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Mikuni Carburetor Information Links

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Mikuni VM Carburetor Parts, by Part Number & Application

Mikuni VM Carburetor Diagrams & Charts

Mikuni VM Jetting Examples for British Motorcycles

Jetting Specs For Yamaha TT500

VM Round Slide Mikuni Carburettor Standard Specifications

Carb Jetting For Amal, Mikuni, Dell'orto, Weber, etc.

Mikuni TM Flat-Slide Carb Info

36mm Mikuni Model TM36-68

Mikuni’s TM Series flat side carburetors provide significant performance improvements over older round slide carburetors.

Air flows faster, smoother through the TM Series venturi and jet blocks due to the flat slide design which help create a smooth bore effect.

The high velocity air flow means a stronger vacuum at the needle jet for more precise metering and will produce better throttle responses due to the advanced operation of the TM series carb the jetting information may seem "off" if compared to the old style VM series or stock carburation figures the following information is the jetting specs for a 500cc Yamaha style motor.

Bore size:  36mm

Main Jet Size:  130

Pilot Jet Size:  12.5

Needle Jet / Series: 784-13002-P-8/568

Jet Needle:  9DZH6-50

Throttle Valve:  N/A

Air Jet:  1.0

Above information from an eBay Ad

The following are some jetting specs provided by Mark at Thumper Stuff.
17461 147th St SE
Suite 11A
Monroe, WA 98272

These specs are from a 38mm Mikuni round-slide carb removed from an FT500.
3.0 Slide
240 Main
32.5 Pilot
6F8 Needle
P5 Needle Jet
0.5 Air Jet

These specs are from a 38mm Mikuni flat-slide carb removed from an SR500.
4.0 Slide
190 Main
55 Pilot (He felt that this spec may be incorrect & that a 25-30 would probably be more appropriate)
389P2 Needle Jet
6FJ40 Needle

Please remember Thumper Stuff when it comes time to buy parts for your Ascot. He has a lot more available than what is shown on his web-site. 8)

Another source of carbs, parts & information is SUDCO.

They will not give out any jetting specs, but they will assist you in selecting the correct components to purchase from them.

Jetting specs for the Mikuni VM34 carb on an FT500

Pilot Jet - #25. You'll get a nice reliable idle that sometimes will yield 900 RPM. A #20 is too lean and the idle is not reliable. I have a #30 but haven't tried it - no need.

Needle Jet - P8. Possibly a P7 if you are running a stock exhaust but I think you will want the P8 no matter what exhaust you are running.

Jet needle - 6DH4 (already installed in the new carb)

Main Jet - #220. I'm running a free flowing homemade air filter and stock airbox which I'm sure passes as much air as a K&N. I have effectively no muffler (steel wool packed "glass pack"). You may want to play here a-bit. A #250 is way too rich, a #240 is too. I have a #230 and #210 which I haven't tried and doubt I will.

You'll want to hit the auto parts store for a piece of radiator hose to make the union between the Mikuni to the Keihin intake manifold. Buy a Dayco part number B71226, S-452. There are other numbers on the hose also - 452, 14-2861-6, S60940. You'll need to hacksaw off about 5/8" to 1/2" off the hose end to act as a filler between the Mikuni outlet and the rubber manifold. Measure the depth from the outer edge of the manifold to the raised "stop" in the throat of the manifold. A stainless hose clamp works fine to attach the carb.

VERY important!!! Make sure you have a 90 degree exit out of your carb for the throttle cable. A straight pull fitting out of the carb and you've got a nightmare in terms of cable clearance under the fuel tank.

You'll find that the fuel line connection is a-bit awkward. The fuel inlet fitting on the Mikuni is straight up. I'm going to install an in-line 90 degree elbow into the carb. Until you do you'll just have sort of a goofy looking fuel line arrangement especially if you install an in-line fuel filter (recommended).

No more yank yank yank on the twist grip to activate the accelerator pump to prime the carb on starting. No more grinding on that poor, over taxed starter. Just flip on the petcock, drop the enrichening lever, hit the starter and in two revs of the crank she'll fire - every time.

You'll notice an immediate and significant improvement in mid range torque. Install a Dennis Kirk, $15.00, 17 tooth counter shaft sprocket and you won't be toeing for sixth gear all the time and your engine will make happy noises as you go down the road. With the Kehin carb and a 15 tooth counter shaft sprocket I could pull 82 MPH in fourth and 78 MPH in fifth. With my new setup I can pull 92 - 93 MPH in fifth.

I bought my carb and jets from I gave them some very complex jet orders and they didn't muck the orders up once. They have very nice prices and you can't stump them on a jet size.

If you go the Motion Pro throttle cable route they will want you to send them your stock twist grip so they can make a custom cable. Make sure they know you are installing a Mikuni and that you want a 90 degree exit out of the carb. Lube your new cable BEFORE you install it, it does not come lubricated. I assume you've lubed cables before. If not let me know and I'll share a cool tip with you.

Courtesy of Bill from the Yahoo Ascot Owners Group.


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