AJS & Matchless Owners Club

I've fitted the Thorspark and managed to get it to fire albeit with the throttle full open. Could it be that the needle and pilot jets are the wrong size? The supplier kitted it as per Plumstead specs Pilot 30cc and Needle 106. Any advice gratefully received.

Fitting a Thorspark unit should not change the carb jetting requirements in any way. It is more likely you have a timing problem

I thought the "correct" main jet was 260. I have a new carb on mine and to get it running right I've put a 280 main jet and a 35 pilot jet but gonna try a 40 pilot as I still have a flat spot just above idle.

Have you checked the float level? Should be correct on a new carb, but you never know...

clanger9 wrote:Have you checked the float level? Should be correct on a new carb, but you never know...

Yes I forgot about that. My new carb it was miles out had to put a shim under the seat.

I might try raising the valve throttle needle

I wouldn't muck around with anything until the float level is spot on. Most carbs (especially Amals) won't work *at all* if it's not correct.
An engine will usually start even if the mixture and jetting is miles out (it just won't run properly once it warms up).
The needle position just changes the full throttle mixture. It doesn't affect starting.

Assuming you've got a Monobloc, it's easy to check the float height. Just remove the pilot jet cap and push a length of transparent plastic pipe over the jet. Switch the fuel on and check that the fuel level settles in line with the bump on the float chamber.

If that's right (and the timing is even vaguely right), tickle it and it should fire.

If it chuffs & coughs, dies something is wrong with the fuelling.
If it spits back, it's lean and/or retarded.
If it kicks back, it's advanced.
If it won't do anything, take the plug out.
If it's wet, you flooded it so kick it over on wide open throttle until it fires. Then start as normal.
If it's dry, something is wrong with the fuelling.

Good luck!

Stupid question but I do block the end of the tube? Supposing the fuel does not rise to the appropriate level how do I alter the float height?

http://www.ebay.co.uk/itm/RKC-SHIM-AMAL ... xyjFpSTDon

Bend the tube around so that you can compare the level against the dot under the word Amal. The fee end needs to be open so the fuel can find its true level.

As Harry said,
Just hold the free end of the tube alongside the carb and an inch or two above the 'dot' on the float cover. Fuel won't overflow.......unless the float needle isn't shutting off, in which case fuel will be spewing out of the carb throat anyway

Regards, Steve