It all started on a trip over a month ago. When the tank got down to 2 gallons of gas the bike would start to chugg as if it were out of gas, so I would have to turn the petcock to "Reserve" prematurely, no big deal right? Well a few weeks ago It started to do this when the tank still had 3 gallons of gas and the bike would lose all power and die. Upon pulling to the side of the interstate and priming the carb the bike would start right up and be good to go for another 20 or so miles at 70+mph and it would happen again... I'm guessing a fueling issue at this point. -I pull the Carbs and rebuild them. -Clean out the vent hoses in/on the gas tank. -Add a Holeshot Stage One jet kit and Timing advancer The bike idles smoother, accelerates smoother, has a stronger bottom end, starts with very little choke if any, and just plain rips now! Problem is... after short bursts of open throttle or cruising at 60+mph in 5th gear the bike starts to chugg like it is running out of fuel And now it does it with a full tank of gas in Run, Reserve, and Prime positions. I have opened the gas tank when it started chugging and nothing changed so I don't think that it's a venting issue. Any pointers would be appreciated here folks. I'm willing to try just about anything at this point. -Jake
Can't count this out, I didn't measure the floats when I rebuilt the carbs so maybe? Seems odd that they'd all be off though. -Jake
Yes it is odd that they would all be off. And it doesn't match the previous symptom of only doing it when the tank was getting towards empty. It's definitely fuel starvation, just have to figure out from where. One thing I would try (on a deserted road) would be to put the petcock in the ON position so that it shuts off when the engine dies. Then induce the stalling condition. Hit the kill switch and pull the clutch so there is no chance of the engine making vacuum to open the petcock. Coast to a stop and then open the drain on one of the float bowls to see if there is any fuel in there. If you want to be really scientific You could compare the ammt that drains out after a stall vs the ammt that drains out when you have it running normally. Maybe the petcock sort of works and can only provide enough flow to supply the engine under cruise conditions. You give it the beans and after the floats bowls empty it stalls out. Its worse now with the jet kit because it uses more fuel now???? Just guessing here but it seems logical. Hope that makes sense.
Just another suggestion, you could put the petcock on the "prime" so that it's flow is irrespective of vacum and see if it still stalls. Could it be that the vacum isn't sufficient to pull the needed fuel at the higher rpms?
I think you mentioned in the Bandit thread you replaced the petcock. Seems to me, that would be all that is left, unless you have an electrical issue.
Petcock was replaced last August with a Suzuki OEM Petcock. I have an innate hatred for electrical gremlins. -Jake
I had a similar issue with a BMW R100 some years ago- and went through all the same diagnostic steps. The tank was venting, the petcock was flowing properly, the hoses were clear, the float height was correct, etc.etc. Yet at a steady 75 mph if I had under 1/2 tank of gas it would stumble and miss. The culprit was a semi clogged in-line fuel filter, one of those see-through brass nugget amalgam types that looked just fine and seemed to flow well enough when I just popped the fuel line below it and ran gas through. Once replaced with a new (and slightly larger) unit the bike ran great. The old one was restricting flow just enough to allow the bike to outrun fuel delivery at high load- but only when the tank was low enough to not provide enough "push". If you have a filter added between the tank and carbs try replacing it with a new one even if it looks OK.
I think I have it sorted I routed the fuel line between the throttle cables where it is supposed to be and turned the breathers on the carbs upwards and ran the rubber hose leads to the top of the air-box. (I had previously had them facing down and running out under the bike) This is what the breather looks like and how it should be pointed when installed correctly. As far as I can tell, having the things pointing downwards with the rubber hose leads under the bike in turbulent air was not allowing the carb diaphragms to breathe correctly causing a fueling issue/lean condition on the top end. Pointing the breathers upwards and running shorts leads to the top of the air-box in less turbulent air is now allowing them to breathe correctly. Regardless, it runs perfectly now! I still need to synch the carbs and check the plugs after the carb rebuild/rejet but I made it 10 miles at a very high rate of speed and it didn't cut out at all.(Before it would cut out after several hundred yards at high speed) I plan to take it to work tomorrow to see if things are well sorted. I understand that this does not explain why the bike ran better with a full tank beforehand but I plan to see what happens late rthis week as the tank gets lower to see if this has cured that issue as well. Thanks to all who gave me advice! -Jake
I have this same exact problem. I thought I needed to run from reserve not primary and that was the reason. I'm pulling my carbs in a few weeks and will try the readjustment of the hose to see how it does and give some feedback. Cheers!
I had this exact problem on my bandit, turned out the fuel tank wasn't venting(creating a vacuum). next time it does it, pop the fuel fill see if it goes away. If so, you've got to clear the vent out. Also, make sure your carb vent hoses are not clogged. (doh!) I see I'm 205
