Engine Upgrade

I have a Tomahawk Pro Chipper with a "12hp" Tecumseh engine that's running slow and giving me a little other trouble.  Rather than doing the sensible thing and take the time to figure out why it's running poorly, I was thinking about using an available "16hp" Brand-X (Duramax) engine to replace the existing engine.  Part of the appeal is getting a bit more power, but the chipper came in two versions 10hp and 12hp and the chassis probably wasn't built to handle much more power and I'm worried about damaging it, so I don't want to give it TOO much more power, at least not at first.
 
If I put the more powerful engine in, I could just about figure out how to lower the hp by lowering the RPM, but that's not really what I want.  Is there a good way to maintain the RPM but limit the torque to see how the thing runs with just a bit more power, while minimizing the risk of bending a tool that I kind of like?  Eventually, I'd probably work my way back up to full power if it didn't seem like the machine was overstressed, but I'd like to start gently and, frankly, how to do this is well beyond my small engine wisdom.
 
Any advice on whether the upgrade is dumb, the idea of de-rating the larger engine is dumb or unnecessary, or if my idea makes some sense of how to go about limiting the torque?
 
Thanks in advance for any input or gentle mockery.

You will likely run into fit up problems with the 16 hp, the crankshaft will probably be too high to line up with the opening in the chipper housing. If it does fit, rather than trying to limit horse power be cautious about trying to feed too much at a time. The impeller will bend or break before the engine stalls.

Roy
You will likely run into fit up problems with the 16 hp, the crankshaft will probably be too high to line up with the opening in the chipper housing. If it does fit, rather than trying to limit horse power be cautious about trying to feed too much at a time. The impeller will bend or break before the engine stalls.

Thanks for the advice. I think the crankshaft would line up, but I need to confirm that. I might also need a different size pully as I think the shaft diameters may be different.

I know myself to well to trust me not to feed the largest branches that will fit in the chute and there's no easy way to control the feed rate on this small chipper.

I think I need to get the engine I have working as well as I can and, only if I'm still having trouble with it bogging down, figure out which slightly larger engine will fit and increase power without being too likely to bend the machine. Actually, since it's belt-driven, the belt may protect the drum and it's bearings and axle by snapping under too much power.

Thanks for your input.