Is it possible to tell what engine my bike has in it by the engine numbers alone?
If not would the fly wheel have any distinguishing marks?

The reason I ask is that my bike is more than likely a bit of a mix bread. Frame and chassis is MC 28 SP, all the signs are there but the motor is most certainly not an 28SP.

It has the 21 carbs on and is wet clutch and on top of that produces somewhat more power on the dyno than what I read on here given the lack of work and parts I have.
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If you want a proper 2 stroke get an RGV.

Crank cases are effectively all the same and other than for originality you're main concern should be making sure the barrels and heads are matched, r barrels/sp heads is a bit high on the compression for normal pump fuel.

se/sp barrels can be distinguished as they are marked with an "L" on the left hand side of the barrel (as it sits on the bike) near the bottom. R barrels have an "H" there

Likewise se/sp heads are marked KV3L on the top, R heads are marked KV3H.

The mc21 flywheel is numbered 037000-2641
The mc28 flywheel is numbered 037000-3321

How do you know the frame is 28sp?

I put a '21 engine in a '28, ran it with a modified '21 airbox and de-restricted pipes but still on the stock card and would guess it made low 50's bhp, the big difference though is the pipes, the '28 ones are restricted with huge washers in the headers, have a look at this picure, the top pipe has had it's restriction removed, the bottom one still has it in place.
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Thanks fontyyy, that is very helpful.

The reason I say it is an SP chassis is that it has the Magtek wheels and the fork adjusters are unmistakable. Gold front discs are also SP specific if I remember correctly.

The flywheel should be a dead giveaway and could be a contributor to my power output.
My pipes are also most certainly not the stock units, might well be 21 pipes, they are super light and not restricted in any way. My pipes are also retained with springs not bolted on as per the picture you posted.

I am running open carbs too.
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If you want a proper 2 stroke get an RGV.

The flywheel doesn't make much difference, it's the pipes that do it.
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RaceFan wrote: might well be 21 pipes, they are super light

Certainly aint stock 21 pipes then , they weigh a ton!
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MC21SP Plaything
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MC21 (stock) pipes won't fit an MC28... well, one won't!

As far as I know, all manufacturers made model-specific pipes (i.e. MC21 and MC28) up until 1995. After that (most) pipes were starting to be made to be cross-model compatible, hence why the later pipes seem to "stick out" a bit more than early pipes.

Anything that weighs less than a boat anchor is most likely to be an aftermarket pipe! You could never confuse the two! Also, ALL aftermarket pipes have a separate manifold/flange.
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Andy.
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Checked the numbers and they all check out as 28 items.

Must be aftermarket pipes then, they have a flange mount.

So all in all I have a pretty good base motor given how well she is running, in my opinion anyway.

Seems it's only the carbs that were robbed off by the race guys. I believe they are good items.
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If you want a proper 2 stroke get an RGV.

I'd run MC21 carbs on an MC28 anyway... much better.
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Andy.
NSR-WORLD.COM

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Andy wrote:I'd run MC21 carbs on an MC28 anyway... much better.

Awesome, next up that pgmII, but later when I can ride the thing.
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If you want a proper 2 stroke get an RGV.

Its both the ignition and the pipes that cause the problem, put pipes on first and it will be held back by the ignition, advance ignition first and it will be held back by the pipes.

Mine made 5bhp more just from the fywheel change, but it already had the JHA pipes fitted. I dont think that the tyga pipes would gain 12bhp on an MC28 if the ignition had not already been advanced as the bike feels like it hits a wall and doesnt produce any power that high up in the rev range.

The curves are all on the Tyga site;

Stock and finished you can see there how much the dyno overreads compared to Steve's, 42 stock is never going to happen.

Just the '21 flywheel, about 3.

Just the pipes, 12 horse.

Flywheel and pipes around 4 over just pipes.
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fontyyy wrote:you can see there how much the dyno overreads compared to Steve's, 42 stock is never going to happen.

I don't believe that the actual hp numbers should hold too much weight. The real truth is in the gains and using the dyno as a toll as apposed to a readout as a bragging sheet.
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If you want a proper 2 stroke get an RGV.