Topic: Fine Tuning the 1 commando

[BomberMann650]

The 1 show commando hits the street 
Now I'm trying to remember the carb tuning flow chart  
Wanted to bounce this off you guys.  Making sure my troubleshooting is accurate.

First test ride went better than expected.  Out of the box the idle jet did a cold start without choke.  Whacking the throttle caused a stall out.  Already took the pilot down a step, did an idle plug chop and things are kosher there. 
That was on a cold November evening, 45° or less. 
The bike ran smooth up the rpms before wanting to break up high.  Felt decent despite how damn cold it was.  Wish i had a tachometer to know exactly where it nosed over   Took the mains down a step and left it there. 

Fast forward to May.  Balmy 66 American degrees at sea level.  The bike wants to stumble around in the midrange until the throttle gets opened more.  Didn't behave like that for the first few blocks.  By the time the oil got warm, trying to hold a 35mph cruise in 3rd gear sucked.  Stumble through half throttle until the slides opened more.  Then it would start accelerating hard.  Rip-roaring around the lake and startling the joggers on the sidewalk.  Rode back to the shop with a gentler hand and smoother ride in 2nd gear.  I suspect its still overfueling. 

Am considering the UFO plug for the slides.  Why mikuni doesn't just make their slides with the optimized bottom idk.  Figured i'd put those in along with moving the needle clip up.  Hoping less fuel under half throttle will smooth out the throttle response.

Unless i'm misinterpreting the partial throttle stumble and should go back to the main that ran good in the cold?

A money shot of the vm32 and stacks so there's at least a penny for your thoughts.

[MauiK3]

Maybe a little more info and some photos would help

[BomberMann650]

Maybe a little more info and some photos would help

Year make model is in my signature.
Picture of twin vm32 carbs was provided.

Bike felt smoother with the out the box jetting on a cold night.  I reduced the main jet by one size (5 on mikuni scale) anticipating warmer weather.  But now it's unhappy
Somewhere between 1/4 & 1/2 throttle the engine misses and pops under load.  Below 1/4 ok above 1/2 it starts to come on hard.
I'll have to move the needle clip and find out what works.

[scottly]

Unless i'm misinterpreting the partial throttle stumble and should go back to the main that ran good in the cold?

A money shot of the vm32 and stacks so there's at least a penny for your thoughts.

There's your sign. The vm36 I've played with didn't seem to care what the temp was. Also, the tight mesh screens inside the stacks are not a good thing...

[BomberMann650]

Unless i'm misinterpreting the partial throttle stumble and should go back to the main that ran good in the cold?

A money shot of the vm32 and stacks so there's at least a penny for your thoughts.

There's your sign. The vm36 I've played with didn't seem to care what the temp was. Also, the tight mesh screens inside the stacks are not a good thing...

Thanks Scottly.

Im sure the rock screens do something to the port vacuum and flow
But they seem a necessary evil for a road going motorbike

[Kelly E]

On the 64' Norton Atlas 750 we did the rock screens were dome shaped screens attached to aluminium rings and screwed on to the threads on the outside of the velocity stacks.

[BomberMann650]

On the 64' Norton Atlas 750 we did the rock screens were dome shaped screens attached to aluminium rings and screwed on to the threads on the outside of the velocity stacks.

Thats something I'll consider making for these stax once i have the lathe up n running

[scottly]

A road going bike should have air filters, not just "rock screens". Save that stuff for the shows. My Webers have short stacks like Kelly's, and I have been using Uni foam filters that stretch over the stacks. Can the screens be removed from those stacks? Are they properly designed, as they seem to narrow down significantly on the OD, right where they meet the carb? You *might* consider K&N pods.

[BomberMann650]

A road going bike should have air filters, not just "rock screens". Save that stuff for the shows. My Webers have short stacks like Kelly's, and I have been using Uni foam filters that stretch over the stacks. Can the screens be removed from those stacks? Are they properly designed, as they seem to narrow down significantly on the OD, right where they meet the carb? You *might* consider K&N pods.

Those foam socks are smart. 
This is not a touring bike.  More of a sunny day pleasure bike.
Thankfully the PNW doesn't have haboobs.

The stacks are from steel dragon.  They make good stuff.

[Kevin D]

Is this the beauty in question?

[BomberMann650]

Is this the beauty in question?

Yep, thats The One

It rides nice.  Despite my questionable decision to rejet it back in November

[Kevin D]

That’s nice… nicer than nice.

[BomberMann650]

That’s nice… nicer than nice.

Thanks.

Hopefully i can keep the trend going and churn out more nice nice nice bikes.

[MauiK3]

Very nice, that motor has the most pleasing appearance.

[BomberMann650]

Very nice, that motor has the most pleasing appearance.

The British bikes of the sixties and seventies were very shapely.  Getting personal with one, its neat to see the classic sand casting marks.  In the spots the factory polisher didn't want to bother with 🤣

I wish you guys could hear it when underway.
It bellows so nicely. 

This particular mill is surprisingly balanced compared to some others.  Oversized pistons must have added enough mass to smoothen things out.

[BomberMann650]

Thanks for following the frustrating norton saga from open forums.
This #$%* keeps testing me.

Had to repair the starter and fix the timing so i could begin making progress on carb tuning.
Having to call a tow for the Norton didn't feel great.  As i spent the next hour running through all the worst-case scenarios in my head.  Was relieved to make some simple fixes and have the bike online again.
Every hop-up-kit part on this engine has needed modification to improve its fit, function, and reliability.  Some of the price tags on these problems are pissed off thread worthy.

Yet I keep building on it and its starting to make some decent power now.  Though it may have reached a tipping point. 
I've come up from the worst performing 230 mains to a decent 260.  The bike is streetable and can pull wot uphill.
But 4th gear reveals a problem.  And according to the sudco mikuni manual, the problem may be too much fuel.  And/or not enough timing or compression.

I've spent the evening sifting through so many pedantic texts on carb tuning and plug chops.  Sometimes the different texts feel contradictory.  Don't get me started on the access norton forums posts.  There are threads covering the dual vm tuning problems.  But they get hijacked by old biker stories, amal adherents, and people who think the jet settings from the single carb setup is relevant.  The few norton race bike people who do post, just say stiff like "i dunno, mine doesn't speed much time at 1/3 throttle so i never noticed".

End Rant.

Anyways, i like the way the 1 Norton runs, until i try to use overdrive.  So far, every spit n sputter had been massaged out by bigger main jet and getting the powerarc ignition to behave itself.  But the book says the issue i have in 4th gear indicates rich condition.  Then gets vague on how to really cure it. 

I know its in the needle jet adjustment zone.  How many steps down to go on needle jet is the mystery.
Or can the volume of fuel its receiving be used better with an extra degree of timing?

Sadly, they quit teaching the relationship of air/fuel/timing to the kids in school. 
Something about breaking the law 😎





 

[scottly]

I warned you about the tightly woven screens down inside the stacks, in the worst possible location.

[BomberMann650]

I warned you about the tightly woven screens down inside the stacks, in the worst possible location.

And the powerarc 😩 Which remains until replacements arrive.

So if the screen is a choke point, is it really trouble to detune the bike around that?  From the few accs.nrtn. threads i read, the jetting i've got now, is in the ballpark of what guys with pod filters end up with. 

Not that going full bore with the v-stacks wouldn't be fun.

What i discovered when troubleshooting the ignition was the encoder disc wandering away from tdc.  The spacer and collared washer supplied may have not made a very good clamp on the stainless disc.  Added a rubber flanged sealing washer to mix and it appears to have helped.

[scottly]

It's like trying to tune around having a rag stuffed into the throat of the carb.

[Stev-o]

Very nice, that motor has the most pleasing appearance.

I wish you guys could hear it when underway.

Hear it?  I wanna RIDE it!

[Kevin D]

Very nice, that motor has the most pleasing appearance.

I wish you guys could hear it when underway.

Hear it?  I wanna RIDE it!

+1
It’s been a long time since I have been to the dragstrip. Way back, 50+ years?, I was treated to an all-bike day at St Thomas dragway in Ontario. Norton’s were by far the predominant bike and I got an all day serenade of sweet Commando motor music in full fury. I have not forgotten that day or that sound.

[BomberMann650]

Very nice, that motor has the most pleasing appearance.

I wish you guys could hear it when underway.

Hear it?  I wanna RIDE it!

Can't do that, not my bike.  And it wouldn't be much fun with the engine sputtering in top gear.

It needs rear sets too.  Hard to get into a sporty body position with the long tank and original footpegs.
Making a set of z plate adapters is on the winter project list as I gather the lathe and mill tooling to make em.

[scottly]

Do me a favor and remove one of the stacks and hold the carb end of the stack next to the carb throat and take a picture. Also, please take a pic looking through the stack with a light behind it.

[BomberMann650]

Do me a favor and remove one of the stacks and hold the carb end of the stack next to the carb throat and take a picture. Also, please take a pic looking through the stack with a light behind it.

[BomberMann650]

There's the money shot on the staxx