single carb conversion

This thread carries a lot of information about 30mm----->40mm single carb conversions. There are a few posts here that seem to seek more and more performance from this conversion...

No one is going to get more high-end performance with a single carb (over a twin carbs), if you want maximum performance stay with a twin carb configuration. The single carb conversion is for individuals that want easy tuning and more robust low and mid range throttle response, which I see as a smart move as the bulk of the Nortons I see in my shop still have original ISOs, shocks and forks that would like their first or second oil change; not great ingredients for high speed road work??

The single carb set-up, generally, provides much better starting, better fuel mileage and more responsive low and mid range grunt, they are easy to install, can be jetted quickly for any altitude that a normal human can breathe at.

The jetting that has been I have seen in this thread appears more on the rich side, the kits I sell come with leaner jetting which is still a tad conservative while providing all the benefits mentioned earlier.

Who should give consideration to a single carb conversion? Individuals that think twin carb tuning is rocket science. People that use their Nortons (and/or other Brit bikes) to enjoy the back roads where speeds, generally, are between 30-50 MPH, with occasional runs to 70 MPH, a short run on the Interstate in transport mode. Riding a properly tuned Norton on a sunny day is like being on a magic carpet. Such an experience brings me back to the days when I was much younger, without the malady's of old age; a time machine...

I think that now that the Premiers are available they are the obvious choice. That is not what I use though.

My bike came in a few boxes. In those boxes was a single 34mm VM carburetor and two manifolds. I used the VM for a while and it worked really well. I think there may have been some reduction in power at over 5000 RPM but since my bike is an 850 I didn't rev it that high most of the time anyway. To me that carburetor looked ugly, also really it is too small for an 850. What is ugly on the VM is the rubber manifold, the fuel lines, and the separate fuel filter. The Amal fits better, it is narrow, there are no rubber manifolds and the fuel filter is built in.

At the swap meet I bought an Amal 1038. It was set up for a 2 stroke but with a lot of tuning and a few parts changed I got it to work on my bike with a spare manifold. I welded up and re drilled for the Amal. I also made a bakelite insulator to keep the carb a bit cooler. The main change I made to the carburetor was putting a slot in the float bowl to let the fuel into the carburetor faster. The Amal Concentric carburetors don't have enough fuel flow for an 850 even with twin carburetors, the fuel flow has to be feed up a bit to make it work with just one carburetor. There is a BSA service bulletin about this problem. My friend the late John McDougal had 750 Norton that went over 150 MPH at Daytona in the 70s. He used Monoblock carburetors because they worked better. Later he realized that the main problem with the concentrics was that the fuel flow was restricted around the float needle. He was the one who told me about slotting the float bowl around the needle to let more fuel flow into the bowl. When people say the single Mikuni won't flow enough fuel the problem is the same as with the concentric really. You just need a big enough hole. With one carburetor no matter how big the air flow won't be as good either, but for road use this makes very little difference.

Seems a set of new Amal Premier 930/932 are the same, or less, then most of the single mikuni conversions........

I get that old Amals that are worn out can be hard to tune, but new ones can not be that hard to deal with.
Maybe I am jaded because I am used to tuning CB750 racks....even did a CBX once.

gillou said:

Hello,

Where can i buy a single carb manifold on which i can fit 34 or 36mm carb?

Gilles

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Salut Gilles, tu peux trouver une grande gamme de manifolds pour Mikuni et autres chez Allen Performance Parts, en nord Albionie. Ils sont sérieux et t'aideront avec professionalisme. Demande à parler (ou écris) à Dave.

Ceci dit, moi je suis revenu à deux Amal 32 et ma bécane pète le feu de Dieu! :mrgreen:

jaguar said:

Seems a set of new Amal Premier 930/932 are the same, or less, then most of the single mikuni conversions........

I get that old Amals that are worn out can be hard to tune, but new ones can not be that hard to deal with.
Maybe I am jaded because I am used to tuning CB750 racks....even did a CBX once.

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The cost difference isn't nearly as dramatic as the operational experience, however, if you look hard I'm sure that you can find a vendor that will charge you more for a Mikuni conversion then a set of Amal Premiers, but, in my experience, people purchase the single carb conversion to simplify their Norton experience. The single carb is much easier to install and tune, assuming that the carb is jetted correctly by the vendor.

For those that have extensive experience with multi-carb racks, tune-on, I salute you! My experience leads me to believe that such cadre are in the vast minority.

Jagbruno said:

gillou said:

Hello,

Where can i buy a single carb manifold on which i can fit 34 or 36mm carb?

Gilles

Click to expand...

Salut Gilles, tu peux trouver une grande gamme de manifolds pour Mikuni et autres chez Allen Performance Parts, en nord Albionie. Ils sont sérieux et t'aideront avec professionalisme. Demande à parler (ou écris) à Dave.

Ceci dit, moi je suis revenu à deux Amal 32 et ma bécane pète le feu de Dieu! :mrgreen:

Click to expand...

Hello,

I find my single manifold now i look for the the carb !! Merci Jagbruno

Most used 34 mm mikunis are in very useable condition but the price has climbed to maybe $30 or $40. I used to buy them for $10 or less in the good old days. They were a dime a dozen, not true anymore. Used ones will come with the afore mentioned minor idle screw problem which is not a deal killer. The price of brand new 34 Mikunis is around $100...the last one I bought was $89..a great bargain in my opinion. So you are money ahead buying a new one. MAKE SURE IT HAS A 2.5 SLIDE!!! Changing this will cost you an additional $30 so make sure. Prepare to change the needle jet and needle. THROW AWAY THE AIR CORRECTION JET. Sometimes they will unscrew but not come out, a shop vac works well in this instance. Happy Carbureting...

well folks - thank you for all the wise and useful advice. Having absorbed it all, this is what I did and why...

I bought a single carb kit from Rocky Point. Why? I had bought a mikuni kit from them previously for my old BMW. When it arrived, I bolted it on, pushed the start button and rode off into the sunset. Everything was there, it all worked the way it should, and I've never had to think about them again.

I know its tempting, in this day of the interweb, to try to save a few bucks. There used to be local experts right around the corner who could do everything you needed done. Online selling has made these folks extinct. Let's not make the same mistake again - there are very knowledgeable folks out there (like Rocky Point, but many others) who are using the interweb to reach more consumers. The extra couple dollars they charge is money well spent.

And yes, I'm sure I could have purchased everything I needed (from various suppliers) for maybe $20 less. But then, I'd probably have to spend an eternity "tuning" everything, ordering more jets, slide, another needle whatever. For me, that $20 is the best money I'll spend.

GREAT REASON on buying from a business that you know and trust! I just installed a single Mikuni kit on my 850. I called Matt at CNW and ordered one of his pre-jetted 34mm kits. Why, even though I could have pieced one together and saved a few bucks? I like the way Matt does business. He supports our weird passion for a non main stream motorcycle with great products and excellent customer service. If you have never ordered anything from him you owe it to yourself just to see that there is still a business that pays heed to the little things. Small details like folding back the packing tape onto itself and marking the edge with a Sharpie to simplify the unwrapping. If he pays attention to something this insignificant I can only imagine how he sweats the big things. I guess what I'm saying is that I want to see him stay in business so that he's there when I need something.

eskasteve said:

If he pays attention to something this insignificant I can only imagine how he sweats the big things. I guess what I'm saying is that I want to see him stay in business so that he's there when I need something.

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Very well said!

I could not agree more with the last few posters.

with a hobby like our, if it is not worth paying a very small premium to buy from specialists who really know their stuff and have a proven track record for quality products and services, then what is?!

Those who do not, deserve the extra hassle they have chosen to accept!

I have a very small list of chosen suppliers that I will always go to first. Matt is most definitely on that list. Although he does need to improve the quality of his baseball caps, they are seriously un-dog proof...!

The back ordered fuel taps arrived for my CNW single carb conversion. Got them on and the bike fired up on the second kick. The only adjustment so far was a 1/8th turn richer on the idle mixture screw. Pretty well set up by CNW. Now that said I haven't put a 50 mile test run on it yet to see how it really works. Way too rainy here on Whidbey Island for that. I did run it up and down a nearby road a couple of times-4 miles total. Ran very nice and smooth. Money well spent

Does this carburetor fit on Commando MK3
http://www.mikuni-topham.de/DEUTSCHSITE ... 36-31.html

I don't know why not. Never having owned a MK111 I can't say for sure. Matt at CNW can answer for sure. coloradonortonworks.com

MrNorton said:

Does this carburetor fit on Commando MK3
http://www.mikuni-topham.de/DEUTSCHSITE ... 36-31.html

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There may be a clearance issue with the bell crank operation at the frame webbing where the loom goes through. Clearance can be made without entering into the hole and wiring grommet. This was the case for my 40mm. I don't know the actual dimensions of the 36 but the diagrams I have seen actually show the TM36-68 is 11mm taller than the TM40-6. Go figure!
If making slight changes to fit this is your intention, don't publish it. Some are quite sensitive to the slightest of bastardizations, but not me.

Anyone have any experience from a "Made in Spain" Amal Mark II? This has been stuffed away for some 35 odd years, remember I had it on the bike at least for a while, but don´t remember how it worked. Probably not too good, otherwise I guess I would have left it on there :? . I suspect it comes from a 2-stroke, judging by the way the protruding piece of the needle-jet(?) looks, on 4-strokes that is usually flat. It´s not in good condition, lots of wear and tear on the throttle and in the carb housing as well.






Tommy

Yup. I had one on a Bultaco.
Probably needs a different spray tube.

Or maybe i must buy JSM motorsport dual Keihin set for Norton.
I have PW3 cam and portted cylinder head,so i don´t know how Jim can jetted correct that set for my bike.
When i have looked cases whera are installated VM36 on Norton,almost everyone has diffefent jets,needle etc...

MrNorton said:

Or maybe i must buy JSM motorsport dual Keihin set for Norton.
I have PW3 cam and portted cylinder head,so i don´t know how Jim can jetted correct that set for my bike.
When i have looked cases whera are installated VM36 on Norton,almost everyone has diffefent jets,needle etc...

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I also have a PW3 on my 850 Featherbed racer, I tried dual Mikunis before going back to dual 32 Amals with 260 main jets. Starts first or second kick, goes like a rocket. Clocked at 210km/h-130Mph.

Jagbruno said:

MrNorton said:

Or maybe i must buy JSM motorsport dual Keihin set for Norton.
I have PW3 cam and portted cylinder head,so i don´t know how Jim can jetted correct that set for my bike.
When i have looked cases whera are installated VM36 on Norton,almost everyone has diffefent jets,needle etc...

Click to expand...

I also have a PW3 on my 850 Featherbed racer, I tried dual Mikunis before going back to dual 32 Amals with 260 main jets. Starts first or second kick, goes like a rocket. Clocked at 210km/h-130Mph.

Click to expand...

What compression ratio are you running in your featherbed racer ?