Topic: VM29 MANIFOLDS

[mark ward]

I bought rubber manifolds for my VM29's a couple of years ago from SUDCO; but they seem like cheap rubber material; and I don't think they make good seal at cylinder head intakes.
     Has anyone found a decent supplier for these, or is it time to search for different carburetion?

[turboguzzi]

and i thought that sudco was a reliable, quality source. normal tube rubber adaptors i bought from them 10 years ago still give good service, but who knows, maybe they are skimping nowadays

if the only issue is head to manifold sealing, sounds solvable with some fuel resistant sealant IMHO....

[mark ward]

yes, I may try some kind of sealant first..... I just re-installed motor after rebuild, and have not had time to dig-in, and troubleshoot lean-running condition yet. (initial fire-up has to be choked, and that forces revs up too high)

[PeWe]

The carb boots I got wirh my VM29 purchased winter 83-84 were really soft. They pulsated at idle. My first thought was loss of power. A few mohths later cracks visible.

I ordered a second set the year after but they were not much better so stock carbs returned.

I started a project ebd of 80's when a friend that worked atva company producing alu parts could weld the rack after theyvhad cut it after my marks bwtween xarb 2 and 3. Max possible was 12mm.
I finaluzed that 2013 andvcould use stock boots with some bending.

I have shown that on the forum before, 2013 or 2014 with photos. Throttle rod had to be cut wirh new holes for throttle arms  3, 4 and mist likely the bolt hole for throttle mechanism too. Alu fuel T- pipe, choke rid shortened too, sone bent connectirsvfir caebs to fit. I made it to work. Replaced by TMR32  2015

It must be possible to find stiffer rubber that fit. Or make new somehow.

[mark ward]

That was an incredible amount of measuring, and adaptation that you did for your VM29's! It would be nice to be able to use the stock manifolds; but i don't wish to modify the VM's to that degree.
     i wonder how well the Cycle X twin carb setup works.

[PeWe]

Here my VM29 setup when I had assembled them
http://forums.sohc4.net/index.php?topic=119335.0
VM29 was a popular upgrade for many years ago, so there is a good idea to get them working as they are. Just find better carb boots/inlet rubbers or what else its called
I upgraded the rack long time ago so it was just to continue.

 The project had stopped due to the throttle shaft that I had idea to make a new one. I finally found that original could be cut and adapted with new holes and tap them. The new holes for 3-4 were not exact, enough making ot possible to make a good bench sync.

Check with MCRider and CBJoe what rubbers used on this bike that has VM29
http://forums.sohc4.net/index.php/topic,36459.msg2087318.html#msg2087318

It must be possible to make new inlets connecting carbs with head.

[PeWe]

I guess your carb boots will work. Are they softer than stock CB750, or strange fitment?
You have placed them correct?
2 are much more curved. I do not recall on which cylinders they were for, 1-4 or 2-3. It's obvious when testing.

[MRieck]

 That material isn't stout enough....as mentioned the pulsing is ridiculous. The CB750 Vintage K7/K8 and Dave Silver Spares 77/78 F2 insulators are closer to OEM material (and work well).

[PeWe]

That material isn't stout enough....as mentioned the pulsing is ridiculous. The CB750 Vintage K7/K8 and Dave Silver Spares 77/78 F2 insulators are closer to OEM material (and work well).

Mike,
The later K7/K8 will fit the VM29 rack ?

[MRieck]

That material isn't stout enough....as mentioned the pulsing is ridiculous. The CB750 Vintage K7/K8 and Dave Silver Spares 77/78 F2 insulators are closer to OEM material (and work well).

Mike,
The later K7/K8 will fit the VM29 rack ?

Not to my knowledge Per. I was just pointing out that some aftermarket insulators are OK.

[PeWe]

OK, good to know.

[mark ward]

i'll likely address the carb / manifold issue, after i drive back from Valdosta next week. i'll need to check floats etc., since carbs sat all summer, while i worked on motor.

[Laids]

I had thought that 1 & 4 were basically Honda stock configuration but 2 & 3 were specific to VM29/CB750 fitment. Can anyone confirm new boots are available at all?

[PeWe]

You can see how the rubbers look like with placement here.
The most curved ones special for Mikuni VM29 are 2-3. 1,4 look like stock
https://www.ebay-kleinanzeigen.de/s-anzeige/rennvergaser-mikuni-vm-29-cr-750-cb-750-cafe-racer-yoshi/1020897881-306-8988

[mark ward]

yes, I believe most issues with VM29 manifold leaks, are usually for the 2 center cylinders. Tighter angles, and they seem to not clamp well to the engine side. They look like they seal to the carbs straight, and tight.
      Also, the SUDCO rubber appears to be thick; but too glossy on the outer surface.

[PeWe]

It must be possible to reenforce the Sudco rubber  with vulcanised nylon or cotton braided rubber tape that wrapped around will vulcanise, melt together. Only a thin layer were clamps sits.

Or a shrink hose over everything. It must be braided to stiffen it up.

[mark ward]

now we're gettin' creative!   
not as much as the modification to your VM's....

[PeWe]

Yes, it must be somethingvout there possible to wrap around the carb insulators making them stiffer.

[Tracksnblades1]

Yes, it must be somethingvout there possible to wrap around the carb insulators making them stiffer.

I'll bet a guy like you could press some very thin wall aluminum oversized bushing inside the rubbers fitting between the intake and carb spigots with a minimum clearance between the two.
Just 🤔 Out load....

[PeWe]

Or have 4 alu pipes of correct diameters, in and out. Right curves and connect it with a short rubber/ silicone hose in each end. 4 clamps each though.
The total lenght of inlet manifold can be a little bit longer and still fit. The curved inlets of 2-3 can have smoother bends.

My Mikuni TMR32 have longer inlets. The KN filters fits exact and stock lenght throttle cables fits too.

[Don R]

 I was able to fit an unknown Weber manifold once by swapping and reversing the stock rubber isolators. Just a thought.

[mark ward]

After many great conversations in Valdosta this past weekend, with many great minds; Mike, Frank, Wilbur, Jerry, Bill, Dennis, Keith, Butch, Rocket, and others; I plan to try stock intakes from '77-'78 carbs; if i can locate where to purchase them.

[PeWe]

Try old cracked ones for free first if you are not sure they will fit. Or have rhe later carbs close numbers of how carbs sits in the rack?

[dragracer]

Mark. I'll shoot you a  pm tomorrow with my source for the boots. I looked at the receipt tonight while I was in the shop cleaning up.

[dusterdude]

After many great conversations in Valdosta this past weekend, with many great minds; Mike, Frank, Wilbur, Jerry, Bill, Dennis, Keith, Butch, Rocket, and others; I plan to try stock intakes from '77-'78 carbs; if i can locate where to purchase them.

Cb750.com iirc

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