What the heck happened!?

[Manix]

Here's the deal: my GS started to leak gas when it had been standing still for 6 or more hours so I decided to open the carbs to see if the float needles are stuck or something. I was in for quite a surprise. The left carb was covered with black gunk and the air intake horn (sorry, don't know the correct term) was burnt to crisp! For some reason the GS decided to use the left carb as a third cylinder and ignite the gas there. My question is, how can that happen? Valve clearances way off?

Pics can be found here

[JamesG]

Yes most likely your left intake valve is way out of tolerance, and I hate to kick a bro when his bike is down, but its very likely that that vavle is also burnt too and will need to be replaced.

[Manix]

Ouch...  

[Manix]

Crap, I can't get a service time until mid-June.  :x

Well, I'm just gonna put the whole thing back together after I get the parts and HOPE that the valve isn't busted. I don't think so because the bike worked normally all the time. I opened the carbs just to see why it was leaking fuel.

I guess the accident happened about two months ago when I first fired the engine up (pun intended). The bike smelled REALLY bad the first few times. In retrospect it did smell like burning rubber but at the time I thought it was just dust and other stuff burning on the exhaust after long winter storage.

[MarkusN]

You do know what happens when an overheated valve rips off and drops into the combustion chamber, do you?

[Blueknyt]

carful bro, you might turn your engine into a one lunger if your not carful. then you'll put out mega cash to fix it or part the bike out to the rest of us.  im sorry to say, its happend

[Manix]

Yeah, well, I'm going to open the cylinders tonight and then we'll see what we'll see. *fingers crossed*

[MarkusN]

No need to do a full top end overhaul yet. For starters just rip off the valve cover and check valve clearance.

It can't hurt to have a peek at the valve itself, though.

[Manix]

Ok, me and couple friends tried to come up with a logical explanation to what happened. Here goes:

One morning (~8 o'clock) when I went to work I had to refuel 'cause I was way low on fuel. I refueled and went to work and at about 12 o'clock a co-worked came and told me that theres a big puddle of gas under your bike. Well lo and behold, I had forgot the fuel-switch on PRI! The bike was on side stand so it was leaning to the left, so the left carb must have been completely submerged in fuel. Later when I started the engine that fuel must have ignited and caused the damage it did. What do you guys think, is this what could have happened?

Oh, about the valves. I didn't have the tool to measure the clearance with me today so I'll measure them tomorrow. But the valves looked ok from what I could tell, I didn't dismantle the cylinders completely.

[aslam]

You'll definitely have to measure.  Won't be able to tell if they're in spec just by looking.

ASLAM.

[MarkusN]

You'll definitely have to measure.  Won't be able to tell if they're in spec just by looking.

Yep, but he can decide if the valve overheated by just looking.

[Wrencher]

Ok, me and couple friends tried to come up with a logical explanation to what happened. Here goes:

One morning (~8 o'clock) when I went to work I had to refuel 'cause I was way low on fuel. I refueled and went to work and at about 12 o'clock a co-worked came and told me that theres a big puddle of gas under your bike. Well lo and behold, I had forgot the fuel-switch on PRI! The bike was on side stand so it was leaning to the left, so the left carb must have been completely submerged in fuel. Later when I started the engine that fuel must have ignited and caused the damage it did. What do you guys think, is this what could have happened?

Oh, about the valves. I didn't have the tool to measure the clearance with me today so I'll measure them tomorrow. But the valves looked ok from what I could tell, I didn't dismantle the cylinders completely.

Did you notice any large bangs or backfires when you started it after this happened? If that damage was from a one time incident I think there would have been some VERY loud tell tale noises. Charing a carb and blowing holes in the intake manifold wouldn't be a gentle or subtle thing!

[Manix]

Yes, and it was really hard to get it started and running too. I guess it's hard for the engine to run cleanly when instead of fresh air it's sucking burning rubber fumes.  

[Manix]

Valve clearances were within specs. So when I get the parts I'll reassemble everything, change the oil in case there's any fuel in it and also change the spark plugs. The left plug was unsurprisingly black as night.

[The Buddha]

When the carbs are off... put your hand in and feel up and sown the intake valves. See if they have any kinks or bends or feel like they are otherwise damages. Also look inside the port and use a flash light if needed. Just make sure they dont look like they are damaged. Then also look at the manifolds and make sure they dont have damage. That should be it. If these are OK... your valve should be fine... an external gas fire could have started when you started riding and went off in a few mins as the supply of gas disappeared... doesn't have to burn a long time and creep up to the carbs and that in turn go to the gas tank and explode... You might have had a little gas that caught fire and burnt out.
Cool.
Srinath.

[Manix]

I did look at them using a flashlight and they looked ok. At least the left valve looked just like the right one. I'll do that feel thing next time. And to the exhaust valves too, just in case.

Luckily it's been raining very heavily here in Finland so I haven't missed any good riding days. And the weather forecast isn't promising improvement so I might as well fiddle with the bike now that I have it dismantled.

[Manix]

Well, I got the parts and reassembled the bike but the problem remains. Left carb is leaking fuel like the Niagara. Valve seat, it's O-ring and the needle valve seemed to be ok. I compared them to the right carb's equivalents too. As I already had called it a day, a possible reason came to my head. The float itself is leaking. Maybe there's a hole in there somewhere, the float fills with fuel and thus it never closes the valve. Oh GS-gurus, tell me if I'm on the right track or am I just hallucinating.  

[The Buddha]

OK take the float off and put it on a bucket of has... and look for air bubbles.
Cool.
Srinath.

[Rema1000]

Weigh both floats on a scale, and see if the left is heavier.

Also, the rebuild kit with new needles and O-rings is quite cheap here:
https://www.partsnmoreonline.com/PNMSite/Carb%20Rebuild%20Kit%20Suzuki%2048-1947%20GS500%20GSX1100.htm

That might be worth a try.

[Kerry]

Try it this way:
https://www.partsnmoreonline.com/PNMSite/Carb%20Rebuild%20Kit%20Suzuki%2048-1947%20GS500%20GSX1100.htm
or
PartsNMore.com carb rebuild kit