Outdoor Power Equipment and Small Engines - troy bilt 475ss linetrimmer troubles

I have a line trimmer that starts, although with difficulty,but it stalls or will not go beyond idle when the throttle is pulled.I have eliminated the carb as the problem and the valves are adjusted correctly.The fly wheel key is intact and the muffler and flame trap are clear.Lastly the fuel filter is new.My question is could this be an ignition problem?does anybody know how to test the coil? does it have an ignition advance?Any thoughts would be appreciated:confused:Thank You

Sounds like a fuel issue to me which is usually related to the carb. How have you eliminated the carb as the problem?

The coil either works or it doesn't, if you have spark, then the coil is working, since it will run I would say you have spark.

Thanks for the reply.When I first got this trimmer I thought all it needed was a filter,replaced same no help.then I thought either inlet screen or bad diaphram,rebiult carb and replaced manifold gaskets,no help.still felt it was a fuel problem and on closer inspection found the fuel nozzle in the throttle barrel split,thought for sure this was the problem...so new carb,no help.Also during all this I checked the exhaust for any blockage and adjusted the valves,they were off a little but no help.So at this point I was wondering about the coil.I do have auto and aircraft maint experience but am just learning these small engines any help is appreciated.Thanks again

What kind of compression does it have?

I,m not sure what the compression is, but I did pull the cylinder to look at the valve seats and I could not separate the eng halfs till I removed the spark plug ,so the rings seem to seal good and the ring gap was staggered .the valve seats and the valves were in good shape.Do you know what the compression should be?

Around 90 psi.

How far are the valves opening and closing? I wonder if a cam lobe is worn down.

I've got .125 on the intake and .115 on the exhaust.

that measure is in inches

I'll have to look at one at the shop... I think there's one I can look at there. That doesn't seem like enough (1/8 inch and less?)