Fuel Starvation

[Rob Frankham]

I'm sure you've tried this but... is the tank venting through the fuel cap OK. It's easy enough to tell, simply run the engine (with the taps on) till it stops then remove the cap. If there is the sound of air rushing and the engine starts right up, that may well be the issue.

Rob

[hudson]

Hey Rob. Thanks for the response. Yeah, no whooshing of air or an effect on the engine running. I didn't get a chance to remove the inline fuel filters - it rained this weekend and I didn't feel like pushing my bike in the rain if that didn't cure it.

[Gibson]

Mikuni's are usually very reliable. Once you get the venting thing ruled out, set float levels and check the little rubber piece on the float needle tip.

[Seth]

So, have you tried pulling the float bowl drain plug as soon as the motor stalls out when you’re out on the road? Are you sure they are dry or close to dry?

If you have fuel, I’ve had the situation when the engine died, stumbling first like it was running out of fuel. Turned out to be a bad condenser. Once I only made it about a mile from my house. Another time, about 5 miles.

[hudson]

Gibson - I agree - never had problems with mikunis - pretty reliable. These are brand new that I bought from Rocky Point. Bill, who is very knowledgeable on these, had me set up the float arms parallel to the mating surface while holding upside down. I also have reinspected the parts, including the floats, float needle - no problem, which I wouldn't imagine as all parts are new. The needle closes with ease. The bike has been running great with them on for several months, so I am gravitating away from them as the cause for now??

Seth - When engine is cold, I turn on the petcocks and I verify the bowls are full, turn off gas- and then confirm the floats are rising. Starts up and I am on my way after a slight warm up. Being cautious (staying around my house) not to completely run out of gas, as soon as I start to lose power or it starts hiccuping, I pull over and find it running on one cylinder, which usually is the RH. The float bowl is empty. Fill bowl up again, and it repeats. This time, while engine running, diverting flow from exhaust, open up the float bowl drain screw quickly and fuel pours out nicely, close it up quickly, and all is well...for now. It's like I am bleeding brakes. In a nutshell, the bowls fill up initially, but seem not fill up during the drive. Since I see the small air-pockets in the inline fuel filters, and the fuel that remains in them disappear when I tap on them.

I really am going to driving around troubleshooting it this weekend. Haven't had time to make it to the garage...

[yourpalcal]

I have had a similar experience on my reserve line. I had to replace the screens on the petcock straws and it cleared it up.

[SteveD]

Can't remember? Have you backwards flushed the fuel lines & taps, without any filters?

[hudson]

Ok, I backwards flushed as Steve mentioned - a no go. I replaced the fuel lines without filters and success! I couldn't imagine this being the culprit since gas flowed so well out of the line with the filters on. Everyone's suggestions were definitely helpful and got me through the troubleshooting. I really appreciate the input when these frustrations arise, no matter how simple. Thanks all!

[SteveD]

Good job.

[Beemerboff]

Just for the record some Mikuni float bowls are vented by by a tube, which on airheads usually points down at the exhaust, but on other bikes the tube is extended a bit further away from the motor.
I drove a Guzzi Cali where the extended pipe somehow got too close to the muffler and the heat collapsed the tube, and , without a vent, the bowl would not fill, exactly the same symptoms as the OP.
So, if the problem returns, check the bowl vents .