Could someone post a photo of a spark plug with color for ideal mixture strength

I a tally have one! That could help me see how the two cylinders vary. I will install the new choke plunger before doing anything more.
Might be 2 weeks to arrive.
 
DennisMo said:
Many thanks.
With my Mikuni I am running to rich at low rpm and have sooty plugs.
If I lean out the low speed circuit to get rid of the sootiness, I get lots of exhaust pops on
overrun and when bike first started from cold.
The idle air screw is about 1 1/4 turns out from its seat to stop the popping.
So I thin this tells me it is time to go for a larger size idle jet
I am going to change the idle jet to next size up before reporting back
Thanks again
Dennis
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Make sure the idle air jet is no bigger than a #1.1. If your kit came from Sudco (now defunct) they had #2 in them which would soot the plugs at low RPMs and throttle openings.
 
New plugs into a warmed up engine, Riden abut 3 miles, then 4000 RPM held
steady for about 1mile, Plug chop/engine killed with switch, and coast into garage. fuel93 pump gas with 10% ethanol. This is from my CHR MK3, a very fast Commando, it is tuned to a T.
 

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yes, Carl H If you refer my previous diagrams you are showing discoloration at the bend of the ground strap showing correct timing, first two threads look to be discolored showing correct plug heat range and carbon ring on base of plug showing mixture is near optimal.
 
OK, , I recently saw all the type of info on a plug tip that affects tuning, but I can tell how a bike is running pretty much how it runs for the brief time I warm up a bike and then how it runs during the first few miles. A very experienced Pro racer always said and wondered how I got my old Amals to respond like a 'Swiss watch" . Jerry Wood #3 has owned, ridden and raced my work and thousands of bikes. And yet he loved my old racer, even with thousands of racing miles on them, They were capable of winning against all comers, including F 750 or Super Vintage bikes. My Nortons are famous for the bikes their results and the Great men who rode them at our home tracks in New Hampshire.. That is the proof in the pudding. And I am very happy that I did it with my Commandos with the help and racing abilities of many great racers and tuners, I call my friends.

.
 
In talking about tuning, there are things which must remain fixed when adjusting carburetors - the exhaust system, the compression ratio, fuel octane rating and ignition advance. Plug colour is not important. What IS important,is the narrow black ring on the porcelain should be there - it is right down inside the plug just before the porcelain meets the metal. It indicates if the main jet is too small. Lower heat range spark plugs burn carbon off quicker. It is normal to have main jets which are slightly too rich. Then most of the metering is done by the needle and needle jet. A slow taper needle jet requires more throttle control, but a slower taper needle used with more control can give better performance. If the needle is progressively lowered, a miss should occur. If you raise the needle one notch it should be within adjustment range. If you have two carbs, the jetting in each should be identical. If the motor misses while the bike is being used - stop and fix it. None of this stuff is big deal, you should be able to do it in your sleep, just think logically about the fuel metering.
 
velo54 said:
more relevant to most people than worrying about mixture when flat out
Click to expand...

You really have to get mixture correct at full throttle, unless you never ever use more than half throttle.

If you putt around for a while, then wander home and take the plugs out to look at them, you’re checking the mixture during the last few seconds of idling, on top of a bit of needle jet and a bit of cutaway and a bit of needle clip position.

Oh- I forgot it’s a Mikuni! A bit of needle taper and probably air correction too then.
 
According to the Mikuni VM tuning manual the air jet begins to influence mixture from half throttle up, with maximum effect at full throttle. Very similar to the main jet. No influence below half throttle. I have been slightly concerned about the size of the air jet for a long time, after reading info on this forum. There is not a lot of info about it. After reading the tuning manual last night i no longer have to worry. Easier to change the main jet to influence mixture at full throttle, and forget about having a 2.0 air jet. That is only if i dared to use more than half throttle! Graham
 
I've only done a few flat out plug chops and that was many years ago due to the fact it is dangerous and illegal to be doing over 110 MPH on the street. But for a stock street bike a main jet is a known given, what ever Norton OEM used. I've seen so many people think a main jet change is going to fix a rich mixture at all or any RPM. And they don't do a plug chop correctly or have the carbs even close enough to do a chop anyways. I have my own ways of doing things and they work, but before I even take a bike for aa ride , I've done everything I can to get the bike dialed in , so I get results that answer the questions or jetting needed to get it good.
 
Carl H said:
I've only done a few flat out plug chops and that was many years ago due to the fact it is dangerous and illegal to be doing over 110 MPH on the street. But for a stock street bike a main jet is a known given, what ever Norton OEM used. I've seen so many people think a main jet change is going to fix a rich mixture at all or any RPM. And they don't do a plug chop correctly or have the carbs even close enough to do a chop anyways. I have my own ways of doing things and they work, but before I even take a bike for aa ride , I've done everything I can to get the bike dialed in , so I get results that answer the questions or jetting needed to get it good.
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You dont have to do the WOT chops in top gear.
 
The pilot retorted that he, Oiva Tuominen, was able to do whatever he wanted to do, while others were able to do only what they could!
gortnipper said:
gortnipper said:
You dont have to do the WOT chops in top gear.
Click to expand...
I/we are talking about a main jet plug chop, Could you explain how I would have to do that in a lower gear without over revving the bike.
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gortnipper said:
I do partial throttle opening tests at 3- 5 k to check the lower speed/ RPM jetting, just to get a feel for what is going on and go at least 1/4 mile at the RPM I choose to let the plug get the burn or color to read.
Click to expand...

 
At least I'm consistent!

I have a longish hill near me and 3/4 of the way up there is a nice big pull out. But, it is an 80kph limit. I do a short WOT chop in 1st and 2nd and hope there's no cops coming down the hill.

From my mother's sleep I fell into the State,
And I hunched in its belly till my wet fur froze.
Six miles from earth, loosed from its dream of life,
I woke to black flak and the nightmare fighters.
When I died they washed me out of the turret with a hose.
 
Carl H said:
The pilot retorted that he, Oiva Tuominen, was able to do whatever he wanted to do, while others were able to do only what they could!
Click to expand...
At least I'm consistent!

I have a longish hill near me and 3/4 of the way up there is a nice big pull out. But, it is an 80kph limit. I do a short WOT chop in 1st and 2nd and hope there's no cops coming down the hill.

From my mother's sleep I fell into the State,

And I hunched in its belly till my wet fur froze.

Six miles from earth, loosed from its dream of life,

I woke to black flak and the nightmare fighters.

When I died they washed me out of the turret with a hose.
 
For quite a few years now, I am more interested in low and mid speed response, and I concentrate on 2-5 K jetting. and how smooth and fast my recent rebuilds are. I hadn't had a fresh rebuilt engine in years , many years, so I get to apply new ideas and get to test them. Most riders and especially new comers to Commandos would be wise to work on the low and midrange jetting and not even worry about the main jetting, Providing the jet isn't loose and ready to fall out or plugged with dirt. But real good low speed jetting is perhaps the trickiest to do with so many variables and things you can alter, adjust and test.

From BSA to Yamaha and finally my CHR Commado.,Yvon Duhamel #17, at the Laconia Hill where so many great racers climbed the mountain to greatness. We were all blessed to see him one last time, doing what he did best!
Could someone post a photo of a spark plug with color for ideal mixture strength
Could someone post a photo of a spark plug with color for ideal mixture strength
 
DennisMo said:
Thanks for asking. It is a VM34
I have listed all below but what I want to do first is replace the choke plunger, adjust idle circuit, check the plugs and then ask the forum!
The right plug is sootier than the left.
I suspect the idle jet is too small.
Also I experimented and dropped the needle a notch at a time. Needle is now dropped as far as it can
and there is no lag/hesitation when I crack open the throttle. So from what I read, it may be I eventually might look to a smaller main jet but then there
is the main jet air corrector that may be the place to start.
In the meantime, if you want to share any observations with me, I am grateful
Thanks
Dennis

Idle jet 30
Air corrector 2.0
Needle 6DH3
Jet 230
Cut away 2.5
Air Corrector 159 P0
Click to expand...
You should use a #3 slide and for the pilot it should be 40 or 37.5.
 
I mentioned earlier that I think the choke plunger on right side is likely leaking and that it could be the cause so I am replacing it and then checking plugs before reporting back. It should arrive within a couple of weeks
 
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