Monoblocs

... the profile on the new one is decidedly angular.

I know that I’ll probably get buried under a hail of negative replies, but is the sharper profile of the new carb  really likely to cause that much of a difference?
Maybe it will make the carb run a bit richer? Then again, maybe it won’t have any effect at all and David can put away his Dremel and grinding wheels before taking action  :-)

Regards

Tony

Is the new Carburettor an Amal or Wassell?

Paul  - Do Wassell sell  Monobollock copies now as well?

David, - To be honest, I'm with Tony, What is the likelihood of needing that last 200rpm, 2mph or whatever the effect will be, (unless of course it is being prepped as a racer..).

I'm sure that after the usual 'set up' tuning, that when being ridden as is it will be perfectly fine as it is.

Also, leaving it unmodified means if there are any issues with it, the guarantee will be valid. As soon as the Dremel hits it.....

Also, whether you fit meshed bellmouths or better air cleaners, you won't even see it.

Regards,

George.

The new one looks bored slightly off centre to the casting. Don’t think originals were machined at all in this area. Interestingly the old one has not had the bellmouth threads machined either. Leave it alone, might be even better as is but I seriously doubt there would be any measurable difference 

I am guessing that whichever factory made the castings was saving some money by not using a multiude of patterns.  They just cast the smallest bore units and then simply bore them out to whatever size is needed.

It would seem to me that the airflow will be upset by the sharp edges at the transition from the casting to the machined out bore.

Mike 

Just an aside - are the chunky float chamber cover screws drilled for wire locking?

Thinking has changed on super smooth inlet tracts and they are only considered a good thing for fuel injected engines. Carburettor engines benefit from a little turbulence.

The Gold Star has a distinct step in its inlet tract, and machining to achieve a smooth bore reduces the maximum bhp. I guess with a 1 1/2" GP that any help getting the fuel to evaporate must be beneficial.

Hi David,

Personally mine never have. The original screws are of course countersunk, which means they tighten up well and the taper helps keeps them there. 

This is both on my 650 now, and also a 'back in the day' racing Bantam (the only bikes I've had with monoblocks).

However,  if you want to have the 'look', go for it, but as a suggestion I would wait until you are sure that the float is working as it should before doing so as you will soon get fed up of threading the wire in and out.

Now, if you were asking about the carb top ring staying tight even with the spring clip to hold it.......

Regards,

George.

To confirm the Gold Star experience,  In Beart's "Single Purpose" there is mention of an improved performance (2 MPH on a 1/4 M run)when the locating lug on a slide was worn and offered a misaligned edge to the inlet tract, proved by replacement and repeated tests.

With regard to the bell mouth; the only advantage I know is that it helps contain whats blown back and deposits it behind the mag instead of on it...

Cheers

J 

.. find it easier to fit the cable to the handlebar lever last giving more slack when fitting the air slide. But as yours is a twin presumably you have a junction box somewhere which may make it more difficult.

David it's a very complex fluid dynamics question, certainly beyond me. But I do know that dimpled golf balls go further than smooth ones.

I read that american tuners no longer favour super smooth polished inlet tracts, but more to do with efficient evaporation of petrol droplets I suspect.