same Kubota 3 cyl engine with different outputs, on same mowers...

[Texwing]

Hi, I have two identical FZ2100 ZTR mowers with Kubota engines rated at 21hp, the FZ2100 is somewhat uncommon but this is more of an engine question.
I bought both used. One is more ragged and beat up than the other, but puts out way more power; you can hear and feel the difference and note that one travels faster in low speed. They both run great and have no apparent issues, one just puts out better power than the other.

The lower power machine came out of city service, and has added a temp and oil pressure alarm. These machines do have some history of cooling issues. both are serviced. two possibilities come to mind:

A. the lower power city service machine may have had the power turned down to help with some overheating issue.
B. The more beat up but higher power machine may have been messed with to turn up the power.

I have no interest in messing up one of these machines, but mostly the low gear travel speed of the lower power machine makes it a pain to use. I do note a simple screw stop on the the throttle shaft where it meets the injection pump. I suppose the real question is how power levels-or travel speeds (hydrostatic) are adjusted in general on these engines? any thoughts appreciated.

 

[RobertN]

They use similar motors with different outputs on a lot of sailboats too...

 

[JWR]

First guess is that the lower power one is hurting for compression and putting out lower power due to the lower compression of a worn engine. Can allways run a compression test and start there. I doubt that it is an adjustment. There are certainly many possible causes including fuel restrictions, worn high pressure injection pump, out of spec injector springs, exhaust restrictions, air intake restrictions, etc.

 

[Texwing]

OK thanks. I was tempted to fool with the throttle stop but I think I will go back and recheck the basics.

 

[100 td]

Like many companies they make the same engine for different uses/markets/options etc. So the engine max output may be at 3600 rpm driving a generator, then also at lower hp in a tractor at max rpm of 3000, and in another tractor at a lower hp again. This is so they don't have to build 3 different engines. They will change or adjust the injection pump to get these variances generally, on petrol engines a different carburetor may be used or one may have occlusion gaskets in the air intake or butterfly stops etc.
However if they are both identical machines and both rated at 21hp I would first check the max no load speed of the engines. Get a digital non contact tacho and see if there is a difference. Of course as the lower power unit has alarms fitted, perhaps it ran hot previously and partially seized etc., and has had the extras fitted to stop it happening again. Go with the speed check, if the speed is correct, then check the adjustment on the hydros to make sure they are running at max output etc. Then perhaps a compression check as noted by JWR.

 

[zzvyb6]

Since one has a temperature sensor, does it have a thermostat and the other does not? Temperature affects power. Also, does one have a higher rated alternator? A 45 amp deal absorbs less power than a 65 amp unit. And what about the airflow thru the deck (blades, chute) and tire pressures. And what about the hour meters....

 

[zzvyb6]

Shouldn't the mowers be F2100 or Z2100 and not FZ2100 ? The F model designation means 'F'ront mounted mower, the 'Z' designation means zero turn (Center mounted mower), according to Kubota. So which is yours? The 2100's were rated at 20 hp. There was also an F2400 model witha 24hp motor. These were available in 2wd or 4wd. Could another possibility be that a 2100 motor was replaced with a 2400 motor ?

 

[Scooby074]

The FZ2100 is a bit of a unique machine. Never saw one before this thread made me look it up. Pretty cool. Check the vid description for its zero turn operation. Dating back to the early-mid 90's

For the OP, I wouldnt go screwing around with the pump or compression just yet. Do a full once over, including fuel and air filters (at least ensure that all filters are new and unclogged if you suspect they been changed recently). Then go from there. Could be in the hydrostatic system too. from the video it seems to have a pretty unique system (read complicated??) with how it shifts power front to rear.

 

[DT86]

If both have the same engine with the same power rating I'd check the fuel and air filters first. Then injectors and compression, then the injection pump.

That's just me though.

 

[Fallon]

Unless they are geared differently, they should be equally fast at the same RPM. If not your HST might be worn out or something. A little confused if you are mixing up power vs. speed.