Single 34mm flatslide carb kit

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jseng1

jseng1

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Just got this together and tested. Runs suprisingly well for a single carb. Very smooth and gobs of torque from the basement. Pulls strong up to 6000 RPM. Now I can understand why some prefer a single carb. Its a clean & simple installation but you have to remove the original airbox backing plate or find a shorter aircleaner. The twin carbs have more upper mid range to top end/redline scream but in other respects the single has sweet advantages (pulls hard from idle etc). I had some requests for it so here it is.

Single 34mm flatslide carb kit


See it at the website below.
 
Re: Single 34mm flatlside carb kit

Nice Jim -
i run a similar setup on all my triumphs w/ the PWKs now and am very pleased with them - i find for around town and "legal" freeway speeds its a tough setup to beat

I'm sure with your fine tuning on the needle it would make it even better for a Norton
 
Re: Single 34mm flatlside carb kit

What about a kit for the Mark III? You can't just change out the twistgrip w/o a lot of work and expense.
 
Re: Single 34mm flatlside carb kit

Lighter throttle spring resistance of a single is nicer after a bit too. I'm a bit confused, [shut it] by the dual vs single carb for best performance as past Peel had better to end performance with single 34 miki than dual 32 Amals. Duals were a bit more responsive for my Gravel travel, needing less throttle motion for slight tire spins to steer but once on pavement they seemed sluggish after 60 mph and ran out of pull before the single. At Norton big twin rpm mixture flow rates, a 34 mm carb throat is not restricting the carb to flow enough for engine, so the split manifold must be the bottle neck for top end. Peel had accidental flow tricks in her spit manifold that I'd like to follow up on purpose. The 40 mm pumper flat slide posted recently seems the hottest ticket to come online but only a few will want it enough to cut out gusset to fit.

It would be interesting/educational to compare touring mpg/mileage between JS's two offerings.
 
Re: Single 34mm flatlside carb kit

milfordite said:
What about a kit for the Mark III? You can't just change out the twistgrip w/o a lot of work and expense.
Click to expand...

I haven't figured out the different cables for different models. If the upper cables to the twist grip are different for the Mk 3 etc then maybe the best thing is to offer a one piece long replacement cable with an extra long inner wire. Then you cut the inner wire to length and solder the small end where you need it. I just ordered 5 cables like this so I can set them up for the single carb kit with my twist grip because this is the easiest way to figure out the the necessary inner cable length (before ordering them in quantity). What about it? Got any input on this subject. Can the average Joe solder ? (need elect iron).
 
Re: Single 34mm flatlside carb kit

Hi Jim,

Two years ago I posted the flow limit on my Mikuni VM34 (5-6 fluid oz per minute, depending on whether the bowl was dropped for the test).

fuel-flow-rate-for-commando-850-t6031.html

This flow limit results in a horsepower limit of 35-40 HP; the carburettor is simply not capable of delivering enough hydrogen at WOT to develop more power, regardless of aspiration. The fuel flow limit is in the float valve and internal piping of the Mikuni, and is not influenced, for example, by the petcocks, which flow at more than 20 fluid oz per minute.

Have you run this flow test on your flatside? If it flows, bowl removed, at greater than 6 fl oz per minute, it would be a very interesting upgrade for the VM34 indeed.
 
Re: Single 34mm flatlside carb kit

rick in seattle said:
Hi Jim,

Two years ago I posted the flow limit on my Mikuni VM34 (5-6 fluid oz per minute, depending on whether the bowl was dropped for the test).

fuel-flow-rate-for-commando-850-t6031.html

This flow limit results in a horsepower limit of 35-40 HP; the carburettor is simply not capable of delivering enough hydrogen at WOT to develop more power, regardless of aspiration. The fuel flow limit is in the float valve and internal piping of the Mikuni, and is not influenced, for example, by the petcocks, which flow at more than 20 fluid oz per minute.

Have you run this flow test on your flatside? If it flows, bowl removed, at greater than 6 fl oz per minute, it would be a very interesting upgrade for the VM34 indeed.
Click to expand...

That matches the average airflow of the MAP 34mm manifold pretty well. Engine software says it is good for about 38 horsepower maximum. The 38mm MAP manifold does a little better. [even with the 34mm carb on it] Jim
 
Re: Single 34mm flatlside carb kit

rick in seattle said:
Hi Jim,

Two years ago I posted the flow limit on my Mikuni VM34 (5-6 fluid oz per minute, depending on whether the bowl was dropped for the test).

fuel-flow-rate-for-commando-850-t6031.html

This flow limit results in a horsepower limit of 35-40 HP; the carburettor is simply not capable of delivering enough hydrogen at WOT to develop more power, regardless of aspiration. The fuel flow limit is in the float valve and internal piping of the Mikuni, and is not influenced, for example, by the petcocks, which flow at more than 20 fluid oz per minute.

Have you run this flow test on your flatside? If it flows, bowl removed, at greater than 6 fl oz per minute, it would be a very interesting upgrade for the VM34 indeed.
Click to expand...

What I have done so far is run main jets so big that the plugs were black at WOT. I then shut off the petcock until it starved. Then, at the same moment, I turned on the (large aftermarket) petcock and gave it WOT through the gears. It never stumbled and the fuel flow caught up. But this is with twin carbs and I probably have to do it all over again with a single (tell me). I also know that you can drill the brass orifice (smallest choke point) that feeds the float needle and I also did that to a pair of carbs befor I found out that it wasn't necessary. So either way - the orifice could be drilled if needed - I could do that to each carb in a minute. Note that the single carb needed the same (or possibly one size larger) main jet and still used the same idle jet and mixture setting as the same carb in twin configuration.

In my opinion a single will never equal the mid/top end rush of a twin setup on a free breathing Nort because of the tight curvature of available 2 into 1 manifolds..
 
Re: Single 34mm flatlside carb kit

Jim,

Thanks for responding.

I was hoping that I could convince you to run a simple experiment, a total of 10 minutes in the shop with the ignition off, to settle the fuel flow question independent of aspiration issues. Simply turn the petcocks off, remove the carb bowl, and place a container under the carb (at least 1.5 pints to be safe). Turn the petcocks on (just the main should be ok), let the fuel flow for 2 minutes, then turn off the petcock and measure the fuel volume in your container. Divide the volume by 2 and compare this volume flow rate to the 6 fl oz per minute I got with my VM34.

I understand your point about enlarging the needle ortifice. Still, if its not too much trouble, this simple comparison between the two stock carbs would be useful in sorting out the fuel-flow limit question surrounding single carb set-ups.

Thanks,

Rick
 
Re: Single 34mm flatlside carb kit

Here's what BSA did to Amals fuel feed flow. Got to keep whole fuel path in mind. I've a Miki 34 in a box and a full tank on bike so can hold carb over a bowl at manifold height if no one beats me too it for ya. I refuse to believe the 38 hp power calculations as correct in real world so some data point is missing.

Single 34mm flatslide carb kit
 
Re: Single 34mm flatlside carb kit

jseng1 said:
In my opinion a single will never equal the mid/top end rush of a twin setup on a free breathing Nort because of the tight curvature of available 2 into 1 manifolds..
Click to expand...
It's hard to argue with that logic, but I gotta tell ya, I'm knocking at the door.
 
Re: Single 34mm flatlside carb kit

rick in seattle said:
Jim,

Thanks for responding.

I was hoping that I could convince you to run a simple experiment, a total of 10 minutes in the shop with the ignition off, to settle the fuel flow question independent of aspiration issues. Simply turn the petcocks off, remove the carb bowl, and place a container under the carb (at least 1.5 pints to be safe). Turn the petcocks on (just the main should be ok), let the fuel flow for 2 minutes, then turn off the petcock and measure the fuel volume in your container. Divide the volume by 2 and compare this volume flow rate to the 6 fl oz per minute I got with my VM34.

Rick

I understand your point about enlarging the needle ortifice. Still, if its not too much trouble, this simple comparison between the two stock carbs would be useful in sorting out the fuel-flow limit question surrounding single carb set-ups.

Thanks,
Click to expand...

Rick

I made the test as described above and got 8 oz per minute. This is for JS modified carbs only with the fuel feed drilled as currently provided for JS single carb setups.

Jim S
 
Re: Single 34mm flatlside carb kit

jseng1 said:
Runs suprisingly well for a single carb. Very smooth and gobs of torque from the basement. Pulls strong up to 6000 RPM. Now I can understand why some prefer a single carb. Its a clean & simple installation...
Click to expand...

This is exactly why some of us have been praising the Mikuni TM34 flatslide setup...Screaming performance....easy setup...set and forget...once dialed-in you'll wonder why you waited so long or put up with the Anal BS.
 
Re: Single 34mm flatlside carb kit

Hobot said:

I refuse to believe the 38 hp power calculations as correct in real world so some data point is missing.
Click to expand...

Steve, this figure of roughly 40 hp maximum from a single Mikuni has been collaborated by a couple people using dynos on this forum. If I remember, a twin carb set up dynoed some 44 hp, all things being equal, blah, blah

This is of course rear wheel horse power.

But getting back to your apparent disbelief.
What is the basis, do you have the dyno figures you can post from your single 34 that are substantially different?

What is it you refuse to believe? More, or maybe less horsepower.

Curious, because I had my 850 in stock set up with a single 34 Mikuni on a dyno: 37 hp at 6500 rpm.
 
Re: Single 34mm flatlside carb kit

Well no one but a hand full of squid squadrons and a dead buddy believed me on the performance Ms Peel had with an out of the box 34 single MIki carb. I had power advantage up 90 and held my own over 130 with 600's and above. I have a 365 lb 70 hp SV650 that no way on God's grey tarmac has the balls above 70 to even keep the squids and hot shots in sight after a few seconds. My buddy Wes has a 34 Miki on his '71 and its as sunky as my factory Trixie Combat with dual 32 Amals. Neither my 2 Amal Trixie nor Wes's 34 Miki 750 can keep up with my SV650 on the boil. I don't need no numbers to tell me the 40 hp fueling or flow limit is off base. Put a UFO kit on it and get even more spunk out of one like Wes does. Ms Peel had against the grain set up that some how made the 34 MIki roar. Surprised the hell out of me too.
 
Re: Single 34mm flatlside carb kit

Jim S,

Thanks for the data point. What you report is 33% better maximum fuel flow than I get from my VM34. It's got to show up as better upper mid-range performance. How much are these rascals? Will my VM throttle cable fit the flatside?
 
Re: Single 34mm flatlside carb kit

1/3 more fuel flow over 40 hp Miki calculations imply 53 hp max from the 34mm flat slide or about 3-4 hp over what the Combat dual Amals delivers in very well tuned factory combo. Seems on conservative side to me, if other power rubbers dealt with. 3-4 hp can definitely be felt by pilot though. Looked into the SV650 forums for some dyno charts of round slide factory carbs vs flat side of similar size, to see at most 5 hp gained over the 70-ish from factory. To get more out of the flat slides requires changing engine components.

In general piston engines require 1.5 to 1.6 cfm per hp and .5-.55 lb of fuel per hp.
 
Re: Single 34mm flatlside carb kit

Maybe it depends which float valves you are using.

VM 34 float valve applicable to 30mm - 44mm round slide carbs mikuni carbs with the single drain hole


Single 34mm flatslide carb kit



VM 36 float valve applicable 30mm - 44 round slide carbs as you can see these have six bigger drain holes


Single 34mm flatslide carb kit



these are what we use to flow sufficent fuel for methanol use ie three times as much as petrol / gasolene

.
 
Re: Single 34mm flatlside carb kit

Boy, I never Knew there were that many "pedestrian bikes" out there. You guys must all be nuts for wanting ease of set up,no maintenance,reliability,smooth running,and longevity. Has anyone ever flow tested one of Sonny Angel's manifolds? Unlike the MAP unit, it is a 2 bolt piece, with a much steeper curve, which makes it sit higher up towards the frame. Mounting is VERY tight on a MK111, but it really works well
 
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