Speedfight 4, possibly running too rich (pics inside)

Hi All,

I have had my Speedfight 4 (2t 50cc LC) for nearly 6 months now and it was derestricted by the Scooter shop where I bought it from. It went in for its 600 mile service and need a new plug as the plug had heavy deposits on it and there was hardly a plug gap left to create a spark. After some discussion this was believed to have been caused by the Castrol oil I had been using for a bit when I purchased the scooter (it wasn't a scooter specific oil but the a race one).

Recently I have noticed a drop off in the scooters performance. It seems when giving it WOT there is no real power increase and whilst the scooter appears to run fine, it just doesn't go anywhere (I appreciate it is only a 50cc but when riding it everyday, I feel I notice any subtle changes in performance). I wanted to check the plug again from the previous experience as this seemed like an obvious place to start. This is what I found









Now it looks like the scooter is running rich to me. On this basis I took the carb off to see what main jet was installed, it turns out it is a 56. I am assuming the Scooter shop will have fitted this when they derestricted it, either that or they also suspected the scooter was running lean which contributed to the first spark plug fouling and they whacked a bigger jet in it then and didn't say anything. I was thinking to try a 55 in the carb to see what effect that has but I have to be honest this is very much trial and error and I am relatively new to the world of scooter mechanics.

Would anyone happen to know what the default main jet is on a Speedfight 4 2t 50cc lc with a 17.5 dellorto carb please?

Also, you may be thinking why am I not taking it back to the dealer when it has two years warranty on it? Well after having a close look at every screw/bolt they have touch, my confidence in them is lacking and I would sooner do things myself where ever possible!

Any advice or input will be much appreciated so thanks in advance.

 

Plugs don't foul through running lean, they foul because they run over rich or the rings or bore is worn burning oil, which looks like what you have.
A 56 jet wouldn't give you that amount of plug fouling, that definately looks like you have shot rings or the oil pump is putting too much into the mix.
You can also get the same effect if you are adding oil to the fuel (pre-mix) whilst still using the oil pump, you're not are you?

 

Thanks for the reply. No I'm adding no 2 stroke to the fuel it is all done through the automatic mixer pump. Are there any other symptoms I would have that would indicate shot rings please?

 

I thought I would post back to close the loop on this one. Here is a snapshot of how the plug is looking now (this was after a good long run out on a new plug, mixture of throttle positions and not doing anything specific other than just riding the bike). I changed the main jet to a 55 from a 56. Needless to say the bike is running an awful lot better now.

 

Personally I'd run it a little on the rich side, especially when the warm weather comes !