Back to the mighty TM 40

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Derek Wilson said:
I am a total newby to the single carb world on a Commando - I have always run twin Amal's. But the bike I am restoring currently requires some carb work and I am open to exploring options.

Just curious on the sizing - why 40 mm? Why not 38 or 42?

Principle reason I ask is it seems (where I am), 38mm are substantially less expensive.
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The reason I chose 40mm was because it was going to replace the 40mm lake (widow maker) injector on my drouin but as that has never reached fruition I thought I'd try it on a normally aspirated commando
There are more than enough posts about single carb set ups
But if you just want a sweet running commando go for the single 34mm VM IMHO
 
Since you are only using the two outer mounting bolts, did you fill and blend the center bolt holes out in the intake? Those mounting hole pockets inside the manifold are probably a big reason for why the twin carburetor versus single carburetor debate exists. Flow
 
Schwany said:
Since you are only using the two outer mounting bolts, did you fill and blend the center bolt holes out in the intake? Those mounting hole pockets inside the manifold are probably a big reason for why the twin carburetor versus single carburetor debate exists. Flow
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The centre holes are plugged and the join between the elbows has been blended to form a small steeple in between the inlets
 
What will it do Moster
baz said:
The centre holes are plugged and the join between the elbows has been blended to form a small steeple in between the inlets
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What will it do Mister with that 40mm carb? Have you had it flat out on any private roads?
 
baz said:
Ha ha it's not professional at all I'm afraid
Just two mild steel elbows welded together
I just thought I'd try it to see if it'd work,I was just a bit taken back with the results
I painted it silver so as not to shock people too much ,plus it stops people telling me that steel is not the right material to use etc etc
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Would never have guessed!

Nice work Baz.
 
FastFred said:
What will it do Moster
What will it do Mister with that 40mm carb? Have you had it flat out on any private roads?
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I've not had it flat out in top gear it'd never pull it anyway because I have slightly overgeared the bike
But it's easy to rev beyond 7000 rpm in the lower gears
The other day I sat between 80 and 90 on a private road for about 25 miles
I'm guessing it'd do just over a 100 mph flat out ,I'll have to try it and report back
 
baz said:
Ha ha it's not professional at all I'm afraid
Just two mild steel elbows welded together
I just thought I'd try it to see if it'd work,I was just a bit taken back with the results
I painted it silver so as not to shock people too much ,plus it stops people telling me that steel is not the right material to use etc etcBut it lo
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Did you do the welding baz?

Any chance of a picture or two of the carb mounted please?

Cheers,

cliffa.
 
cliffa said:
Did you do the welding baz?

Any chance of a picture or two of the carb mounted please?

Cheers,

cliffa.
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Yeah it's just two elbows welded together
I'll take a photo later
Cheers
 
I just took 2 welding elbows, welded them together
Made a flange to fit the head
And a spigot for the carb
 

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baz said:
I just took 2 welding elbows, welded them together
Made a flange to fit the head
And a spigot for the carb
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I'll say it again, nice job and great welding from what I can see around the stub tube :)
 
cliffa said:
I'll say it again, nice job and great welding from what I can see around the stub tube :)
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Thank you
But I've been doing it for 44 years and I'm at best average
I can remember looking at the stuff the BOC blokes could do when I was at college
Razor blades butt welded together etc etc amazing stuff
 
baz said:
The centre holes are plugged and the join between the elbows has been blended to form a small steeple in between the inlets
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I misinterpreted, oops. I thought you were modifying one of the retail single intake manifolds and welding your larger spigot mount on top. The typical retail single intake manifolds with the two center bolt holes in the manifold are not what I would ever consider a performance product. Yours is a improvement over the 4 bolt setup as long as it doesn't leak, and apparently it doesn't. Well done
 

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Schwany said:
I misinterpreted, oops. I thought you were modifying one of the retail single intake manifolds and welding your larger spigot mount on top. The typical retail single intake manifolds with the two center bolt holes in the manifold are not what I would ever consider a performance product. Yours is a improvement over the 4 bolt setup as long as it doesn't leak, and apparently it doesn't. Well done
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Most of the single carb kits I have seen these days have done away with the two centre screws so I can't claim any credit there
Cheers
 
cliffa said:
Perfect thanks baz. Removing the gusset really does leave a lot more room for experimentation doesn't it.
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I'm wondering what carb/carbs were on the bike before I bought it?
The frame was also chrome plated!! It had CMA mag wheels fitted
It was about 70% of a bike
I re worked it doing away with all the stuff that I didn't like on previous commando's I'd owned
There's no attempt at gasflow on this manifold,I just thought I'd try it and I was surprised by the results
I dare say a longer more Y shaped manifold would work better?
Cheers
 
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