Carb#1 CV Boot question/running ice cold

[bwringer]

Cylinder # 1 has a bad attitude. But swapping slides might not be a bad idea. We'll see. Maybe just a trip to the mechanic and let him deal with my headaches.....

A...a...MECHANIC? Wash your mouth out with soap! That's filthy talk for a GS owner, and we'll have none of that around here.

If you have found that rarest being of all, a competent motorcycle mechanic, keep his name a secret and keep him well supplied with donuts or whatever his preferred stimulant might be. I've never seen or heard of a decent mechanic who will work on older bikes, myself, but I suppose it's possible.

Anyway, you don't have to remove the float bowl or the carbs to check the gas flow in #1 -- just the drain bolt at the bottom of the bowl. Since you're getting flow sometimes, there will probably be gas in there, but you'll need to drain that and then get an idea if it's only a tiny trickle or if it's enough to sustain the engine.

With the engine off and the petcock set to "ON", you shouldn't get any flow. With vacuum applied to the vacuum line, you should get plenty of flow. It's coming through the small hole in the needle seat, so it won't be a gusher, but it should be enough to fill the bowl quickly. There shouldn't be any difference in the way it flows when it's "ON" and vacuum is applied and when it's on "PRIME". If there is a difference, replace the petcock.

If you're not getting much fuel flow either way, then you likely have some sort of obstruction that is probably sitting on the little screen on the #1 float needle seat.

The original petcock is 24 - 25 years old, and no matter what the mileage on your bike, it is almost certainly dead or it will die very soon at the worst possible time and leave you stranded in a bad neighborhood or dump a tank full of fuel all over your garage. The petcock may or may not be the cause of your current problem, but for your own safety it would be an excellent idea to replace it ASAP. Install a new one and forget about it for another 20 years.

[bwringer]

1 thing came to mind. The carbs have screens at the needle and seat and #1 might be a little clogged. I know the petcock runs a bit more fuel on prime so maybe that's helping the situation but I really wouldn't bank on it.

Exactly what I was thinking, too.

[bwringer]

Also, you've mentioned the choke plunger a couple of times. Is there something abnormal about it?

As long as it moves out when you move the choke lever the left and back in when you move it to the right, you should be OK. And moving the petcock to PRIME wouldn't affect the enrichment system at all.

Also, have you replaced the vacuum line betweeen the #2 carb and the petcock, or at least verified that it's 100% OK?

My leading theory is still some sort of mung partially blocking fuel flow in #1, possibly combined with a deteriorating vacuum diaphragm in the petcock.

Also, make sure you don't accidentally leave the petcock on prime overnight through all this. The float valves are not designed to be absolutely leakproof for long periods of time, and you could end up with a crankcase full of gas.

[UncleMike]

My leading theory is still some sort of mung partially blocking fuel flow in #1,...

Even after he completely cleaned/rebuilt the carbs three times?

[Rocketman]

Checking the screens seems like an excellent idea and that will be one of the first things I do. I also have no problem replacing the petcock as a preventative measure, but again, if it were defective, or marginal, wouldn't that affect fuel flow to all carbs, not just #1? Also, I will check and/or replace the vacuum line between #2 carb & the petcock, but what carbs would be affected by a defective vacuum line, #1, #2 or BOTH because #2 is firing fine?
When I pull the drain plug and check for fuel flow with the petcock "on" or on "Prime" should the engine be running at that time in order to apply vacuum?
Lastly, do you know if an OEM petcock is still available for my '82 GS850L through Flat Out Motorcycles or other source. How complicated to install? Do I have to completely remove the tank, drain it, etc, and what other parts do I need other than just the petcock to do it complete? Any other washers, O-rings, etc?
Oh, how can I see the choke plunger moving up and down when I move the choke lever left and right? If I have the carb top off, can I see it move through the slide?

Thanks again.

[Dave8338]

A...

The original petcock is 24 - 25 years old, and no matter what the mileage on your bike, it is almost certainly dead or it will die very soon at the worst possible time and leave you stranded in a bad neighborhood or dump a tank full of fuel all over your garage. The petcock may or may not be the cause of your current problem, but for your own safety it would be an excellent idea to replace it ASAP. Install a new one and forget about it for another 20 years.

There may be particulate matter (pieces/parts) of the petcock gasket, seals, diaphragm, or vacume line that are getting into the fuel rail from the petcock. It is one source that is an easy fix and like Brian said...forget it for another twenty years. Got mine from 'georgefix' I think or was it bike bandit? Also, if you've never had it out of the tank, there may be a tear in the screen. It is great piece of mind...

(I wouldn.t even bother with the rebuild kits, I bought one and was P.O.'d at the quality and lack of fit)

[bwringer]

Checking the screens seems like an excellent idea and that will be one of the first things I do. I also have no problem replacing the petcock as a preventative measure, but again, if it were defective, or marginal, wouldn't that affect fuel flow to all carbs, not just #1? Also, I will check and/or replace the vacuum line between #2 carb & the petcock, but what carbs would be affected by a defective vacuum line, #1, #2 or BOTH because #2 is firing fine?
When I pull the drain plug and check for fuel flow with the petcock "on" or on "Prime" should the engine be running at that time in order to apply vacuum?
Lastly, do you know if an OEM petcock is still available for my '82 GS850L through Flat Out Motorcycles or other source. How complicated to install? Do I have to completely remove the tank, drain it, etc, and what other parts do I need other than just the petcock to do it complete? Any other washers, O-rings, etc?
Oh, how can I see the choke plunger moving up and down when I move the choke lever left and right? If I have the carb top off, can I see it move through the slide?

Thanks again.

Do not pull the drain plug with the engine hot or running. It's rather hazardous, and the carb won't operate with the float bowl removed. You'll need to apply vacuum to the petcock with a Mity-Vac pump or some other means to test it.

This could be totally off-base, but my thinking is that the combination of a marginal petcock and some mung in the #1 carb could cause the problem. In fact, it could be debris from deteriorating rubber in the petcock. If the other carbs aren't blocked, they might be able to get by, which would explain the differences.

The OEM petcock assembly is only $41.04 according to the fiche at http://flatoutmotorcycles.com . (Probably the best price you'll find.) You should probably get the o-ring, too -- I'm not sure if the new one includes the o-ring. Rebuild kits are not available for this petcock, and they usually don't work anyway.

To install the new petcock, you will need to remove the tank and it will need to be empty enough to tip it up on the right side a little so the gas flows away from the petcock opening. From there, it's dead easy -- remove the two bolts, clean up the sealing surface a bit, and install the new petcock with its new o-ring.

The choke plungers move left to right -- you may have your terminology mixed up with some other part. When you move the choke lever to the left, you should be able to see the linkage move and pull the choke plungers out of the carb bodies slightly. When you move the choke lever to the right, they should go back in.

[Rocketman]

Thanks guys..I appreciate all your advice and will take and use it. You guys are still the best.

[chuckycheese]

Needle valve screen

On my bike, the needle valve screens (and almost everything else) can be removed from #1 and #4 without pulling the rack. It takes a hand mirror and a little patience but it doesn't take long at all.

[txironhead]

To install the new petcock, you will need to remove the tank and it will need to be empty enough to tip it up on the right side a little so the gas flows away from the petcock opening. From there, it's dead easy -- remove the two bolts, clean up the sealing surface a bit, and install the new petcock with its new o-ring.

HOWEVER, if you think you may have some crud floating around in your tank (very possible) it would be a good idea to slosh the gas around a bit and dump out as much as possible. Try to flush as much crud out of the tank as you can, and the filter on the new petcock will be much happier.

[bwringer]

HOWEVER, if you think you may have some crud floating around in your tank (very possible) it would be a good idea to slosh the gas around a bit and dump out as much as possible. Try to flush as much crud out of the tank as you can, and the filter on the new petcock will be much happier.

Good point. I was sort of assuming the inside of his tank was as immaculate as the outside. Have you seen the pictures? WOW! =D>

[Rocketman]

For now, I'm just going to try to glue down the flanges of the diaphragms to make sure the seal is tight. I'm thinking they might not be laying as flat as they should be, and maybe sucking too much air. If that doesn't work, carb screens are next. I'm going to save the new petcock, vacuum and fuel hoses as a winter project and cleaning out the tank as well, this way I don't lose anymore riding time in the short remaining season. Think just tipping and shaking the tank is enough or is some cleaner and/or sealer necessary after all these years? Still don't think the petcock is at fault right now, or I wouldn't be getting fuel to all 4 carbs, not just #1. But as a precautionary measure I will replace it before next season.

[UncleMike]

For now, I'm just going to try to glue down the flanges of the diaphragms to make sure the seal is tight. I'm thinking they might not be laying as flat as they should be, and maybe sucking too much air. If that doesn't work, carb screens are next. I'm going to save the new petcock, vacuum and fuel hoses as a winter project and cleaning out the tank as well, this way I don't lose anymore riding time in the short remaining season. Think just tipping and shaking the tank is enough or is some cleaner and/or sealer necessary after all these years? Still don't think the petcock is at fault right now, or I wouldn't be getting fuel to all 4 carbs, not just #1. But as a precautionary measure I will replace it before next season.

I wouldn't recommend gluing down the diaphragms. Just switch them for now and you'll know if they're an issue. Then we can go from there.

[Rocketman]

Can you buy just the diaphragms, and if so how the heck do they go on? It looks like mine are part of the slides.

[UncleMike]

Can you buy just the diaphragms, and if so how the heck do they go on? It looks like mine are part of the slides.

You can if I'm reading the schematic correctly, but it'll run you over $100.

For now, just switch the whole diaphragm/needle assemble and see if the problem switches cylinders. Once we see that, we can diagnose from there.