36mm Mikuni vs. 34mm Mikuni. Is one better than the other?

I needed to order a new rubber flnge/adapter that fits between the 2 into 1 manifold and the carb on my MKIII.

I always assumed it was a 34mm that was on there so of course without looking, I ordered the part for a 34mm.

After measuring the dimensions of my old air filter so I could order a new K&N replacement something wasn't adding up.

I soon discovered I have a 36mm carb on there and soon ordered the proper rubber fitting and a new throttle cable just in case.

This prompted me to start this thread about 34mm vs. 36mm. I have heard the increased velocity of the air/fuel going into the head from a 34mm carb is better than a 36mm.

Thoughts or observations?

Well a 34 is an easier fit considering the air cleaner sizes and all. But the 36's fit up, just. Most times a smaller carb will give better grunt down low off the line and a bigger carb will breath better at the top. It's the type of manifold that comes into play more than anything if you are talking performance. Many of the castings are not very impressive.
If your going single carb and and your worried about these small differences your missing the point of the conversion from the Amals. Most people who do the single carb thing just just want a set it and forget it system. Many of these folks are the ones who cant figure why their bike wont start after a small backfire. Look down dude your carbs not on that rubber thingy. You see the heaver the system the more likely it is that it will fall off the rubber adapter sooner or later. You may want to look into a rubber band to help hold that huge thing up.
So please note that a well tuned set of Amals will blow you off the road man. In old posts I have written some tuning info for Mikuni fixes and tuning, very few have the salt to pick up the gauntlet and make them run the way they can because if they were into going fast they would get a nice set of Mark two's. Yea I know not what you wanted to hear. Sorry.

Yup, if you want that bike to run good a pair of Amals is the way to go!

Of course, you'd have to learn how to tune them...

Debby

debby said:

Yup, if you want that bike to run good a pair of Amals is the way to go!

Of course, you'd have to learn how to tune them...

Debby

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Isn't that part of the fun ? A well set-up Commando with twin Concentrics and reverse-cones makes an incomparable sound.

I must confess to running mine with two cables and a twin-pull quick action Tomasselli twist grip which might help but I really don't know where the horror stories come from about the carbs not staying in tune.

norbsa48503 said:

If your going single carb and and your worried about these small differences your missing the point of the conversion from the Amals. .

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I'm not worried about a thing.

The bike came with the 36 when I bought it and I always thought it had a 34mm.

I was just simply curious if one was better or more preferred than the other, that's all.

I don't plan on changing anything for the time being, so I'm leaving it as is.

norbsa48503 said:

Many of these folks are the ones who cant figure why their bike wont start after a small backfire. Look down dude your carbs not on that rubber thingy. You see the heaver the system the more likely it is that it will fall off the rubber adapter sooner or later. You may want to look into a rubber band to help hold that huge thing up.
So please note that a well tuned set of Amals will blow you off the road man.

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I have a zip tie holding the throttle cable to the frame.

I do want to go back to a twin carb set up someday, but there is other things I have to deal with first.

Re: 36mm Mikuni vs. 34mm Mikuni. Is one better than the othe

If you go the twin Amal route at some point, make sure you get them sleeved. Amal slides are well-known to wear quickly resulting in air getting past them and difficulty in getting a good idle. My 74 Commando came with twin Amals and I could never get the bike to idle properly. Turned out one of them had a pretty badly scored slide. I switched to a 36 mm Mikuni and the bike idles and runs perfectly now. Mikuni carbs are very well made, are more "tuneable" and it is far easier to keep one carb in tune compared to two. That is why it is such a popular upgrade. However, as several others have mentioned, a single Mikuni won't touch the twin Amals in terms of performance. I would like to go back to the Amals at some point but when I do, I will make sure that the slides are sleeved.

Re: 36mm Mikuni vs. 34mm Mikuni. Is one better than the othe

tpeever said:

Mikuni carbs are very well made, are more "tuneable" and it is far easier to keep one carb in tune compared to two. That is why it is such a popular upgrade. However, as several others have mentioned, a single Mikuni won't touch the twin Amals in terms of performance. I would like to go back to the Amals at some point but when I do, I will make sure that the slides are sleeved.

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What about twin Mikuni's?

If your going there prepare for some work. They are too wide to sit straight side by side so you need some curved adapters. Mark two's are best and just as good. A little filing of the unused idle screw boss. and they go right on.

norbsa48503 said:

If your going there prepare for some work. They are too wide to sit straight side by side so you need some curved adapters. Mark two's are best and just as good. A little filing of the unused idle screw boss. and they go right on.

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Future food for thought as there is a boatload of stuff to do before carbs, like exaust and an engine rebuild.

I seriously doubt I'll switch from the single Mikuni to dual carbs, but if I ever did I might consider the dual Keihin set up from CNW. It looks pretty nice, but damn are they ever expensive.

http://www.coloradonortonworks.com/cata ... sp#carbkit

34mm vs 36mm

I have a 36 mm mikuni which had a peculiarity off hanging on when shutting off it would hover at around 2 thousand rpm before dropping back to tick over, after checking for air leaks and the like I resovled it by fitting the 38mm(normally used for racing)carb slide spring, it is actually 5mm shorter but is made of a heavier grade of material. The previous owner had the engine modified by Norman White and he had not used the bike due to illness so did not encounter the problem. even with the heavy slide I suspect that all that suck from the motor was causing the slide to hang..... :!: :!:the twist grip is still light and it really motors and sounds excellent through the K&N, I agree with a previous post that some sort of elasticated mounting would be an advantage...but have not quite figured out a work around yet

bloody hell Coco that Colorado Norton carb set up looks a serious bit of kit
a visit to the Bank Manager would be in order for one of those :shock:

Yup, if you want that bike to run good a pair of Amals is the way to go!

Of course, you'd have to learn how to tune them...


You wanna try sortin out a badly running Trident :lol: ,,,,3 bloody Amals to fix. :cry:
Took me months.


millard

one carb only one thing to go wrong only one thing to fix

not-ron said:

bloody hell Coco that Colorado Norton carb set up looks a serious bit of kit
a visit to the Bank Manager would be in order for one of those :shock:

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No kidding. I don't think I'll ever go that route, but it is nice to think about anyway.