Back to Mikuni carbs

998cc

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As desirable as is keeping the original 289/276 carbs on the Shadow, I have decided to go back to the Mikunis and have ordered the Mikuni adapters from VOC Spares.

I had installed 30mm VM's on the bike back in 1982 using home made adapters. The carbs were never set up properly; however, it ran fairly well though a bit on the rich side. I will address that this time around. The Victory manual has good info but nothing specifically for Vins. Any suggestions for basic setup of jets, needle, etc.?

Thanks.


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998cc

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After posting this, I realized I left out a vital piece of information. I had re-jetted the Mics for my T140 and failed to note the original jet/needle configuration. The original jetting itself would have been a fair starting point. :confused::confused::confused::confused:
 
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I removed 30 mm Mikunis and replaced them with new 34s on my Rapide( 35 mm ports)
John McDougall gave me starting points for jetting.
I started with that then moved up and down a bit with the main jets then came back to the starting point as best.
Trouble is, I don't think I wrote any of this down!
Will have a look.

Glen
 

998cc

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No worries on the 30mm specs, Glen. Just received the carb adapters from VOC Spares yesterday--they need a little internal streamlining prior to using. This will likely be a long-ish term project. Too many irons in the fire. :)


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998cc

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The Mikuni's are back on and after a few days of testing, I think I am at a good starting place to dial them in. If anyone is interested, here is the current setup. Heading out for a ride as soon as this is posted.:)

Engine: Vincent 1000cc
Bore and stroke: Standard
CR: 7.3:1
Cam: Vincent Mk I
Exhaust: Stock with VOC spiral silencer/muffler

Carb: Mikuni VM 30mm
Pilot jet: 40
Slide: 3.0
Needle jet: 159 P4
Needle: 6DH2
Needle clip: Center slot
Main jet: 250
Air jet: 1.1

Notes:
1. The #40 pilot jet may be slightly lean since a dead spot appeared after 1/4 throttle. Adding a set of EMGO air filters increased the internal carb vacuum enough to eliminate the dead spot. #45 pilot jets are on order just in case.

2. I am thinking the 250 main jet is slightly rich. Bike runs well and strong up to 70+ MPH. After a few thousand miles or so of run-in, I may take it out to a long stretch to see if it will hit the ton. ;)

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Fast Eddie

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Make sure you check the float heights. 30mm Mikunis weren’t really designed for gas guzzling 1000cc twins! They can struggle to keep up with the fuel flow at WOT.
Well, actually, they can’t keep up!
Ensuring the floats are high enough doesn’t solve this, but provides enough WOT usage for most road riders.
 

998cc

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Make sure you check the float heights. 30mm Mikunis weren’t really designed for gas guzzling 1000cc twins! They can struggle to keep up with the fuel flow at WOT.
Well, actually, they can’t keep up!
Ensuring the floats are high enough doesn’t solve this, but provides enough WOT usage for most road riders.

Nigel, that opens a new can of worms! ;)

Didn't have any trouble with the 30's over the years other than they were significantly rich. Original Amals are 1.125" which is roughly 28.6mm--even 1-5/32" carb spec for the Lightning were just under 30mm. Given that, my thought back in the day was the 30's would be more than adequate.

I have a newer set of 32mm VM's which are right/left throttle adjust (a feature I would like to have on the Vin) but believed they were too large for the Vin. If it is a fuel flow issue with the 30's, do you think the 32's will provide adequate fuel for a stock motor?

In any case, I really don't have a need for 100+ MPH these days. :D

Thank you.
Russ
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Im running a pair of VM 34s on a Vincent.
They work well. It is a bit hotrodded, nine to ones, 2 front heads ported to 35 mm+-,


Glen
 

Fast Eddie

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Nigel, that opens a new can of worms! ;)

Didn't have any trouble with the 30's over the years other than they were significantly rich. Original Amals are 1.125" which is roughly 28.6mm--even 1-5/32" carb spec for the Lightning were just under 30mm. Given that, my thought back in the day was the 30's would be more than adequate.

I have a newer set of 32mm VM's which are right/left throttle adjust (a feature I would like to have on the Vin) but believed they were too large for the Vin. If it is a fuel flow issue with the 30's, do you think the 32's will provide adequate fuel for a stock motor?

In any case, I really don't have a need for 100+ MPH these days. :D

Thank you.
Russ
998cc

I honestly don’t know if 32s would flow more fuel through the float bowl than 30s, my guess is they would, but it’s only a guess.

As you say though, unless your doing sustained WOT it isn’t an issue.
 

998cc

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Glen, Nigel. Thanks.

With the current configuration of the 30's, there is no hesitation throughout the throttle range, and the bike pulls hard at WOT. However, the 30's have both idle adjustments on the left side which means the battery has to be moved a good 1/2" or more to the left to accommodate the rear carb idle adjustment screw. Not fun. The 32's are left and right handed; for that reason alone, I am willing to try them in lieu of the 30's.

Side note: As far as the lack of fuel, I found high flow float "needle" valve assemblies for running methanol. These should solve any problems of fuel starvation.

Regards,

Russ
998cc
 

Fast Eddie

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Russ, yes I imagine those high flow assemblies should do the trick!

FWIW, my guess is that you’ll not notice any detriment using the 32mm carbs. It’s only a small increase and (I assume) you’re not gonna alter the ports any, so I doubt it’ll make any noticeable difference to low rpm running. As to whether or not they give any gains higher up will be interesting to see. I always considered 30mm to be incredibly small for a 500cc cylinder personally.

Sadly, until Comnoz gets interested in Vincent’s we’re just guessing !

Of course, another fix for the left hand only adjusters would be to fit two front heads...
 

998cc

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Add the richer pilot jet, and lean out the needle one clip?
Thanks Gortnipper. Have not tried that yet. Installed 32mm carbs for above reasons and are working them out. The 32's show promise.:)
 

998cc

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The 32's went on today, and after a few so-so test runs, black smoke, dead spots and jet changes, it now idles "OK" and accelerates surprisingly well. I thought that a larger pilot jet would be necessary with the larger carb and started with a #45, then #40, then #35.

Started out with a 270 main jet which produced no power at WOT. As the pilot jet sizes were reduced, a dead spot around 1/2 throttle appeared and became wider as the pilot jets were changed. I put in a 290 main along with the #35 pilot jet and now have good power throughout the throttle range. That's enough for today...:)
 

998cc

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Are the 32s a bigger body than the 30s ?

Excellent question.

The bodies are the same size but are different.o_O I found a photo online of various models, clipped and added a few circles and arrows. It shows my 30mm style on the left (identical) and 32mm on the right (similar to mine with variations). My 32's have the larger stack feeding the intake, but they also have the channel above the intake as the 30mm has. All internal parts are interchangeable. The slides are the same physical size but only the left handed 32 slide is interchangeable with the 30's. The float bowls on all my carbs are identical to the 30mm. Fuel connections are different (as shown). Notes: My 30's are 38 years old. The 32's are 10.

There are apparently several styles of VM's; however, I am finding difficulty in finding specific model numbers for each variation. Perhaps the 32's are available in the 30mm variation--or not. :confused:
Mikuni Types mod.jpg


The front carb (32mm) mounted on my old homemade adapter.
IMG_0718.JPG
 
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