No fire trimmer

[38racing]

Fellow asked me to check a trimmer he bought. Cub cadet 2 cycle cs202. Has spark. Tried 2nd plug. It won't fire on carb cleaner. Pull seems easy but 4 pulls gets to 92 psi. I haven't remove muffler. Would a plugged exhaust prevent any fire or just give bad performance. Any other ideas on the problem.

[KE4AVB]

Yes a plugged muffler would do it but I doubt that is going to be the problem. With compression @ 92 psi it is below what I have seen as bare minimum compression (100 psi) for a 2 cycle ignite the fuel mix. Actually you should be seeing compression around 120+ psi. Btw there is no replacement parts when comes to the PNC and crankcase other the two o-rings; therefore, if the it fuel or ignition related it is a throw away unit.

As for the easy pulling it is probably one those starters that has helper springs.

[jwales]

I had something similar with a Echo SRM 210 weed trimmer. The unit had been sitting for a while. Had spark, known good plug, clean screen, no fire with starting fluid. Looked closer at the muffler... a mud wasp had started a nest, plugging the exit on the exhaust.

[38racing]

I had something similar with a Echo SRM 210 weed trimmer. The unit had been sitting for a while. Had spark, known good plug, clean screen, no fire with starting fluid. Looked closer at the muffler... a mud wasp had started a nest, plugging the exit on the exhaust.

I guess I'll pull the muffler then. Service manual did say 90 was in range for it but combined with other problem might not be enough.

[KE4AVB]

38Racing I was just speaking from personal experience working on 2 cycles for the last 9 yrs. So far I had only 2 cycle that even hit at 95 psi and it still would not run but as I said it is just my personal experience. I even got one Stihl chainsaw that registers 135 psi on the gauge but after going thru it I can see why it will not fire up as right at the top of the stroke it losses most of it compression due to a bad cylinder.

[38racing]

I guess maybe it could be case of coil that sparks but not under compression. I assume that unless the electrode is somehow grounded that the plug is sparking if the inline tester is sparking?

[Skywatcher]

Hi 38

When ever I'm going through a trouble shooting sequence on any two cycle engine, I always use a 40:1 premium fuel mix in a squirt bottle for testing. I feel that carb cleaner has a tendency to dry out the internals of a two cycle engine, whereas the oil in mixed fuel helps the ring seal improving compression. The other thing to check is to see if the spark is actually hitting at the right time. In other words, has the flywheel key been sheared? If flywheel is OK, try dribbling 1 or 2 ml of two cycle oil onto the piston through the spark plug hole as if you were doing a wet compression test, then try starting the engine. Just a couple of thoughts,

Sky

[KE4AVB]

Yes carburetor cleaner and starter fluid are both bad for use on any gasoline engine especially 2 cycles. To me if it won't start on what it is meant to run on then there is a problem. Even starter fluid on diesel can make them dependent on it like a drug addict.

Now with some handhelds just be aware that the old magnet pointing to the coil trick don't always apply. Stihl 4 mix and Shindaiwa C4 for examples align differently so you must verify the flywheel key if you suspect ignition timing problem.

Personally I don't trust those inline testers. If suspect a coil of being weak then an end of the line spark gap tester should be used. That should eliminate any false readings though it doesn't test the plug itself.

For inline testing just use your wife or kids for you might get just as good results. Just plain shocking and mean. Just indicates voltage is present but not how strong; although, a smack across the chops might be a good indication.