single carb conversion

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I run a mikuni on my p11 which is 750, that is what it came with, it ran really really bad when I bought it as they built it as a show bike I think so didn't set anything up. I went to a firm called Motocarb, a guy called Steve Doran runs it and gave me the following. Slide 2.5 needle 6DH3. Main 230 Needle 159 p-4. Pilot 32.5. Main air jet .2.
I have a great set up on this bike, I know it is 750 but should give you a good base to start from. keep it pinned Neil
 
I put a Mikuni TM34 on my Mk3 and I love it. The flatslide carb is noticeably stronger than the VM models from my experience. I put a 38mm manifold adapter on for better flow based on a recommendation by Commoz somewhere here, months (years?) ago. I don't believe I lost any power from the Amals.

Jaydee
 
jaydee75 said:
I put a Mikuni TM34 on my Mk3 and I love it. The flatslide carb is noticeably stronger than the VM models from my experience. I put a 38mm manifold adapter on for better flow based on a recommendation by Commoz somewhere here, months (years?) ago. I don't believe I lost any power from the Amals.

Jaydee
Click to expand...

+1 I also have a TM34 on my stock MKIII and it performs very well. Calculating air flow for the 850 shows carb size range of 34mm to 36mm (actually 35mm).
 
does the tm carb have the tendency to stick like the vm
most of the kits come set slightly rich
 
All the 34mm single carbs I've tried run out of fuel and start surging if held wide open for too long. Takes a lot of drilling of the fuel passages to avoid that. Usually not a problem unless you're passing a long truck and looking at oncoming traffic. If the carb is big enough say 38 or 40mm then it will flow enough fuel through the bowl and not run dry. But its a problem fitting big single carbs under the Commando backbone frame with its gusset.
 
jseng1 said:
All the 34mm single carbs I've tried run out of fuel and start surging if held wide open for too long. Takes a lot of drilling of the fuel passages to avoid that. Usually not a problem unless you're passing a long truck and looking at oncoming traffic. If the carb is big enough say 38 or 40mm then it will flow enough fuel through the bowl and not run dry. But its a problem fitting big single carbs under the Commando backbone frame with its gusset.
Click to expand...
That's exactly the problem I had with the single VM,S that I tried and a single CV if you hold it flat out it just dies and seems to take an age to cut back in when I went to a tm40 it changed all that better bottom end way better mid range and will pull way past the redline in the lower gears top speed is around 110mph but its a bit harder to start and very easy to flood with pumper if your not careful cheers baz
 
This thread has me wondering about the pair of TM-36 flatslides that are tucked away up in my attic, which were off a race Ducati Pantah 750 engine that was badly blown up at Mosport several years ago. Should I be considering adapting one of these (jetting and set up aside) for the '72 750 Roadster I'm starting to completely rebuild? I've found nothing to indicate that it is a Combat. I'm just working on all the stuff from the steering head forward this winter, but can't help thinking ahead a little. BTW - this bike's proper model designation is a 750 Mk IV - correct?
Bill
 
baz said:
jseng1 said:
All the 34mm single carbs I've tried run out of fuel and start surging if held wide open for too long. Takes a lot of drilling of the fuel passages to avoid that. Usually not a problem unless you're passing a long truck and looking at oncoming traffic. If the carb is big enough say 38 or 40mm then it will flow enough fuel through the bowl and not run dry. But its a problem fitting big single carbs under the Commando backbone frame with its gusset.
Click to expand...
That's exactly the problem I had with the single VM,S that I tried and a single CV if you hold it flat out it just dies and seems to take an age to cut back in when I went to a tm40 it changed all that better bottom end way better mid range and will pull way past the redline in the lower gears top speed is around 110mph but its a bit harder to start and very easy to flood with pumper if your not careful cheers baz
Click to expand...

I had 30mm VMs on a Vincent, this is a popular fitment. But I also found that they could supply fuel fast enough to keep up with the engines needs at WOT.

I adjusted the float height which cured the symptoms. Of course, this didn't solve the root cause, it simply meant I was using the float bowl contents to supply fuel at WOT. But at least this allowed quite a prolonged use of WOT that I was unlikely to ever exceed.

As purchased, I suffered fuel starvation quite quickly when using WOT. I can only assume that this shows that most customers do not use WOT at all, despite what may be boasted in bars!

Bottom line for me is that VMs do seem to need a close look regarding their ability to flow enough fuel when fitted to our old bikes. My guess is that this is because a typical Japanese bike would use a far larger carb relative to the engine size than we use on our bikes. For example, a 36mm VM is a popular fitment on a 500cc single cylinder XT, whereas my Vin used a 30mm carb for each 500cc cylinder and a 34mm VM is a popular fitment on an 850cc Commando. Maybe we are just expecting more from the design than the designers intended.
 
baz said:
jseng1 said:
All the 34mm single carbs I've tried run out of fuel and start surging if held wide open for too long. Takes a lot of drilling of the fuel passages to avoid that. Usually not a problem unless you're passing a long truck and looking at oncoming traffic. If the carb is big enough say 38 or 40mm then it will flow enough fuel through the bowl and not run dry. But its a problem fitting big single carbs under the Commando backbone frame with its gusset.
Click to expand...
That's exactly the problem I had with the single VM,S that I tried and a single CV if you hold it flat out it just dies and seems to take an age to cut back in when I went to a tm40 it changed all that better bottom end way better mid range and will pull way past the redline in the lower gears top speed is around 110mph but its a bit harder to start and very easy to flood with pumper if your not careful cheers baz
Click to expand...

You guys lost me here completely :? Lets get this straight if you really want to go flat out that much you should not run any type of single carb at all (have you ever seen a single carb on a racer). I have done countless miles on a single Mikuni VM34 on my Commado 850 (which I like to ride pretty sporty) and have been passing countless trucks at oncoming traffic and never ever experienced fuel surging problems by doing so :!: And yes I am aware of the top speed limitation of a single carb set up but hey this is a '74 Norton Commando not a modern Ducati :wink:
 
nortonspeed said:
baz said:
jseng1 said:
All the 34mm single carbs I've tried run out of fuel and start surging if held wide open for too long. Takes a lot of drilling of the fuel passages to avoid that. Usually not a problem unless you're passing a long truck and looking at oncoming traffic. If the carb is big enough say 38 or 40mm then it will flow enough fuel through the bowl and not run dry. But its a problem fitting big single carbs under the Commando backbone frame with its gusset.
Click to expand...
That's exactly the problem I had with the single VM,S that I tried and a single CV if you hold it flat out it just dies and seems to take an age to cut back in when I went to a tm40 it changed all that better bottom end way better mid range and will pull way past the redline in the lower gears top speed is around 110mph but its a bit harder to start and very easy to flood with pumper if your not careful cheers baz
Click to expand...

You guys lost me here completely :? Lets get this straight if you really want to go flat out that much you should not run any type of single carb at all (have you ever seen a single carb on a racer). I have done countless miles on a single Mikuni VM34 on my Commado 850 (which I like to ride pretty sporty) and have been passing countless trucks at oncoming traffic and never ever experienced fuel surging problems by doing so :!: And yes I am aware of the top speed limitation of a single carb set up but hey this is a '74 Norton Commando not a modern Ducati :wink:
Click to expand...
Sorry I lost you !!let me explain If I just wanted to go fast I would fit twin carbs but what I wanted was better mid range better mpg less maintainence etc and that's what I have ,but the bike happens to go faster than I expected cheers baz
 
baz said:
what I wanted was better mid range better mpg less maintainence etc
Click to expand...

Bingo :!: Thats exactly what I got with my single Mikuni VM34 :wink:
 
I got my single carb conversion kit from jsmotorsports and as mentioned earlier in this thread, the kit came with everything needed for a bolt on installation and was very reasonably priced. That along with great customer service made it the right choice for me. Cj
 
I would say the same performance results for my single VM34 too .... better midrange, better MPG and fit and forget ease of use :D
Craig
 
my 2 CENTS...I have used 34 MM mikuni VM carbs for years on Nortons and Triumphs. Here is an excellent set up:

2.5 slide
#25 pilot jet
series 159 P-6 needle jet
6F9 needle clip in middle position
230? 240? main jet

Any fuel starvation problem can be solved by replacing the float needle / seat combo with the biggest one they have...there are about 5 sizes. I always do this. You will be happy. VM Mikunis are cheap and work very well. Best bang for the buck.

What I like a whole lot is the start up procedure when cold. Pull on the choke, then turn in the throttle screw about one full turn (varies with each bike). Kick it over and now it is on fast idle and keeps running. while it is warming up you can be doing small tasks instead of blipping the throttle for 2 04 3 minutes.
 
Hello,

Where can i buy a single carb manifold on which i can fit 34 or 36mm carb?

Gilles
 
nortonspeed said:
baz said:
what I wanted was better mid range better mpg less maintainence etc
Click to expand...

Bingo :!: Thats exactly what I got with my single Mikuni VM34 :wink:
Click to expand...
Ok if you have to resort to using a few lines from my quote instead of the whole quote them that's me out !!!
 
gillou said:
Hello,

Where can i buy a single carb manifold on which i can fit 34 or 36mm carb?

Gilles
Click to expand...
I think rgms will have them
 
Since I´m more interested in low and midrange power in my 850, I wonder if there´s any specific numbers on the length of the intake? I know that it effects the torque, but has anyone out there got a number? So I don´t have to begin with a half meter pipe and then cut it down cm by cm.... :wink:
 
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