LCGB Forums

Hello

I want to experiment with a Polini cp24 carb on my GT186, without changing the manifold.
The OD of the Polini is 28.5mm. The OD of the fixed GT186 25mm Manifold is 31.0 mm

I've been searching the internet without success for a stepped rubber 28.5 > 31.0 - any ideas? (......and I need it by Sat 5th!)

Try Allens in Notts, they have a decent website listing rubbers with dims

I wanted to step a MB TS1 VHSB manifold to take a 30mn Phbh, but couldn't get one ... So I had an Ali sleeve made for the Phbh....you might have to go that way.

Cheers I’ll take a look

If you can acquire a conventional, unstepped rubber connector that is 28.5 x 28.5, one end can be enlarged to 31 mm.

I don't recall modifying anything so small, but have done so for larger carburettors.

Ideally, one end (that you wish to keep the same) is mounted on a spigot in a lathe, Before any modifying, the thing is then spun up & trued up as best as the eye can see, because rubber is so flexible.

Then the bore is opened up with it spinning in the lathe by grinding with a die grinder, bearing in mind that there is usually a locating rib. Grinding is the only way. Using conventional lathe cutters will just dig in.

I've made it sound in the description a lot harder than it is but anybody that does a bit of porting (Ahem!) should be able to do it.

If you get really stuck acquiring a new made to measure part, let me know, but if the "Cov" in "Covboy" is Coventry, then there must be resources in your area, surely

Thanks mark
I’ve ordered a 28.5 x 28.5. I’m going to put it in very hot water and see if I can fit it on the manifold end whilst the rubber is expanded and flexible.
The place I’m going on Saturday has all the facilities you describe below so if the above doesn’t work well give your method a try !
I’ll report back.

I think you might have better luck using a straight silicon reducer. One of the standard sizes is 32 to 28. Depends if it will stay airtight at the 32 end. If you heat the 28 to go onto 32 it's naturally going to want to force it's way off. This type of thing. https://www.ebay.co.uk/itm/Silicone-Hos ... SwFdRe1mKR

Thank you Martin
I’ve ordered one of these now too - watch this space !

A 28.5 x 28.5 rubber was a perfect fit to the GT manifold and the correct size for the carb. Result. No heating needed.