Gas Leak?-1980 GS850G

[trdhrdr007]

When I went out to move my bike in to the garage this morning I noticed there was gas dripping out of the airbox. The petcock was in the ON position, when I pulled the fuel line gas was pouring out of the petcock.

I just cleaned/rebuilt the carbs, used all new o-rings , replaced all the jets, & installed new float needles. I did a petcock test before I reinstalled the carbs & everything seemed fine, so I didn't replace it. Obviously the petcock has gone bad since then, so I ordered a replacement.

I went ahead & pulled the airbox & the carbs to check things out. It was obvious that gas had been running out of the #2 carb, through the boot & into the airbox. Gas was also in the boot between the #2 carb & the engine.

Here's my question. Is the bad petcock my only problem? It would seem like the float needle should stop the gas from overfilling the carb. None of the other carbs were overflowing, so why was the #2? This was a fairly slow drip from the airbox, so the float needle has to be mostly sealed. Is there some other way for gas to leak through the carb? I'm going to pull the float needle & clean it again, then recheck the float level, but is there anything else I should be looking at while I have the carbs off?


EDIT: I said I ordered a petcock, but haven't yet. BikeBandit wants almost $70 for theirs, anybody know a cheaper place to buy?

[Dave8338]

Your vacuum pickup for the petcock is on the #2 carb and if the diaphragm springs a leak, it will flow down the vacuum tube and into the #2 carb. Make sure that you check your oil for signs of fuel as this is also a common problem that will arise from the same issue. Replace the petcock with a new one and find something else to deal with for the next decade or two.

I bought mine from georgefix on ebay...45-50 american, delivered.

Also, pull the #2 plug before you turn it over, just to make sure you don't have a hydro lock set up going.

[bwringer]

CHANGE YOUR OIL!

There's almost certainly gas in the oil.

If there's a lot of gas in there, put in cheaper oil, then change it again in a hundred miles or so to make sure you get all the gas.

Ride happily ever after.


Also, the float needles in these bikes are not designed to hold back the gasoline forever. Even perfect needles and seats will let through a few drops of gas per hour, enough to create a significant problem after the bike sits for a couple of days.

In your case, the vacuum diaphragm was also bad, letting gas run down #2 and straight into the cylinder. As Dave said, better pull that plug before cranking. And stand back. And don't smoke.

These bikes need a new petcock every 20 years or so. (Rebuilding them often doesn't work.) There are a lot of things I wish were that reliable. BikeBandit can probably get the petcock to you the fastest, but check with WiredGeorge and Cycle Recycle II to see if they have anything cheaper and/or more quickly available.

http://crc2onlinecatalog.com

Flat Out's cheap, but a little slow. Watch their shipping charges, too.

http://flatoutmotorcycles.com

Buying from unknown people on eBay is also chancy unless they post a part number you can verify. Some of these goobers have incorrect data on what fits what.

[Nessism]

I don't want to come across as argumentative but I'm conflicted regarding whether or not the float needles should be able to hold back gas and keep the floatbowls from overflowing. I've owned and ridden many bikes that did not have a vacuum petcock and I rarely used to turn off the gas when parking the bike. Despite this I have never once had a floatbowl overflow. So what's different about the Mikuni carbs on our GS bikes? Basically nothing other than the fact that everything is 25 years old. Floats are heavy, needles/seats worn, ect. Probably wouldn't be a bad idea to verify actual fuel height with a sight gauge. By all means make sure the petcock is working properly but also make sure the float needles hold back the gas the way they should. If float needles leak it will lead to a high float level when running, which will effect mixture strength and make the bike run rich. Petcock may keep the engine from flooding but it won't keep it from running crappy.

[robertbarr]

I don't want to come across as argumentative but I'm conflicted regarding whether or not the float needles should be able to hold back gas and keep the floatbowls from overflowing. .

When things are working correctly, yes. They should hold back a full tank of fuel indefinitely. The vacuum petcock is mainly a safety device.

I'm still wondering why new needle valve/seat combos leak. For older, somewhat worn combos, I still wonder -- since some pairs can function perfectly and look horrible, and vice versa. I have a really weak theory about friction between the needle and the seat bore...

People often develop some mistaken notion that the petcock can in some way regulate flow. I suppose when the filter screen is all clogged up it can... but under normal conditions, no.

[jetta90]

Make sure your carb floats are set to proper float level specs. And even more important is to make sure that when you measure float level you take your measurements from the right locations on the carb and the float.
On my 1984 750 E - I thought my floats were set properly after I had taken the carbs apart and cleaned them, and adjusted floats. Wrong ! Leaked fuel.
Adjusted float level per specs from carburator bowl base (with no gasket) to top of float step. No more leaky carbs. I had fuel spilling out the carb breather tubes before the proper adjustment.
The measureing technic may only be valid for my GS model, I don't know.
Something to make sure about, though.

[Nessism]

When things are working correctly, yes. They should hold back a full tank of fuel indefinitely. The vacuum petcock is mainly a safety device.

I'm still wondering why new needle valve/seat combos leak. For older, somewhat worn combos, I still wonder -- since some pairs can function perfectly and look horrible, and vice versa. I have a really weak theory about friction between the needle and the seat bore...

People often develop some mistaken notion that the petcock can in some way regulate flow. I suppose when the filter screen is all clogged up it can... but under normal conditions, no.

I agree that the floats/needles are responsible to hold back the gas flow. A small amount of incremental leakage may occur but not enough to flood the crankcase.

[trdhrdr007]

Lots of good points here, which is what I was looking for. When I did the carbs I set the float height exactly like it said to in the manual, in the middle of the range given. I've put a little over 200 miles on the bike since I got it running. I had planned to change oil at 500 miles anyway, this just moved things up a little. I didn't think about pulling the plug on #2, but it makes sense.

I looked on ebay, but the only petcock I could find that was supposed to fit looked different than mine. It had all the same settings & outlets, but it looked like they came out on the wrong side of the petcock, if that makes sense. I ended up ordering from Bike Bandit.

I finished up the carbs 2 weeks ago but didn't have insurance or helmets so I couldn't ride beyond the end of the driveway. In the last few days I put a little over 200 miles on with no problems, so I have to assume the float needle on #2 was fine. No real reason for a brand new part to fail, unless some kind of trash got into the seat, so I will check for that.

[Nessism]

The Suzuki manual shows checking float level with a sight glass tool. You might want to do this to varify the float level is correct. Maybe the float is heavy and sinking a little. Not sure. Also, sometimes when the petcock fails it sends fuel back down the vacuum line and directly into the engine. Maybe this is happening?

Good luck.