just converting my mc21se to pre-mix when i removed the oil pump i found an extra oil feed from base of pump to drive side main bearing and only one oil hole from transfer port other two mains have two holes, mi mates mc18 does' not have the extra feed from the pump but has two oil holes to all three mains do i need to drill an extra hole as per mc18 or will it be ok whith one hole without the pump and on pre-mix. can anyone help please.

Dave,

The hole you are talking about was added on the later model MC21's. This allowed the oil pump to feed oil directly to the right side main bearings on the crank.

You will want to block this off if possible (to not get crud/crap/dirt) down intot he crank area.

You will be okay running with out the feed

I have run 21's and 28's with this blocked off and on pre-mix with no issues.
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Charles Gallant

Charles
Thanks for your info feel more confident now about going pre-mix would you recomend drilling another oil hole from transfer port as per MC18 thanks again.

An MC18 uses a very different oiling system to and from its main bearings compaired to the MC21.

Personaly I would leave the cases as they are and just use a good premix oil.
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If I have to take the carbs off once more...

If you're really daring you can actually fill up all the feed holes, run premix, and then the bearings are oiled by the mixture in the cases.

I wouldn't recommend it though.

I was after every bit of mojo I could get and I wasn't paying for the engine bits New crank every 1000 miles

Thanks Stephen Thanks Matt