36mm Mikuni vs. 34mm Mikuni. Is one better than the other? 2

36mm-mikuni-34mm-mikuni-one-better-than-the-other-t1736.html

norbsa48503 said:

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.

Click to expand...

As I am wondering the same thing (i.e. 34 mm vs 36 mm single Mikuni), years after this thread was opened in 2007, I still have the feeling this issue was never really answered. The above answer at least was somehow addressing this, but I would like to see what this "rubber thingy" exactly is ? Is it a sealing rubber ring with a damping function, located between the manifold and the carb ?

Another thing is: I don't give much about the performance as I like best to drive the smaller winding country-roads, but I like to have a strong low-end couple (around 2000-3000rpm) and a stable idle run. So am I then to choose a Mikuni VM34 or the VM36 ?
Any details and pictures of mounting welcome !

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

i have run my 750 commando on both 34 mm and 36mm single VM mikunis i couldnt tell any difference between them in performance but both of them ran out of fuel at sustained high revs there are plenty of kits out there to convert to single carb,also if you dont want to use the rubber mount you can get a manifold that will take a single concentric i used to run a setup like this 30 plus years ago back when i had no money on my 850 mk2a it ran well and was economical but did lose out on top end i now have a 40mm flatslide mikuni fitted on my 750 which is the best all round performance but can be hard to start cheers baz

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

Hi, as per Jim Comstock advise , it is better to fit a single 36mm manifold to a 34mm Miki, it flows better, I have done it with some fiddling ( a bushing to adapt the rubber to the cast manifold ), and I am happy with that ............!

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

I go you one better. I put a TM34 Flatslide Mik on my 75 with the 36mm manifold adapter Jim recommended. I made an aluminum ring bushing to adapt the carb to the manifold.
Driveability is excellent and I don't detect any loss of power. Starting is first or second kick all the time.
Jaydee

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

@Jaydee:
Do you know whether the Mikuni TM34 and VM34 can be mounted using the same manifold ?
I have a question in addition to this:
(start quote) There are two versions of manifolds, one for 30-34mm carburetors and one for the 36-38mm carburetors. The bolt pattern on the intake manifold rubber adapter is 60mm (2.36") center to center for the 30-34mm carburetor manifold and is 70mm (2.75") for the 36-38mm carburetor version. The manifold bolts directly to the Norton heads and cylinder head mounting bolt spacing is 51mm (2") center to center for both cylinders. Rubber carburetor holders are available separately. (end quote)
-> Would I better purchase the 36-38 mm version then ?
-> How did you adapt for a 34 mm carb ? What size of (homemade?) ring would be required then ? Does the ring not cause any sliding of the carb body ?
-> Is the carb supporting rubber required ?
-> Could you post a detailed picture of the carburetor mounting on your Commando ?
I've got a 850 MK 2 roadster...

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

I can't give you a comparison of a 34 vs. 36 but can tell you that I'm satisfied with the single 34mm kit that I bought from CNW this year for my stock '73 850. I've owned and ridden Nortons since 1970 and after that many years I'm pretty well versed on the ins and outs of the Amals. When new they work very well. As they wear their performance does suffer. A quick and simple reconditioning gets them back up to snuff. So why did I switch? I was just curious. I was also contemplating the new premiers at same time but ended up going for the simplicity that a single carb offers. I did lose a bit of top end but hey, this is a 43 year old motorcycle. Low end grunt may be a bit better, but not a night and day difference. I don't own this old bike to do mile after mile of top end runs. I have a modern bike for that. My feeling after about 3500 mile of riding with the 34mm is that the 36mm might be too much carb. It has been an install and forget about it modification.

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

single-carb-750-commando-t23614-15.html?hilit=manifold%20bushing
Hi Red Rooster here are some more info about the manifold by jim Comstock.........hope this help !

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

I'm with eskasteve on this one .... have had the Mikuni 34 mm on for many years ( 16 ) and the way I ride my Norton , I have not even given a thought to the loss of top end .... i have other much more capable bikes for speed ... it's a love affair with the Commando and I try and treat with respect ... it has lots of get up and go and surpasses modern traffic no problem , but I don't flog it often ..... most importantly for me , I know when I go to shed it will always start first kick ( second really , first is with no key on just gas ) and run reliably all day every day , what's not to like ... with no fiddling with carbs ... i can spend my time and money on other areas of the bike like bling , ha! ha!
Craig

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

I ran a 36mm Mik and it ran sweet. But it definitely struggled to gasp enough air above 5000rpm.

Given how it is pretty much accepted now that a single carb (of these sizes) impedes flow on high throttle openings, and how a 36 runs so sweet anyway, I'd have thought a 36 was thus a better choice over a 34.

I'm now running twin 35 FCRs tho, and cannot think of anything that would ever persuade me to go back to a single carb.

Apart from, of course, buying a single cylinder bike...!

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

If you have decided to switch from dual carbs to a single, then the 34mm Mikuni is the carb for you, the 36 is too big, it is more difficult to install, though it will fit, but it puts such a bend in the throttle cable you have to wonder if it is really safe, and it will not give you appreciably better performance. Part of your decision making (to go to a single carb) was coming to the conclusion that most 40 + year old motorcycles can't safely do the ton any more, not that you'd want to. The majority of Commandos on the road today have OE ISOs, OE shocks, OE fork oil and OE wiring harnesses; most have OE brake linings/pads; don't you have enough to worry about?. The 34mm conversion will give your Commando the ability to get a speeding ticket anywhere in the US and has a readily available set of reasonably priced spares.

The beauty of the single carb (no matter which make or size) is that it gives you much better low end grunt, where you need it, and a good boost well into the mid range, along with better starting and decent fuel mileage, although not quiet as well as a sorted dual carb set-up.

There are several single carburetor makes that can get you there, but the Mikuni, by far, is the least expensive to maintain, and the least complicated to strip.

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

I've had twin cylinder British bike with both twin and single carbs. I have never noticed a difference in performance in changing from one to the other. It doesn't seem to matter what carb configuration you use as long as you get it tuned right. One thing which is very good about Mikunis is the range of needle tapers and jets which are available for them. You will notice that on almost every Japanese bike of the 70s, there were different taper needles used on most of the various models. In comparison Amal carbs are a bit crude. ( I use Amal Mk2s with Mikuni needles). One thing which is important to consider when tuning carbs is the amount of restriction in the exhaust system. An open exhaust will sometimes make the carburation lean off. If you fit megaphone exhausts in place of mufflers on a well-tuned bike, you are likely to burn a piston if you don't richen the jetting.