Bike dies after few minutes of highway drone but restarts.

[richeffect]

So I took a different ride today than my usual 30 minute romp through the hills near my house which starts out as a 30 minute freeway drone to the other side of the valley.
Three quarters of the way there the bike sputters and dies and I coast to the side of the freeway. It proceeds to do this several more times on my ride so I give up and head home before I find myself completely stuck in the middle of the Santa Cruz mountains with no cell signal. I didn’t feel comfortable staying on the freeway so I took the expressway and stayed in the right lane. This behavior happened one more time on the way home. The very last time it started sputtering near my house I performed an experiment. Instead of pulling off to stop I let off the throttle and pulled the choke all the way. After a few seconds it returned to normal and it was ok after that for the rest of the way. A fellow biker suggested that my float bowls are going empty faster than usual. I’m running unipods with 168/163 jets and a cored out stock canister with dual outlets.
I suspected it may be a tank venting issue again—but I have gone through this before and I have a 49-state cap with a vent on the cap so that is most likely not the problem. The carbs are clean.
My suspicion at this point is that the yellow weed whacker fuel line I run with the vacuum fuel pump is collapsing under the higher heat generated from the longer freeway ride (and higher speeds in those hills!) and choking the carbs.
so my questions is: what spec fuel line do I buy for the lines from the Mikuni to the carbs? Specifically, the inner diameter?

[wildwhl]

"My suspicion at this point is that the yellow weed whacker fuel line I run with the vacuum fuel pump is collapsing under the higher heat generated from the longer freeway ride (and higher speeds in those hills!) and choking the carbs."

Tygon (if that's what you have works great as long as it is run without any kinks - but not on the vacuum side of the pump (only for the fuel lines).

My suspicion is you are losing vacuum on the pulse side of the pump

WW/R

[richeffect]

Thanks for the info!—I’ll replace that with something thicker.

[squirrelman]

you could have a clogged tank vent or partially blocked petcock.

[wildwhl]

Thanks for the info!—I’ll replace that with something thicker.

You can buy actual vacuum line from your friendly auto parts store by the foot (Napa, for example). The soft fuel line heats up and collapses with the pulses...and SM above isn't wrong. Those two things could contribute as well.

WW/R

[richeffect]

you could have a clogged tank vent or partially blocked petcock.

Thanks! The partially blocked petcock makes more sense since I’m running a vented cap. I’ll first buy some dedicated vacuum line and try that. If that doesn’t provide results then I’ll check the petcock.

[richeffect]

You can buy actual vacuum line from your friendly auto parts store by the foot (Napa, for example).

WW/R

Do you have any info on inner/outer diameter? Otherwise I’ll try to match what I’m using now.

[richeffect]

Thank you for your post jspeed. I was trying to provide as much details as possible. When I jetted the carbs I made sure the float levels were set properly. Since this hasn't happened since and the only difference being the temperature (was 76 yesterday!) I want to believe it’s what wwresto pointed out that I’m using fuel Hose as a vacuum hose.
The more I think about it the more I believe that’s the issue. If that’s not it then I’ll check the carbs.
It’s too bad—yesterday was awesome because those roads are usually filled with Drivers out to meander through nature but since it was Super Bowl Sunday the roads were relatively sparse!

[bitzz]

Is the tank FULL when this happens?
If your fuel pump is defective or not up to snuff, the thing will run out of gas if the tank is less than half full. If the tank is full there is enough "head" to fill the float bowls.
A RC31 will run fine without a fuel pump, as long as the tank is more than half full.
If you have a tank ventilation problem when the bike dies you should hear a WOOSH when you open the tank when the bike dies.

[richeffect]

Thanks Blitz—I did fill up before I left. I’m running a vented cap and there wasn’t a sound upon opening the tank.
the bike would start up fine after cooling down a few minutes.
only when I wasn’t pushing it did it not start sputtering and stall.

[bk94si]

Just because there is a vent in the cap doesn't mean it can't be plugged up.

[squirrelman]

Just because there is a vent in the cap doesn't mean it can't be plugged up.

..........also there is a screen on the intake filter of the petcock that can clog easily with rust flakes or tank debris

[6]

..........also there is a screen on the intake filter of the petcock that can clog easily with rust flakes or tank debris

This was what I was thinking. In tank screen, clogged petcock, clogged filter, bad fuel pump or incorrect setup (as we mentioned), tank vent are what comes to mind when cutting out after sustained high rpm.

THats going to be a fuel delivery issue 9/10 times..

[mparker]

I've had a similar problem and it was my orientation of the pump. I want to say I had it with the vacuum source on the bottom (pointed towards the ground) on one of WWRestos mounts, then I turned it 180 and problem solved. Just a thought! This made me dig through my build thread to confirm a few things. I think when my bike was dying at freeway speeds and would restart and run fine again after like a minute of rest, the issue I found was my choke needle wasn't seated all the way. The mikuni problem was bike was dying when I would pick up the throttle at high rpms. But both are probably worth looking at!

[edubGT]

I kinda had a problem like this recently... It ended up being one of my float bowls wasn't seated correctly. I had opened up the carbs and gave it a good cleaning and after I put everything back, the bike died on the freeway after about 20 minutes of riding. I opened up the carbs again and double checked everything. The rear float was about 3mm off. I reset the bowls, and now problem solved.