incontinent '78 GS750 (gas leak)

[jshoun]

So here is the background. I have a '78 GS750 with around 15,000 miles that sat unused for a couple of years (the wreck is for another post). I have since rebuilt the bike and the final problem I have is a fuel leak.

I have just rebuilt the carbs (followed the posted guidelines and they were scrubbed, dipped, all new o-rings, etc) and the bike now starts and runs great.

However ...

It leaks gas out the overflow tubes on the bottom of the carb bowls. The wierd thing is that it is erratic. It is not a constant slow drip; instead it will just suddenly spit out a couple teaspoons of gas even when the bike has been sitting for several days. [The bike is garaged.] I have caught it doing this when I am working in the garage.

So the only thing I have been able to tie it to is weather. We have cold nights and warmer days this time of year and I am wondering if expansion/cooling in the tank is forcing gas out? We had a streak of several warm nights in a row recently and it stopped for a few days. Has everone ever heard of this.

I have checked the petcock and it works fine. No fuel flow in ON/RES and it flows in PRI position.

Any pointers appreciated.

-- john

[Nessism]

A float is not sealing properly. Possible reasons that come to mind are worn float needle/seat, float that is not floating properly, or float height too high.

Time to pull the carbs back apart and have a look see.

[BassCliff]

Hey howdy hey!

Mr. jshoun

Congratulations on the successful restoration of your classic GS motorcycle! Even though you're no rookie, I just can't stop myself from giving you the one, the only, all-out, no-holes-barred, pedal-to-the-metal, over-the-top, fantabulous, super-elastic mega-welcome! \\/

Let it be known that on this day you are cordially and formally welcomed to the GSR Forum as a Junior Member in good standing with all the rights and privileges thereof. Further let it be known that your good standing can be improved with pictures (not you, your bike)! :-D

Perhaps you've already seen these, but I like to remind all the new members. In addition to the carb rebuild series, I recommend visiting the garage section via the GSR Hompage and check out the Stator Papers. There's also a lot of great information in the Old Q&A section. I have some documentation on my little BikeCliff website to help get you familiar with doing routine maintenance tasks (note that it is 850G-specific but many tasks are common to all GS bikes). Other "user contributed" informational sites include those of Mr. bwringer, Mr. tfb and Mr. robertbarr.

And here are some edited quotes from one of our dear beloved gurus, Mr. bwringer, with ideas on basic needs, parts, and accessories.

***********Quoted from Mr. bwringer************
Carburetor maintenance:

Replace the intake boot o-rings, and possibly the intake boots. Here's the procedure:

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

Here's an overview of what happens with this particular problem:

http://cycleorings.com/intake.html

You'll also want to examine the boots between the carbs and the airbox. There's a good chance these are OK, but check them over.

And finally, if things still aren't exactly right, you'll want to order a set of o-rings for BS carbs from the GS owner's best friend, Robert Barr:
http://cycleorings.com

Once you receive these rare rings of delight, then you'll want to thoroughly clean and rebuild your carburetors. Here are step-by-step instructions that make this simple:

http://thegsresources.com/gs_carbrebuild.htm

***********************************
Every GS850 has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.
***************************************
OEM Parts/Online Fiches:

I would definitely double and triple the recommendations to use Cycle Recycle II and Z1 Enterprises as much as possible. These guys are priceless resources. Z1 tends to have slightly better prices, CRC2 has a wider range of goodies available. If you're near Indy and can bring in an old part to match, CRC2 has a vast inventory of used parts.

http://denniskirk.com - Put in your bike model and see what they have.
http://oldbikebarn.com - seems to be slowly regaining a decent reputation, but it's still caveat emptor. They don't have anything you can't get elsewhere at a better price anyway.
http://www.babbittsonline.com/ - Decent parts prices. Spendy shipping. Don't give you part numbers at all. Useful cross-reference if you obtain a part number elsewhere. Efficient service.
http://bikebandit.com - Fastest. Middlin' prices. Uses their own parts numbering system to obfuscate price comparisons -- can be very confusing for large orders. Cheapest shipping, so total cost usually isn't too bad.
http://flatoutmotorcycles.com - Slow. Cheapest parts prices, crazy shipping costs. Don't expect progress updates or much communication. Real Suzuki part numbers.
http://alpha-sports.com - Exorbitant parts prices. Different type of fiche interface that's quite useful at times, especially with superceded part numbers. Real parts numbers. Shipping cost and speed unknown due to insane, unholy pricing.

Stainless Bolts, Viton o-rings, metric taps, dies, assorted hard-to-find supplies and materials, etc:

http://mcmaster.com - Fast, cheap shipping, good prices. No order minimum, but many items like bolts come in packs of 25 or 50. Excellent resource.
http://motorcycleseatcovers.com - Great quality, perfect fit (on original seat foam), and available for pretty much every bike ever made. Avoid the textured vinyl -- it's perforated.
http://newenough.com - You DO have riding gear, don't you? Great clearances, always outstanding prices and impeccable service.
***************End Quote**********************
Here are some extra parts links:

The Rice Paddy (salvage/used)
http://www.ricepaddymotorcycles.com
Ron Ayers Motorsports
http://www.ronayers.com
MR Cycles
http://www.mrcycles.com

Thanks for joining us. Keep us informed of your progress. There's lots of good folk with good experience here.

Thank you for your indulgence,

BassCliff
(The unofficial GSR greeter)

[jshoun]

A float is not sealing properly. Possible reasons that come to mind are worn float needle/seat, float that is not floating properly, or float height too high.

Time to pull the carbs back apart and have a look see.

I've been down that road (maybe I should have included that in the history). I checked the needle valves and seats. I purchased the float setting gauge that attaches to the drain port and verified that all the floats are set correctly.

I could understand a slow drip, but the fact that is suddenly spurts out at random times has me stumped.

-- john

[Nessism]

Another idea...if there is debris in the tank a chunk could be holding the needle open seemingly randomly.

[bwringer]

I've seen this happen on a GS850 that had a bad petcock.

The bike was quietly minding its own business when a friend of the owner noted that the petcock was "on" and "helpfully" forced it to what he thought was "off" (which was prime).

As it turns out, that was the first time the petcock had been moved in 20 years, and debris from the raunchy innards of the petcock quickly made it way to the needles, propping them open and leading to incontinence of petrol.

Thankfully, when they moved the lever back to "on" (which is "off" when the bike isn't running), the petcock didn't leak.

A new petcock and a quick carb cleanout solved the problem.

So in other words, this problem is often due to debris of some sort from the tank or petcock that makes its way down to the needles and seats.

A petcock includes an excellent filter, but it's entirely possible for an old petcock to contribute its own corrosion and mung. A new petcock will generally keep out anything big enough to be harmful from the tank. (Aside from very fine rust powder.)

So if your bike is peeing gas through the airbox, your first thought should be to replace the petcock and clean out the needles and seats.

[jshoun]

Update:

I did the following test and found that the gas leaks (from the carb bowl tubes) stopped. I unscrewed the gas cap while the bike is parked. It seems that this prevents any air pressure build-up on warm days forcing gas pass the petcock.

I assume this means the petcock is bad. I would expect that ordinarily it would hold even when the tank warms up.

[Dogma]

Update:

I did the following test and found that the gas leaks (from the carb bowl tubes) stopped. I unscrewed the gas cap while the bike is parked. It seems that this prevents any air pressure build-up on warm days forcing gas pass the petcock.

I assume this means the petcock is bad. I would expect that ordinarily it would hold even when the tank warms up.

I'm thinking that points to the cap not venting correctly.

[bwringer]

Update:

I did the following test and found that the gas leaks (from the carb bowl tubes) stopped. I unscrewed the gas cap while the bike is parked. It seems that this prevents any air pressure build-up on warm days forcing gas pass the petcock.

I assume this means the petcock is bad. I would expect that ordinarily it would hold even when the tank warms up.

I'm thinking that points to the cap not venting correctly.

I believe you're both right.

It's easy enough to disassemble and clean the innards of the gas cap and the check ball and spring.

Replacing the petcock requires only a bit of exercise of one's Visa card, to the tune of $50 or so. Not bad, considering it will last another 20 years.

[jshoun]

end of the story

It was a bad petcock. I pulled the tank off and let it set on the work bench and it would drip, drip gas pretty consistently.

I replaced the round, plastic washer that sets behind the petcock lever and it fixed the problem. All is well now and no more gas on the garage floor.

-- john