In praise of Mikuni flatslides!

Two wildly successful projects this weekend - along with many small victories.

The big one was installing a relatively expensive Mikuni TM36-68 single carb. http://sudco.com/catalog/Page%20132-136.pdf (page 2 of the pdf)

Its a flatslide 36mm carb with an accelerator pump. Flatslides are supposed to have better metering and higher intake velocities (compared to a similarly sized VM series). This allows the use or a larger carb without sacrificing low-end torque and throttle response.

Mikuni specs the accelerator pump to cover low-rpm roll-on flat spots on 650cc "big singles." A parallel-twin looks a lot like a "big single" to me.

It requires a push-pull throttle, but the generic Sudco kit worked great.

So, how'd it work? Outstanding.

Sudco did an approximate jetting for me - and sent two spares. I turned on the fuel spigot, rolled the throttle a couple of times (until I could see fuel come from the accelerator pump), partially opened the throttle and -two swift kicks later- it was running.

It idles nicely at 900 rpm and is torquey and responsive from 1400-4500 rpm in 2nd gear roll-ons. Plugs look great, but I'll wait to come to a verdict on jetting.

Updates and pictures to come.

And, no, my Amal's aren't going in the waste bin - just on a shelf for now.[/url]

Doc.,

Congratulations on the successful installation of your new Mikuni carburetor. Thank goodness for small wins! However, some may claim what you just accomplished a major victory.

At the risk of sounding impudent, how does the air cleaner fit?

Regards,

Jason

Flatslide airfilter

The air filter is a K&N spigot-thingy - and it fits just fine.

However, I had to remove the sheetmetal that formed the back of the stock filter (between it and the battery) to give me the room to put it on.

Now I have to cobble together something functional, clean and aesthetic to provide a small measure of protection for the battery compartment. C'est la vie.

David,

Congrats on the new carb fitting. As someone with a pair of worn again Amals I am interested in what others are up to with Carbs before I get brave enough to spend, and I do like what I have heard of flat slide carbs. So just curious as to whether you considered the Keihin flat slide before going with the Mikuni?

On the battery box I understand that CNW move the front plate back on their bikes so that it actually holds the battery in place – so you will be in good company.

Regards,
Iain

Thought about FCR's too

Mikuni flatslides, Keihin FCR's, Lectron's and the Edelbrock Quicksilver were all on my list to check out.

The FCR's are hard to find listed as single carbs, and I was having trouble getting guidance on sizing, throttle cables, etc. That said, I think a 35mm FCR should be great in a single carb 750 setup. FCR's aren't cheap though, which would have made for an expensive experiment in my case.

The Lectron HV's had some grumbling about quality control lurking on the web and a serious lack of information. The Edelbrock (based on the Lectron) was also too much of a mystery for me at this stage of the game.

It came down to the TM36 because Sudco made it easy. They have experience with upgrading the VM single carb kits to the TM carbs. The TM36 is only $188 - making it a reasonably priced swap for the Mikuni single kit.

I went whole-hog, however, and got the TM36-68 - bringing the carb alone to $357 (OUCH!).

flatslide

How about the clerance to the backbone of the frame and the throttle cables? Did you cut out the brace plate?

Clearance was good, no cutting was required and the cables routed easily.

Although the 36-68 is 1/2" taller than the TM36, the cables are routed to the side of the carb. In actual terms, its clearance looks to be better than a non-pumper TM.

For reference, see the carb on the far left of page 2 at this link: http://sudco.com/catalog/Page%20132-136.pdf

As soon as it stops pouring rain I'll roll the bike out and take some digital pics of the install.

David,

Thanks for the reply, any reason for limiting the FCR commment to the 750? I have an 850 that has had the head planed by PO, not sure of the comp ratio.

Regards
Iain

I was doing a little surfing this evening and after some time back found an excellent general bike shop on line. www.bikebandit.com sent me an email stating they have expanded Overseas.
So I was looking at their Mikuni carbs. I figure that the carb/s listed might just be the "go" for my Commando ~ what do 'you ' reckon ??

http://www.bikebandit.com/PartsBandit/p ... 811785.asp

Fitting of course is the challenge.. but the dimensions look good and the price is very good to me as an Ozzie.. as the excahnge rate has inproved even further in the last few days!
Does anyone have the web addres for Boyer ?
Thanks
Stuart SS

I've bought parts for my Suzuki from bikebandit and have been happy with their service.

One problem you may have with this carb is getting the jetting right. It's probably set up for a two stroke mx bike and likely isn't even close for your Norton. Maye sudco or motorcyclecarbs.com could help with that. Could be quite a struggle to get the jetting sorted out if you have to do it on your own. It's a lot more complex than jetting an amal.

Debby

Stuart,
This is one of those cases were the low initial cost ends up beng excessively high in the end. Nothing in that carb is set up for Norton. The slide, the needle jet, the needle, main, nothing. You'd be far better off buying one from a supplier that can set it up right.
I don't know anything about exchange rates but www.rockypointcycle.com sells the whole conversion including manifold, cable, fuel lines etc, etc for 235.00 US. Prejetted, ready to go.