MX FCR Project (Monster 750).

[koko64]

Fitting these dirt bike Keihin FCR MX 39 carbs to my 750 Monster. MX style flatslide carbs have a choke (unlike Ducati specific Keihin flatslide carbs), dont freeze like stock CV carbs and usually have adjustable accelerator pumps. So who wants flatslide performance with a choke and without selling a kidney?

The carbs I purchased are used and are side draft items, but they are cheap and plentiful from dirt bike yards. Being side draft carbs means friggin' around with the manifolds, pod filters, 2 into 1 throttle cables, etc.

Some assembled parts so far.

20200129_121203 by Tony Kokonis, on Flickr

I have plenty of jets and some needles which will work for a 750.


Mikuni-45-degree-rubber-sleeve by Tony Kokonis, on Flickr
20181005_115746 by Tony Kokonis, on Flickr
images (2) by Tony Kokonis, on Flickr
These are new, mine are going to be crusty. One is off a Husky and one from a KTM. They are slightly different but both side draft with TPS and choke and one has a hot start knob. One is more this style
images (3) by Tony Kokonis, on Flickrimages by Tony Kokonis, on Flickr

Some of the MX carbs have cast bell mouths like the one above, so I avoided them. I was hoping for 37mm carbs, but 39mm carbs were available with bolt on velocity stacks/airbox adaptors. This gives me options to mix and match parts I already have. I'm trying to do this cheap, simple and functional.

[koko64]

 Both carbs will face forward and be in a similar postion to the stock carbs except that they will be horizontal. The rear cylinder carb will sit on a modified manifold and the front cyl carb will have 45 deg manifold rubber to level it.

More updates to come.

[koko64]

Looking at a throttle kit like this from Powerbarn. It works with split FCRs for big KTMs. The Ducati version are on their way.

http://power-barn.com/motion-pro-throttle-cable-set-for-ktm-950-adventurer-with-keihin-fcr/
a207919132a89fe885605d_l__60861.1415401385.386.513 by Tony Kokonis, on Flickr

[koko64]

s-l1600 (1) by Tony Kokonis, on Flickr

Red knob is hot start, flood start. Choke hidden behind it.
s-l1600 (4) by Tony Kokonis, on Flickr

[koko64]

s-l300 (5) by Tony Kokonis, on Flickr

s-l1600 (1) by Tony Kokonis, on Flickr

These two carbs above are the actual carbs I purchased. 2005 and 2009 models. You can see they are a generation apart MX models, one slant body side draft and one later straight body side draft. As they both will face forward they will have different clearance from the frame struts in the vicinity.  I will remove the tps for now as the aggressive oem Kokusan ignition suits the stock low compression motor. Running an Ignitech programable ignition and tps is another project for another day.

[koko64]

a20792012e8af9235892cd_l__83734.1415401439.386.513 by Tony Kokonis, on Flickr

These will be handy and save me buying new filters. They are a low cost solution with a nice shape for flow.

[koko64]

a20791913210eb4a41e6a_m__55419.1415401402.386.513 by Tony Kokonis, on Flickr

These adjustable slow air jet screws are absolutely worth their bloody weight in gold (but cheap to buy).

[Howie]

a20791913210eb4a41e6a_m__55419.1415401402.386.513 by Tony Kokonis, on Flickr

These adjustable slow air jet screws are bloody absolutely worth their weight in gold (but cheap to buy).

Phenomenal gift to tuners!

[koko64]

Phenomenal gift to tuners!

Sure is mate. The way the SAJ screw overlaps with the pilot jet, IMS, needle root diameter and slide cutaway means it can be used to cover a multitude of sins . I like how it lets you choose the off/on throttle character you prefer at smaller throttle range. But of course you know all that I'm stating the obvious because most people have no idea how powerful (Speeddogs words) a little component it is.

[koko64]

I've organized a mate to cut and machine a couple of manifolds so I have options for the rear cylinder carb.  The top of the rear Cyl carb must clear the rear frame spar and the float bowl has to clear the forward struts. The manifolds have subtle differences in angle and length giving some options for a good fit. I'm starting to get excited.

[koko64]

20200204_080719 by Tony Kokonis, on Flickr

First carb being prepped. Only one leak, not bad.
If I'm happy with the outcome I'll offer a kit to customers, but once again I'm answering questions no one is asking (or 20 years too late). Having fun though 

[koko64]

20200204_220441 by Tony Kokonis, on Flickr

First and second gen MX FCR's. First gen on the right. It's familiar to us road guys as its a road race carb modified for MX. Second gen on the left has a broader body with more parts encapsulated internally to protect them from mud. All the jets and needles are the same except the pilot jets due to the different float bowl design.

[koko64]

20200204_220422 by Tony Kokonis, on Flickr

Heres another pic showing the differences yet they are internally functionally identical except for the float bowl which has resulted in very different looking pilot/slow jets.

[koko64]

20200204_215805 by Tony Kokonis, on Flickr

The slow jet many of us know on the right is also used in Harley butterfly carbs.  The jet on the left is from the 2nd gen MX carb. Are these jets calibrated on the same scale? I'm guessing yes. Can anyone confirm this as all the other jets are the same? Jet on the left is a 42 one on the right is a 52. Bore size fits the relative size too by sight. Jet cleaning tool also confirms that the 52 is larger, but are they drilled to scale?

[koko64]

20200204_215805 by Tony Kokonis, on Flickr

The slow jet many of us know on the right is also used in Harley butterfly carbs.  The jet on the left is from the 2nd gen MX carb. Are these jets calibrated on the same scale? I'm guessing yes. Can anyone confirm this as all the other jets are the same? Jet on the left is a 42 one on the right is a 52. Bore size fits the relative size too by sight. Jet cleaning tool also confirms that the 52 is larger, but are they drilled to scale?

These are the N424-21(long) Vs N424-25B(short)