R&D TM 40mm FlatSide pumper R&D

BrianK · Apr 26, 2012

worntorn said:
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

I run a pair of 35mm Keihin FCRs on my 850 Commando. The bike is not overcarbed. Low end is prodigious; indeed the whole powerband is. Throttle response too (accelerator pumps - easy chokeless starting too, for the same reason), and mileage to boot. Only downside is the admission ticket - they're spendy. But awesome carbs.

comnoz · Apr 26, 2012

rpatton said:
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.

Oh boy the yds3c- that was my first step up from the super 65 when I was 15 also. Man would they wail without the exhaust baffles. Our local chief of police barred me from entering city limits on it. I got a good long stay in the hospital from that bike. Jim

pete.v · Apr 27, 2012

Re: R&D TM 40mm FlatSide pumper R&D Cont.

I have good news and bad news.
Good new, damn that thing runs fine. One notch on the needle and the very slight lag at low rpms is gone.

Hit the highway ran to 6000 rpm to 90 in third, shifted and it kept on pulling.
Running a K&N RU-0981 filter. Not very big but seem to not effect the running.

Ok, as far as the notch in the frame web. Up to the grommet and 3" across. I'd show a picture but I need to clean it up a bit and line the edge.

I really think I have a winner and would only recommend it for similar setups. (see previous posts in this thread)

I need to go for a longer run and do some hi speed plug chops.

As i said before, the only adjustment I have made so far is to raise the needle one notch.

The Bad News. I sort of feel bad about the JS PWK twin 32's set up. They have been good. They have served their purpose, to run this bike to its potential until I could get it together to try out my hunch.

mikegray660 · Apr 27, 2012

dyno?

or the winner is - the guy that sold it to u ? :shock: :mrgreen:

pete.v · Apr 27, 2012

mikegray660 said:
dyno?

or the winner is - the guy that sold it to u ? :shock: :mrgreen:

I'm not sure what you mean or what you're getting at but after reading some of the history of your posts I gotta say this, You are consistant.

geo46er · Apr 27, 2012

The only thing I am not crazy about is the push/pull throttle cable (which always looks like excess clutter to me).
Did you consider running it with just one cable?

Diablouph · Apr 27, 2012

I would think the PP cable would be a plus. Less return spring force I would think.

Got a good source for the carb and cable?

geo46er · Apr 27, 2012

This is where Pvisseriii said he got it. I think this company is the same as MAP cycles out of Clearwater Florida (at least they used to have the same address).
http://www.nichecycle.com/Items.aspx?co ... AT&key=cat

swooshdave · Apr 27, 2012

Would it be possible to mill off some from the manifold and clear the frame?

mikegray660 · Apr 28, 2012

pvisseriii said:
mikegray660 said:

dyno?

or the winner is - the guy that sold it to u ? :shock: :mrgreen:

Click to expand...

I'm not sure what you mean or what you're getting at but after reading some of the history of your posts I gotta say this, You are consistant.

as are you! :shock: :mrgreen:

pete.v · Apr 28, 2012

geo46er said:
The only thing I am not crazy about is the push/pull throttle cable (which always looks like excess clutter to me).
Did you consider running it with just one cable?

Although the spring seems more than adequate, I chose to follow the suggested warning.

pete.v · Apr 28, 2012

geo46er said:
This is where Pvisseriii said he got it. I think this company is the same as MAP cycles out of Clearwater Florida (at least they used to have the same address).
http://www.nichecycle.com/Items.aspx?co ... AT&key=cat

Yes, these are the exact items I purchased. The manifold and adapter from Rocky Point Cycle, items 2535 and 2565.
I have some jetting coming from Jets R Us. I may richen the pilot and needle jet. The carb came with the 1 foot cable choke pull. I have the shorty coming too( although choke not needed for cold starts. On that note, when warm starting don't touch the throttle.
http://www.nichecycle.com/ProductDesc.a ... ump&key=it

That idle screw is very nice.

Hobot · Apr 28, 2012

I had to bone up on history of flat slides to find why they have fallen out of favor with modern elites even though flat slides flow better than a butterfly in air flow as slide sticking-ness was a very big reason for PP operation. No they didn't stick open much like on unboosted engines - just enough delay response till over responsed when on traction edges. PP bike clutter is rather less than bike and pilot parts scattered. The issue increases with the flat area of the slide. This is separate issue of cascades of intake and exhaust resonance power spikes and dips over a few 100 rpms.

Btw could you point me at a 40 mm PP throttle as I've only found 38 mm throttles so far.

pete.v · Apr 28, 2012

swooshdave said:
Would it be possible to mill off some from the manifold and clear the frame?

I looked at that. The MAP manifold has as low a profile and is very clean. I do not believe that milling any safe amount would offer a benefit in this regard. The adapter is also quite low in profile. This carb is beefy and although not particularly big, it is substantial

pete.v · Apr 28, 2012

hobot said:
I had to bone up on history of flat slides to find why they have fallen out of favor with modern elites even though flat slides flow better than a butterfly in air flow as slide sticking-ness was a very big reason for PP operation. No they didn't stick open much like on unboosted engines - just enough delay response till over responsed when on traction edges. PP bike clutter is rather less than bike and pilot parts scattered. The issue increases with the flat area of the slide. This is separate issue of cascades of intake and exhaust resonance power spikes and dips over a few 100 rpms.

Btw could you point me at a 40 mm PP throttle as I've only found 38 mm throttles so far.

Yes, these carbs were very popular with the Sportsters (Easy Kits) for a while which is kind of where I got the notion to try it. I think that they may have been slightly under sizes for that application. They have gone to 42, 44, and 46 mm HSR's since then.
This is what I got but I paid 45 for it at https://www.powersportsuperstore.com
http://www.nichecycle.com/ProductDesc.a ... type=0&eq=
Also Google "Mikuni push pull throttle".

Hobot · Apr 28, 2012

Thanx for the throttle shopping site, I've a 38 mm QuikSilver and a 40 mm Lake so likely get a 50 mm throttle reel.

pete.v · Apr 28, 2012

It's 41 degrees and gonna rain all day. I am going to ID all jetting. They say what it is in the description but they lie. I need a sure base to work from.

Oh, failed to mention, I will be relocating my Dzus fastener to the side cover.

Yes, this system requires some modification and I am posting these results for informational purposes only. I believe my setup is 95% complete to attaining dual flatside performance with a single carb on a "hot street" setup Commando. I don't have a dyno in my pocket and I am not trying to prove anything to anybody but myself. I am merely sharing what I am doing. If you don't like it, fine. If you dig it and can benefit from it in any way, fantastic.

That being said, if I find a dyno near by, I may try to see what I have. As far as change is concerned, I am not going to swap around for base line results.

Diablouph · Apr 28, 2012

good post pvisseriii, learned a lot.

swooshdave · Apr 28, 2012

pvisseriii said:
swooshdave said:

Would it be possible to mill off some from the manifold and clear the frame?

Click to expand...

I looked at that. The MAP manifold has as low a profile and is very clean. I do not believe that milling any safe amount would offer a benefit in this regard. The adapter is also quite low in profile. This carb is beefy and although not particularly big, it is substantial