Hi

My new (to me) trials cub has a rear Pirelli MT13 fitted, What is the difference between that and a MT43 rear tyre.

The carburation is not good(mk1 Concentric fitted ), at idle its ok, as I open the throttle it coughs and sometimes stalls as the slide lifts initially, ok at quarter throttle plus.

I have 120 main jet and #4 slide fitted needle in centre groove. The plug is very black, my next plan is 110 main jet, #3 slide too richen it up off idle, and weaken it at high power thru the reduced main jet.

Any help appreciated.

triton

MT13 is a very old design from the 70s, hard compund, MT43 replaced it in early 80s, softer compound than the 13 with unique tread pattern. Either will work OK on mud but are way behind current super soft tyres from Michelin, IRC or Dunlop. Those three will give superior performance by a long way, like you wouldn't believe, on mud and especially rocks/rocky streams. The pirellis will be unbeatable on snow or ice though as their harder compounds bite in better.

Chances are your MT13 has been on for many years so may now be very hard and pretty much useless.

Can't really help with the carb as don't know much about cubs. Guess you've elliminated the basics like the carburettor body being worn out, old jets etc. Apparently the Amals differ in some way depending on whether they are for 2-stroke or 4-stroke engine but don't know how. Make sure you have the correct type if that is the case. Someone else on this forum is bound to know.

Could also be electrical?