MIKUNI SINGLE CARB BREATHING ARRANGEMENT

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madwilly600

madwilly600

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Hi,
I have a 1976 mk3 850 running a single Mikuni, standard pea shooters. The carb was supplied with a small pancake filter.
The bike has a modified 4 pole starter and uprated battery.
The bike starts easily and runs very smoothly but I feel the intake is severely restricted by the air filter. (INDUCTION NOISE )

Obviously the original airbox has been removed. I was going to revamp some of the space provided to turn the battery for better clearance and site the Pazon and podtronics rectifier .

I appreciate the purists out there are cursing my choice but to me it's about making the bike as reliable and easy to keep in tune rather than top end or originality.(All original parts are safely stored so i can reverse setup )

My question is how do i get a better air intake. The choices as i see them are.
1. Fit the " ham tin" type filter with single carb rubber,
2. Fabricate a mk3 type arrangement with less depth and a single carb rubber.
3. Run a modified/ CUSTOM KnN filter ie the two carb outlet one with modified plate to connect just on carb rubber. (Anyone fitted a standard available KnN big enough to cope with the Nortons breathing requirements?, if so which one did you use.?.). not sure the extra weight of filter would secure on one carb rubber.

Am sure this isn't the first time this query has been raised, any advice greatly appreciated.

Regards
Steve
 
My Commando 850 with pea shooters runs great with a single VM34 Mikuni carb (main jet 250, idle jet 35, needle centre notch). The Mikuni carb kit standard included (large) K&N air filter. I suggest to replace that smothering small pancake filter for the bigger standard Mikuni K&N filter and you will never regret fitting that single carb kit :wink:
 
The large k&N air filter for use with Mikuni 34 is RC-2880 for chrome backed, RU-0650 for rubber backed.
these are well big enough, available from ebay etc.
sam
 
i dont think your small pancake filter will be restricting your norton ,but if you are concerned just remove it and see if it runs any better ,if it does then fit a larger filter the ham can looks good on a commando
 
madwilly600 said:
Hi,
I have a 1976 mk3 850 running a single Mikuni, standard pea shooters. The carb was supplied with a small pancake filter.
The bike has a modified 4 pole starter and uprated battery.
The bike starts easily and runs very smoothly but I feel the intake is severely restricted by the air filter. (INDUCTION NOISE )

Obviously the original airbox has been removed. I was going to revamp some of the space provided to turn the battery for better clearance and site the Pazon and podtronics rectifier .

I appreciate the purists out there are cursing my choice but to me it's about making the bike as reliable and easy to keep in tune rather than top end or originality.(All original parts are safely stored so i can reverse setup )

My question is how do i get a better air intake. The choices as i see them are.
1. Fit the " ham tin" type filter with single carb rubber,
2. Fabricate a mk3 type arrangement with less depth and a single carb rubber.
3. Run a modified/ CUSTOM KnN filter ie the two carb outlet one with modified plate to connect just on carb rubber. (Anyone fitted a standard available KnN big enough to cope with the Nortons breathing requirements?, if so which one did you use.?.). not sure the extra weight of filter would secure on one carb rubber.

Am sure this isn't the first time this query has been raised, any advice greatly appreciated.

Regards
Steve
Click to expand...

I have both a Mark II and a Mark III, both with Mikuni 34 and the K&N air filter that usually comes with that carb. They both make
air sucking noise and they both perform quite nicely. I have seen little (if any) performance difference between running a single Mikuni and a pair of 32mm Amal Concentrics UNTIL above 5000 rpm (which is quite rare for me as I am not a racer). The main reason for the plastic air box of the Mark III was to tone down the air sucking noise to help bring the bike into noise compliance (along with the performance stifling black cap mufflers) as required by USA environmental pollution laws. Take off the K&N air filter and see if the air sucking noise isn't still there and see if you can tell the difference in performance.
 
lazyeye6 said:
I have both a Mark II and a Mark III, both with Mikuni 34 and the K&N air filter that usually comes with that carb. They both make air sucking noise and they both perform quite nicely.
Click to expand...
Likewise. '74 with Dunstall mufflers, stock balanced exhaust, and the sucking noise is not the filter, but air passing under the carb slide. Noise sounds the same with or without filter. As pointed out earlier, that was what the plastic air box was designed to address.
Early '70's cars were under the same constraints. My '73 Buick 455 GS has a single inlet air snorkel that wouldn't pass a 50-cent piece!

Nathan
 
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