Python 250 carb

[nickg]

Hi

I'm after carb advice/source for 250cc Python.

Progressing with Johnc's Cotton Python 250 project that I have taken on. Alan Freke has been really helpful and provided an advance retard points housing for the Miller dynamo.

I have a bucket full of carb bits but none seem right. 2 Bowden carbs that would fit but a bit worn and not something I am familiar with.

I have a 1" pre monobloc Amal but assume this is a too big and that 7/8" would be better?

Not keen on a horizontal Amal but do need to miss the frame and tank, starting to appreciate the downsides of the triangulation:-)

Any help appreciated.

Thanks

Nick

[chris1]

I would say it depends on your objectives and budget. A 7/8" 276 Amal would be about right although your 1" might be quite Ok. You can get new ones but are not cheap. Another cheaper route is second hand and a refurb from Martin Bratby. He does an excellent overhaul including reboring the body and making an oversize slide.
I found a straight inlet (downdraught) works best but for clearance a remote float chamber gives a more flexible instalation. Again you can buy the proper Amal one or maybe make from a bolt-on chamber. You need to be creative with the mounting as there are no level or parallel frame tubes on a Cotton. I found no need for rubber mounting the chamber on my 350 Blackburne engine.

[cottonjo]

I have some spare Bowden parts and a Bowden catalogue if needed.
Paul

[nickg]

Thanks both, not ignoring you, thought I'd enabled forum alerts but obviously not!

Useful responses and I think I will try the 1" Amal and the Bowden as is and see how they work. The Bowden does seem very complex even though mechanically simple! So many pathways for fuel and air.

I found some Bowden literature from Justin Faithfull.

I'm some way off hitting the road but trying to get stuff in advance of actually needing it.

A bit nippy in my unheated shed at the moment!

Cheers

Nick

[cottonjo]

I have been running a Bowden on my 350 JAP for over 30years. Picked up a new old stock one on eBay last year for £168. Label on it said 12s6d. Choke seems to be just an ornament, but otherwise performs well.
Paul

[cottonjo]

There is an RH29 for sale in this month’s OBM £125.
Paul

[nickg]

Interesting to hear Paul, I assumed they were a vintage curiosity!!

I don't have Old Bike Mart sub, have just subscribed but cant buy latest edition and can't see add on website.

As I say I'm a little way off firing it up!!

Cheers

[cottonjo]

OBM says email [e-mail] or ring 014422 884280 W Yorkshire

[nickg]

Thanks, we got out of step!

[cottonjo]

The RH refers to the float being on the right. Bowden was fitted as a standard when new to Cotton and one other make. It was generally an aftermarket product used to gain a little more performance. The Brooklands Cotton that achieved 12 records in 1935 had one with twin floats.
Paul

[nickg]

Sorry Paul, were contacts for the seller or the mag? Email bounced 'user unknown'.

Nick

[cottonjo]

A typo on my part, it is the seller. Should have read [e-mail]. Substitute an l for an i .
Sorry
Paul

[nickg]

Arrived today and looks fine at first view. Thanks for the heads up Paul.

[nickg]

Second inspection not so good!! Full of white powder and all threads seized. I'm guessing ultrasonic clean with caustic degreaser and not properly rinsed and dried? Cleaned up now but took a while to get it all apart without breaking anything. Float needle was bent but I think I managed to fix it, seems to seal now.

Paul, do you think I need to remove the jet next to the float chamber that connects to the 'choke'? Blown out with air and poked with guitar wire but looks like it needs a special spanner to remove.

Pic of main jet attached.

Attachments:

[cottonjo]

I would leave that jet alone. Main jet at 110 on the large side. I run my 350 on a 90 and 100. Float needle is a bit delicate.
Paul