Single Mikuni Flatslide carb

Tomato man · Jul 26, 2013

Has anyone used a SINGLE... Mikuni TM 34 TM 36 or TM38 flat slide on an 850 COmmando?
I have talked to the SUdco rep and they do have those kits both single and dual carb setups available with jetting particular to a Norton COmmando motor.

I have been running a single Mikuni VM carb on my 850.

It runs solidy with std settings but I have seen some really good performance from the use of a device from Thunder products called a UFO ultimate Fuel Optimizer. It cleans up the airflow under the bottom of the mikuni slide and provides a more effective stream of atomized fuel. Thunder products requires a lot of personal jetting efforts form the purchaser to get those results. They will offer some guidelines but make no claims that you will use this jet or that to get the results.

I had to file down the cutaway on my slide to get the proper idle and low speed operation.

WHen I did, it worked like a well performing ram air induction with the revs spinning up fiercely. I have seen that how the atomized fuel going through the throat of the carb is very crucial to a good punch from the single carb. Thunder also has an extra stainless crossplane part which snaps into the motor side of the carb. DIrt bike and snowmobile competition has been ecstatic over their use of these carb enhancements. I mention this to say that carb performance depends a lot on the design which pays attention to HOW the air enters and exits the carb throat without being unduly disturbed from a planar airstream. Thunder products did their homework and made their UFO device to demonstrate this. I know a couple of Norton people who have stepped out of the mikuni VM tradition to give it a try with much excitement. Now my curiosity has turned to the TM Mikuni flatslide. Keihin flatslides have gained a lot of popularity. They are also very expensive. The Mikuni is within reach of my curious inclinations and lust for
growling excitement as simply as possible. I want... whiter knuckles! at least up to 80 mph. High speed high rpm performance is not important to me.

I want to stay with a single carb to keep fuel consumption under control ( roadster tank) . The mikuni flatslide is built to do precisely what I was doing with the UFO installation but with less demands from my experimentation. The SUdco rep, CHad, said I would want to use the TM 34 or the TM 36 flatslide for my objectives.

Any experience with the TM Mikuni flatslides...single or dual carb use on an 850 would be much appreciated.

C'mon BACK!

Stop your laughing Comnoz.

Can you say... pilot jet ....without spilling your coffee?

Tomato Man... high up on the Allegheny Ridge ....with his raccoon and tomato patch and overbearing tiny poodle. Claims the cul de sac belongs to her. Everyone else is an interloper.

comnoz · Jul 26, 2013

No coffee, this time I spilled my milk.

comnoz · Jul 26, 2013

Oh, and my experience with the single carb MAP manifold is if you want more power then use the manifold that is designed for the 36-38 mm carb. Then install the 34mm carb with an adapter ring to make it fit. The regular 34mm carb flows more than enough for a streetbike up to 6000. The 34mm manifold is the restriction.
The 36-38 mm carbs also work fine too but they are a little tougher to get the low speed jetting just right. And the performance increase over a 34 on a 38mm manifold is negligible. Jim

dennisgb · Jul 26, 2013

I have a single 34TM on my 1975 Commando 850 MKIII. Just got it running a few days ago. Still working through pilot sizing although it is pretty close. Has very smooth and quick throttle response. It had a VM on it before.

The velocity at the base of the slide that you are talking about is very different on the TM. You can match slide cut away as there are multiple slides available, but the match really is to "your" bike as the amount of air and fuel is based on what the engine needs and can take depending on mods, etc. If too much cut away, it will run rich no matter what you do. Not sure that what you did on your VM really makes the difference you are citing as it needs to be calculated to the engine. You may see an increase a lower throttle positions but it will change as you open the throttle. There is an art to tuning carbs, and getting the best performance.

The TM is the bomb as far as I can tell...and really all you need to do is match the right jets to get awesome response.

dennisgb · Jul 26, 2013

Go to this thread for video of my 850 running the first time with the Mikuni TM34.

video-first-run-mkiii-t16978.html

acotrel · Jul 26, 2013

Why does using only one carb give better fuel consumption , unless you tend to fang the bike more when you have two ? I'd like to try two 34mm Mikuni flat slides on my 850 - not legitimate for a certain historic race class - but who gives a stuff ? The scrutineers are cross-eyed anyway. There are certain things about the flat slide carbs which make them very attractive.

comnoz · Jul 26, 2013

acotrel said:
Why does using only one carb give better fuel consumption , unless you tend to fang the bike more when you have two ? I'd like to try two 34mm Mikuni flat slides on my 850 - not legitimate for a certain historic race class - but who gives a stuff ? The scrutineers are cross-eyed anyway. There are certain things about the flat slide carbs which make them very attractive.

I have a feeling if "the scrutineers" read this forum you may have a lot of safety wiring to do.

Jim

concours · Jul 26, 2013

"snowmobile competition has been ecstatic over their use of these carb enhancements."

Actually we chuckle and roll our eyes at the snake oil placebo.... :roll:

Tomato man · Jul 26, 2013

This is some good feedback and what I was hoping I might find on this forum.
There has been some concern about the flatslide Keihins being a tall carb and a tight fit in the COmmando.
Is this also a concern with the Mikuni TM flatslide?

The SUdco rep also mentioned that there is not a factory ready throttle cable for the single TM Mikuni and would require some spacers to be used in the available throttle cable for the COmmando set up.

Any feedback on the situation with the throttle cable?

Tomato man

comnoz · Jul 26, 2013

Two Keihin flatslides are a good fit on a Commando with the new manifold from CNW. It sets the carbs slightly lower and forward.

A single Keihin flatslide will not fit with a Map manifold -too tall.

A Mikuni TM flatslide will fit but the cable is pretty tight and usually means the carb ends up slightly tilted. They do have good fuel control and run nice at low speeds. I installed a few some years ago and had some complaints of slide sticking when ridden in the rain. I always made up my own cables or modified a cable designed for a VM. Jim

Tomato man · Jul 26, 2013

Jim, I was at Mid Ohio Vintage Days last weekend at Lexington OH. A hard rain started and just before it broke loose, I made a concerted effort to make it to a pretty solid building since the sky got real black.
I headed for the racing pit garages. There was a covered balcony accessed by steps so I went up under the roof cover and walked along to peek into each garage. One garage had 2 racing Honda CBX 6 cylinders and one more that was all restored into beautiful condition. As I walked along, I came to one garage with a racing Norton COmmando. After the rain let up I went down to his garage and he invited me in. He had some kind of velocity stacks that were out turned with a outer curve like a donut. He said that those were a stroke of genius and worked really well. I also noticed that he had dual Mikuni carbs with extra long rubber connector boots setting them way back toward the battery box. Those boots must have been six inches long.

I am curious what the those long intakes actually accomplished. The new sport bikes from Japan are using variable intake tracts. Maybe varied with a servo motor??

Ed

mikegray660 · Jul 26, 2013

yes - extensive use w/ single TM's and VMs (and dual of both in 750's /850 etc)

PM me and i can give you detailed info

Tomato man said:
Has anyone used a SINGLE... Mikuni TM 34 TM 36 or TM38 flat slide on an 850 COmmando?
I have talked to the SUdco rep and they do have those kits both single and dual carb setups available with jetting particular to a Norton COmmando motor.

I have been running a single Mikuni VM carb on my 850.

It runs solidy with std settings but I have seen some really good performance from the use of a device from Thunder products called a UFO ultimate Fuel Optimizer. It cleans up the airflow under the bottom of the mikuni slide and provides a more effective stream of atomized fuel. Thunder products requires a lot of personal jetting efforts form the purchaser to get those results. They will offer some guidelines but make no claims that you will use this jet or that to get the results.

I had to file down the cutaway on my slide to get the proper idle and low speed operation.

WHen I did, it worked like a well performing ram air induction with the revs spinning up fiercely. I have seen that how the atomized fuel going through the throat of the carb is very crucial to a good punch from the single carb. Thunder also has an extra stainless crossplane part which snaps into the motor side of the carb. DIrt bike and snowmobile competition has been ecstatic over their use of these carb enhancements. I mention this to say that carb performance depends a lot on the design which pays attention to HOW the air enters and exits the carb throat without being unduly disturbed from a planar airstream. Thunder products did their homework and made their UFO device to demonstrate this. I know a couple of Norton people who have stepped out of the mikuni VM tradition to give it a try with much excitement. Now my curiosity has turned to the TM Mikuni flatslide. Keihin flatslides have gained a lot of popularity. They are also very expensive. The Mikuni is within reach of my curious inclinations and lust for
growling excitement as simply as possible. I want... whiter knuckles! at least up to 80 mph. High speed high rpm performance is not important to me.

I want to stay with a single carb to keep fuel consumption under control ( roadster tank) . The mikuni flatslide is built to do precisely what I was doing with the UFO installation but with less demands from my experimentation. The SUdco rep, CHad, said I would want to use the TM 34 or the TM 36 flatslide for my objectives.

Any experience with the TM Mikuni flatslides...single or dual carb use on an 850 would be much appreciated.

C'mon BACK!

Stop your laughing Comnoz.

Can you say... pilot jet ....without spilling your coffee?

Tomato Man... high up on the Allegheny Ridge ....with his raccoon and tomato patch and overbearing tiny poodle. Claims the cul de sac belongs to her. Everyone else is an interloper.

comnoz · Jul 26, 2013

Tomato man said:
Jim, I was at Mid Ohio Vintage Days last weekend at Lexington OH. A hard rain started and just before it broke loose, I made a concerted effort to make it to a pretty solid building since the sky got real black.
I headed for the racing pit garages. There was a covered balcony accessed by steps so I went up under the roof cover and walked along to peek into each garage. One garage had 2 racing Honda CBX 6 cylinders and one more that was all restored into beautiful condition. As I walked along, I came to one garage with a racing Norton COmmando. After the rain let up I went down to his garage and he invited me in. He had some kind of velocity stacks that were out turned with a outer curve like a donut. He said that those were a stroke of genius and worked really well. I also noticed that he had dual Mikuni carbs with extra long rubber connector boots setting them way back toward the battery box. Those boots must have been six inches long.

I am curious what the those long intakes actually accomplished. The new sport bikes from Japan are using variable intake tracts. Maybe varied with a servo motor??

Ed

The long intakes are a way of taking advantage of the pressure pulses in the intake to trap more air in the cylinders. The length is determined by the RPM, the exhaust system, the camshaft timing, the volume of the intake manifolds and the volume of the combustion chamber and is usually tuned by the cut and try method. When everything is just right the gains can be significant but they are only over a short RPM range unless you have a way of varying the length as you go. Jim

Single Mikuni Flatslide carb

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