4-Cycle engine question

I have a small weed-eater with a four-cycle engine. It’s been running fine, but this time it won’t stay started. I primed it and finally got it to turn over, but it runs for 10-15 secs (starting high revs then throttling down) and then cuts off. Hitting the manual throttle at any point kills it instantly. What gives?

Did you leave the choke on? Make sure that you open up the choke after starting and it is warmed up.

Are you sure that it is a 4 cycle engine? Just about every small string trimmer I have ever seen has had a 2 cycle engine. It sounds like your carb may be clogged from old/bad gas, try removing, disassembling and cleaning the carb with with a spray on or soak in type carb cleaner.
Good Luck

make and model helps with questions like this

Good idea. Troy-Bilt TB425CS. It is clearly a 4-cycle (it even says so in big print! ;)). No choke that I can see.

I would really look for a choke lever. It sounds like its flooding out (to much gas when you hit the throttle.)

Otherwise, have you used it this year? Pull the air cleaner and see if you get the same results.

Honestly can’t see a choke lever, but I’ll look again later. I’ll also pull the air cleaner since that sounds like a pretty easy thing to do. If that doesn’t work, I’ll pull the carb, but I know from experience that’s a total pain in the ass (I had to replace the primer bulb about a month ago). I have run it once a week or so since spring.

Odd. It has been running and will start. It seems to run on the gas from the primer.

Suspect fuel line from the tank. You replaced the primer bulb, in doing so perhaps the main fuel line has since become kinked or even fallen off. If you pull the fuel line, does gas run? It may have some sort of a check valve in it so that might be clogged.

Those engines have a complete valve train that needs periodic adjustment. I loved the power mine provided, but after a couple of years, no amount of adjustment, cleaning, etc. could get it running again. I thought the 4-cycle engine would outlast the 2 bangers, but I’ve never gotten more than 2 years out of any trimmer. (Not that I’ve done everything possible for maintenance either).

Raining like hell now, so I can’t check to see if removing the air cleaner helped.

enipla, it’s not the fuel line. I can see both of them and they are not kinked or blocked. Also, once I got it primed, I didn’t have to keep doing it.

Almost sounds like it has a vacuum operated fuel valve that is not operating properly.

Its a safety feature where there is a pilot flow to top up the carb, and when the engine runs the carb inlet produces a vacuum - thats just the way of things. This vacuum is someties used by conecting a tube from the carb manifold which goes back to teh fuel valve. Here is opereates a diaphragm in the fuel valve that opens it fully to allo fuel to run through at the full rate.

It certainly does sound like a fuel restriction of some sort, if it was choked up plugs then it would run and cough a few times and then not restart at all.