81 GS850GLX carb & fuel questions

[DaveDanger]

Alright guys, I have several questions here all in one place, so grab a glass of tea and help me out a bit.

I finally finished the de-rust and seal on my fuel tank (I LOVE the POR-15 seal kit!) and mounted up the fuel level sending unit, and the petcock and installed the tank. Cranked the engine, warmed it up a few seconds and began to ride around the parking lot for a bit. Took about 3 minutes to starve the carbs and shut off the engine 'cause the petcock's not flowing anything. Doesn't matter what location I place the petcock lever in. I removed and opened the petcock and found all the rubber parts were stiff and brittle.

#1... I can buy an entire new petcock from my local Suzi dealer for about $50.00 but they don't show an OEM rebuild kit for it. They do show a few aftermarket kits for about $20.00 but had difficulty determining which one fit my exact model. Does anyone know of a cheaper alternative for a rebuild kit or entire petcock?

#2... When my carbs began to run dry, my idle speed increased from 1000 to nearly 3000 RPM. This tells me I'm pretty heavily rich on my mixture. I thought that the screws down inside the recess on the top-front of the carb body were the mixture screws, but mine refuse to turn without VERY heavy torque.. almost to the point I'm afraid I'm going to break something. Anybody up to describing exactly what I need to do to set these mixtures correctly? (I'll then go back and redo my carb synch again).

#3... While I was going through my carb synch the first time.. I noted a huge amount of condensation building up inside the manometer tubes. I had an inch or better of moisture built up after a short while. Water bouncing up and down on top of the mercury with the power pulses. Made it difficult to read the mercury after a bit. Anyone know a way to prevent this?

[dpep]

Dave, are you saying that nothing comes out of the petcock, even on Prime? That is a gravity feed. What happens if you pull the gas line off and swich to Prime? If you pull both the gas line and the vacuum line off? with finger over the vaccuum hole?

[DaveDanger]

Don, I did exactly that... pulled the fuel line from the petcock while trying to figure why the engine wouldn't crank. Made absolutely no difference where the lever was pointed, no fuel came from the petcock. On, reserve or prime. I pulled the vacumn line from the carb, and sucked on it with enough force to nearly collapse the petcock (NO JOKES CLOWNS!) and got no fuel from the fuel port in any direction. I finally connected my temporary tank and cranked the bike and drove it back to my hangar to begin figuring out the problem. Amazing what a little petroleum will do.

[dpep]

Dave, it sounds like an osbstruction somewhere in the fuel path. Are you sure you had the petcock out when you Por'd the tank.

[DaveDanger]

Don, I swear I did, have the petcock out I mean. Obviously there's something out of whack inside that petcock. That's one reason I want to at least obtain a rebuild kit for it, if not just outright replace it completely. I completely disassembled the petcock after removing it, and even after removing the vacumn diaphram, I couldn't suck air through the fuel port. The o-rings and seals on the rotor valve inside the valve were hard as ceramic.

[duaneage]

Either something got into the petcock during your repair that clogged it or else bad timing. I would replace it, someone got a new petcock for around 80 dollars that should last another 20 years. Rebuild kits are on ePay for about 22.00.

The kicker is no fuel on PRI. That says blockage to me.

We promise not to change your name from dave danger to Monica :P

[DaveDanger]

duaneage, you have my eternal gratitude that my remark will simply disappear into the dusty old files of "little interest".

As for the petcock price, I actually was quoted today from my local Suzi dealer for a brand new one at $50.00. I'm thinking hard about that.

I had not actually considered that there might be a physical blockage of old sealer or something similar inside the petcock. That's an angle to consider. I may look a mite closer at that first thing in the morning before I call the dealer and give them the go-ahead to order that new one.

I may try and flush a little MEK through the petcock backwards and forwards with a little air pressure and see if it cleans out some. Thanks for the thought guys.

[duaneage]

Try air pressure, put 20-30 psi through the fuel outlet and see if something comes out. Maybe a frog crawled in there. The screen comes off easily enough so you might be able to dip it in cleaner.

Did you try this with the fuel cap off the tank? could be a blocked vent, especially with a full tank, causing it to lock. You did have gas in the tank, right?
(sorry, could not resist that last one) :twisted:

[DaveDanger]

yessir, had about 2 gallons of 100 octane in the tank, and I did open the cap very first thing to make sure the venting wasn't a problem. No dice.

I will see what happens with it in the morning with some MEK and air pressure.

[duaneage]

Re: 81 GS850GLX carb & fuel questions

#2... When my carbs began to run dry, my idle speed increased from 1000 to nearly 3000 RPM. This tells me I'm pretty heavily rich on my mixture. I thought that the screws down inside the recess on the top-front of the carb body were the mixture screws, but mine refuse to turn without VERY heavy torque.. almost to the point I'm afraid I'm going to break something. Anybody up to describing exactly what I need to do to set these mixtures correctly? (I'll then go back and redo my carb synch again).

#3... While I was going through my carb synch the first time.. I noted a huge amount of condensation building up inside the manometer tubes. I had an inch or better of moisture built up after a short while. Water bouncing up and down on top of the mercury with the power pulses. Made it difficult to read the mercury after a bit. Anyone know a way to prevent this?

Just before the carbs run dry the engine speed tends to pick way up, I would not touch the mixtures at all. Fix one thing at a time, namely that petcock.

3. That was probably not water but fuel vapor. The carbs atomize the fuel with the air, gasoline naturally wants to be in a liquid state and it collects in the tubes. The tubes are cooler than the engine so that contributes to the effect. It's normal, mine do it all the time.

[DaveDanger]

I will fix the petcock before I do any more to it, but I'm still convinced that my mixtures are way rich. I mean it hit me like a ton of bricks as it began to shut down. "I see this every day, but not on a bike!"

One of the standard maintenance checks that I perform on a aircraft piston engine is to verify the idle mixture every time I do a ground run-up... running at normal idle, I slowly pull the mixture control all the way back from full rich to full idle cutoff (lean). If the idle mixture is set correctly, the rpm will increase about 25 to 50 rpm before it falls off and shuts down. That means that the engine is operating just a few % rich of perfect when idling. That's what's desired on an aircraft engine. To be understood is that because of the widely varied altitudes that an aircraft engine has to operate at, the mixture is completely controllable from the cockpit with a lever just like the throttle. One setting simply will not work.

On a bike or automobile however, there will be a relatively normal, fixed mixture setting that should work across a wide range of ground level conditions. If an engine rises 2000 RPM as the float bowls dry out, it's waaaaaaaaay rich and needs adjusting badly.

[duaneage]

Try using an oxygen sensor. An oxygen sensor for a car can be used on a bike as well. With a 5 volt supply and a voltmeter you can read the O2 content and determine fuel/air ratio exactly. 14.7 to 1 will cause the sensor to drop the voltage across it to .45 volts. A rich mixture of 8-1 at idle gives .8-.9 volts and a lean mixture sends it down to .2

it is pretty interesting to see what the gasses look like on a meter, expecially under load.