Bikes dies after few miles at highway speeds...

[Gixxer Dan]

hey guys,

So my bike is cleaned up and running now (i'll get pics up later). I've taken her out street riding and around the neighborhood, but I took her out for a quick freeway run last night. I started noticing the fuel gauge started to slowly drop even though the tank is full then she gradually died on me after a few miles at 75+MPH. I've come to realize it is a fuel delivery problem because I noticed the fuel line empty when I walked the bike to the light. So I did what I had to do and pulled the petcock vacuum line and sucked on it to pull gas into the carb (trust me, wasn't pleasant) put the vacuum back on and she started up.

So my question is, what could the problem be? is it a petcock problem restricting fuel flow to the carbs at the higher rpms/speeds? or is my fuel mixture off? my RPMs at idle are turning at around 3K since I dumped seafoam into the crankcase/gas tank. Don't know if thats temp or normal either.

edit: There is no fuel filter on and my fuel hose is about a foot long ( I should shorten it huh ) would it make a difference?

[jpaul]

My first guess would be the vacuum diaphragm in the petcock is bad, and doesn't allow enough gas flow to the carbs. Try running the bike on prime, and if the problem goes away, replace the petcock.

[chiphead]

Along with what jpaul said, you could also have a clogged vent in the fuel cap.

[bonanzadave]

my fuel hose is about a foot long ( I should shorten it huh ) would it make a difference?

Could be getting kinked when you put the tank back on. BTDT ! Make sure you have good quality fuel hoses and not some cheep plastic tube.

[uudfourty]

My bike does the exact same thing. It's the petcock.

[Billyboy]

I second the prime suggestion. jpaul's on the money.

[mortation]

I had this problem and it was caused by the clogged fuel cap. I would fix both and see how she rides.

[rapidray]

Go out & ride the bike again before you change anything. If it does it again,crack the gas cap open & listen to hear if it sucks air in when you crack it. If it does, it is the cap vent. This is what I am guessing is most likely from your description. If it doesn't, switch it to PRIME & go for another ride. If it doesn't happen again with it on PRIME you will know to order a petcock. This way you eliminate symptoms instead of just buying parts till you find the right one. This will help you to only have to buy ONE part to replace the REAL culprit. Good luck, Ray.

[jadesystem]

Replace all the gas lines with clear 8-10mm metric hoses impervious to gasoline. This way, you can see and troubleshoot the gas lines with fuel
being drwn by gravity into the carb bowls. You will know instantly
and not guess if the carb bowls are being filled.

Sounds like a petcocks issue, or venting as mentioned by the others.
If you are getting gas in now, then it is not the needle valves.

Good luck friend. :-D

[Dogma]

Go out & ride the bike again before you change anything. If it does it again,crack the gas cap open & listen to hear if it sucks air in when you crack it. If it does, it is the cap vent. This is what I am guessing is most likely from your description. If it doesn't, switch it to PRIME & go for another ride. If it doesn't happen again with it on PRIME you will know to order a petcock. This way you eliminate symptoms instead of just buying parts till you find the right one. This will help you to only have to buy ONE part to replace the REAL culprit. Good luck, Ray.

Can this not be checked by disassembly of the cap? Mine came apart pretty easily. I saw no reason for a blockage. (But I wouldn't mind finding a source for a new seal for it.)

[EJMAMMO]

I can ride my 850L all day at 55 to 60 with no problems, but if I run it up to 75-80 on the freeway, it does the same thing, like the petcock can't keep up with the fuel supply, everything else seems to work fine, does anyone know a way to solve this? I am running 8MM line, as short as possible, and petcock is cleaned, no filter installed, fuel cap good. Any suggestions? Oh, and it does it on prime as well, it is an 1981, so has the cheezy not lever petcock. Thanks

[Gixxer Dan]

great suggestions you guys. I'll troubleshoot with all of them. one problem though...
my petcock looks like this:


So, I have no idea have setting its on... any way to tell?

[andrewclaycomb]

seriously make sure the hose isn't kinked, the exact thing happened to me. Bike ran fine at lower RPMs but once I got it up above 2500 RPM I would just lose power and the bike wouldn't run until I switched to prime and the bowls could fill up again.

I spent two hours trying to figure out what was wrong until I realized that every time I put the tank back on, I was kinking the hose.

[Gixxer Dan]

Ok, I am really beginning to believe I have a faulty petcock valve. I shorten the fuel hose from 1' to about 6" and have it running straight into the carbs at a downward angle. take the bike out for a ride about 30 miles there and bike and had no problems at cruising speeds of 70. It wasn't until I kind got on it to 80 at a constant 6K+ RPM did it begin to die out on me. Pulled over the side of the freeway on once again notice the fuel line was empty again.](*,)

Another reason I think the petcock is bad is that I turn it 360 degrees to find PRIME on it but it never releases fuel freely, only through vacuum.

Do you think it could possibly be anything or is the general consensus a bad petcock? And where do I find a good one? Thanks guys

[Junkie]

I had the same issue on my GS700, but it works fine on Prime even for sustained high speeds. I go up a 3 mile 7% grade on the freeway every day, so it needs to flow decently... it would do 80 on flat without a problem on On, but not up the grade. At this point my jetting isn't quite right (need bigger mains I think), but the carbs don't starve for fuel in any situation I have come upon so far.