Engine upgrade

[ukrkoz]

Hi all
I have tow behind flail mower with this engine:
15 hp 420cc JiangDong electric start
Engine has been rather reliable so far.
Problem is, it is also quite underpowered for the job. I was mowing yesterday not even that tall of grass, a bit wet, and it clearly strains.
Engine has centrifugal clutch on the shaft and runs 3 belts down to flail.
Far I know, it's Honda knockoff.
Engine has electric start and charger, what comes handy. But, starts from pull every time, if battery dies.
My question is - is there engine that I can directly replace it with, that will have more power?
This mower is, pretty much, my last hope as, I have to mow through partial wet land and none of mowers I had before will go there. And, if I let it be till it all dries out, I have to deal with 3 ft tall grass. I tow this flail behind with UTV, so we can go through wet areas but, here;s question of power demand.
I really don't want to major rebuild, to get larger engine. If possible, one that will directly retrofit, so that I can re use clutch.
Thank you.

 

[ILENGINE]

Bolting a larger engine up should be possible, but to go bigger you are most likely looking at V-twin engines. Also the dealing I have had with that engine manufacturer on other equipment has resulted in the engine having a metric crankshaft. And most US engines you will find have SAE diameter so your clutch may not fit from the old engine to the new one.

 

[ukrkoz]

Well, is there point in going from 15hp (current) to 18hp? Plenty of what looks same engine just with larger volume, I presume.

 

[bertsmobile1]

Look at the cc's not the Hp.
Honda use restrictors on the intake to change the Hp
The gasket that goes between the manifold & the head may be as small as 1/2 the hole size
Cutting the restricting bit out will up the Hp .
Some also use different governor springs to modify the Hp

 

[ukrkoz]

Ok, so how exactly do I get to that restrictor? Tech from the place that I bought it from told me engine comes from same factory that makes Honda engines. I'm pretty sure they are identical.