I have a 2-cycle trimmer that was working just fine. Then during it's last use the speed began declining while in full throttle mode until it finally died. I changed the spark plug and now it only runs with the choke closed. If I try to open the choke or let off the throttle the engine dies. Any sug gestions?
Just guessing, dirt in a carburetor port.
Closing the choike limits the air and increases the ratio of gasolne to air. If there is very little gas going into the gas-air mixture in the first place, that could be making it rch enough to run.
Does it put out black smoke when it's running with the choke closed? If it usually does and now it doesn't that supports my view.
What to do? What's that spray int he black and white can meant to clean carburetors. I'd try that, all over, before rebuilding the carb. Gum out. And maybe mix some gum-out that's designed to be mixed with the gas with the gas,
If you decide to clean the carb better than this, post back.
Mine is nearly 35 years old, but I guess they are the same in many ways.
I have a Walbro carb. On the side with the fuel inlet is a plate held by a center screw. That's the pump compartment. With the choke on and the throttle open, the pump gets bigger air pulses to pump harder. For me, the problem has usually been that moisture in the fuel has caused the outlet screen of the pump to clog. A q-tip and a little cleaning solvent will fix it.
The last time, gas deposits on the face of the body against which the pump gasket seated, showed that I had an air leak, which kept the pump from working right. Removing the deposits fixed it.
I'd go with what J B said. (After all, he invented welding.)
I don't know how old it is but exhaust port maybe plugged up with carbon/dirt. Just remove muffler and look, see.
Carburetor deposits and vacuum leaks are much more likely on today's
2 strokes since most run on a weak oil mixture, using low ash clean-burning (relatively) oil - and ethanol gasoline. This adds up to low exhaust deposits, and all kinds of sneaky stuff clogging up fuel systems and deteriorating gaskets etc.
last use the speed began declining while in full throttle mode until it fin ally died. I changed the spark plug and now it only runs with the choke clo sed. If I try to open the choke or let off the throttle the engine dies. An y suggestions?
Someone gave me a WeedEater leaf blower recently that had the problem that Tony describes...nearly closed-off exhaust port.
Not saying that can't happen, but it is a LOT less common than in the
18:1 mix days using #30 engine oil
I believe port blockage is a gradual process that reduces noise and power, but the motor still starts normally. I've cleaned carbon from ports and sometimes mufflers, but I've never had enough to notice a loss of power.
Then this one should be written into the books...it would barely start and stay at low speed. Nearly 100% blocked. I don't know what they used for gas/oil mix?
... or the gas/air mix. Mine can easily be set too rich, and it might seem satisfactory. I set it as lean as it will still respond to the throttle.
The OP said his problem happened suddenly. Mine has usually happened because the screen got gummed by a material caused by getting moisture in the fuel. It's hard to see because it's colorless and translucent. It hasn't happened so much since I started mixing fuel 500ml at a time in a 600ml soda bottle, so it's sealed against air and used pretty quickly. I discovered that epoxy cement could seal the hole where the fuel line exits the tank. That helped, too.
The second cause in my experience has been air leaks around a carburetor gasket.
I found a third cause at my neighbor's this year. His fairly new trimmer suddenly wouldn't run without the choke. He'd refilled it with fuel that had been sitting in a milk jug a couple of years. When I finally figured it out, I dumped the tank back into the bottle and filed it with fresh fuel from my bottle. After it burned the fuel in the line and carburetor, it ran like new.
Second this. Esp, if you run it part throttle. A factory service guy told me these engines are designed for either idle or WOT. Ours gets plugged every couple of years, . (I do run part throttle.)
Anyway, there's a 'spark suppressor' screen in the exhaust port. I hit it with a propane torch. That ignites the wet stuff. After that burns off, just brush the residue out, and good to go.
I would caution doing this...with fumes and mix in the crankcase? Not a good idea! *L*
Do I need to say, "after taking it out"? OK: AFTER TAKING IT OUT.
Yes, and you would need to say, "take the screen out first..." because someone might think you meant take the fuel out...which would leave fumes to explode. Sorry you took a caution as a criticism.
A momentary overreaction.
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