Small engine diagnostic help - Yamaha generator

There's a strainer in the tank neck; as far as I can tell there's no filter in the tank or between the tank and carb. The pump seems to push plenty of fuel -- it only took a few pulls to refill the carb after draining the bowl. I did wonder if there's any problem that would cause the pump, which is apparently powered by crankcase pressure, to lose flow at higher engine speeds.

Absolutely. I calculated power by measuring both current and voltage at the heater.

A leak wouldn't surprise me. The carb mounts outside a plastic shroud that surrounds the engine, and as best as I can tell, the shoud is sandwiched between the carb and engine. When I removed the carb, the gasket between the carb and shroud looked OK, but I have no idea what's going on at the other interface.

Right, no accelerator pump.

Weak

Probably wise to replace the plug as well then, but that means a trip to town.

Then a fresh plug is on the list for the next time I go to town. I did get a noticeable improvement after cleaning the carbon out of the spark arrester.

You're right, it should behave as you describe when overloaded.

Well if you need a *simple* answer, OK.

:)

--Winston

David Lesher wrote: (...)

I bow to your experience here. Still, I think that space heater is going to draw more current in its relatively cold state than when it warms up.

We seldom can power a 1KW load with a 1KW generator, simply because most loads have additional power requirements for inrush.

--Winston

The next thing to check is the high voltage coil that is breaking down. Magneto coils have a habit of doing that. I had one that was doing exactly the same thing as yours. dropping out under heavy load. After doing all the usual stuff with the carb. I finally put an ohm meter on the coil secondary and it was open but still ran the engine under a light to medium load. It was a 7 kw generator but would only load up to about 3 kw. and then conk out.

John

If you don=92t have the owner=92s manual, I found it here:

There=92s a wiring diagram on pg. 33.

Propane torch is the way to find such leaks. Twenty years ago, cars were CHOKED with hoses going every which way.

[I watched a friend work on totally screwed up one. I asked "How's it going?" and he said "THIS one was connected to the carb.." The other end of that hose was ... the washer reservoir..."]

When you HEAR a loose hose but can't figure out which... or suspect a carb gasket leak... just squirt some propane around. When the engine sits up and idles smoothly, you're there.

Thankfully Detroit finally discovered digital computers...

With lamps, quite true. Not so with heaters that are cooler than that....

That is quite true...

The smell of the exhaust is different for rich, normal and lean mixtures. Put your fingers in front of the exhaust for a second and then sniff them.You might be able to calibrate your nose to the differences by playing with the idle mix screw on another engine running the same gas.

On Mon, 9 Mar 2009 06:07:28 +0000 (UTC), the infamous David Lesher scrawled the following:

It always amazes me when someone suggests using flammable liquids or gases to locate a leak on an engine. One guy I read about used gasoline in a squirt bottle until he was killed from the fire which started as the gas dripped onto the exhaust system. Others explode with ether in their hands. What fun!

I suggest (to Ned and all) the use of -water- as a leak finder. Any flammable liquid or gas will go into the intake and cause an RPM jump (said the guy who used to use Berryman's B12 in his young and foolish days.) Water being sucked into the intake leak makes a loud slurping noise while the engine slows and is a much safer and better test liquid.

-- The wealth required by nature is limited and is easy to procure; but the wealth required by vain ideals extends to infinity. --Epicurus, Principal Doctrines

I would never squirt gasoline like that. A propane torch puts out a small amount of gas, and propane is not ether; plus an open hood with the fan going is hardly a closed chamber.

I'd skip squirting water around a warm engine as it's a good way to crack something. One exception is a mist sprayed into the carb throat; you can actually clean carbon out with that..

Thanks to all who responded. I was happy that there were no suggestions to replace the jug, piston and rings (not gonna happen).

The agenda, starting with the easiest:

-replace plug

-check spark and coil

-observe throttle actuator as load increases to make sure its behavior seems appropriate

-drain fuel tank (into my '54 Farmall which ain't fussy) and refill with fresh fuel

-check for air leaks

-tear carb down and clean thoroughly

-reluctantly spend $50 on a shop manual (RTFM)

I'll report on the outcome, but I may not get back to it 'til next weekend.

A bad spark plug could be the cause, or perhaps a bad magneto coil. Will it run indefinitely at 50% load? If it runs a while, then sputters and dies at 50%, that is a strong sign of a bad magneto. Another possible cause is a plugged-up jet in the carb. Up to 50% the idle/low-speed circuit gives an ignitable mixture, above that, the high-speed jet is needed, and isn't working. If you run it at 50% for an extended period, with a really lean mixture, it will fry the engine.

Jon