R&D TM 40mm FlatSide pumper R&D

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pete.v

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Well....there it is. A TM40mm Mikuni flat side pumper carb. Preliminary results look good. First kick start, rock solid idle and great throttle response. Started raining so I could ring it out.

No jetting changes have been made at this point. Bone stock Mikuni jetting right off Niche's shelf.
Idle may be a little rich. Pilot screw is a good 3 turns out as it sits.

Tight fit. Had to notch the frame webbing where the wires go through to allow the throttle and accelerator pump to actuate.

I still love the JS setup, this is just something i have always wanted to try. My thinking is if 2 FCR 35's go, why not 1 40. I am running a Combat Head, stage 1 radius cam and 1 1/2" pipes.
Again, this is just R&D at this time and not a debate on my sanity.
More to follow.
R&D TM 40mm FlatSide pumper R&D

R&D TM 40mm FlatSide pumper R&D


It's my bike, I do what i want!
 
very cool!

Please give us a comparison report vs Jim's twin flat slides when you get a chance?
 
The longer I spend working on motorcycles, the less I understand carb size/ to engine size ratio.

A Honda black bomber came with two 36mm carbs. That is one 36 mm carb for a 222 cc pot!
Logic would say it is overcabureted and would bog like an old Yammy Big Bear, except they didnt. From my memory those Black Bombers had very good low end throttle response plus made good use of the big carbs on up higher in the rpm band.

I recognize that this was a higher revving engine than a Norton or Vincent, but how did they get it to work so well at lower and middle RPM.
By the Honda black bomber yardstick the carbs on an 850 Commando ought to be about 46 mm x2 and those for my 1360 Vincent should be maybe 60mm or some such thing (guessing here, havent done the pi r squared)

Glen
 
Did the Black Bomber have CV carbs? My first real motorcycle was a Big Bear Scrambler, ridiculous in the dirt, but a killer canyon bike. At least it seemed to me at the time, 15yo. :)
 
Im not sure what type they were, except the throat size is listed as 36mm.
A friend lent me his 305 Big Bear for awhile. Open the throttle and bog, bog, bog, then finally wheeeeeee.....!! Off we go at warp speed, or so it felt at the time.
But then I was still getting used to the power of my 9?hp Honda Super 90(overhead cam), a big step up from my previous bike, a 6.5 hp pushrod 90, the c200

Glen
 
Again, this is just R&D at this time and not a debate on my sanity.
Click to expand...

We own Nortons, the debate about sanity ended long ago.

May I ask, where did you get the carb, what about cables, and price.

By the way, good pics.
 
How much did you have to notch that frame web?

Hopefully the rain will subside soon...
 
cb450 had the "old" type CV carbs with an alloy pistons, not a rubber thingie. Same type were found on CX, CBX, 900 four.... not a perfoming carb by any standards, me guess: same performance than a 32mm "normal" carb! This being siad we used to put CB450 carbs on CB350 for better performance...go figure!
Philippe
 
grandpaul said:
How much did you have to notch that frame web?

...
Click to expand...
At this time I will plead the fifth. If it doesn't work out, then it won't matter. If it does run like like I think and hope it will, then I will divulge the truth. Then you will all have to decide if it is worth the process.
I did not know how things would fit and going as far as I have and with the desire to know, I am more than willing to do what it take to make them go. It's not huge but it will require some subtle changes.

I took a run down the road to open it up as far as the end of the block. Got to 5500 with no problem. A very slight lag is noticable down low. The plug show a little on the lean side. I will raise the needle 1 notch and give it another go.

This is sort of good news in that the base jetting starts out on the lean side of the scale with available needles and needle jets going toward the rich side as you needed.



R&D TM 40mm FlatSide pumper R&D
 
Diablouph said:
Again, this is just R&D at this time and not a debate on my sanity.
Click to expand...

We own Nortons, the debate about sanity ended long ago.

May I ask, where did you get the carb, what about cables, and price.

By the way, good pics.
Click to expand...

Niche on ebay. Manifold and adapter from Rocky point. Mikuni Push-pull kit KRS-001. Misc. jetting from Jets R Us, but I don't think I will need any. We'll see, though.
 
Hi Pvisseriii,
I was wondering with a 40mm carb how uneven is the interface from carb to flange to manifold?
My single carb manifold was originally designed for the stock Amal. When I went to the 34mm single Mikuni I had to
remove quite a bit of metal to get it smooth.
 
geo46er said:
Hi Pvisseriii,
I was wondering with a 40mm carb how uneven is the interface from carb to flange to manifold?
My single carb manifold was originally designed for the stock Amal. When I went to the 34mm single Mikuni I had to
remove quite a bit of metal to get it smooth.
Click to expand...
There are 2 manifolds available. The larger has 70mm mounting screws on center for the adapter. The ports to the head are 32mm and the port to the carb is 40. MMM MMM good.
 
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