Fuel delivery problem

[dankamus]

I've been having a problem with my '04 ever since I replaced the left needle valve and seat.

Originally the valve was sticking in the seat, stopping gas getting into the bowl. Cleaned it and the seat twice. Didn't work, so I finally bought a new one. Worked great except that now my bike wouldn't go over 60mph w/o sputtering and acting starved for fuel. Slow down and after a few seconds it would stop sputtering and run normal again.

I checked the gas cap vent...not the problem. checked placement of the carb vent hose (will not vent at high speeds properly if hose is in bad position)...not the problem. So I took the carbs off to check the internal carb vent ports for obstruction, etc...everything seems fine. Also checked the float height at least three times according to the procedure in the Suzuki service manual so I know that's good.

So finally I realize that fuel isn't flowing from the gas tank to the carb properly (I have a clear inline fuel filter). If I pull the hose off of either end of the filter, gas will POUR out (so this would make me think the filter isn't the issue since gas will flow through it), but as soon as I put the hose back on gas will only trickle into the filter if any flows at all. (I get the same results on any petcock setting.. even on PRIME no fuel can be seen flowing into the filter.) Sometimes if I pull the line off and let some gas pour out then quickly put the line back on the filter enough gas will flow into it so that I can start the bike... then it will run all day unless I try to get over 60. You can actually watch gas being sucked out of the fuel filter when you rev the bike making me think that there's still something restricting the flow of gas. All the lines and both petcocks are brand new. I'd think that if one of the lines had collapsed inside it would still just trickle once I pull the line off of the fuel filter. *the fuel filter is inline right before the carb*

Oh, and now the left needle valve is sticking again!

If anyone has any thoughts please help! I'm completely lost and don't want to bring this thing to a shop if I don't have to.

By the way, this thing ran superb for months with an aftermarket fuel filter on it. It only started acting up once I went in and replaced the needle valve. I replaced the fuel filter just to be sure anyway...no difference.

[BockinBboy]

What needle valves did you buy? OEM or K&L?

Many members have proved the K&L (the cheap ebay ones) to be problematic, and that OEM is the only way to go when replacing the needle valves.

Also, regardless of having ran with a filter before and the different scenarios you have tried, I would ditch the filter unless the tank is swimming in rust.  That way you can eliminate variations from stock.  There is no question that stock configuration works, and it does not require a filter.  You can always drain the float bowls to clear anything out once you figure out the problem.

As an afterthought, check the fuel inlet on the carbs to see if there is any obstruction there.

- Bboy

[mchollan]

If removing the hose from either end allows fuel to flow and only when you attach both hoses to the system does it trickle sounds like a pressure problem.  You are sure that the tank vent isn't the problem?

Either no air is getting into the tank to replace the fuel that is leaving, or air isn't leaving the carb bowls to allow fuel back into them.  Open the gas cap and see how much fuel flows through the filter then.

[dankamus]

The new needle valve is OEM. I tried cleaning it twice only b/c I'd got an aftermarket carb kit that came with new needle valves and i wanted to make sure it was an issue with the needle itself before I coughed up the money to go with the more expensive OEM stuff. (I think the carb kit I originally bought was K&L actually).

I hadn't ditched the filter b/c the tank is loaded with rust (the bike had sat up for a few years before I bought it). Several weeks ago I put a straight coupling in place of the filter and had the same problem. I don't know if a coupling could also cause flow restriction but it was definitely not a small coupling. It was a huge pain to put in and take out!

Also, the last time I took the carbs off to check the vent ports I checked everything from the float height to the inlet ports, etc. Everything seems perfect, but just to be sure I put lots of carb cleaner through the ports just in case. Came out clean.

And to mchollan, I've tried everything you've suggested also. I've tried opening the fuel cap will riding with no difference. I even replaced the fuel cap since the time it started acting up b/c it was leaking and letting water in. Even with the new fuel cap still the same problem. In fact I'm in total agreement with your line of thinking. Since gas pours out when I pull the line from the filter which sits after the petcock, that should rule out everything from that part of the line up (petcocks, lines, screen), which would lead me to believe that there must be pressure from air not escaping the carb bowls to allow fuel in. Since I've checked the carbs thoroughly I can't see how that's the problem unless I've overlooked something.

The only thing I can really think to do now is dip the carb just to be absolutely sure... I still don't think that will be helpful though b/c when I blow through the gas inlet or through the vent hose with my mouth I can get a ton of air through there.

Thanks for all the advice guys! Let me know if the extra info gives you anymore ideas, b/c at this point I'm absolutely stumped.

[X-ray]

I have had this problem for a long time and can't seen to come up with an acceptable solution.  I replaced my fuel line originally with clear vinyl tubing just to get a view of what was going on and later actual clear fuel line. I also attempted to add a filter.  My ride would starve of fuel because for some reason a air bubble would form in the line.  If I left the filter on that would fill with air too.  I have come to theorize that any clear line or maybe the new fuels create some vapor bubble that unless the lines a routed perfectly too allow the bubble to clear, it gets caught, causing starvation. My only solution so far have been run a line from the tank too the carb using only the tank petcock(no reserve). Try filling the entire line with has,no filter, and then let the bike.doc for 2-3 days and see if a bubble spontaneously forms. Maybe using the original stiff outer tubing on the fuel lines can get a good path for any bubbles to clear.

[twinrat]

Is there an oring under the needle valve? i myself dont know as i have not had a similar problem just a thought .

[dankamus]

Is there an oring under the needle valve? i myself dont know as i have not had a similar problem just a thought .

Not sure what you mean. The needle has a pointed rubber tip which fits into a brass (looks like brass to me) seat to make the seal.

[dankamus]

I have had this problem for a long time and can't seen to come up with an acceptable solution.  I replaced my fuel line originally with clear vinyl tubing just to get a view of what was going on and later actual clear fuel line. I also attempted to add a filter.  My ride would starve of fuel because for some reason a air bubble would form in the line.  If I left the filter on that would fill with air too.  I have come to theorize that any clear line or maybe the new fuels create some vapor bubble that unless the lines a routed perfectly too allow the bubble to clear, it gets caught, causing starvation. My only solution so far have been run a line from the tank too the carb using only the tank petcock(no reserve). Try filling the entire line with has,no filter, and then let the bike.doc for 2-3 days and see if a bubble spontaneously forms. Maybe using the original stiff outer tubing on the fuel lines can get a good path for any bubbles to clear.

I have thought about replacing the line that I cut to put the fuel filter in but haven't been able to find a suitable alternative to stock that is thin enough to fit easily where the stock one goes. You know where I can find something like that. Even online bike parts websites I've looked at only sell that really thick walled fuel line that is hard to fit in place of the stock stuff.

[bigfatcat]

If I were having this problem I would simplify as much as possible , by installing a temporary fuel line directly from tank to carb inlet T - no petcock, no filter - using 1/4 "  tygon or similar from hardware store.

Then ride the bike for a while over couple days, see what happens and go from there.

If it fails then you know your problem is downstream of the tank-to-carb line (maybe trash is lodged in the inlet T fitting, or something else. process of elimination.)

If it doesn't fail, then you'd suspect the 'real' fuel line set up is at fault somehow.

[X-ray]

I've actually done this in my attempts. I didn't like the idea of having just the float needles being the shut off for the fuel. Who wants a cylinder full of fuel if something minor goes wrong. For peace of mind I took a threaded rod and ground down the end like a flat screwdriver so that it would mate with the tank petcock. I drilled a small hole through the petcock "knob" and the end of the rod. I used a cotter pin or bit of wire to hold the rod in place. I then angled the rod past the carbs, between some fins to the other side of the bike. I attached a fender washer between two nuts for a knob to turn it all on and off.

[adidasguy]

The float needles have to be working or your bike won't run well. If you worry about them shutting off the fuel, you have a problem.

So, lets say you put on a fuel valve to shut off the gas when the bike is off. Isn't that what the vacuum frame petcock does?

Now back to running .vs. off. The floats control the fuel into the carbs. If you worry about them with the bike off (and remember the frame petcock already shut off the fuel flow), what about when running? If they are not working correctly, then wouldn't one carb flood while running? The floats are the only thing that controls fuel flow into the carbs when running. Floats that stay open would flood a carb and result in one side running very rich.

So back to needles and floats: they have to be working correctly, both with the bike on and off.

[X-ray]

+1 on the needle valves, make sure the're up to par or any testing will result in inconsistent results.

Fuel line: you can pick clear.
http://www.chaparral-racing.com/Product/helix-5-16-x-7-16-racing-colored-fuel-line/353-0495.aspx

[dankamus]

The float needles have to be working or your bike won't run well. If you worry about them shutting off the fuel, you have a problem.

So, lets say you put on a fuel valve to shut off the gas when the bike is off. Isn't that what the vacuum frame petcock does?

Now back to running .vs. off. The floats control the fuel into the carbs. If you worry about them with the bike off (and remember the frame petcock already shut off the fuel flow), what about when running? If they are not working correctly, then wouldn't one carb flood while running? The floats are the only thing that controls fuel flow into the carbs when running. Floats that stay open would flood a carb and result in one side running very rich.

So back to needles and floats: they have to be working correctly, both with the bike on and off.

I actually had the stalling problem start right after I put a brand new needle valve in and adjusted both float heights to specs. Both  needle valves were working fine and I still had the starvation issue. It's hard to tell if the issues are related or just coincidence. The new needle started sticking in the seat a few weeks after I replaced it, just like the old one had been.

The funny thing is that the whole reason I replaced the needle valve was because it started to stick. If I tapped on the carb bowl the needle would break free and the bike would run great until I shut it off and let it sit overnight, then it would be stuck the next time I tried to start the bike, I'd tap on the bowl and the needle would break free again..... I tried cleaning the thing twice. That didn't work, so I replaced the needle and seat with factory parts. It would no longer stick, now I didn't have to tap the bowl to get the needle to free up, except that now instead of running great it would stall at 60+ speeds. Then after a few weeks from replacing the needle and seat, the needle spontaneously started sticking again.

I followed the procedure for setting the float height in the bike manual, and can't imagine what else would cause the needle to stick in the seat and whether or not it's related to the stalling/fuel starvation issue.

[X-ray]

You said earlier you tank was full of rust making it entirely possible that your needle valve sticks again due to debris. The needle and seat may be perfectly fine.