Kohler M series questions?

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1. Was wondering what the main differences between my M12 (late 90's Wheelhorse 312-8 application) and the other M series like M16 through M20, etc.?

2. Was told mine has (or had as I haven't checked yet and not original owner) a restrictor plate to choke it down a bit. Any idea what it'd be equal to if the plate was removed? i.e. would it be equal to a M14?

3. If I then run a jet from a M20, what could it bump up to?

4. Is there a point where they altered bore/stroke? How about the valve sizes?

IF they altered bore/stroke/valves at some point, my thinking is my M12 can hopefully be bumped up to the the power level of the last size it's identical to before or if they tweaked bore/stroke. i.e. if the engine is physically identical to a M16 then hopefully I could get similar hp/tq as that.
 
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StarTech

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Well the bore changes on each next step from M14 to M16 single then the M18 and M20 are twin cylinder engines. Changing jet sizes will only over rich the fuel mixture; although, remove the restriction will give a little more top end power. but still won't be 14Hp or larger.
 

ILENGINE

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Well the bore changes on each next step from M14 to M16 single then the M18 and M20 are twin cylinder engines. Changing jet sizes will only over rich the fuel mixture; although, remove the restriction will give a little more top end power. but still won't be 14Hp or larger.
Here is something that is interesting. The M16 is a horizontal single cylinder but the MV16 is a vertical opposed twin engine.
 

StarTech

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That is what I seen on PSW but the OP was asking about M series which I assume he meant the horizontal series.

I actually have yet to see a Kohler M or MV opposed engine. The only oppose engine I have seen is the Briggs and the 4 cylinder on the Piper Tomahawk I use to fly.
 
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Ah well. Was hoping they were all similar. Didn't realize they went with a V-Twin.

How about head work? Anyone make/sell a higher compression head? Or any heads better than others?

Engine runs good, so definitely prefer to keep it vs. swapping it out unless something makes sense.
 
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Yeah, whatever my 312-8 from late 90's is. Funny thing is I never new you could do half the stuff to these types of mowers that you can having been in suburbs most of my life. Having been a car guy since a kid it's odd discovering these riding mowers can do more than cut grass lol. But still picking things up here and there. Fish out on land atm.
 
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Guessing you more hardcore guys know of this site but stumbled upon this just now:

Has lots of info from heads to specs.
 

bertsmobile1

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There is an effective limit on the power you can get from a side valve engine.
If you do a LOT of head work you can get the compression up to the low 8's but the killer is the inlet exhaust tracts.
So you need to weld up the head and make a tangential inlet tract in the head with a corresponding funnel shaped exhaust.
As ,you have now welded a lot of the combustion chamber you can then grind more of the squish zone over the top of the piston and move the plug to being central to the piston.
Down side is you are going to use a lot more fuel so you don't get power for nothing.
The carb needs to be smaller and moved further from the inlet valve to get better gas flow and prevent reversion .
The inlet tract around the valve needs to be cut out on the opposite side to the piston so the incoming charge curls around it and comes out heading strait down the inlet path you made in the head
Then the exhaust has to be tuned to suck the gasses out and encourage it to go out the exhaust pipe & not down the inlet tract .

or

you can increase the bore by 1mm to achieve the same increase.
Old Goughy got an ex army WM20 ( 500cc side valve ) to do 115 mph but the best he could do on an official speed record run was an average of 105 mph.
HD decried him as being full of BS till he took it to the UK and the speeds were confirmed by "real people "
THen there was Claudius, another very fast WM20 sprinter that took the sprint record to 112 mph ( or there abouts ) .
But it ain't cheap and aint easy .
SV engines are momentum engines that store a lot of energy in heavy flywheels.
They are designed to be relatively low reving . around 5000 rpm high torque engines.
 
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