fuel starved? near WOT for extended period (550LZ)

[DimitriT]

I was going into a stiff wind doing about 80 mph and was trying to pass when I noticed a gradual loss of power. I had just switched to reserve since I was low (needle was on the left edge) but I knew I had enough to get me to the next filling station.

Power continued to drop off so I pulled over. The engine stalled as soon as I stopped. I did the following: took the cap off the tank, switched it to PRI, waited about 30 seconds, switched it back to RSV, hit the starter. Bike fired up and ran great like nothing happened.

I do have an inline automotive fuel filter on the bike. Otherwise she is stock.

Could switching to RSV have caused a bubble to enter the fuel line which would cause vapor lock in the filter? This is the only explanation I can think of. The filter lays sideways under the tank and is only about 50% full of fuel and the rest air.

[Guy]

Dump the inline filter. It doesn't need it, and they're prone to causing fuel starvation at high RPMs. The filter in the fuel tap does the job fine on it's own.

[hungryman]

You cannot run a paper type automotive filter. They are pressure fed and your system is gravity fed.

[DimitriT]

I replaced the auto-style filter with an inline bike filter. Its a small filter which fits in between carbs #2/#3 using a short piece of hose. I also removed 2-3" from the gas hose to allow the gas to run straight down (with no places where air could get trapped).

The results where good. We have a hill on Rt. 2 coming out of Arlington/Belmont which is great for WOT runs. I did a good run in top gear for almost a minute and the previous symptoms have gone away. Last night I ran it doing 80-85 (damn cold out there) for about 5 minutes. No problems there either. Now this was all with an almost full tank of gas so its not a conclusive result, but it is positive.

[Superfly]

HA! I added a auto fuel filter on my bike once....

once!

Had to fight that bike all the way home, kept on dying on me (on the freeway). I could not take it out because I did not have a hose long enough to go from the petcock to the carbs.

Some things are learned the hard way!!!!

[jeff.saunders]

One other item to check - under the gas cap is a pin-hole vent - these can get partialy or fully clogged with crud / rust. If this happens, it's like pouring gas out of a gas can without opening the little vent - some comes out initialy, but you build a vacuum inside and it cannot flow effectively.

This problem is especially true when you'd coated the inside of the tank and done it with the gas cap fitted.

Usually you cannot clean the vent hole out without disassembling the gas cap as the hole often routed thru a convoluted route.

[tconroy]

I run an inline bike filter and have no problems with it at all as long as it is below the petcock and NOT horizontal.It should fit in between the carbs and face downward.You can also run a 5/16 hose to the filter and 1/4 in .to the carbs so the filter doesnt have a chance to "starve".