Fuel Problems

[B Evil]

I searched and didn't find a clear answer so here's the issue.

I have an 81 550 L and for the most part, runs pretty well. Cold natured and has to be choked to started but after that she runs fine other than, after the choke is completely off, she'll stall out when stopped at traffic lights. I loosend the intake boots on the carbs and sprayed in some carb cleaner and after that and a 50 mile highway journey, it seemed to run all the bugs out of it. Saturday morning I wasn't able to choke her to get her going. The cable seems to be froze or binding somewhere. I was able to pull the choke out manually on the carbs to get her going and get home. Decided to go ahead and replace the Choke cable and since the throtle cable was the only other cable that wouldn't have been replaced, I went ahead and replaced it too.

As I'm sure most of you know, replacing the throtle cable was no walk in park. Since I had to pull the carbs off to get the throtle cable in place I decided to take the bowl off just to see how they looked. Seemed fine so I went ahead and bolted everything back together.

Tried to start her up after all this and she wouldn't even cough for me. Double and Tripple checked, everything is connected how it should be. Drained the battery turning her over so I figured I'd charge her up and try again the next day.

Before I tried again, I checked the bowls and there was no fuel in them. So I check all the hoses again and they're all connected and no kinks. So I pulled the tank off, and replaced the fuel filter and pulled the petcock. The petcock looked fine so I put it back together and put it back in the tank. But no fuel would flow, even in the prime position. Sucked on the vacum line and got a little fuel to flow but still wouldn't flow in the prime setting with no suction.

I put it all back together again and still nothing. So here's my question(s). Should I put it all back together and suck on the vaccum line to get fuel purged in the system again? This should be enough to get her started and allow the engine's vaccum to do the work again right? What could have changed from the time I had it running Saturday to still having problems with the petcock Tuesday? And also, I've read someone mention about altering a petcock to be non-vaccum and have Res-On-Off settings instead of Res-On-Pri could someone point me in the right direction to figure out how to do this.

One last thing, the hose that connects to the fuel gauge is just a vent hose, correct?

Thanks for any advice
Bradley

 

[arveejay]

I searched and didn't find a clear answer so here's the issue.

I have an 81 550 L and for the most part, runs pretty well. Cold natured and has to be choked to started but after that she runs fine other than, after the choke is completely off, she'll stall out when stopped at traffic lights. I loosend the intake boots on the carbs and sprayed in some carb cleaner and after that and a 50 mile highway journey, it seemed to run all the bugs out of it. Saturday morning I wasn't able to choke her to get her going. The cable seems to be froze or binding somewhere. I was able to pull the choke out manually on the carbs to get her going and get home. Decided to go ahead and replace the Choke cable and since the throtle cable was the only other cable that wouldn't have been replaced, I went ahead and replaced it too.

As I'm sure most of you know, replacing the throtle cable was no walk in park. Since I had to pull the carbs off to get the throtle cable in place I decided to take the bowl off just to see how they looked. Seemed fine so I went ahead and bolted everything back together.

Tried to start her up after all this and she wouldn't even cough for me. Double and Tripple checked, everything is connected how it should be. Drained the battery turning her over so I figured I'd charge her up and try again the next day.

Before I tried again, I checked the bowls and there was no fuel in them. So I check all the hoses again and they're all connected and no kinks. So I pulled the tank off, and replaced the fuel filter and pulled the petcock. The petcock looked fine so I put it back together and put it back in the tank. But no fuel would flow, even in the prime position. Sucked on the vacum line and got a little fuel to flow but still wouldn't flow in the prime setting with no suction.

I put it all back together again and still nothing. So here's my question(s). Should I put it all back together and suck on the vaccum line to get fuel purged in the system again? This should be enough to get her started and allow the engine's vaccum to do the work again right? What could have changed from the time I had it running Saturday to still having problems with the petcock Tuesday? And also, I've read someone mention about altering a petcock to be non-vaccum and have Res-On-Off settings instead of Res-On-Pri could someone point me in the right direction to figure out how to do this.

One last thing, the hose that connects to the fuel gauge is just a vent hose, correct?

Thanks for any advice
Bradley

Yes, take the hose off the carb and suck and maintain a vacuum on the hose for 30 seconds. It's the same as priming the carbs. Then hook up the hoses and try to start it. It is required that the choke be used full out when motor is cold.

 

[ron bayless]

if you dont get it to go by the trick suggested here,you take the vaccuum line off the number 2 carb intake,plug off that vacuum port.Plug off the line where it comes off the petcock.That eliminates the vaccum part of the petcock.Then you turn the petcock from run to prime.that will flood your crankcase with gas unless you have an inline turn off valve-stopcock type of deal.problem is if you ever forget to turn off the inline petcock the bike will flood into the crankcase,and if you forget to open it when you want to ride it wont run because it wont be getting any gas.i am sure you knew that already.often times the petcock is shot and the vacuum part doesnt work so a new petcock or bypass method such as this is required.A petcock rebuild kit is a really poor alternative.

 

[duaneage]

I disagree that a rebuild kit is a poor alternative, new petcocks are very expensive and can be hard to find sometimes. I've not heard ofany problems with the kits so far.

Don't use your mouth to apply vacuum to the petcock tube. There are lots of bad things in gasoline that you would not want to eat. Either use a vacuum pump or manually prime the carbs. You could drop a little gas in the carb throats to get her kicked over. Do all of this outdoors, gasoline vapors travel well.

 

[B Evil]

Well I was able to get her going again. I had to suck on the vaccum hose to get some gas flowing and use starter fluid to get her going after turning her over dry for so long. She fired right up and maintained a steady flow of gas.

Since the fuel didn't flow from the petcock in the prime position, it still needs replaced, right? The bike is running right now, but it's only a matter of time before the petcock is totally shot and flows free in all settings, right?

A couple other things. What is the hose on the fuel gauge for? Is it just a vent hose? And lastly, is the inline fuel filter between the petcock and carbs factory or is it something one of previous owners added in? Any pros or cons with the inline filter that really matter?


Thanks again for all the feedback
-Bradley

 

[Pearson]

Since the fuel didn't flow from the petcock in the prime position, it still needs replaced, right? The bike is running right now, but it's only a matter of time before the petcock is totally shot and flows free in all settings, right?

Thanks again for all the feedback
-Bradley

It's frequently recommended to replace the petcock on these old bikes. Bite the bullet and do it now or you'll pay later. I personally went to a Pingel. Good quality stuff. Just never, ever forget to shut it off. In fact, I try to shut if off in the neighborhood to keep fuel from sitting in the carbs. I took off my inline valve. The screen on the petcock should keep things pretty clean.

 

[arveejay]

If it doesn't flow fuel on prime it isn't working right.

 

[Highcountry2000]

...and another thing!

...and another thing!

I noticed in the first post that you mentioned "fuel filter". These bikes did not come with an inline fuel filter, so someone must have added it. That being said, there are TWO types of small filters.

Type A) Designed for a "gravity feed" fuel system. This is what we have.

Type B) Designed for a "pump feed" fuel system. NOT what we have.

Very, very few people know the difference, so if it were me I would eliminate that filter first and test again. I found this little fact out the "hard way" while fighting with my balky Lawn Tractor!

Bruce

 

[tkent02]

What is the hose on the fuel gauge for? Is it just a vent hose?

It's a drain, in case the sender or it's gasket leaks, gas will drain down on the ground instead of on top of the hot engine.
It should end down below the swingarm someplace.

 

[Nessism]

Then you turn the petcock from run to prime.that will flood your crankcase with gas unless you have an inline turn off valve-stopcock type of deal.problem is if you ever forget to turn off the inline petcock the bike will flood into the crankcase,and if you forget to open it when you want to ride it wont run because it wont be getting any gas.

The float needle controls how much gas enters the float bowl. If the bowl overflows the needle needs attention first, not the petcock. The vacuume action of the petcock is a safety feature, nothing more.

Regarding a rebuild kit, why are they a poor option?

 

[Steve]

Please don't tell either of my GSs that they will overflow the gas into the crankcase if I don't turn the gas off. :-s

I went through both sets of carbs when I got the bikes a few years ago and have never had any problems with them since. If you have gas leaking into the crankcase, you need to address the problems you are having with the float needles and their seats.

Bradley, try removing the external fuel filter first to see if that restores proper fuel flow. As Bruce (highcountry) noted, many of the ones that you will find at an auto parts store are not proper for our gravity-fed carbs. If you still have no fuel flow, carefully disassemble the petcock and clean out all the passages. While you have it apart, polish the mating surfaces of the twisty-thingy (the part you actually turn) to free up its operation. Re-assemble it and I'll bet it's working a whole lot better.

Unfortunately, it is the nature of those EPA-regulated beasts to be cold-blooded. Yes, choke is necessary to start it when cold. Driveability will be minimal until it is properly warm. You can help considerably by tweaking the mixture screw to richen the idle up just a bit, and also by shimming the needle to richen the mid-range, where you do most of your riding.


.

 

[B Evil]

I was able to suck on the vaccum hose to fill the bowls and then gave her a few quick shots of starting fluid and she fired right up. Runs better than before now.

Thanks for all the help.

 

[earlfor]

If the bowl overflows while the engine is running either the floatbowl fuel inlet needle "O" ring is faulty or the float levels are set too high. If the engine is not running and the bowl overflows, then those two faults still exist plus the petcock is faulty. I would not call the petcock vacuum shut of a "safety" feature. It is the primary fuel shut off. New bowl fuel inlet "O" rings will normally seep a slight amount if there is fuel flow available.

Earl

The float needle controls how much gas enters the float bowl. If the bowl overflows the needle needs attention first, not the petcock. The vacuume action of the petcock is a safety feature, nothing more.

Regarding a rebuild kit, why are they a poor option?

 

[Nessism]

If the bowl overflows while the engine is running either the floatbowl fuel inlet needle "O" ring is faulty or the float levels are set too high. If the engine is not running and the bowl overflows, then those two faults still exist plus the petcock is faulty. I would not call the petcock vacuum shut of a "safety" feature. It is the primary fuel shut off. New bowl fuel inlet "O" rings will normally seep a slight amount if there is fuel flow available.

Earl

Vacuum petcock not a "safety" feature? It keeps fuel in the tank and not on the floor/crankcase if the float needles stick.

And since when do new O-rings seep? O-rings do not swell like a gasket does and thus they should not seep at all.

 

[earlfor]

Its OK, you dont have to believe me. I dont mind, really I dont.

E.

Vacuum petcock not a "safety" feature? It keeps fuel in the tank and not on the floor/crankcase if the float needles stick.

And since when do new O-rings seep? O-rings do not swell like a gasket does and thus they should not seep at all.