What does the SU Capstat jet do?

[Bumpa]

On my 1977 model 1850 the SU carbs are fitted with the Capstat jet assemblies (ringed in my picture). What is their purpose? How do they work? I will be having a look at the carbs and cleaning them (FZX1265 type) and don't want to spend £90 replacing the jet assemblies if they don't usually wear out. I've worked on lots of SU carbs before but never one of these later types, so any advice is gratefully received.

[cliftyhanger]

They are a temperature compensator, so lean the mixture off as temps increase. they contain a waxstat capsule.

Trouble is they have a nasty habit over over-leaning the mixture, with poor running a result once hot.

You can prise the base off them, and replace the waxsata with 2x 1p coins,abd then replace the cap. Saves a good few bob in the process.....

[Bumpa]

You can prise the base off them, and replace the waxsata with 2x 1p coins,abd then replace the cap. Saves a good few bob in the process.....

Now that I approve of . Alternatively, will the original style jet (as shown in the upper part of the drawing) fit that carb? They are about half the price.

[cliftyhanger]

Yes, but you need the linkage bits for them. I believe you can buy a "waxstat conversion kit" with those included. Should be the same as spitfire/dolly 1500 (I think, but check. Same sized jets are fitted so that is what I am basing my reasoning)

[Magenta Auto Sprint]

Here is a link with photos from the mini forum

http://www.theminiforum.co.uk/forums/to ... onversion/

or the SU carb webs site
http://sucarb.co.uk/waxstat-jet-conversion.html

malcolm

[SprintMWU773V]

I highly recommend the 2p (4p on twin carbs) conversion, works a treat.

[AlanH]

You can prise the base off them, and replace the waxstat with 2x 1p coins,and then replace the cap. Saves a good few bob in the process.....

I wonder how necessary it is with the 1850 being a crossflow engine. Having said that it's a cheap, quick job. I did it on my 1300.

[soe8m]

When you can't remember when you or don't know when the needles and jets were changed the last time the best is to replace them. Better running and more economics. Two full fuel tanks and the new needles and jets have paid themselves. These parts do wear and better not changed seperate.

Jeroen