norvin

[roy the mechanic]

Glenliman, I make you right, small ports+ carbs = torque, big ones = horse power. High horses are not required on the "street" as useful as they may be on the race course. A quote from the tuner C R Axtell "I done wore out the dyno proving that tourque out of the turns wins""

 

[Monkeypants]

Right Roy.
One of the well known race tuners in the Commando world has put up a lot of info on the AccessNorton site. In doing countless experiments on donor heads he has produced some interesting data.
Hes been building Norton race engines for years and talked about some of his early attempts that sounded great on paper but did not turn out well. One problem with overly large intake ports was the loss of charge density as mentioned. In some cases this was so severe that the engine did not have sufficient mid range grunt to get thru to the higher rpm where the oversized ports and carbs might have worked. In other cases the engine got there eventually but lost so much in the midrange that it was not a competitive engine.

Most interesting was to see what the screens on open velocity stacks do to flow. The wire to wire intersections create little vortexes which impede flow drastically. On the other hand a decent sized K&N type air filter has little effect on flow and in some cases can even increase flow by smoothening things out.

Glen

 

[roy the mechanic]

cold still air has always been the best thing to "feed" your motor on, it's more difficult on a cycle than a car due to the lack of space. ps might be worth googling c r axtell.

 

[John Jones]

Little Honda.
Sorry for the delay in getting back to you.

Kickstart is 2 CB 750's spliced and welded. The first one I had made was a little too long so had one made a little shorter to fit into the frame.

The centre stand was also bespoke and I had to have 2 lugs welded to the frame as a manx has no provision for a stand.
The stand uses a wide flat spring as it was impossible to find a location to mount a normal coil spring. I don't know what the spring comes from as a friend of mine had it in his workshop.
A lot of work for what looks like a very simple piece of kit.

 

[John Jones]

This is the latest kickstart, shaped to fit under the top frame tube so it doesn't stick into your leg when riding.

 

[Howard]

Hi John,

Does it turn over ok with the extra length? My standard CB750 Kickstart (long version) takes a lot more effort than the standard Vin one.

H

 

[John Jones]

The 1st one we made was the same length as the original vinnie.
The problem was it was too long to tuck in under the top frame tube so the 2nd one is about 1" shorter than standard and tucks in nicely.
It's not the length of the kickstart lever that makes it more difficult to start but the fact that it is so much higher in a Norvin than a standard bike.
This is the main reason for the centre stand.
I didn't want a Norvin that I couldn't start, and with clipons and most of your weight over the bars it can make getting a good kick on the lever difficult.
Note the decompression lever on the right handlebar.
This has been put here so the bike can be started on the centre stand with my right hand on the throttle and decompression lever and my left hand on the seat so as to get most of my weight over the kickstart lever.

 

[ogrilp400]

The effective length of the original kick start is not the distance from G83 along the kick start lever and up to the foot piece. The effective leverage is a direct line from G83 up to the foot piece. To illustrate my point, if you were to make a kick start lever that extends from the pivot G83 all the way to the back axel then back to G83 and put the foot piece adjacent to G83, then you wouldn't be able to kick it over because there is no effective leverage. So make the kick start the same distance as the original from G83 to the foot piece.

Phelps.

 

[Howard]

The effective length of the original kick start is not the distance from G83 along the kick start lever and up to the foot piece. The effective leverage is a direct line from G83 up to the foot piece. To illustrate my point, if you were to make a kick start lever that extends from the pivot G83 all the way to the back axel then back to G83 and put the foot piece adjacent to G83, then you wouldn't be able to kick it over because there is no effective leverage. So make the kick start the same distance as the original from G83 to the foot piece.

Phelps.

Give me a lever long enough and a solid place to stand and I'll start the Vin - Archimedes, a man before his time.

Don't forget, if the lever reached the back spindle your foot would hit the ground before you turned the crank far enough, or fast enough to start the engine.

H

 

[jim burgess]

This is the latest kickstart, shaped to fit under the top frame tube so it doesn't stick into your leg when riding.

Hi John, this is lovely looking work and your kickstart/footrest setup looks like the answer to my prayers. My Norvin uses the standard Vincent arrangement plus sidestand, this makes a bit of a balancing act for starting... And gets in the way for riding. You say your kickstart is made from 2 CB750 units? Is there a particular model I should be looking for when trailing thru e bay? Or is that it? Did the splines match up? Or was there some further engineering involved and the footrest/gearchange, bought in or made by you?