Hi all,

'92 Mc21 here, roughly 34k km on the clock.

Starts fine, idles fine, but barely opening the throttle, about 1.5k rpm she stalls. Occasionally can push past 1.5 and winds up fine through the rest of the revs. Partial choke alleviates the stalling.

For all I know bike has never had top end rebuilt, not sure if compression loss could cause this, or if it is a clogged jet perhaps? Something else?

Any ideas/advice are greatly appreciated!

Best
Aaron
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PROSPEC QUARTER !!

Sounds like a lean condition just off idle.
I would check your idle jets: size and blockage.
Possibly a slight air leak downstream of the carbies could be the problem?
Check the 'inlet volume corrector bottle thing' just downstream of the carbs is pushed right in and sealing well?
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

Crank centre seal?
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If I have to take the carbs off once more...

Another possibility, if the carbs have been sitting idle for a fair while, is that the idle circuit has got a slight build up of "petrol plaque" that is leaning out the idle circuit.
A bit like having a build up of fat on the walls of the arteries leading to the heart I guess? Or something like that.

I can vaguely remember a friend who put an old carb on a single 4 stroke, about 10 years ago, having a similar problem.
He cleaned out the carb to no effect, but after a few hundred miles the problem went away.

I think what happened is that the "petrol plaque" was too stubborn to be cleaned off, but slowly and surely dissolved away with use.
Hence, zero to 1/8th-ish throttle response was restored after riding the bike for a few hours.

Had your carbs been siting idle for a fair while?
If so, maybe just put a few hundred miles on it and see if it fixes itself??
Wishful thinking perhaps?
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

Thank you all for the replies.

Yes, lately the bike has been sitting for a month or two at a time.. some gunk in the idle circuit seems possible. Certainly would be nice if it were to clear itself out after a few long rides. More fun than removing the carbs, anyway!

Hello, an update -

As it turns out, there was indeed an air leak in that 'inlet volume corrector bottle thing', or more specifically the rubber intake manifold.. aka. the "Carb Insulator."

It is old and cracked.

Going to replace it and see what that does.
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PROSPEC QUARTER !!