I have an MC21 that has been stripped down to crank over winter and rebuilt with adding HRC stuffers and rear head conversion, i also plan on drilling airbox but think its best holding off doing this major change (that will upset jetting massively) until the motor is bedded in.
Bike was on standard jetting with no mods except dogfight pipes. Engine had new crank bearings, pistons and rings.
I have no experience really with 2 stroke jetting other than cleaning and rebuild carbs so my questions are.

Do you think i should just drill airbox and then start off with bigger jets (around 150's) and then work my way down as normal or dont mod airbox yet and just go 1 or maybe 2 sizes up to allow for the slight mods (stuffers and head conv)to allow me to get engine bedded in without added trouble of possibly fowling plugs then when all is well drill airbox and jett to suit?

Also any recommendations on starting points for jetting or which size jets to buy as i dont have any?

Advise greatly appreciated,

Andy

Get in there and do the air box mod. Use your head first time you start to really use it and jet safe to start with.
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If I have to take the carbs off once more...

Any suggestions for a safe start point considering,

dogfight pipes, drilled airbox, wire splice, rear head conv, hrc stuffers.

bike is mc21 used for road use in north england.

ideas greatly appreciated, cheers

Andy.

The biggest you have!

I've got an HRC kit that runs up to 210...

the reason i was asking so i can order a few sets up as i have the grand total of 2 jets and they are standard and in the current carbs. Ordered a few up today.

It's a very subjecive question. Are you going to run PWJ's or not? The transition between PWJ setups and non-PWJ setups tends to be around the mid 170's.

With #0 PWJ's I'd start off with something 185/188, maybe even a tad bigger, and then look to work down.

With PWJ's you're probably looking at mid 160's as a starting point. Bigger's always better when starting out, and 10 main jets are considerably cheaper than 2 top-ends!

If you don't mod the airbox, then absolutely no idea! They run like crap without it done, so never bothered messing about trying to make one work without being able to breath properly.
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Andy.
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Cheers for the input guys i really do appreciate it as i am a novice here. On a side note got the bike running with airbox mod and passed MOT yesterday with the trip to centre being the last heat cycle. Put 150/148 in and it ran clean on throttle, i couldnt do a plug chop because of time of day/traffic but hell there was a plume of blue smoke down the road when i nailed it. Pipes were v wet and i did look at plugs anyway but they were a bit ashy. I have dropped a size on each jet and will get a chop in tomorrow to get a true reading on plugs and report back.
Thanks again for all input from members over last 6 months, i have asked a lot of questions and had very supportive and informative answers which have enabled me to strip my bike and rebuild a motor for the 1st time.
Cheers,
Andy

That's great to hear! Well done you.

Cool,enjoy the bike mate