see in the photo, it's the hose to the right of the tank petcock. You can see the permanent kink even after I straightened the hose out.



Hopefully that's the problem, because everything looks perfect! Zero crud in the tank, mesh at the fuel pick up is spotless, all lines clear, both petcocks flow perfectly. If this fix doesn't work, I'll just get rid of the frame petcock and convert to a full gravity fed system. Either that, or start troubleshooting the carb side of things.

This was really a blessing in disguise. I figured out why I ran out of gas the one time while the petcock was set to "on". The hoses were routed wrong. The PO gave me a haynes manual with the bike so if he followed the diagram in there, I can see why the hoses were routed wrong.

[gsJack]

Tank petcocks are all the same but 3 different frame petcocks were used over the years and the 01-02 models are the only ones where the fuel lines cross between the petcocks.  Manual probably shows early years.



That kinked hose from the bottom of the tank drains gas/water from the area around the gas cap, it does not vent the tank. Tank is vented thru the cap and if you opened the gas cap when the engine cuts out it should clear up your running problem by venting the tank if it's a plugged vent hole in cap.

If it's not an electrical problem that I would expect first it could be a problem with the hose that vents the carb bowls.  If it isn't routed to the space between the air box and battery out of the wind it can be affected at high speeds and cause your  carb bowls to run low on fuel.  It's the hose that tees of the top of the carbs and runs rearwards.

I've done 20 or so valve checks in 180k GS miles and never seen that hose off the bottom of the tank kinked like yours in pic.

[Wagoneer]

I've done 20 or so valve checks in 180k GS miles and never seen that hose off the bottom of the tank kinked like yours in pic.

That connection with the kinked hose seems inevitable. It sits down right on top of the carbs. There's only about a 1/2"'clearance. I'm going to get a 90deg hard elbow so it's not kinked with a straight hose coming off of it.

I'm going to keep digging and maybe even pull the carbs and check them. It's definitely a major vacuum issue.

[gsJack]

You could take that kinked hose off and throw it away and it wouldn't affect the running of your bike although you might drip a little gas on your engine if you overflowed the tank while filling it.  Good luck with your search for a fix.

[Wagoneer]

So I've replaced every vacuum hose on the bike with silicon, and fixed all the kinks. I had a very big kink on the vacuum hose at the frame petcock. There's no way to route the hose without it being squished up against the airbox (I'm surprised this isn't a regular problem?). So I made a spacer for the petcock that lowers it about an inch so the vacuum line is kinked anymore. I also replaced the plugs, checked for spark, checked for intake leaks, compression is perfect, float heights are still perfect, not a bit of sludge in the carbs. Put everything back together and started right up again. The real test will be driving it to work tonight, hopefully that fixed my problem, otherwise I have no idea what's wrong.

[Wagoneer]

No dice. Still happening. This is kind of getting frustrating now.

[Big Rich]

Bummer....

Did you try the normal fuel starvation fixes? Popping the gas cap open, checking the carb vent line, etc? I may have missed it earlier if you posted it somewhere....

The timing of the power loss is odd to me... I would say something is definitely starving the carbs of gas.

[Wagoneer]

Yep, I left the gas cap open and it still took the normal 2hrs before the carbs were full again and I could ride it.

I replaced the carb vent line with brand new silicon and ran it all the way under the rear fairings, so it's for sure out of the wind.

I'm going to drive it home on prime and see if I can make it. If so I can assume I need a new petcock and its leaky.

Somehow I don't think it'll be that easy though.

[Big Rich]

What about clamping a clear section of tubing to each carb, and carrying a small cup & wrench to open the float bowl drains when it happens? If a small amount of gas comes out of each carb, you'll be one step closer....

[Wagoneer]

Happens even when petcock is on prime. So back to pulling bike apart again...