Mikuni Tuning Notes

P

PMcQ

Joined
Jul 26, 2012
Messages
8
Hi all,

I’m running a 1974 Norton Commando Mk2A with the following setup:

- PW3 cam
- Open peashooter exhausts
- K&N air filter
- Pazon Sure-Fire ignition
- Genuine Mikuni VM36 carb

Current jetting is:

- Main jet: 290
- Pilot jet: 32.5
- Needle: 6DH3 (clip one notch above centre)
- Needle jet: 159 P0
- Air jet: 2

The plugs are coming up black, so clearly running rich. I’m considering moving to:

- Main jet: 240–250
- Pilot jet: 45
- Needle: 6DH4 (clip in centre position as baseline)
- Needle jet: 159 P2
- Air jet: 2

Location is roughly 120 m above sea level (≈400 ft).

Appreciate any views before I start changing things.

Thanks.
 
PMcQ said:
Hi all,

I’m running a 1974 Norton Commando Mk2A with the following setup:

- PW3 cam
- Open peashooter exhausts
- K&N air filter
- Pazon Sure-Fire ignition
- Genuine Mikuni VM36 carb

Current jetting is:

- Main jet: 290
- Pilot jet: 32.5
- Needle: 6DH3 (clip one notch above centre)
- Needle jet: 159 P0
- Air jet: 2

The plugs are coming up black, so clearly running rich. I’m considering moving to:

- Main jet: 240–250
- Pilot jet: 45
- Needle: 6DH4 (clip in centre position as baseline)
- Needle jet: 159 P2
- Air jet: 2

Location is roughly 120 m above sea level (≈400 ft).

Appreciate any views before I start changing things.

Thanks.
Click to expand...
Welcome! 14 year member, first post.

"The plugs are coming up black, so clearly running rich."
Or burning oil.

How long did it run well?
Other symptoms?
Fuel consumption?
 
concours said:
Welcome! 14 year member, first post.

"The plugs are coming up black, so clearly running rich."
Or burning oil.

How long did it run well?
Other symptoms?
Fuel consumption?
Click to expand...
Good observation, I warm up slowly:-). So the motor is freshly rebuilt by Norman white, one of his last before retiring, its not burning any oil. Fuel consumption is i wouod estimate, on the high side.

I am certain it is fueling but finding the baseline is critical as you know
 
PMcQ said:
Good observation, I warm up slowly:-). So the motor is freshly rebuilt by Norman white, one of his last before retiring, its not burning any oil. Fuel consumption is i wouod estimate, on the high side.

I am certain it is fueling but finding the baseline is critical as you know
Click to expand...
WOT plug chop?
Or dawdling about on the needle?
Compression test reading?
 
What fuel?

Where on planet earth are you?

What symptom are you addressing by proposing increasing the pilot jet size?
 
Last edited:
If you are not test riding it and sitting in your garage trying to dial it in, the plugs can show black or very dark. A new engine might show dark as well until the engine is fully broken in. The PW3 probably has some unique characteristics, and I seriously doubt they were designed for use with a single carburetor. Peter Williams was trying to make as much power as he could and that is not going to happen with a single 36mm carburetor unless using forced induction.

I can't help with tuning a single Mikuni, but there are a lot of them are in use on Nortons and working well enough. I always ran 2.

Only note I have is the jetting that came in the twin Mikuni kits for Norton being sold back in the 1980's worked fine with a SS cam in a 750 engine. My plugs however only looked good (mousey tan) when I ran the engine over 4K RPM. Otherwise they were on the dark side.

If you got the single Mikuni kit from MAP Cycle talk to their support people. They might know something that can help.
 
concours said:
What fuel?

Where on planet earth are you?

What symptom are you addressing by increasing the pilot jet si
Click to expand...

im running it on RON 98 Total Exellium or similar, im in France.

As originally asked, im looking for a baseline setting ti start from and then I can work from there
 
Schwany said:
If you are not test riding it and sitting in your garage trying to dial it in, the plugs can show black or very dark. A new engine might show dark as well until the engine is fully broken in. The PW3 probably has some unique characteristics, and I seriously doubt they were designed for use with a single carburetor. Peter Williams was trying to make as much power as he could and that is not going to happen with a single 36mm carburetor unless using forced induction.

I can't help with tuning a single Mikuni, but there are a lot of them are in use on Nortons and working well enough. I always ran 2.

Only note I have is the jetting that came in the twin Mikuni kits for Norton being sold back in the 1980's worked fine with a SS cam in a 750 engine. My plugs however only looked good (mousey tan) when I ran the engine over 4K RPM. Otherwise they were on the dark side.

If you got the single Mikuni kit from MAP Cycle talk to their support people. They might know something that can help.
Click to expand...
Im doing both at the moment and I do agree PW probably worked on the principle of twin carbs, I do have the original Amals and I may look at refitting them
 
PMcQ said:
im running it on RON 98 Total Exellium or similar, im in France.

As originally asked, im looking for a baseline setting ti start from and then I can work from there
Click to expand...
Heard.

"Appreciate any views before I start changing things."
 

Super-Tuning Mikuni VM Carburetors and Intake Systems for British Motorcycles

Mikuni Tuning Book: how to install and adjust 26-38mm VM carburetors on classic British machines such as Triumph Bonneville, BSA Lightning Rocket, Norton Commando
www.victorylibrary.com

No disrespect but I sincerely hope you are a real person and not a BOT.
Because you are going the wrong direction.
The link above will get you most of the info you need for tuning a Mikuni for a Brit.
Start with the pilot and work your way up. You don't mention slide cutaway.
 
MichaelB said:

Super-Tuning Mikuni VM Carburetors and Intake Systems for British Motorcycles

Mikuni Tuning Book: how to install and adjust 26-38mm VM carburetors on classic British machines such as Triumph Bonneville, BSA Lightning Rocket, Norton Commando
www.victorylibrary.com

No disrespect but I sincerely hope you are a real person and not a BOT.
Because you are going the wrong direction.
The link above will get you most of the info you need for tuning a Mikuni for a Brit.
Start with the pilot and work your way up. You don't mention slide cutaway.
Click to expand...
I can assure you I am a real person simply looking for community assistance, and many thanks.
 
MichaelB said:

Super-Tuning Mikuni VM Carburetors and Intake Systems for British Motorcycles

Mikuni Tuning Book: how to install and adjust 26-38mm VM carburetors on classic British machines such as Triumph Bonneville, BSA Lightning Rocket, Norton Commando
www.victorylibrary.com

No disrespect but I sincerely hope you are a real person and not a BOT.
Because you are going the wrong direction.
The link above will get you most of the info you need for tuning a Mikuni for a Brit.
Start with the pilot and work your way up. You don't mention slide cutaway.
Click to expand...
In all respect, what on earth would a bot have to gain from a conversation such as this??

To close this, I have managed to get the base line i was originally looking for from Andover Norton and I wish on hindsight I had gone there first, this has been an ...."ordeal " that i probably would have rather avoided. As said somewhere above, 1st Post after 14 years and probably my last.
 
PMcQ said:
In all respect, what on earth would a bot have to gain from a conversation such as this??

To close this, I have managed to get the base line i was originally looking for from Andover Norton and I wish on hindsight I had gone there first, this has been an ...."ordeal " that i probably would have rather avoided. As said somewhere above, 1st Post after 14 years and probably my last.
Click to expand...
My thumbs up was because I understand what you are saying, not because you are leaving. Hell, I'm probably part of the problem. That's what my wife tells me every other day.
 
PMcQ said:
In all respect, what on earth would a bot have to gain from a conversation such as this??

To close this, I have managed to get the base line i was originally looking for from Andover Norton and I wish on hindsight I had gone there first, this has been an ...."ordeal " that i probably would have rather avoided. As said somewhere above, 1st Post after 14 years and probably my last.
Click to expand...

Soooo, I politely make a comment, and then go on and give advice.
And you take offense at it. Very thin skinned for Norton rider.
If you have doubt about the character and make up of this web site, do a search.
You can start here.....https://www.accessnorton.com/NortonCommando/ashmans-cnw-starter.41548/
 

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