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[Rex Piekarczyk]

Dai,

Oh yes there will be a nice radius on the carb side of the adapter, engine side will match the head port. I've been advocating replacement of the Micarb for years, finally won approval. Pipe next, but will be a harder sell. High efficiency filter element within the military tin box will be the best that can be done for intake.

[Adrian]

The problem seems to be the oversize hole in the alloy spacer, and possible the rubber flange mount/boot thingy with the bore of the carb and inlet tract being quite close. I'd heard the USA market Bullet heads were nearer 32 than 30mm in diameter, but that doesn't explain the alloy spacer.

The rubber mounting flange/boot thingy needs to have an inner bore of 30mm, with 8mm stud holes at 58mm centres - sorry, centers. The outer bore needs to be 40mm to fit the Mikuni of that size. Double check, but have Sudco sent the correct parts?

A.

[Wheaters]

The step from the adapter to the head casting is against the flow and will cause a lot of turbulence in the port. The new carb may actually flow less than the smaller original one.

The adapter needs replacing with one of a more suitable inner diameter. Alternatively, it might be possible to press fit a smaller diameter sleeve into it to match the port, so it can be gas flowed.

[Rex Piekarczyk]

Adrian,

Converting-

Carb ID engine side: 1.028" 26.1mm
Rubber Boot ID engine side: 1.449" 36.8mm
Aluminum adapter ID: 1.458" 37.0mm
Head & gasket ID: 1.298" 32.9mm

The boot fits perfectly on the carb and the head (upgrade version w/better guides & Kibblewhite valves) port is for all practical purposes 33mm.

I sent pics and inquiry to Niche but have received no response at this point.

[Rex Piekarczyk]

The step from the adapter to the head casting is against the flow and will cause a lot of turbulence in the port. The new carb may actually flow less than the smaller original one.

The adapter needs replacing with one of a more suitable inner diameter. Alternatively, it might be possible to press fit a smaller diameter sleeve into it to match the port, so it can be gas flowed.

Waiting on response from vendor @ right or wrong adapter. Kit was presented as drop-in for this application.

[Adrian]

Adrian,

Converting-

Carb ID engine side: 1.028" 26.1mm
Rubber Boot ID engine side: 1.449" 36.8mm
Aluminum adapter ID: 1.458" 37.0mm
Head & gasket ID: 1.298" 32.9mm

The boot fits perfectly on the carb and the head (upgrade version w/better guides & Kibblewhite valves) port is for all practical purposes 33mm.

I sent pics and inquiry to Niche but have received no response at this point.

A complete and utter mis-match! They've sent you a VM26 carb instead of a VM30 by the sound of it. The whole POINT of a 30mm carb (Mikuni, Amal, Dell'Orto or anyone else) is that the choke has a 30mm bore right the way through (or thru), unless it's some fancy piece of oval choke kit. OK, I did once have a 30mm Mk1½ Amal Concentric which tapered out to 32mm at the engine side (that was for a BSA), but that's just a bit of late 1980s strangeness.

Once you actually HAVE the 30mm carb you originally wanted (a VM32 would be a better match for your inlet port), one way forward would be an alloy sleeve 37.9mm OD with a 30mm bore to fill the gap in the rubber boot and the alloy spacer, but I'm still amazed Sudco couldn't find the parts that matched. Don't let them off the hook, I don't know what consumer protection laws apply in your part of the world, but it certainly looks like they've screwed up.

A.

[Rex Piekarczyk]

Everyone,

I must apologize for the previously stated dimensions, multitasking strikes again.
Re-measured dimensions in logical order-
Carb outlet: 30.8mm
Boot: 35.9mm
Adapter: 37.0mm
Head: 33.1mm

Adrian,
I transposed the 1.208 to 1.028 before the conversion resulting in 26mm, thanks for catching that mistake. You're right, it seems as if Niche may have supplied the wrong adapter. I'll give them until this afternoon to respond then I'll make a phone call. Are Niche & Sudco the same company?

A better picture to visualize the size difference. Hole in the original gasket picture was for the 28mm carb.

[Rex Piekarczyk]

Just spoke to Niche, that's the only adapter they produce for the 30, 32 & 34 conversion kits. Would need to open the head port or cut a new adapter. I think a reducer ring would be too thin to be practical.

[Adrian]

Good, at least they sent you the right carb.

I think a reducer ring would be too thin to be practical.

Too thin to be practical? How so? 37mm OD minus 30mm ID for the carb gives you 7mm, divide by two gives you a wall thickness of 3.5mm or just over 1/8 of an inch. 36mm OD, 3mm wall thickness, which is still fine. It will be just an alloy ring which only has to sit there smoothing the inlet out, it won't be under any kind of mechanical load.

Why don't you get a piece of THIS stuff, cut to length?

https://www.ebay.com/sch/i.html?_from=R ... 9&_sacat=0

It just needs the OD reducing slightly from 1.5"/38mm to your 37/36.5mm holes, the inner bore @ 1.25" works out at 31.75mm which is slightly less than the 32mm hole in your head which is the inlet port, not too big a step up from the 30mm bore of your carb.

Couldn't be a lot easier, could it?

Hope this helps.

A.

[Rex Piekarczyk]

Adrian,

Tapered reducing bushing successfully fabricated & installed.