I noticed on my mc21 that it is missing the pastic bottle that is attached to the reed cage. (16310-KV3-000 CHAMBA COMP. in let )
what is the purpose of that bottle?

I believe that it's main function is to help equalize the pressures in the carb inlets. There is more to this, as someone will tell you I feel sure, BUT one thing is for sure...you must not run the bike without it...if it will run at all.

Mike
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that could explain why it runs like sh*t at the moment.

you want me to add them to the shipping quote for you mate?

Well mine runs without them, they have been capped and filled in so the intake is nice and smooth.

If your bike is not running very well then I doubt its down to the boost bottle not being present
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MC21 300
Aprilia RS250 track bike

t3racing wrote:Well mine runs without them, they have been capped and filled in so the intake is nice and smooth.

If your bike is not running very well then I doubt its down to the boost bottle not being present

Unless his insulators haven't been plugged?
If someone just took the chambers off and left the holes open it would run like sh!te.

Like you Mark, I would guess they have been blanked and the bike is running rough due to some other issue.

That's true, I just assumed the holes had been plugged and I should know never assume anything.....
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MC21 300
Aprilia RS250 track bike

"The road to hell is paved with assumptions"
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MC21SE, KISS box
MC21SP, HRC box, racing loom

Hobbit210 wrote:I believe that it's main function is to help equalize the pressures in the carb inlets. There is more to this, as someone will tell you I feel sure, BUT one thing is for sure...you must not run the bike without it...if it will run at all.

Mike

I'm not sure that's an accurate statement being that HRC manufactured plugs for those holes. The only difference I noticed was a slightly rougher mid range and smoother top end when I removed the bottles.

Andy

http://www.totallyamaha.com/snowmobiles/aaTECH/BoostBottle/boost_bottle_theory.htm

I guess if you're racing the boost bottle has little effect, but does on the road
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Yes the holes were plugged.
today i swapped the reed cage from the spare motor with with boost bottles onto the bike. it helped a bit but not too noticable.
i played around with the bike and for some reason, it only seems to run semi smooth is when i run it without an air filter.

bandit_7 wrote:
I'm not sure that's an accurate statement being that HRC manufactured plugs for those holes. The only difference I noticed was a slightly rougher mid range and smoother top end when I removed the bottles.

We've had varying degrees of success removing the intake chamber, depending on the state of tune, and the setup. My current setup performs best with the bottle, but previously we were running it without.
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Personally I'd say my bike would be better off with the bottles on too considering it's only used on the road. It's just that after having the old girl off the road for about 2 years I'm just happy it's running again and can't be bothered pulling the carbs off again.

sparky wrote:Yes the holes were plugged.
today i swapped the reed cage from the spare motor with with boost bottles onto the bike. it helped a bit but not too noticable.
i played around with the bike and for some reason, it only seems to run semi smooth is when i run it without an air filter.

Have you checked your idle circuit is clean and carbs set to factory settings?