Motor Revs Down On Its Own

[griffin5657]

I have a Lastec 3372 lawn mower that will be mowing along at let's say hypothetically 4000 RPMs, when suddenly the engine will drop down to possibly 2000 RPMs or less. I must quickly disengage the mower deck and hydraulic mower arms or the engine will stop. I cleaned out the excess buildup of grass from underneath the mower deck, but later found that when I didn't even engage the deck, the engine would lug down again when just sitting with no work load on it whatsoever. The mower is powered by a 33 HP Turbo Charged Model D1105-T-ES Kubota Diesel Engine. Could it be a faulty fuel pump or maybe air or water in the fuel lines? Any guidance would be appreciated.

 

[seville009]

Check all of the easy stuff first - fuel filter, air filter, fuel lines, gunk in the fuel tank, possibly bad fuel, check your belts, fluid levels, etc

After the rpms drop, do they come back up on their own? If you shut it off, and then tutn it back on, does it run normal?

 

[griffin5657]

Seville, The rpms usually come back on their own, but it then happens again a few minutes later. If I shut it down and restart it, it runs normal for a few minutes, but it happens again.

 

[seville009]

I’m no mechanic, but if it were me, I’d check everything I mentioned above. Sounds something fuel related.

 

[Slowpoke Slim]

I'm thinking the same as seville. First thing I thought before even done reading your description was it was fuel related.

Could be the fuel itself, not just filters or pump, etc.

 

[AndyMA]

Sounds to me like a fuel issue. Probably runs on what is in carburetor and the carb doesn't refill fast enough.

 

[griffin5657]

Thanks guys. Sounds like good advice. My fuel tanks are almost empty. I'm going to check for gunk in the tanks and all of the items that Seville mentioned. I did replace the fuel filter in April of 2022 and I want to bleed it again to make sure all of the air is out of the lines. Also, I want to even consider the diesel fuel. I use diesel fuel from United Dairy Farmer. I do, however, have a Kubota B2150 and a Kubota B1700 and use the same diesel fuel in both of them and have experienced no fuel-related issues in either of them. I'll let you all know what I find out.

 

[griffin5657]

Found excessive gunk in the right fuel tank. I mowed the lawn twice since I cleaned out both fuel tanks. Normally it would rev down 10 or so times over the course of a three-hour mowing. After cleaning the tanks, it revved down once or twice. So..., much, much better but not perfect. I also bled it for air in the lines. Will update everyone after further use of the mower.