Hey all,

I have a mountfield SP414 with and RS100 Engine, it's 2 years old, it starts up fine but after a few seconds its starts hunting and running lumpy.

I've made sure the fuel cap isn't too tight, Drained the fuel and put some fresh fuel in, tried adjusting the idle speed, took the carb to bits and it all seems clean inside, Replaced the Oil, Air filter, spark plug and all the gaskets on the carb and its still running bad.

Before I give up and take it in, can anyone else think of anything I can try?

Thanks

Vacuum leak?? Not familiar with that engine but if there are any vacuum control lines then they might be suspect.

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sent from my laptop using my fingers - because we REALLY need to know where it's come from.....

There is a long legged thin spring (about 3" long) that has a hook at both ends that goes to the carburettor to the throttle linkage. This is on the crank at the engine end of the throttle cable. This seems to keep the running balanced and over time it stretches a little. If you bend the hook a bit more at one end it tightens it a little and often cures it from hunting.

DWD

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Painting with BIN

changed the inlet/carb gasket ? has the fuel line gone crispy ?

ive changed all the gaskets on the carb yes.
Oh cool ill give that spring a try tomorrow.
Thanks for your help everyone ill get back to you with my findings

The spring is part 35 on Flash's diagram

DWD

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Painting with BIN

just fixed my rs100 mountfield from hunting revs remove carb
remove plastic idle screw remove black plastic plug which was located under screw and found small O ring had broken off .throw O ring fit plug without O ring .jobs a good one