Makita/Dolmar 7900 tank vent replaced, still getting starved of fuel after a few minutes

lenbates · Oct 13, 2023

When I set it down and open the tank a little, the idle speed and throttle response returns to normal. I've shifted the tank and replaced the white foam plug and the rubber nipple, but it still acts the same. Before I put it together I used a little air pressure (~10 psi) and made sure that air would go through the valve into the tank. What else could cause this issue?

Thanks,
Len Bates

old guy · Oct 13, 2023

It may be a soft fuel line being sucked flat, I have a 7900 that does the same thing in hot weather and the fuel line is very soft but I haven't changed it yet./

lenbates · Oct 13, 2023

Hey thanks! Does it clear up when you open the cap? And would the line open with the higher atmospheric pressure when you do? Sorry to debate you but this is maddening. My plan B right now is to add an echo vent, hopefully in the cap.
Thanks again.

old guy · Oct 14, 2023

I don't remember now, it seems it was ok next time I used it, I just grabbed another saw at the time.

ballisticdoughnut · Oct 14, 2023

Doesn’t sound like a tank vent issue, especially since you’ve replaced those parts. I’d replace the fuel hose and filter, mite be a good idea to clean the carb and install new gaskets/diaphragms.

Lightning Performance · Oct 14, 2023

ballisticdoughnut said:
Doesn’t sound like a tank vent issue, especially since you’ve replaced those parts. I’d replace the fuel hose and filter, mite be a good idea to clean the carb and install new gaskets/diaphragms.

Bingo

lenbates · Oct 20, 2023

Actually was the venting. I was able to order Echo Part#13131406320, and just installed and tested it. Problem completely gone. Not surprising that an Echo part would do the trick; I never have such problems with my Echo gear. The design looks identical. Maybe the problem is down where the Dol/Kita nipple sits. This vent takes a 1/2" hole, cleaned up. Presses in with a smooth low profile and holds tight. I made a few cuts, idled a while... no leaning out. Wish I could find the post where it was suggested so could thank him.