My What Am I Getting Myself Into Combat Build Thread

What an excellent and inspirational thread! I have been working on my '72 Combat on and off (a lot more off than on!) for years, literally. I knew the rebuild would stretch out over a good part of a lifetime so I opted not to open a rebuild thread until it was done and would then use my pictures and notes to make a retroactive one. 2023 is starting to look like the year when I can finish this thing. The motor and trans are both done and sitting patiently, with the exception that I don't have the head on the motor. The frame and larger associated parts are cleaned up and painted and I've got the swingarm installed on the transmission cradle, ready to work on the isolastics. Of course, we are out of the country once again right now and have a couple of medical things to get out of the road but it looks like I'll be back on it in late February. This thread brought back some memories of the struggles and triumphs experienced so far, and it's a pretty good review of what's ahead for me. THANKS for the top notch write-up and pictures, and especially your willingness to share the miscues that we all make (and sometimes don't talk about).
I might be in a position to start publishing by late March if my plans hold up.....
 
texasSlick said:
You forgot "perseverance "
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+1 on that. It's a matter of priorities. I spent many a cold night in the garage working on it. You just have to press through. All told, think it took over two years to get it to a ride-able state, and that's with putting it aside for the better part of one summer. The worst was all the cleaning and polishing :mad:

And it's not yet "done". Will post pics when i finally get there.
 
So i've been puttering around in an effort to break in the engine and looks like i have some carb tuning to do. It rides really strong with quick on-throttle responsiveness and no bogging. Problem is plugs are fouled. This is where my ghetto A/F meter comes into play. It was reading around 10 at idle and it would actually go up (get leaner) on throttle and then go back down at higher revs. I think the going down part is good, i.e. 1/3 to full-ish throttle (it was reading around 10 near at about 3/4 throttle). I'm just not sure about the 0-1/4 throttle positions. My first order of business was leaning out the air screw. I opened this up and got the AFR up to 13.

Question for the peanut gallery, what would be a good target AFR at idle? Or do most folks tune by senses. I would think an AFR lower than 12 is too rich at idle (target 13-14?). The Mikuni pilot jet is a 30 (it came from Sudco with a 35). I'm wondering if i need to go down to a 25 (lower is leaner). I may also need to lower the needle a notch by raising the clip (it's on the mid notch and came from Sudco 2nd from the bottom), so raising the clip one would be a delta change of two positions in the leaner direction from where Sudco initially set it up. And/Or should i change the needle jet back to a P0. It's a P2. Lower is leaner and came from Sudco with a P0.

I mention Sudco because i bought the set from them specifically for a Commando, but that doesn't mean their settings are the best.
 
You need a bit of a rich idle to help stop ‘bogging‘ as you open the throttle. At the end of the day, how the bike rides takes priority over searching for perfect settings at idle.

12:1 is not crazy rich on an old air cooled engine at all. You need to err on the side of caution with these old air cooled lumps.
 
I have a rotary Mazda (shown in an earlier post) and i run it crazy rich (~10) to protect against detonation which will trash those motors. Not sure though if i need to be running 10 AFR on-throttle for the Commando and 12 at idle. FWIW, I found this on target AFRs. It's saying 12 for on-throttle, 13.5 for idle/light cruise, and 14 for cruising. My guess these values are for a water cooled V8s.


Also wonder if these engines runs hot, if an oil cooler is advised
 
Sudco sells carburetors for racing. If you want a nice looking plug that stays cleaner with the current jetting either use a warmer running plug or ride a lot faster. I could talk about AFR and tuning, but don't own a Commando anymore so I'm already asking for trouble here. lol

Says "racing u.s.a" in script in the blue section of that decal. That is on my 34mm Mikuni pair I don't use.

My What Am I Getting Myself Into Combat Build Thread


Correct in that those AFR numbers you found are good for modern pump gas in a V8, but they are also good for a lot of other things. My Mikuni jetting is not the same as yours for the set of twin 34mm Mikuni carburetors I had on a 750 with a ported head, 2 into 1 exhaust, and 2S cam in it. My "wrong bike" would lift the front end under power without pulling up on the handlebars. I did not do wheelies on it. Not my thing. It only did that when pulling out into traffic and I needed to get out of the way. Just a little 3 inch lift.

I'm sharing thoughts based on experience and not disagreeing with anyone.
 
Schwany said:
I could talk about AFR and tuning, but don't own a Commando anymore so I'm already asking for trouble here. lol
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Is a P11 really that much different. Go ahead and post your Mikuni settings (if you can remember them 🙃). It would be a good reference point (assume you had to go bigger on the jet sizes to compensate for the larger slide opening)
 
With a Commando engine you will always need to jet on the rich side of maximum power to avoid piston damage.

How rich depends on the piston in use.

Most engines will do OK with full throttle mixture around 12.8 or 13 to 1.

Maximum power seems to be about 13.3 to 13.5 to 1.

To darken a plug's insulator immediately with unleaded fuel requires a mixture around 11.5 to 1.

www.accessnorton.com

main jet test

What is a valid test of the main jet ? Difficult to test because it means wide open throttle, screaming it down the freeway, way over revving, for at least a mile or so. I need a better method.
www.accessnorton.com www.accessnorton.com
 
TomU said:
Is a P11 really that much different. Go ahead and post your Mikuni settings (if you can remember them 🙃). It would be a good reference point (assume you had to go bigger on the jet sizes to compensate for the larger slide opening)
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I have the settings around here somewhere, but they are nothing special. My P11 at the time was geared lower than a Commando, so I was on the pipe more, so to speak. Regarding the P11 being different... Major differences are motor sits straight up an no isoelastics. It's also s little shorter and mine weighs 65lbs less than a Commando. Fun bike to ride.

Another difference in this situation is the intake manifolds are not in as much of a downdraft orientation on a straight up motor. Plus, I modified the intakes that came in the MAP (Sudco) Commando Mikuni twin carburetor kit. I turned them into spigot mount and used automotive fuel tank filler hose for the connection. Probably useless info on the jetting, and totally irrelevant on this website as most of my suggestions seem to be.

This is the configuration.
My What Am I Getting Myself Into Combat Build Thread


My What Am I Getting Myself Into Combat Build Thread


This is the jetting I could find written down.
6DH3 needle, Clip in 2nd position from top.
P0 needle jet
2.5 slide
2.0 air
30 pilot

Bike was a little hard to start when cold but the cam was advanced to 9 pins between the dots. Timing was 32 degrees BTDC set static. Ignition was Boyer. I was young and slightly more clueless than I am today when I did that.

I would not expect it to work like magic, but it might be sort of close.

I've been accused of being a parts changer and nothing more here. I think that is subliminal derogatory horse hooey because I don't have a machine shop in my garage. lol

Only thing I use an AFR gauge on is my retrofit MPFI fool injected 1965 El Camino, and that's only because the kit came with software and an O2 sensor.

I've posted all this BS before. Beautifully irrelevant it is.
 
gortnipper said:
With a Commando engine you will always need to jet on the rich side of maximum power to avoid piston damage.

How rich depends on the piston in use.

Most engines will do OK with full throttle mixture around 12.8 or 13 to 1.

Maximum power seems to be about 13.3 to 13.5 to 1.

To darken a plug's insulator immediately with unleaded fuel requires a mixture around 11.5 to 1.

www.accessnorton.com

main jet test

What is a valid test of the main jet ? Difficult to test because it means wide open throttle, screaming it down the freeway, way over revving, for at least a mile or so. I need a better method.
www.accessnorton.com www.accessnorton.com
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That's an interesting thread. The last post before it was locked was Jim's map. It basically goes from 13.4-14.3 at no load to 12.5ish at full load (across all revs).

afr_zpsszpdb0a0.png


I was thinking something similar. 13ish at idle/no-load to 11.5/12 at full load. That's a little richer, but i'd rather run rich at full load than lean. I was running 10 at near full load and i thought that was a little too rich. This seems to confirm that. Unfortunately, i don't have a dyno. My wideband logs AFRs, but i don't have any way to input RPM so i'm left at watching the gauge while i drive down the road hoping i don't run into something :rolleyes:
 
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So i went with a smaller pilot jet (#25) and put back the leaner Sudco needle jet (P0). The idle AFR bounces around but seems to be about 12 so that's better. It is also leaner on-throttle (11-12 vs 10). Only problem is part throttle (like just begging to twist it) is very lean, like 16. So i think my next move is to raise the needle a notch.
 
TomU said:
So i went with a smaller pilot jet (#25) and put back the leaner Sudco needle jet (P0). The idle AFR bounces around but seems to be about 12 so that's better. It is also leaner on-throttle (11-12 vs 10). Only problem is part throttle (like just begging to twist it) is very lean, like 16. So i think my next move is to raise the needle a notch.
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That’s exactly why I said earlier that it is normal to have the idle a tad rich, precisely to avoid that ‘just off idle’ weakness.

If it’s a steady state weakness (ie if it stays weak when held at that exact throttle opening) then it is most likely the slide cutaway that’s too weak.

But if it’s only a ‘snap’ weakness when opening the throttle, I believe your best bet is a richer idle.

Using Comnoz’s guide above is, I believe, a tad erroneous as his bike was EFI and therefore had infinite input points. You just don’t have that, so you cannot have the same level of perfection at the cross over points between one carb circuit and the next.
 
I have heard good things about those UFOs but have never tried them.

They do require alterations to the carb settings though, so if you wanna try one, best to do so before you spend more time on the current carb settings IMHO.
 
"I have heard good things about those UFOs but have never tried them.

They do require alterations to the carb settings though, so if you wanna try one, best to do so before you spend more time on the current carb settings IMHO."

Yeah, supposedly it creates a serious venturi that pulls gas from the needle jet at low load conditions, therefore the pilot circuit needs to be leaned way down. Only downside is it requires modification to the slide
 
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Cute tattoo.

Girls in shorts were known to get similar burn marks on their legs getting out of a Corvette with side pipes in the 70's. :)

TomU said:
Yeah, supposedly it creates a serious venturi that pulls gas from the needle jet at low load conditions, therefore the pilot circuit needs to be leaned way down. Only downside is it requires modification to the slide
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You can make what you have work without that UFO contraption.
 
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