I have a new (5 gallons) 3w-100. It is the SS version
from Cactus. The first start of the day goes real
easy, choke on flop it until it pops the choke off
three flips and it starts.

Second flight, maybe thirty minutes later, it is very
hard to start. The above will not work. It takes lot
of flipping and choking(not me but the engine).

Any ideas? Thanks.

Bill

Hi Bill,

I would take a look at your carb settings. When an engine is cold It'll run rich. As it gets warmer they tend to lean out.

I'd try fattening up the low end.

Let me know if it helps. It worked great for helis with similiar probs.
Roy

Bill

Sounds like after it warms and things grow, it sucks air form some place or another.

I would look at the reed block manifold, make sure there are gaskets both sides... Verify the surface is true with a straight edge.

Is this the new light-weight version engine?

Tighten all the bolts on the engine.

Look for obvious leaks at the cases and at the cylinder head to case areas. Should be a film of oil and or dirt if leaking.

As Helidude mentioned you may want to check the needle settings, I suspect this is not the problem though...

I'd also make sure you are not flooding the engine when warm. Cold engines need to be very rich (wet with fuel) because they do not vaporize gasoline well. Hot engines do not need as much choke because the hot surfaces vaporize the fuel very well, creating the correct mixture. Try restating the engine without the choke, immediately after landing. This should tell you if the carb is drawing fuel at idle with a hot engine, and if the low end needle is close enough to correct for starting.

it could be the heat in the cowel is warming the carb to the point that the fuel in the carb is evaporating? apparently, i've read somewhere that the zenoah 80 twin with the carb on top is a ***** to start when hot if in a cowel.

Bobby at Cactus suggested this to me and it solved all my problems with said engine. Remove the 4 screws holding the carb to the engine. There is a phenolic resin block that separates the carburetor from the engine block. It tends to warp from the heat. After removing it, check it for flatness with a straight edge. Mine was warped about 1/16 inch. Put some sandpaper on a glass surface and rub the block until it is flat again. Replace it back on the engine. Note there is a rubber gasket that fits into a recess in the block. Make sure it is fitted within the recess before you tighten it back down.
My symptoms were rough running after a few minutes in the air and quitting in the air at low engine rpm. Mine would generally start OK after it had cooled off. Still I would check the phenolic block as I suggest. If you already have the cowl off, it only takes a few minutes to check this.