MX FCR Project (Monster 750).

[Speeddog]

It's an aluminum part with the rubber cast/molded/vulcanized over it.

34.3mm ID where it mates to the head, 48.6mm ID on the straight bore in the rubber.

~47.3mm diameter on the.... anti-groove(?) part.

There's at least 2 different versions, I suspect small block/big block like carbie manifolds are.

[koko64]

You reckon its about a 15-20deg bend? The TB to airbox rubbers are more like 45 deg, but are they stiff enough and sufficiently petrol resistant?

Unfortunately the 45 deg biscuit needs a little too much reaming. Not impossible, but annoying.

[koko64]

20200212_173234 by Tony Kokonis, on Flickr

I got the bikkie to work by reaming it out with the die grinder, sandmop and elbow grease. It's on firmly.

[koko64]

20200212_173153 by Tony Kokonis, on Flickr

Because the cylinders are rocked back a little in the frame the 45 deg bikkie is going to place the carb very close to horizontal and within its range of operation.

[Speeddog]

You reckon its about a 15-20deg bend? The TB to airbox rubbers are more like 45 deg, but are they stiff enough and sufficiently petrol resistant?

Unfortunately the 45 deg biscuit needs a little too much reaming. Not impossible, but annoying.

Sorry, missed this post.

Off the top of my head, I'd say 15-20 degrees.
But I'll check tomorrow and get a real number.

You're making good progress with the 45 degree rubber.

[koko64]

Thanks mate, appreciate your help. I was concerned that I would have to remove too much material and render the 45 deg boot useless. Fortunately the silicon content makes it hang on tight and conform well to a slightly larger object. The vertical cyl manifold is being cut and machined to run straight out of the cylinder under the cross brace with enough clearance when the oem spigot rubber is added. I'll end up running the carbs on the cylinders which give the best clearance. I'm concerned about the sheer bulk of the later gen MX carb. It's a big rig.

[koko64]

A question about the float bowl vents, each carb has four which is a touted feature. Are they really vents or extra overflow ports for the inevitable dirtbike tip over. I think the latter. They are on T fittings/junctions, so I have plugged two vents of the four so that I can reduce hoses leaving only the float bowl overflow hoses. I plugged the vents that could face wind turbulence, leaving those that face down or rearward. I would block them all if anyone could confirm it would be ok.

[Howie]

Float bowl needs a vent.  No idea of anything else.

[Speeddog]

IMO, I think you're correct, overflow for tipovers.

Float bowl needs a vent to ambient air pressure that's not subjected to wind, that's all.
In normal running there's no filling or draining of the float bowl that's fast enough to need multiple vents.

[koko64]

It's interesting how the road bike FCR's don't have extra vents, although the one shared on tandem FCR's is quite a large volume pipe. The tandem FCR's on Ducati's don't have traditional overflow vents from the bottom of the float bowl like OEM CV carbs, but these carbs do. That makes five small vents per carb with one designated for conventional float bowl overflow. With any serious flooding will the conventional vent be enough? I'll keep an eye on that. I have capped the forward and side facing vents to protect them from wind. If I can get away without extra vent tubes I will.

[Speeddog]

Offset due to big-block cylinders being taller, IIRC it's 10mm:




Apparently the big-block heads have slightly longer intakes, the corresponding manifolds are ~4mm shorter.




Total bend angles are quite close.

[koko64]

Cheers.
That's a handy little device

[koko64]

  photo-134-400x400 by Tony Kokonis, on Flickr

     Mikuni-VM-TM-2-1-cable-set-w.-Quick-Action-Throttle by Tony Kokonis, on Flickr



This combo of TM36 and 2 into 1 throttle for about $510 Oz. An option for a 600 or 750 as there is no accelerator pump, I would opt for the smaller sizes, so 36mm for the 750 and 38mm for the 900. Go bigger and you need the FCR's with acc pump (which are the same price used) in 39 and 41mm. TM's are a cheap option however. One other thing, smaller 44mm spigots..

[koko64]

Cool project, I just got a bike and had posted about the exact same idea, seems like it should work fine 

https://www.ducati.ms/threads/keihin-carbs-anyone-tried-an-oem-version.725957/

How is it coming along?

[l88m22vette]

I haven't picked any up yet, I've got a couple other things to do first and adding power definitely is not advised. I'm a new rider and I tend to go down the rabbit hole when I buy any kind of vehicle, but you never know what you can find out there as far as deals so I figured they might be something to keep an eye out for. I've definitely been following this thread with interest.