lister fr

[spencer1885]

I have a fr2 and a fr1 ,the fr2 is up and running as a 10 kva generator but I only use it for very short runs and then I only use a 3 hp motor and a 180 amp welder so I am not using its full capacity.
It uses a lot of fuel  starting up and when running is much more economical ,so should I use the fr1 engine which would use half the fuel or should I slow the fr2 down to 550 rpm and us pulleys to drive the alternator?
At the moment they run at 1500 rpm.
At 1500 rpm there noisy compared to a cs but the fr2 at 550 rpm  would be  good.
I don't know if the engine would work well at that speed.
Cheers
Matt