[Boarder255]

Ive got an issue that popped up one day in the middle of riding. I was on my way home from a great weekend excursion on the TW when all of a sudden I started surging anytime I gave the throttle more than 1/4-1/3 turn. It was almost like I was running out of gas. I checked that I had plenty of fuel remaining (had close to 70 miles on that tank of gas already), I did. I limped it home thinking it had to be a carb issue. Upon my return home,the major thing I noticed was the throttle cable plate had one screw missing and the other was barely attached. This must hace been the issue for sure. So i promptly replaced thd missing screw and tighted the second. Additionally I tore the carb all the way apart and cleaned all jets and even found a questionable gasket on the top of the carb, which I changed out. Putting it all back together things were working fine (slide, float, etc).



BUT! The bike is still surging at the 1/3 throttle position. What else could be causing the issue? I thought bad gas, but I had run nearly 1/2 tank on the gas in question. Thought could be something partially clogging the screen on the petcock, but would that change when I switch to reserve? And when the bike is stationary, I can rev it to the moon without hesitation. I have 8000 miles on the bike. Could it be the valves? I checked the at about 4-5000 miles and they were within spec. I am out of ideas. Please someone with more carb/motorcycle skills offer their thoughts.



Thanks guys!

 

[Boarder255]

Oh, just so to answer the re-jetting question, the carb was running perfectly fine, no surging, great idle, and high speed. It was like someone flipped a switch during my 50 mile ride home. It wasn't even between stops.

 

[TWBARR]

Oh, just so to answer the re-jetting question, the carb was running perfectly fine, no surging, great idle, and high speed. It was like someone flipped a switch during my 50 mile ride home. It wasn't even between stops.

Have you checked the fuel flow to the carb? It might help to pull the petcock and clean and inspect it. Make sure you have good flow out of the fuel tank.

 

[Point37]

stock tank or aftermarket?...if aftermarket, it could be a tank venting issue

 

[Boarder255]

stock tank or aftermarket?...if aftermarket, it could be a tank venting issue

Clarke Tank.



I'll pull the gas out and clean the mesh screens on the petcock today.



Also thinking check the fuel level in the carb bowl/float adjustment.



Something else I noticed, on the exploded view of the carb, there is only one screw on the throttle cable plate. But on mine there are two holes for M5x0.8 12mm screws (one screw I'm assuming was lost on the ride). Can someone with an older carb (mine is a '99) confirm that there are two screws holding the throttle plate to the carb?



Dale

 

[small's]

Venting issue or maybe something in the fuel line.

 

[Point37]

Clarke Tank.



I'll pull the gas out and clean the mesh screens on the petcock today.



Also thinking check the fuel level in the carb bowl/float adjustment.



Something else I noticed, on the exploded view of the carb, there is only one screw on the throttle cable plate. But on mine there are two holes for M5x0.8 12mm screws (one screw I'm assuming was lost on the ride). Can someone with an older carb (mine is a '99) confirm that there are two screws holding the throttle plate to the carb?



Dale

yea the Clarke tank has a big vent port...you could try loosening the cap to see if there is any blockage or check your vent hose if you have one



mine is a 2000...not sure if this helps but it's the best i can do right now

 

[lizrdbrth]

Clarke Tank.



I'll pull the gas out and clean the mesh screens on the petcock today.



Also thinking check the fuel level in the carb bowl/float adjustment.



Something else I noticed, on the exploded view of the carb, there is only one screw on the throttle cable plate. But on mine there are two holes for M5x0.8 12mm screws (one screw I'm assuming was lost on the ride). Can someone with an older carb (mine is a '99) confirm that there are two screws holding the throttle plate to the carb?



Dale

O/S carb has two screws for the plate.

 

[Hotrodjohn]

Dont forget to check the mesh screen inside the carb, on the top of the float needle. Check that flow all the way INTO the bowl.

 

[Boarder255]

Ok. Checked flow out of gas tank with and without cap, and was consistent with both conditions. Cleaned the screens on the petcock draws (weren't visibly dirty)



Shimmed and un shimmed needle, re jetted back to #114 main jet both did not have and effect (ran worse).



What does bad gas feel like? I double checked my math this morning and I believe the surging started approx 45 miles after filling up after hitting reserve. Reserve gets me 35-40 miles. So it could be I burned through the good gas and then hit the bad stuff on my way home. Would they stay relatively seperated or would they mix? I have never had an experience of bad gas. I put some seafoam in the gas and put new stuff on top of the old... Dumb I know, but I didn't have this brainstorm until this morning. It seems not as bad. But still doing it. Thinking about dumping out the whole tank and filling with fresh gas. Thoughts?



I will clean the screen above the float needle tonight.



Thanks guys. It's frustrating driving my car to work when it's 80 and sunny!!

 

[Boarder255]

Eureka!! Well it was the cheapest and most annoying solution, the gas! But a couple of good things came out of it, I discovered an out of spec spark plug, dead nuts on jetting, a bad gasket on the top of the carb and cleaned the sh*t out of it 7 or 8 times. So if you've got a sudden surge, check your freaking gas. Just wish I could go back to the station and give them the finger.



Thanks anyways for your support and ideas.



Happy memorial day and get out and ride!!

 

[srs713]

I'm reminded of a movie I saw a looong time ago. About a cross country motorcycle race in the very early days of motorcycling. The bad guy (in the lead of course) stopped at a gas station & topped off his tank. He then distracted the station owner long enough to dump several ladles full of water into the glass top of the fuel pump. When the good guy rode by the station he checked his fuel and decided he didn't need to top off. Further down the road he started passing all the other racers who had stopped at the station after the bad guy. Jumped from about 7th to 3rd with that one decision.



Wish I could remember the name.