Fuel flow limitations of the concentric carb

[Rocket Racer]

Glen,
It could be many things including and not limited to; gearing, cams, compression, condition, valves, springs, cam followers, porting, dragging brakes, flywheel/piston weight...
I recall a few years ago I was racing a norton 750 atlas (before I saw the light) with a fellow competitor who had the same model bike (his had a commando engine) and from what he told me in a higher state of tune: It always used to wind him up that my motor could routinely out accelerate him , so he just couldnt beat me. Arguably they were both comparable both being norton twins but they weren't the same. I guess if I had owned the slower bike I would have looked further so I understand you'd like your super rocket to be on the par you would expect.
Tim

[Brian]

came across this in another club magazine.

[muskrat]

G'day Brian.
Yes I've seen those bowls and yes they do help. Methanol bowls are better again with a 4mm hole.
Cheers

[worntorn]

Hi Brian
Thanks for the post. This is exactly what Jim Comstock found with his dyno testing . It really confirms that there is a potential problem when using the stock single Concentric.

I think something else is holding my A10 back but I would know for sure if I could ride a "good" one.
A friend has just restored a plunger Golden Flash, maybe I'll cadge a ride on that. If it is quicker than my Late model Super Rocket I'll know something is truly wrong!

Glen

[Brian]

I have run A10's with concentric carbies and must say I have never run into problems with fuel starvation. I must also say I dont like concentrics, in my opinion Amal's worst design ever. The monobloc was a far superior carby in design and quality of manufacture.

I note worntorn you are using a GPS so dont compare the speeds your GPS shows with what literature says or other riders claim to be getting. A lot wont like hearing this but there were very few British twins of any make that would do a genuine 100mph. Road tests of the day and smiths speedo's are optomistic to say the least.

[worntorn]

Good point about period road tests although I have a couple here that claim close to 110 MPH for the late Super Rocket and they also state that timing equipment was used.
Also, the comparison between the two 650s, my Norton  650ss and the BSA SR has me perplexed. That test was done using the GPS to rule out speed variations between the two bikes.
I could imaging the twin carbed SS would be a smidge faster than the BSA but not the amount I'm seeing.

Glen