old propnut

I have a new TT91 FS and the compression feels very high. No matter how rich you run it stlll sounds like eggs frying , lean it out enough to get off the ground and it will kick the prop. Sent the engine to Ace and was told nothing wrong , yes there is I keep losing props and nuts. I am burning 10% and turning a 14X6 Master air screw.
I think that I will add a head gasket to lower the compression. My question is how thick of a gasket do I start with,I have shim stock to cut from, .002,.003 .004 or .005.
Any help from the engine experts out there would sure help.
Fred

w8ye

My Feedback: (16)

Sounds like they left out the head gasket?

I would go with the .005"

Enjoy,

Jim

MrMotor

A lot of the Thunder Tiger 91 four strokes need about a gallon of fuel through them before they run well. Even if you don't plan on using the choke assembly, make sure it is installed or the engine will lean out too much and go lean in the air. It is usually difficult to fly a plane with the reccomended break in prop installed. The engine needs to be rich to prevent it from throwing the prop nuts and prop.
You should be OK if you follow the owners manual for prop, plug, and break in of the engine.

old propnut

I have run almost a gallon of fuel throught this engine and I have not seen any improvment.
My other TT91 FS was an easy break in and is still running great and has been hauling a EXTRA 300 around for 3 years now.
and the choke assembly is installed.

Flypaper 2

Something else you might try is a colder plug.

pikebishop

in the past it was not uncommon for this engine to come with the timing one tooth off. I think they would have caught this but it's worth checking.

old propnut

checked timing and found it to be right on.
Think I am going to try a colder plug if that wont work then I will add a head gasket, thanks for the help.
Fred

w8ye

My Feedback: (16)

Have you checked to see if the head gasket is in it. I bought a used OS 48 and flew it a couple years before I discovered no head gasket.

Sport_Pilot

Try the K&B 4S plug, that is about the coldest four stroke plug I have seen. Still gives a good idle also.

pikebishop

if you do pull the head check for burrs around the glow plug threads. little tiny burs on the machining or casting can lead to preignition problems.