Motorcycle Repair: Fuel problems with 1976 KZ750 Kawasaki, vent hoses, tank lid

Question
QUESTION: In the process of restoring the bike installed two inline filters between gas valve and carbs. After riding for a while the fuel in the filters drains out without refilling quick enough to keep up with the demand, especially the right side. This lead to the bike erratically loosing power. Fuel flows freely in front and directly behind inline filters. Vent hoses are free of obstructions as well.

What might be causing lack of flow?

I'm going to try running without filters tomorrow to see if they are causing too much restriction.

ANSWER: I've had problems running auto fuel filters which are designed for pressure feed systems (not gravity feed). The trouble is that the air trapped in the filter can cause the feed to vapor lock. They sell motorcycle filters which usually point straight down and sit between carbs #2 and #3. They are designed for gravity feed.

Also check your gas line. I use a clear blue gas line so I can check for any bubbles. Make sure the gas line has no upward bends to it which can trap air.

Also check that the fuel tap doesn't have a clogged mesh screen. They also sometimes put a small screen in the carb (over each float valve) which can clog.


---------- FOLLOW-UP ----------

QUESTION: The mesh in the tap defiantly needed cleaning and further more I think you were right about the vapor lock. To fix it I actually bypassed the right fuel feed out of the gas valve and installed a y splitter into the left fuel line. I think it increased the pressure in the gravity feed system. The bike seems to run fine now.

Also, as a side note, I found that when cleaning the gas tank care must be taken not to let fuel get onto the fiber separator in the tank lid. It will swell and add to vapor lock problems.

Thanks for the help.

Now for me to get on to the next problem, finding a pesky short in the electrical system. Is there any trick to finding where a problem might be, or is it just going to come down to tracing the wires?


Answer
Glad you figured it out. Gravity feed systems seem simple but they do require proper venting.

For your electrical issues I would start at the battery and trace wires. Maybe you can eliminate portions by using a multimeter continuity check, if you are looking for a short. The wiring diagram in your service manual might be helpful.