Sick Babe Bee

Have you pressed the drive washer off of the crank and removed the crank? A crank that has sat for a long time can heavy heavy varnish on the crank and inside the case surface which the crank rides on. This acts like a brake and gets worse as it heats up.

How is it ported? There are a number of different ways cylinders and tanks were made.

You may have a single bypass no boost cylinder - the least powerful of the bunch. If this is mated to a smaller than typical fuel tank air passage then you will have a VERY mild engine. Note: this configuration is actually desirable for certain situations. It will have a long steady run suitable for freeflight type uses.

A dual bypass no boost is the next least powerful cylinder, followed by the dual boost per bypass double bypass, finally the most powerful is the single boost per bypass dual bypass.

Exhaust porting can affect power too. SPI - Sub-Piston Induction - is air let in under the piston skirt, adds quite a bit of rpm alone on reed valve engines.

The fuel tank can be modified in a simple manner. Use a 2mm or 5/64 inch drill bit and open the passage up carefully. Tape the shank to protect the reed seat and drill from the reed seat end.

If the reed or reed seat is damaged that will cause rpm loss too. Check with clean fuel line by trying to suck air through the intake.

Phil

This should be good. I have one of these bees also. Looks like I will be disassembling and cleaning myself. Hope you can get your problem solved.

You may want to check the radial "play" of the crankshaft in the crankcase. Unbalanced propellers of pre-owned engines may have widened the stock fit between the 2 components, and poor shaft sealing may also contribute to erratic running due to loss of crank pressure

What fuel are you using? All castor plus lean runs can cause a varnish buildup in the piston/cylinder fits also. It used to be a normal procedure for racing guys to clean the cylinder with Hopp's (or other) gun oil and a bore cleaning brush from a gun kit, or use a Brillo pad (wet), or some other means.

Running part synthetic will clean off the varnish but keep some castor for lubricating the ball socket during an over-lean run. Apologies to those who already know this stuff but perhaps it will help someone.

George

The varnish condition is something I need to check with all my Bee's. I've never had the cranks out of any of them.. (I never knew how to disassemble them before joining CEF) Another thing to do since you'll be taking it apart again.. is replace ALL the gaskets with new ones. Check to see if the case screws are bottoming before they actually tighten. This can happen.. and there could be more than one reason. New screws could be slightly longer.. an old gasket will be thinner than a new one.. the back-plate screw-holes could be enlarged causing the screws to seat deeper and if by chance you decked the back of the case for a better seal; screws that fit before could now be bottoming before they tighten up the assembly. Removing too much stock from the back of the case could cause binding of the crankpin against the front of the reed-housing too.

Screws that run out of thread in the case is a common problem from not being tapped deep enough from the factory. Obtaining a 2-56 tap and re-tapping the holes deeper will fix that problem. You can alternately cut a tad off the screw(s).. but you have to make sure that the threads are clean, so as not to bugger the threads in the case.

Thanks for all the help guys. I Have not worked on it yet but all these ideas ya'll gave me will help.I might add that when I said it ran slow I meant about 100-200 rpms. you could almost count the reps as it was running.

If so slow then it was probably only oscillating without passing the TDC. It happens e.g. when the engine is flooded and/or has too much compression ratio.

akjgardner wrote:Thanks for all the help guys. I Have not worked on  it yet but all these ideas ya'll gave me will help.I might add that when I said it ran slow I meant about 100-200 rpms. you could almost count the reps as it was running.

Maybe it was meant for a slow flier?
That is really slow. I did not think that they could run that slow.

Over compressed. Try making sure there are 3 gaskets in it for 15% to 25%. You can remove or add later after it is running healthy and you have a means to compare to find the best gasket count for that engine on the fuel you are using.

Phil

It absolutely is flooded and oscillating. If you are using an aftermarket Merlin drop-in plug and clamp-ring, you may need even more head shims.

I agree sounds over compressed and doing the bouncy bouncy. My tach race engine took 4 shims in order to start easily (Merlin head equipped), anything less and it would bounce back and fourth as long as you let it, it took the spring starter to get it going. As stated start with 3 or four shims or enough to get it to start easily on the fuel you are using and go from there. Also a small or light prop can aggravate the problem like the light Cox 5x3 grey on engines with more compression than usule. (Bandit)