Need Advice With a 340 Trailfire

[Jwesty]

I'm younger and newer to small engines and was looking for a cool project, so this winter I purchased 2 Trailfires for $100. One was more of a parts machine and the other was to fix up. So I got the one up and going (kinda). The engine's compression is about 120 for each cylinder, I replaced the carb and fuel pump, and i had it idling at one point. I was using starting fluid to get it going (i know not the best idea for a 2 cycle) and it actually was running for a solid minute, i just had to kind of figure out the idle. So, i tried to get that focused in but i just couldn't and now it only runs for a second on starting fluid then dies. I don't know if it's a gas problem or something like a bad crank seal, and any input would be greatly appreciated. I just would love to get this figured out.

[jep_800]

Welcome Joe,

There is a whole list of things that will probably need to be gone through if you want to make this a sled that you ride on a normal basis. But one of the things you mentioned is absolutely 1st priority, which is the crank seals. No matter if they look decent, just replace them, as you just can't trust them after sitting a long time.

Your compression seems good so you can move past that for now (just know it may need to be addressed later as you really won't know the condition of your pistons, rings, cylinders, etc until you take it apart): So next is carburetor, fuel lines, filter, condition of the tank, pickup line, fuel pump. Everything must be clean, and in good condition inside your carb, or it just won't work right. Get a manual and make sure it's adjusted to factory spec. Idling for a Mikuni carb relies heavily on the slide cutaway, pilot screw, and idle set screw. But past 1/4 throttle other things are in play like your needle jet, jet needle, main jet, etc. Best to set it all to factory so you have a good baseline for tuning. If it's dual carb, it's even more tricky because the two carbs must be synched in unison.

I place ignition next. A weak CDI or stator, or both will leave you scratching your head. A CDI can work on the low end allowing starts, but cut out on the high speed side which prevents higher RPM. A stator can work fine on the trail, and then when everything is warm, lose continuity and won't restart, or run as it should. Both need to be in good working condition. After that, you need to address coils, timing, plugs & caps, proper gap and heat range, etc.

Does the sled have the correct air box for the carb? It actually makes a difference and needs to be there for the proper air intake for your carb. Check your pipe to make sure there isn't a blockage. Sometimes they are filled with a mouse nest or something that restricts airflow.

This is just a short list of things that must be checked over. It can get much more detailed than this, but it's a good starting point to get that thing to run consistently. Let us know how you're doing.

Jason

[Jwesty]

Ok, thank you! The carb is new and airbox is correct. Also fuel moves through the lines, and I feel like with a new crank seal I'll probably get better air from impulse/vacuum line. Thanks for your input and I will let you know how it goes!

[Jwesty]

so, i tinkered around with the sled a little bit. And what i've figured out is that it runs pretty well with some gravity fed fuel from a bottle! it idles and accelerates, but i just can't get it running good with the fuel system. I can get it to run a little bit when choked but if i unchoke it with the fuel system it dies. I'm still thinking crankseals as that should affect the impulse line's power coming from the engine? but i also feel like the engine wouldn't run well with bad crankseals. Any imput is greatly appreciated!

[JDT]

First thing to do with any old sled engine is renew the crank seals.

[Cabindweller]

Best thing you can do to start out with is change the crank seals.

[AirborneX4Special]

Did someone say crank seals?

[nick80lf]

You mentioned the carb is new.....if you haven't already you might want to compare the jet sizes in this new carb to manual specs.

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