small engine: wouldn't run, now won't start.

[George]

Stihl FS36 string trimmer. Walbro carb, diaphragm pump.

Sad story: starting last year, it would lose power after running for 15 mins or so. I could usually keep it going by nursing the throttle for a while, after which it would return to normal power for a few minutes, and then do they same thing again. This year, it did that same thing the first time I ran it; but, after that, it would die after running for about 30 seconds. I restarted OK, but then just died again.

Spark seems OK, but I replaced the plug anyway. No help.

I got a carb rebuild kit, and replaced the filter, needle valve, and the fuel pump and regulator diaphragms. This was a 'learning experience', and didn't go that smoothly; but, I got it back to where it would ... do the same thing - start, run 30 secs, die.

Then, I took out the high-speed adjust screw. (Not gummed up.) Since then, it won't start. Alas.

The needle valve appears to be working: if I pump the primer bulb with the regulator diaphragm removed, nothing comes up out of the needle until I press on the actuator lever; when I do, fuel wells up into the regulator chamber.

AFAICT, the regulator diaphragm is working: if I pump the primer with the carb assembled, it gets fuel to the regulator chamber. And, if I don't pump the primer, the regulator stays dry. However, I could be confused about what I'm seeing, or how to interpret it.

Any suggestions would be appreciated.

Questions:

1. When I press the primer, should I see fuel squirt into the carb throat? (I don't.)

1. Should I have (liquid) fuel sitting in the crankcase, after trying to start it repeatedly? (I do.)

Thanks, George

[Tom G]

Not sure about your questions but I had a similar problem with a lawn mower and garden tractor this year. Lawn mower would only run while pumping the primer bulb and garden tractor only with full choke until finally not at all. Had to disassemble the carbs on both and blow all of the passages out with my air compressor. When put back together they ran just fine. I think last years gas had jelled and plugged up a vital passageway in the carbs. Didn't put gasoline stabilizer in last fall as I was in too much of a hurry to head for Arizona.

Tom G.

[Hogwild]

If you have fuel in the crankcase, fuel is not a problem. That is a normal flooded condition for a 2-stroke motor.

Unless your carb settings are way off, it sounds like an ignition problem.

To check for this you can take the plug out, connect and ground it and pull to see if there is a spark.

If not, check all connections, look for loose wires or a buildup of grease or grunge on anything. This could ground and shut the motor off. Clean it well. After cleaning you can apply a silicone spray to protect and insulate all the electrical components.

If still no spark, change the plug - try that.

Sometimes the electronic ignition systems develop an internal short that is first noticed intermittently until it fails completely.

[George]

I'd donethat - the spark looks good.

[Joseph Meehan]

Get an electric?

I gave up on all those small gas powered devices long ago and never once was sorry. Plug and play, no worries about starting or gas.

[RobertM]

You're sure right on that. I bought a new Stihl top of their line string trimmer. Just about yanked my arm off trying to start the damned thing. Kept it a week, gave it away and bought a Black & Decker cordless. As you say, plug & play. I don't know why anyone would waste time screwing around with a gas powered trimmer. Anything that is 2 cycle isn't going to be fun to start regardless of what the packaging says.

Bob

[m Ransley]

Try Either-starting fluid to see if the spark is good enough or timing is right. It has fuel if Either wont do it, its ignition related. I have the manual if you need factory carb settings.

[Hogwild]

It could be a weak spark. Something a new properly gapped plug might help.

Before adjusting a carb a good practice is to fully seat each screw and record the number of turns so you can start that way again after disassembly.

Typically the smaller fuel screw is set at about 1.5 turns, the larger air screw at about 3.

I suggest, setting the carb, drain the crankcase and try the starting fluid. (Don't use it too much because it has no lubricating qualities).

If it only runs with starting fluid, there is something wrong with your carb.

[Ulysses]

Me too and it still turned out to be a bad ignition coil. Sometimes they will become intermittant before they finally die.

[rdglide03-dbasedos]

Most carbs jet settings are 1 and 1/2 turns out. Becareful not to over tighten when screwing in to dead bottom. An empty squirt bottle filled with 2cyl mix squirted directly into the intake is the best try. If you can keep it running while squirting, then it is the carb or bad rings. Remember to mark the bottle or empty and destroy, because it can be very dangerous just sitting around afterwards. Only good way to test the rings is a compression tester. Less than 50 pounds compression means big problem.

[Chris Lewis]

According to George :

Your initial problems sounded like the one I had with my FS85.

Turned out to be that the spark arrester on the muffler was plugging up. It would run somewhat weakly for a while, and then quit.

The small engines guy simply ripped it out, and it worked fine ever since. [Spark arresters aren't particularly critical where we live.]

Now I'm wondering whether you jarred loose/plugged a fuel line.

[George]

Current status: my car won't start.

WRT the trimmer: After a number of disassemble-inspect-reassemble cycles on the carb, it got to where it sort of ran. I don't think I did anything different, but I could be wrong about that. Then, I played around with the high speed mixture, and got to where it better. Now, it starts as well as it ever did (not on the first pull, to put it mildly), and power is OK. It hasn't died while running. OTOH, it doesn't start well (like, at all) when it's hot.

So, it's useable, but not really great. Cold compression was 50 psi, which seems OK. I plan to check the compression when it's hot, but haven't had the chance.

Thanks, George

[Chris Lewis]

According to George :

Strange.

My FS85 is over 10 years old now. It's needed no maintenance (other than the aforesaid spark arrester screen). I do no "prep" to store it away for the winter (usually leave it half full of gas).

Using the basic instructions in the manual (set switch in start, full choke, prime 6-7 times, pull until it coughs, then switch to medium choke, pull), it virtually always starts in the second pull (first pull under full choke coughs, first pull under medium choke starts). Even after sitting idle for 6 months.

In contrast to the homelite I used to have - after the first year it was extremely frustrating to start, and then it started spewing gas...

Now with a complete overall and new "high performance" carb, that motor is going to live out the rest of its life powering a windtunnel.

[randy_47712]

Exhaust ports need to be cleaned occasionaly and ethanol in the fuel can cause problems.