Dolmar 7900 issue.

[sneno77]

My 12 yo 7900 just developed an issue I don't understand. It starts up and runs great for 4-5 minutes then starts to act fuel starved and dies. It will restart easily and then starve out more quickly each time. Air and fuel filters have been replaced with no change. Ran it without the air filter with the same results. Pulled the fuel line at the carb and it is getting plenty of juice.
I'm not very mechanically inclined. Can anyone lead me to a solution?
Thanks!!

 

[Andyshine77]

Sounds like you need to check the tank vent. Drain the tank, pull the fuel filter, put the fuel cap on and hook up a vacume pump to the fuel line that goes to the carb. No vacume should be held. If that's not it you may need to rebuild or replace the carb. I had a few of them that developed leaky wash pubs and I could never get them to seal up correctly again.

 

[blsnelling]

+1 on the tank vent.

 

[sneno77]

Thanks guys! Appreciate the help!!

 

[epicklein22]

If it hasn’t had a carb kit since new, it’s probably due for one. A little deformation of the gaskets can cause all kinds of problems once you’re putting a load on the saw and the carb can’t pump enough fuel.

 

[Poleman]

If the carb hasn’t been off since new or a couple years of hard cutting they have a tendency to collect fines in the carb filter and lean out. I’d check the carb out, clean it up and put a new kit in it.
Your description sounds like how a saw acts with this issue. Seen it lots on these.

 

[777funk]

Also could be a varnished fuel filter. Will soak up fuel slowly while sitting then burns it quickly and can't pass more fuel fast enough to keep running.

A varnished fuel filter looks fine, but isn't. I fill them with water and they hold it without a drip. A clean filter without a fine film of varnished gas will let the water drain almost instantly. I do the same thing with the screen in the carb. Clean looking screens many times do not pass water and of course will not allow the engine to run. I blame it on ethanol... But could be old gas in general.

 

[Busmech]

I had a problem like this with my 7910, turned out to split impulse line at the cylinder barb.

 

[sneno77]

Thanks everyone for the help! Tank vent checked out ok, so I put a carb kit in and she's back up and running.

 

[Andyshine77]

Thanks everyone for the help! Tank vent checked out ok, so I put a carb kit in and she's back up and running.

Nice[emoji106][emoji106]

 

[Chris Ross]

I faced this about a week ago and carb kit fixed the problem.