Carburettor spacer and gasket

[Billington]

It’s hot (28 C) and my 1932 BSA doesn’t like it. The bike experienced vapour lock after traveling just 1.5 miles, hence I’m going to try a Tufnol spacer to reduce heat transfer to the Carburettor body.



Will the spacer act like a gasket or should I place a gasket either side of the spacer?



Thank you for any help.

[TGR90B]

Tufnol is fairly soft and should be good enough on it's own if the faces are flat and sound. That spacer in the picture looks very hard and I would use gaskets with it. I'm no expert so weigh it up for yourself or ask the supplier when you order it.

[Billington]

Thank you TGR90B that is helpful.

[R]

It’s hot (28 C) and my 1932 BSA doesn’t like it.

Thats about winter temp in warmer climes !, and a VERY short timeframe, so you may have other problems ?
Was the carb very hot to the touch ?
Checked for blocked jets or debris/water in the carb ?
Blocked fuel supply somewhere ?

Tufnol washer sounds like a good idea anyway.
Give the carb and fuel system a good clean at the same time...

[cardan]

I bet it's a sidevalve - they do get a bit hot. I had a 1930 Sloper and the spacer was an improvement.

Just a smear of sealant on either side of the spacer. I prefer non-setting stuff.

Leon

[john.k]

Plus the usual warnings not to bend the carby flange with thick soft gaskets.A hard spacer and a smear of silastic on thin paper gaskets is the go.

[iansoady]

I'd use a thin paper gasket with wellseal on the engine side. Same but with grease on the carb side to allow for easy removal / replacement.

I don't think Tufnol is soft and in my experience won't conform to a less than true mating surface.

[john.k]

Ian ,you are correct ,it is a hard fabric reinforced phenolic resin,and quite expensive at times......Anyhoo,to all intents and purposes,it will be rigid as a carb spacer.....On the subject of vapor locks ,is the expansion coil in your fuel line horizontal,and allways sloping downhill.......but vaporlocks can be problematic......I had a Ford V8 flathead engine truck,and after a hot stop ,it just would not start......but of course ,the tank was a lot lower than the fuelpump,and that is the typical scenario for vaporlocks.

[Rex]

Yes, the spacer pictured looks to be made of what we used call "Paxolin" in the electrical industry and has no "give" at all, so I go for a gasket on both sides.
"Tufnol" as I recall it, was a hard rubbery stuff but with a little give in it. Is it still available?

[iansoady]

Tufnol is essentially the same as paxolin - hard, fabric reinforced phenolic resin (as you can smell when you machine it) as John says. I'm not sure what you're thinking of Rex......

[chaterlea25]

Hi All,
If it gets hot enough to give trouble in 1.5 miles then I would think there are some other problems ?
Retarded timing?
Blocked or restricted fuel flow / fuel cap vent ?
Too tight valve clearance / poor valve seating?
Wrong plug heat range?

Double up on the 1/4in insulators or get a thick one will help some more
Add fibre washers to the carb stud nuts,
I have seen sleeved stud holes with top hat insulating sleeves on Guzzi's
A BSA M21 carb spacer and long studs can also help by moving the carb away from the cylinder some more if there's space available

I have a little JAP sv OK Supreme that has a long inlet tube so the carb sits behind the maglita
This does not suffer the problems I have encountered with sv BSA's with stub fitting carbs from the 20's
that boil the fuel in the carbs

Paxoilin or Tufnol ? In my experiences it is the same stuff just trade names maybe different in other countries ??

John 

[john.k]

I do recall carby spacers made of semihard black material back in the day when we all had hair and rode 650s like we didnt want to make it to 25......and Ive seen plenty of carbys with bent flanges ......I would doubt a carby spacer would be made of the genuine material......its very expensive ,and also notoriously hard to saw or machine.....I have a 4'x3' sheet of the stuff  that cost $1100 ,used to make the vanes for air compressors........its also used as a bearing running in water,like ship stern tubes,where strips of phenolic and soft rubber line the tube,also used as a bearing in rolling mills ,running in water for cooling.

[iansoady]

I've seen spacers made out of a soft asbestos-like material (I assume not actual asbestos....) which would exacerbate any flange bending tendency.

Rather than fit 2 spacers I'd buy (or make) a thicker one like the one I have on my ES2. Eg from Hitchcocks: http://accessories.hitchcocksmotorcycles.com/Amal-Carburettors/Tufnol-Carburettor-Spacers-20mm

[john.k]

And 28C isnt hot ,its lovely mild riding weather..........42C is hot,and petrol boils in the tank if you park in the sun.

[Billington]

Thanks guys for your advice, I’ve now purchased a Tufnol spacer and two gaskets.

Cardan, you are correct with your guess about it being a side vale. It’s a 1932 BSA W32-6 500cc.

It runs sweet at temperatures below 20 C the problem gets progressively worse as the heat rises above this point. Back in the 1930s this set up must have been fine; either I’ve got another problem like you suggest Chaterlea25, or do modern fuel burn hotter?

I think I may have to change the carburettor body mountain studs for longer ones. Where should I look for imperial/Whitworth thread studs?