Hi guys,

I'm aware this has probably been discussed, but for the life of me I can't seem to find solid info.

I'm looking to put another engine into my MC21 while I get the blown one rebuilt. However it is an MC28 model. I'm aware that the engines are basically the same, but are there any bits that are different between the two?

I.e. do I have to swap the flywheel, change the ignition timing etc?

Keen to get any advice to help maximise the setup.

On that note, does anyone know where I would find a bottom end gasket/seal kit nowadays? Tyga don't seem to stock them anymore.

Your correct with a different flywheel, but main difference is the MC28 had an extra oil way from the 2 stroke oil pump (although the last year of MC21 had this too) to feed one of the main bearings directly. Can't remember which one exactly.

More minor changes are the generator has a shorter wire to plug it into the loom and the internal gearbox ratios are slightly different.

racer38 wrote:Your correct with a different flywheel, but main difference is the MC28 had an extra oil way from the 2 stroke oil pump (although the last year of MC21 had this too) to feed one of the main bearings directly. Can't remember which one exactly.

More minor changes are the generator has a shorter wire to plug it into the loom and the internal gearbox ratios are slightly different.

Gotcha, I assume this will be irrelevant if running premix? Or is it advisable to stick with the pump on the later models?

Other than that is it simply a case of switching the flywheels and swapping them over?

What's the main purpose for the bike ? Track ? If so then swap the gearbox too , everything will slot straight in .

Neal wrote:What's the main purpose for the bike ? Track ? If so then swap the gearbox too , everything will slot straight in .

Yeah it's a race bike. Are the 28 ratios no good or something? Not something that can be tuned out with sprocket choice?

The gap between the upper gears is greater , the recommended mod is to run the 21 box .
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NSR300

If you access to other gearboxes , you can choose other gears to make a box that suits your track and tune , read up on the gear ratios and you will see some interesting info .

Neal wrote:If you access to other gearboxes , you can choose other gears to make a box that suits your track and tune , read up on the gear ratios and you will see some interesting info .

Thanks Neal, I'll have a read up on the subject. Is there anything else I should be considering?

Can you get the mc28 carbs ? They are bigger and could give you more vroom vroom .

Neal wrote:Can you get the mc28 carbs ? They are bigger and could give you more vroom vroom .

Unfortunately not, but I have a few sets of M21 carbs so would be hard to justify another set!

Bore them out

Have you done it? To what size and what difference did you find?

Yes I had it done a few years ago ' I think they got 1-1.5mm out of them , on our dodgy dyno we saw an improvement in the mid range right to the top but I think it levelled out on top to similar hp as the stock ones . Jetting went up a few sizes too . If you send me your email I can try look for the printout