Tips For Fitting The 34mm Mikuni

Next week I'll be switching out my slightly worse for wear Amals for a Mikuni, I've been reading and researching about this for a few weeks but before I start the job I wanted ton ask if any of you have tips to make the install easier/better? Any advice would be appreciated, up to and including tuning the carb once it's on.

As I recall straight forward ... tune carb close to the old ones ... watch out for air leaks ... use blue loctite on carb adapter mounting bolts ... careful routing of cable ...
Craig

there IS a real danger inherent in the single Mikuni's manifold design in the application because of the risk that the two threaded bolts that are inside the manifold to secure to the head can, and have, come unthreaded with a bolt being sucked in the combustion chamber with bad consequence

all you can do is remember to loc tite those inside bolts, after running a single Mikuni for some 20 years I would make it a practice to slip the carb off the manifold occasionally and check the tightness of those bolts with an allen, and especially so after the first couple of heat up and cool down cycles

I drilled the two center manifold bolts for stainless safety wire AND I'd use blue locktite. Last fall I had a bolt come loose and I ended up bending a valve and pushrod. Regarding the carb ,since you are using a single carb you can usually install a larger main jet. Naturally depends on exhaust and altitude but I'm running a 230 with single head pipes (no crossover) and Emgo peashooters on a Combat 750. If I was running the bike really hard I'd probably be at a 250 main. Don't be discouraged if your initial set up on the carb is not right. Mikuni's take a bit of trial and error......Skip

Mikuni's are great carb - despite the amal blah blah blah stuff you'll always here from the carb police- i have them on both my nortons and have replaced the dellortos on my laverdas with them too

have you read the vistory library's tuning mikuni carbs for british twins manual? http://victorylibrary.com/MIK-BT.htm

if not, and your unfamiliar with mikuni carbs, you may get frustrated as the degree they are tunable is quite extensive- and despite all the internet advice you'll receive ever bike is slightly different and these suggestions may not be quite correct for your bike. That being said a general search of this site will pull up a few recommended jetting setups to get you started - depending upon if you have a 750 or 850. tuning carbs is fun, but requires some patience if you really want to get them correct

Branch said:

Next week I'll be switching out my slightly worse for wear Amals for a Mikuni, I've been reading and researching about this for a few weeks but before I start the job I wanted ton ask if any of you have tips to make the install easier/better? Any advice would be appreciated, up to and including tuning the carb once it's on.

Click to expand...

If you haven't bought it yet RockPoint Cycle is a good source of Mikuni's pre-jetted for Commando's.
http://www.rockypointcycle.com/c-norton ... _kits.html
A nice excessory is the cable adapter that allows you to use the Amal bar mounted lever for choking instead of having to hand down at carb.
http://www.rockypointcycle.com/p-norton ... -2900.html
The cable for it
http://www.rockypointcycle.com/p-norton ... -2938.html
A filter that fits Commando with the Mikuni
http://www.rockypointcycle.com/p-norton ... -2590.html

There are a number of other bits and pieces needed and listed on RockyPoint's site.

I had one and it worked really well. I found it worked better if I had the carb tilted a bit to one side so that the cable did not have to make quite as sudden a bend coming out of the top of the carburetor. Before I did that the carburetor was sometimes a bit slow to close.

Also I found that I preferred to set the idle air mixture by adjusting it so that it would give the best pick up from closed throttle rather than adjusting it for the best idling speed. The pick up from closed throttle is very important for smooth riding but the idling doesn't matter much as long as the engine doesn't stall. I found the air screw made a lot more difference to this low speed pick up than with twin Amal carburetors. Jim Comstock explained the reason for this difference when there was a discussion about the balance tube between the two manifolds.

In the end though I switched to a single 38 mm Amal 1038 Concentric just to be different. I got a bit more top end from the bigger carburetor and also it looks better.

Nigel

Thanks to everyone for these replies, they've been very helpful! I'll check back in with either tales of success or more requests for advice in a few days

Just wanted to say thanks for all the advice above, the Mikuni is now installed and somewhat amazingly it started first kick. I spent some time trying to tune it to get the idle correct, it seems to be about right now but I still have some reading to do to see if I'm running lean or rich. Carburettor fiddling seems to be a dark art.