Engine bogging down

[MetalHed]

Okay...I'm still waiting on all of the parts to come in to switch from the weber's to mikuni's. But in the mean time, I'm having a little problem. I think it might be temperature related.

It starts great and runs fine for the first few minutes, but once I get going faster (around 65 mph) for a couple of minutes it bogs down. By that I mean moving the throttle doesn't do anything but make a noise. Even if I slow down and down shift it still just won't accept any throttle, then it dies. But then, if I just wait about 2-3 minutes it will start right back up and ride fine. I've only had a chance to ride it around a couple of times, so I haven't pin pointed exactly when it happens. There was a time when I was riding it slow through town and doing fine with temp up just past 180 or so, but once I picked up speed temp went down to the bottom of the guage (I think around 120) and it died shortly after.

Does this sound like it would make sense? Looking at it, I think the oil coolers seem way too big for the bike, maybe I should plug one of them off? What does everyone think?

I will say though, in between breakdowns this bike was a lot of fun!

Thanks

[jcslocum]

I don't have the webers anymore but it sounds like it's sdtarving for fuel. Chsck the fuel filter and make sure the vent is open into the tank. If air can't get in, the fuel can't get out.

[jfiore]

I agree with jcslocum. When the engine bogs down, pull over and try opening the gas tank cap. If you hear a "whoosh" of air going into the tank, then your vent line is blocked.

If there doesn't seem to be any problem with vacuum build-up in the tank, then either your fuel line is clogged or your fuel pump is not working. Check for voltage at the fuel pump terminals as a first test. If the voltage is at least 10 volts DC, then disconnect the fuel line from the tank to the pump to check for fuel flow. If there is a decent flow of fuel out of the tank, then hook the line back up and disconnect the fuel line going into the carburetor to check for pump output. If there is flow out of the pump, the last check is to tap a fuel pressure gauge into the line downstream of the pump to check the pump output pressure, which should be at least 2.5 psi.

Good luck!

[jomo]

Good advice from the others, may also be worth taking the float bowls off and making sure your main jet hasn't unscrewed itself and is sitting in the bottom of the float bowl.

It happened to me on a tour, about day 4, 2500 km allready done and could not cruise above 110 kph. About 200 km later, some fantastic tight mountain corners with short staights, no problem. Open roads...problem came back. Got to the hotel, copious quantities of beer, sleep, wake with the answer. It had happened on my old Bultaco only a month before. In 30 years of motorcycling, they are the only two times it has happened!

Good luck, worth a look,