MX FCR Project (Monster 750).

[koko64]

Check out these bad boys.

20200318_113705 by Tony Kokonis, on Flickr

[koko64]

20200318_113616 by Tony Kokonis, on Flickr

[koko64]

  20200318_113637 by Tony Kokonis, on Flickr   20200318_113659 by Tony Kokonis, on Flickr

Its a tight fit for sure.
I wanted to test the concept and it ran. I have another MX wide body FCR on its way from ebay. I will have to run two of those to be able to synch them which will be by cable adjustment like the old days. So they must be matching models as the throttle cams vary in size throwing out the synch as you turn the throttle. The slant body version has the synch screw under the cap which is a bonus.
Short choke knobs are needed as there just aint enough room for the long version on the lhs carb.

My custom rear manifold will give the carbs better clearance by positioning them in a staggered formation.

Throttle slides, etc must match or synch will be trashed. I say that because I have been buying used carbs off various dirt bikes. They are cheap but there are hidden pitfalls adding to cost if you have to replace too many parts.

I will probably run two FCRMX37 or TM36 and use the 39's on a customers bike.

[koko64]

20200318_191342 by Tony Kokonis, on Flickr

[koko64]

I refitted the stock carbs. I've gotta shelve the project until my machinist mate comes out of quarantine. Poor bugger.

[l88m22vette]

So this is obviously a very cool project and I'm excited to see what happens since it seems like you're getting to the home stretch. You're also the one doing all the legwork and prototyping, which is the most "fun" part of a project, but at the end of the day do you think this will beat using Duc-specific FCRs?

[koko64]

Im only trying this because the Duck specific FCR kits have no choke and are costing well over 2 grand to buy new (1 + grand used) in local money (Aussie). The FCR kits for Ducatis are easy to fit and tune imo, so its a pity I dont live in a year round warm climate. The lack of a cold start device really annoys me

[Duck-Stew]

20200318_191342 by Tony Kokonis, on Flickr

Such an aptly names product!  Couldn't tell ya how many times I've uttered that! LOL

[koko64]

 

[koko64]

Some things to note. The MX type of FCR are very aggressive with a large diameter throttle cam making them rev very quickly as they are a dirt bike racing carb. They are the most sophisticated FCR made and reputedly designed for absolute maximum response. This would suit a track bike or balls out street bike (or gutless ol' 750 needing a wake up?). I figured they wouldnt be too much on a stock ol' M750. The slant body FCR is responsive, but allows better modulation with a smoother bottom end to midrange transition and easier to dynamically synch. I really noticed the relative behaviour of each carb on the manometer. Just did an M750 with racked 39's and it was easy since I had separated the battery box from the airbox leaving a handy gap to get to the top of the carbs.

[Pinion]

Nice, with the Mx carbs, a lighter flywheel and clutch hud, twist the throttle and bike is gone (whilst your still hovering in the air Wylie coyote style)

[l88m22vette]

So MX = motocross?

[koko64]

Yep.

[koko64]

Nice, with the Mx carbs, a lighter flywheel and clutch hud, twist the throttle and bike is gone (whilst your still hovering in the air Wylie coyote style)

The bike came with an alloy flywheel (looks like a Nichols or Kamna). The 750 motor has a short stroke too, 61.5mm, so it spins up ok. Yeah I want a more responsive carb.

[Von Eisen]

VE, I reckon you'll be able to use the PB velocity stack filter adaptors and larger filters because the angled boots you have are more like a 30 deg angle. The carbs will have more clearance from the frame struts and the filters will have more clearance from the front frame cross member. As long as the float angle isnt too much causing flooding those boots have advantages. I'm keen to see how you go.

Velocity stack adapters have arrived and are a really nice fit, good to get something and not have to fettle. I think your correct about the larger filters fitting  . All that's holding me up is the Venhill one into two cable, think it's held up in customs due to the virus thing, The slant bodies not having a choke isn't a prob for me, I live in a permanently warm climate. What jetting are you looking at koko ? . My engine is lightly ported with FbF 11/1 and free breathing pipes, it likes to run leaner than one would think on the oem Keihin's and K&Ns ie Main 140, slow 37.5 ... I am thinking start off approx main 145, slow 42, on the FCR, your thoughts ? ... Btw those carbs look mean sitting in there on the manifolds, wicked work