Mikuni Carbs ?

What is the best Mikuni carb that I should purchase for my 1972 Norton Commando 750cc?

Should I do a 2 into 1 carb set up? Or should I purchase 2 carbs?

As of now I have the original Amal carbs, Please let me know what you think.

i have the single 34 mm on my norton and it is really trouble free. the best thing is that parts can be gotten at about any bike shop. sleeved amals do ok but this is very nice for general performance and ease of adjustment.

Best?
RS34

The 2 into 1 single carb conversion is much easier to keep in tune than twin Amals. I use a VM36 Mikuni on my 850 and have better off-idle pick-up, better starting, more stable idle, better low and mid range throttle and lighter throttle action. On my single 36mm carb I cannot detect any significant power loss at the top end either.

I have dual 34mm VM's on my 850 cafe. Works great with a modified motor, but you have to use splayed manifolds which do not allow use of a stock airbox. I am using oval - taperedl K&N filters that just clear the frame loops.

The single Mikuni kits I have seen have a quite sharp bend to the throttle cable as it exits the carburetor.

My biggest complaint with Mikuni's is they tend to varnish up rapidly when not used often and cause sticking of the floats and gas flowing from the overflow tube. Of course the obvious answer is to run the bike more!

However, if total performance is not my ultimate goal, I still like the simplicity of sleeved Amals.

Well i just went the other way as i found the single Mikuni to be very frustrating.

The Mik is great when the bike is going, idles nicely and seems to have plenty of power, but starting was a complete b&*^%h. Without the option of an adjustable choke or ticklers to flood the motor you are left with the one-position-only cold start device. I know that some have not found this to be a problem, but for me a year round rider in a variable climate i had to have more reliable starts.

I now have my new Amals fitted and half way tuned and starting is already so much easier, both on me and the somewhat fragile kickstart mechanism.

There are a few ways to tweak the starter circuit included, but the obvious is to enlarge the starter bushing a bit, or blank off one of the siphon break holes above the fuel level.
You can also increase the vacuum at the starter by restricting the starter air entry in the air-horn with a piece of tape etc. This will enrich the starter circuit, but also reduce the idle speed with the starter engaged so not suitable for colder weather.
Most often the starter function isn't the only problem - try raising the float .020" and/or adding 2.5 to the existing pilot jet size.
Also important: if the spark timing is off or pilot circuit (both idle mix screw and jet size) isn't fairly close, the idle speed will too low. The higher slide position required to keep a stable idle speed partially disables the starter by allowing too much air to bypass the starter, reducing vacuum at the starter jet.
http://victorylibrary.com/CONC.htm

Re:

scim77 said:

The 2 into 1 single carb conversion is much easier to keep in tune than twin Amals. I use a VM36 Mikuni on my 850 and have better off-idle pick-up, better starting, more stable idle, better low and mid range throttle and lighter throttle action. On my single 36mm carb I cannot detect any significant power loss at the top end either.

Click to expand...

HI I just bought a VM36 but the seller cannot supply a filter as they do not know what will fit what filter did you use?

Cheers Paul

On the subject of air filters for VM's I got a VM34 on my 850 and I fitted a KN "pancake" filter, thats the one that has the filter element about an inch wide. Space is a bit limited between the frame junction and the carb so that is a factor. When I reconned the head, I found I did not get the maximum revs and top speed I expected. The suspicion was on the filter being too small, simply not flowing enough. The motor was hesitating at 5,500RPM. Removing the filter performance jumped, indicating there was a restriction. I modified the filter back plate by numerous perforations and added a layer of similar filter material over it. In effect the carb now gets air directly in front of the mouth as well as coming in from the sides. The performance regained at the top end neccesitated upping the needle one notch. So far the 240 main jet seems good. I understand KN make a version now with filter element all round and I recommend getting the largest one you can fit onto your Commando.

Mick

Re:

Ron L said:

I have dual 34mm VM's on my 850 cafe. Works great with a modified motor, but you have to use splayed manifolds which do not allow use of a stock airbox. I am using oval - taperedl K&N filters that just clear the frame loops.

The single Mikuni kits I have seen have a quite sharp bend to the throttle cable as it exits the carburetor.

My biggest complaint with Mikuni's is they tend to varnish up rapidly when not used often and cause sticking of the floats and gas flowing from the overflow tube. Of course the obvious answer is to run the bike more!

However, if total performance is not my ultimate goal, I still like the simplicity of sleeved Amals.

Click to expand...

Hi Ron L.
I am thinking of fitting dual VM34 Mikunis on my 850.. would you please have any info on the specs for what jet sizes and slide combination that would work, as a basic starting out point?

Thanks,

Brewer