MX FCR Project (Monster 750).

[koko64]

Oh the 50mm Powerbarn ones . I think Motion Pro  make them. No they're on order with the 2 into 1 cable kit etc. Packaging considerations will determine the combination of parts to clear frame spars and struts. PB 50mm adaptor stacks, the oem 35mm adaptor stacks, RU-0800 filters and RU- 2780 filters. Mixing and matching those parts will allow a 27mm difference in length and the conical 2780's allow some lateral wriggle room. My hope is that they all fit fine and I'll use the more used parts leaving the nicer new parts for customers.

I'm watching a pair of FCR37MX carbs on eBay. I think they would work well on my stock 750 if I can epoxy or JB weld the indentations in the bell mouth, then port them. I'm open to any advice about that.

[koko64]

 Looking good koko   ... So you have decided not to use the PB-853000  ? Ive ordered a couple, from the same source, in the hope I can squeeze them in. The short bend manifold adapter I ordered http://www.nichecycle.com/ncs/categories/carburetor/flanges-adapters/carb-holder-elbow.html arrived yesterday, its quiet pliable and both ends will shoe horn onto the 46mm spigot no worries.  Im just waiting on the one into two cable and the PB-853000 before I move onto the fun part ... Great thread btw

You have pics of your carbs?

[koko64]

Fcr Mx oem by Tony Kokonis, on Flickr

Above is an FCR37MX carb. They came as an oem part or catalogue performance upgrade on some dirt bikes. The bellmouth is cast to the carb body, so you can't unbolt it and fit a nice filter adaptor or velocity stack.
Is it possible to fill the slots in the face of the bellmouth with JB weld or a special epoxy and then port a nice velocity stack? My concern is some of the filler medium breaking loose and getting injested.

[koko64]

https://www.swiftsupplies.com.au/weicon-titanium-repair-stick

Think I found the product to do the job. Any advice?

[Speeddog]

I've used the regular JB weld a bit recently, and it's pretty good.

Came highly recommended from a trusted guru.
Sticks well to intake ports.
Reportedly digestible, he cited a 2-stroke that dropped a chunk from a transfer port without damage.
Evidently it left out the pipe as dust.

It's a bit runny, so needs dams or molds if you're trying to build something like a carb bellmouth.

Thorough mixing is crucial, at least 3-4 minutes confirmed with a timer.
Mixing until the color is consistent is not adequate.

He emphasized to NOT use the fast JB.

[koko64]

Thanks mate. If I can do this I can port the cast stack of 37mm FCRs, which I think are a good street size for stock  750's. I was thinking of filling those slots on the face of the bellmouth and then giving the ID lip a mild radius.

My plan, run the 39s and get all the bugs out, then sell the 39s to owners of modified 750's and 900's and opt for the 37's on my 750. Im thinking maximum part throttle air velocity and response on a stock motor.

[koko64]

My package from Powerbarn arrived.
Modifications were necessary to suit this custom application. Mixin' n match'n the 2 into 1 throttle cables accommodates the MX carbs as the kit is for the Ducati split carb kit. A bit of friggin around, but you know whats required after the first time. The filter adaptors will also need the air jet holes drilled deeper to fit the adjustable slow air jet screws which protrude a couple of mm.

[Von Eisen]

You have pics of your carbs?

  I haven't progressed very far koko, still awaiting parts ... These are the carbs with elbows         https://ibb.co/mRqx2Kv

[koko64]

 

If my cut n shut rear cyl manifolds dont work I'll go double elbow boots. Me mate is working out how to machine them so I may go double boots to start with. The factory must have machined them first before welding the flange on, so how does he hold it in the lathe or milling machine? He'll work out a way. With two angled boots, at least the manifolds will be closer to equal length. I'm mindful of resonance issues so well see. With that in mind an angled boot on the rear cyl manifold creates an S bend (pretty bad), but only a "curve grande" on the front cyl manifold (bad enough). I wanted to avoid an S bend creating a "water hammer" in the plumbing, it might be fine, but there's one way to find out.

[koko64]

Major Edit: I was able to fit the larger bodied MX carb on the rhs manifold. This makes everything easier now. I now have the option of runnjng a 45deg boot on the lhs manifold or one of the modified ones being machined to run straight.


VE, it's a good thing you got two slant bodied carbs because the fat MX type take up so much room. You have more margin for adjustment.

I have one slant body carb and one MX. With two 45 deg boots on stock manifolds they just fit. The MX carbs are about 110mm wide with a very deep float bowl. They are very large carbs.

The easy set up is two TM 36 or 38 carbs which are 75mm wide and not as long below the bellmouth, so more room side by side and more clearance above frame struts. You buy two 45 deg boots, a Mikuni 2 into 1 quick turn throttle and the carbs. The issue is the jetting. Consulting Powerbarn or Mikuni Oz for a baseline is essential.

I have to decide if I should sell my FCR MX kit to a Supersport guy (easy fit) and buy the TM36 carbs or squeeze the FCR MX carbs into my M750. The FCR's are a better carb imo, but the TM's are cheap and easy to fit, the tuning will require patience however.

The air filters will be small with 45 deg boots. The conical filters just fit.

Clearance of the oil cooler lines is very close with 45 deg boots. You may have to adjust the lines a little. If Kamna sold a TDMR38 I'd fork out and buy it. I think 40mm carbs on a stock M750 is over kill, and so is the price (for me). Two TM36 carbs, manifold boots and throttle kit would come to around $600 Pacific Pesos.

I should have a modified manifold by the end of next week and this will stagger the carb back about 40mm which will help fitment. That makes me hopeful.

[koko64]

20200312_214444 by Tony Kokonis, on Flickr

Got the bastard to fit.

[Duck-Stew]

That’s cool right there! ^^^^     Good job!

[Von Eisen]

  Great news you could shoehorn it in, its looking good  ... Very interesting to see one in situ.

 I moved my oil cooler down to the lower cover many moons ago, the modified lines run low, so should be all good there   

[koko64]

  Great news you could shoehorn it in, its looking good  ... Very interesting to see one in situ.

 I moved my oil cooler down to the lower cover many moons ago, the modified lines run low, so should be all good there   

I thought about moving the oil cooler, but left it in place as my 750 also has scrambler/adventure duties. I did have to replace the rhs oil cooler line to remove the carb heating kit.

I'm glad you have the slim slant body version, the MX version is a beast of a carb. Clearance to frame struts and oil lines, etc is in the 5-10mm range.

[koko64]

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.