A couple of weeks ago, my ride was cut short when my engine started acting like it was out of fuel and died after I made the switch to reserve. At first, I thought that I ran out of gas, so I pushed my bike to a gas station which was about 100 yards away. The tank wasn't empty, though becuase I could only put 1.5 gallons in the tank. After I filled up, I put the frame petcock on PRI and could not get fuel flowing to the carbs and ended up pushing my bike 1.5 miles home.

I figured that since I have a low milage 93 this was a tank rust problem so I got some kreem and treated the inside of my tank. When I put everything back together, I still couldn't get any fuel to the carbs. Needless to say, I was a bit frustrated.

I came back the next day and there was fuel in all the lines after I left my bike on PRI all night. I went for a ride and everything felt fine for a few blocks. Then I lost most of my power, and my exhaust started crackling like the mixture was really lean. It died, and I coasted to the side of the road. I sat there for a few minutes and restarted my bike. She started up fine, and I was able to ride for a few blocks before the whole process started over again.

My first thoughts were vacuum loss, bad petcock and vapor lock. I have run on prime, bypassed the petcock and rode around with the tank lid loose. None of those things worked. Then I took apart and cleaned my carbs. That didn't help either. However, I was suprised by the amount of soot that was in my carbs. I think its time to check my valve clearances again.

I have an inline fuel filter, but I have run fuel through it into a bucket so that isn't the culprit. I don't think that the intank fuel filter on the petcock is clogged, but that is possible. I have run my fuel lines into a tank and the flow from the tank seems ok.

Any thoughts, guesses or suggestions as to what I should try next would be appreciated.

93 gs500e
8000 miles (1300 since engine rebuild)
k&N lunchbox
yoshi slip-on

Kinda sounds similar to this

does it only die while riding?  when it starts,  will it idle for long periods or does the idle surge then stall?

I did a little test this afternoon. I put my bike on its center stand in front of a fan, and let it sit at fast idle (3k) for a while to see if I still had the same problems.

I have an inline fuel filter that stores a decent amount of fuel. Fortunately, the outer casing is made out of a clear plastic so I can tell how much fuel is going to the carbs.

This is a picture of the filter shortly after I started my bike:


And this is a picture taken after it had been running a while:


I didn't let it run until it died, but it looks like the carbs are sucking more fuel than the tank and petcock can provide, even at idle.

I'm going to hook the tank up directly to the filter and see if this happens again. It might be time to get a pingle, but we'll see. Those things are pricy.

I tried it again with the tank petcock directly attached to the filter. The same thing happened.

When I look in my tank, there is nothing obviously blocking the tank petcock's filter. Other than replacing the petcock, does anyone have any suggestions?

If not, its pingel time. Another $100 on my bike. yay.

EDIT: pingle != pingel

goat,
Your initial post sounded exactly like a problem I had in the past:

Scenario:
While riding on the highway the bike began to misfire, become very jerky, and bogged down as if it had run out of gas. I had a hard time getting it started, but when I eventually got it back on the highway it happened again.

Hypothesis #1 (Incorrect):
I figured it had something to do with all the vacuum tubes and frame-mounted petcock everyone keeps complaining about. So, I ended up removing all that and put a larger ID fuel line directly from the gas tank to the carbs with a quick-disconnect in the middle. Well, that wasn't the source because it ended up doing it again.

Hypothesis #2 (Incorrect):
This time I could actually see clear fuel line was starved for fuel before reaching the carbs, but there was plenty of gas in the tank. Therefore, I figured the only other explanation was the petcock directly underneath the gas tank was to blame. I ended up forking over $112.74 for a Pingel petcock + fuell filter (click here for info & pics). After installing it I did a test run with a full tank of gas to make sure it was working properly before I put everything back together. Wouldn't you believe the fuel was still being starved!!! I was in disbelieve. The tank was flowing beautifully before it slowed down to a trickle after 1 1/2 gallons.

Hypothesis #3 (Correct):
There had to be a vacuum being created inside the gas tank that was not allowing the fuel to flow freely to the carbs. If I opened the gas cap the gas flowed fine. After much research I learned there is a tiny hole within the gas cap that allows air into the gas tank that prevents the vacuum effect. Be careful, I ended up dismanteling the gas cap without paying attention and I almost didn't get it back together again with all those little bitty pieces. Anyways, what happened was the rubber gasket surrounding the underside of the gas cap had a slight tear that just so happened to cover the tiny little hole perfectly. In case you are wondering, you cannot just buy the gasket itself. Instead, you have to buy the whole gas cap. So stupid! After rotating the tear away from the hole it works fine.

Conclusion:
After a lot of headache, lost time, and $113 down the tubes my problem was lurking in the gas cap all along :x  :x Because I kept running it like this my bike was running very lean and I am now in the process of having to replace my valves, valve springs, and piston rings, and possibly the pistons themselves. Talk about an expensive lesson. Ouch! At least I caught it before blowing my engine up.

Oh well. I'm not sure if you have the same problem goat, but I hope this gives you some relief knowing you are not alone.

I've tried running it with the fuel cap open, and riding it with the fuel cap open. Niether of which made a difference.

Now I'm completely confused and slightly embarrassed. I think I figured out why the carbs weren't getting enough fuel. A kink in the fuel line. Yeah. I'm glad that I figured that out before buying a new petcock.

However, I'm still having problems with my bike. After I go a couple of blocks, it still loses power in the mid RPM range under low to mild throttle (<<.5). However, if I give it some gas (get close to or above .5 throttle) she wakes up and runs like she is supposed to. The problem gets worse until I have a hard time taking off from a stop sign without reving up to 6-7k and letting the clutch slip a lot. If I kill the engine for a few minutes, start it back up and start riding, this whole thing starts over again.

The throttle ranges that I am having problems with made me think that I am having carb issues as the .25 to .5 range matches up with the range over which the slide is a major player in fuel delivery.

I adjusted the pilot air screw to make the mixture a bit richer, and that helped but didn't solve my problems. I still don't understand why this changes over the course of 10 minutes. If this was strictly a mixture issue, why does my bike run fine when I start riding, get worse as I ride and better when I stop the engine for a few minutes?

The only thing I can think of is my valves. Either the shims are too big or they aren't seating correctly. I'm not sure of this at all, but its the only thing that I can come up with. This isn't just random guessing, though. Ever since I rebuilt the engine, every once in a while my engine will sound like it just sent air back into the carbs and the RPMs will dip. It only happens when its at idle and somewhat warmed up. A lot of times, the RPMs dip enough to kill the engine but I can start it right back up again. It also likes to backfire after I have been riding a while (corresponds with the loss of power in the mid range). That and the fact that I did find a bunch of soot in my carbs when I cleaned them yesterday.

Is it possible that if my valves aren't sealing like they should, a backpressure is being created that is preventing the slides from acting as they should until enough throttle is applied?

Any thoughts, suggestions or wild guesses? As you might be able to tell from the valve theory, I'm starting to take wild stabs in the dark. Different thoughts (agreement or disagreement) would be appreciated.

I may start a new thread, though as this has kinda morphed into a different beast.

It could be several problems, not just one.  I'll throw in my $0.02 here.

Firstly, the fuel starvation problem.  You might want to eliminate your fuel filter.  What you see (the developing air pocket) was what I was experiencing for a while.  I had the same fuel filter as yours (or they look the same), and I saw the same thing--fuel starvation in any spirited highway run (actually, the only times it did not starve for fuel were when I purposefully rode like a grandma, i.e., steady RPM, 60 MPH, no throttle twist-happy).

After some clear hoses and observation, I concluded that air was getting into the fuel line (lower petcock to carb).  Once air gets in there, it is hard to get rid of.  And the starvation happens (this is my guess, since it is hard to look at the fuel hose while riding ) when the air bubble gets too big, and the carb float bowl is almost dry and it sucks in a bunch of air instead of fuel.  And whammo, bike hiccups.

I never found out how the air pocket developed.  Leaky petcock, leaky connection, back frow from the carb, etc., I don't know.  But developed it did.  For me, it was not the restrictive nature of the petcock, because (a) I tested it and it flowed fuel plenty fast, and (b) I fixed my starvation problem without bypassing the petcock.

If I followed my guess of a large air pocket forming and getting sucked into the carb at the moment when I needed the fuel most, then that left me two ways to solve the problem.  (a) Find and fix the air "leak".  I opted not to go that route.  So I tried the second solution which is to (b) prevent the air pocket getting large enough to become a problem.  My steps to implement that is as follows.

I eleminated the fuel filter.  I also made the hose as short as possible.  Remember that only one hose (petcock to carb) is problematic.  Lastly, I made sure to position as little as possible any part of the hose to be below level of the petcock.  This last part is tricky, since the petcock is same level as the carb and the outlet points downward, making it necessary that the hose looks like a "U".  Why so?  Because once air gets in, it will not flow through the petcock back into the gas tank.  The only way to get rid of the air is for it to flow into the carb.  So the idea is to make sure that as much air flow into the carb as soon as possible.

I hope I am not being too confusing here.

Secondly, it seems that your bike is running progressively worse.  I am guessing that your plug is messed up from too much experimenting.  Take them out and clean them first before going into other things that involve more work, e.g., valve clearances, leaky carbs.

Cheers,
e.

P.S.  Here's more confusing ramblings from me in this matter.

P.P.S.  Oh yes, after my "fix", I have yet to experience any fuel starvation problem since.  So I guess my "theory" is correct, or I got lucky.  :dunno:

Well, I cleaned off my plugs. One looks a little whiter than normal but not too white and the other is matte black. This is wierd, since my carbs were balaned recently and I just cleaned them a couple days ago. I adjusted my idle mixture screws and they look better, but the same thing happens.

I removed the fuel filter, and nothing changed. I am a bit worried about the grit that is inside my filter. I should get another filter to put in there if there is  crap in the fuel line.

I'm still having the same problems, though. My exhaust sounds different than it used to. It's a lot louder, its popping/backfiring, and when I have lost power it sounds like I am dogging the engine.

I still don't know whats going on. All suggestions and thoughts would be appreciated. I would prefer things related to what my bike is doing, though.

check your carb boots for cracks.

Matte black plugs mean "rich", according to this pic from the Haynes manual:



Wouldn't a cracked boot result in "lean"?  :dunno:

Bottom line, carbs are evil.   :lol:

My next bike will be a fuel injected VFR - sweeeet!  

Regarding  your specefic problem, I've had similar problems.  My bike would stall on the highway as though it was fuel starved.  Never did find out the problem.  I assumed it was because of the inline fuel filter or petcock but havn't messed with it.  For one it only did it twice, secondly my bike's currently out of commission.  

Good luck to you, I know how frustrating unexplainable problems can be.

I checked the boots for cracks, and there aren't any visable ones.

I haven't done the wd-40 test yet, though.

I think that I am running lean in a certain throttle range (given the loss of power, noise, dogging and popping) after I have been riding for a little while, but wouldn't cracked boots cause the mixture to be lean all the time?

I ordered a set of feeler gauges tonight. I'm doubting that this is due to valve clearance, but I've been meaning to get a .001 feeler gague for about a year now. Hopefully they'll get here by the weekend, but I kinda doubt it. Friggin KBC tools has a $20 minimum order, so I had to get some random stuff in order to get the gagues (which I will use, but its still annoying).

Well, I'm going to be checking my valve clearances and checking for leaky valve seals this weekend.

Any other thoughts on what could be going on?

I ran a similar plastic fuel filter in my old 1977 GS400 for a couple of years, then started to have the problem you describe with starvation. I noticed that the flow of fuel might have been compromised due to the line being almost level where it flowed to and from the filter. I finally eliminated the filter and made the line as short as possible, and the problem disapeared.

The only other time I had fuel problems was when I had the tank valve only partially open on my 01 GS500. Now it runs fine.

A sooty plug might also indicate a faulty float valve in that carb. Try cleaning the float valve.

Well, I fixed something. I don't know what I did, but my bike is running fine now. I even got to go out on a 70 mile ride before it got dark.

I checked my valve clearance, did the flashlight test for leaky valves and cleaned my carbs again. Two of the shims will have to be replaced soon, but they're all within spec and as far as I can tell, my valves aren't leaking.

My theory is that there were multiple problems. I think that the initial problem was related to the inline fuel filter. Either getting clogged (there is some grit floating around in it) or from a kink in the line. I also think that I didn't put something together right when I cleaned my carbs the first time. I still don't know what I did wrong or how I fixed it, though.