Mikuni manifolds and intake tract length

[DewCatTea-Bob]

By: vintagetour...
"190 main, 22.5 pilot, 00 needle, 5E75 jet needle, 1.50 cutaway on the slide "

____ Thanks ! _ I have an old Mikuni (I removed from a 250-Duke I once aquired long ago), which happen to fit right-onto a stock 27mm-manifold,, so I now have some trusty part-numbers to compare with what IT has.
__ So can you review how you happen to have chosen those particular meter-parts in YOUR Mikuni ?
And BTW, what size is your Mik.carb ?


" (previously posted in Where to buy Mikuni Jets). "

____ Sorry, I've not bothered to read-through THAT thread (cuz of it's particulr topic-title).


" Mine is for a four stroke "

____ It's been sad how so many engine-tuner want-a-be types think nothing of simply bolting-on a carb from a 2-stroker and then expect their 4-stroker to 'go-fast' -(run well) with it.


Dukaddy-DUKEs,
-Bob

[JimF]

Graeme,

It turns out the previous owner could not get the revs past 6000 rpm.
So it has not run in this configuration.
The previous owner says it came to him with an SSI29 but he couldn't figure out the SSI and he put the Mikuni on it.
The mileage is very low and said to be original milage so the engine has never been opened.

[ecurbruce]

____ It's been sad how so many engine-tuner want-a-be types think nothing of simply bolting-on a carb from a 2-stroker and then expect their 4-stroker to run fast with it

Well I'm wondering, where there are two types of needle jets, the primary type, with part of the needle jet protruding up into the venturi, mostly used for two stroke engines, and then the bleed type, with the needle jet flush with the bottom of the venturi, used on four stroke engines...
IF the jet needle, needle jet, and main jet are exchanged from a primary type to a bleed type, will the mikuni carb function as a bleed type to be used on a four stroke? Any reflections on that, Bob?

Bruce

[DewCatTea-Bob]

" IF the jet needle, needle jet, and main jet are exchanged from a primary type to a bleed type, will the mikuni carb function as a bleed type to be used on a four stroke? Any reflections on that, Bob? "

____ Well first I should point-out that I-myself had preferred to most-always avoid messing-around with most anything to do with 2-stroke engines and so hardly-ever got my hands involved with the carbs from 2-stroke engines, so I never directly became very knowledgeable on exactly how carbs intended for 2-strokers actually differ,, so I only learned indirectly from the experience of others.
It's been my (somewhat vague) understanding that even amongst carbs meant for just the 2-stroke type engines employ differences, depending on whether intended for 2-stroke engines made to work with oil-injection systems, or, pre-mixed oil & fuel.
Anyhow, I had also once assumed that the carb.body of a carburetor taken from a 2-stroker could simply be made suitable for a 4-stroke engine, by merely replacing most-all of the carb's internal metering-parts. _ However, I've been informed that doing just that work alone is not really enough, cuz the 2-stroke type carb.body has differently designed passageways built-in - (I'd assume that that's probably the case for such carbs intended to work with pre-mixed fuel, but don't know for sure).
__ I-myself don't really know if any of that stuff is true in all such cases, and that (possibly incorrect) info was conveyed to me back in the '70s by various Brit.bikers who were trying to adapt Jap.bike-carbs and also Amal-carbs from Bultaco-engines to their BSA/Triumph & Norton engines, (as well as a number of Ducati-owners too of-course, [as back-then the SSI-carbs were considered as junk by many] ).
Other sources had since seemed to confirm troubles which seemed could never become entirely worked-out completely, so I-myself only became even more convinced to avoid ever trying to attempt to make a carb from a 2-stroker work-right on a Duke !
While I sure can't proclaim that it can't be DONE, I've learned from others that trying to do so is a big time-waster. _ Although I'd bet that true EXPERTS on motorcycle-carbs could surely convert a 2-stroke type carb to work perfectly on a 4-stroke engine (even if not really economically done).
____ I'd sorta like to learn of other's experience on this matter (of trying to adapt whatever various carbs between 2 & 4-stoke engines), so long as the subject doesn't stray-away from being useful for us Duke-owners, of course.

____ It seems to me that JimF hasn't been having enough time to read ALL the posts posted these days, so I hope he has thought-of on his own to ask the "PO" -(previous owner) what that Mikuni-carb (which he's been stuck with) came from originally.
Cuz I've heard of many others having wasted their time trying to get carbs from 2-strokers to work-RIGHT on their DUKEs !
____ It would be nice if fellow-member 'wcorey' would tell a bit more about the Mic.carb which he has adapted to his R/T - (looks like a really well-done installation!), as it would be interesting to learn what jetting-work he has had to do with that.



Dukaddy-DUKEs,
-Bob

[graeme]

Quite a few F1, TT1 and 2 in the US use Mikuni TM39 and TM41 flat slides for racing.
The jets and float needle are changed. One of these should work well on a 450 that can breath well, like wcorey's should do.
graeme

[Harvey]

I had a 41mm 2st Malrossi Delorto carb on a 360 Bultaco that I used as a club race bike. I converted this to fit my 450 by changing the shouldered needle jet for a 4 stroke one. The shouldered needle jet is to allow the low vacuum level of the two stroke to pull up the fuel on acceleration. It did not need any other changes, other than jetting, worked very well.

[JimF]

Visually I am guessing this is the 2-stroke needle. Correct?

IMG_0795.JPG

As for carb size, the outlet diameter appears to be 28.5mm. Do these come in half millimeter sizes?

Needle jet says "182" followed by "N-8."

How do I get the pilot jet out?

I am debating if this is a 2-stroke carb whether I should just put together an SSI29 and run it without an air filter....

[graeme]

Jim,
see this link on VM tuning and parts.
Look at the 2 different primary and bleed type. I think the bleed type is 2 stroke????

http://www.mikunioz.com/download/pdf_files/vmmanual.pdf

graeme

[Harvey]

Visually I am guessing this is the 2-stroke needle. Correct?

IMG_0795.JPG

As for carb size, the outlet diameter appears to be 28.5mm. Do these come in half millimeter sizes?

Needle jet says "182" followed by "N-8."

How do I get the pilot jet out?

I am debating if this is a 2-stroke carb whether I should just put together an SSI29 and run it without an air filter....

I would say the is a 2st carb, they will run with that shouldered emulsion tube, just rich on opening the slide, acts like a slide with small cutaway.

[graeme]

I don't know much about Mikuni carbs, but the VM 34 on my Norton has the bleed type needle jet or jet needle or what ever it's called.
The one that doesn't stick up in the bore like the one in your Mikuni does.

graeme