Honda FL 440 Build

[aschn]

One of the cylinders had some pitting on the cylinder wall, which will be honed out for the rebuild. I think the culprit was my diaphragm carb, which pumped fuel based on the crankcase pulses. The needle in these carbs are known to get stuck, which I believe led to a lean condition. I am replacing this with a gravity fed Mikuni VM34 since my tank is above the carburetor anyway. The carb is meant for motorcycles with a similar tank-above-engine setup.

The port edges were also pretty sharp, and I think one ring caught on the intake port or the pitting in the cylinder wall.

Another theory is that the rings cooked due to lack heat flow away from the engine. I have a shroud for the exhaust side to help move air away from the engine. This, combined with the new carb and pipes (See pictures) should help out with cooling.

Hopefully I can get the engine back together this week with the new carbs and pipes on before the snow starts to fall here in Michigan.

[LIDUNO]

I know the pumps on FL 350's are super sensitive to vacuum leaks, your 440 might be the same. I know on an FL 350, a bad crank seal can causes the engine pulse to be weak so it doesn't pump enough fuel.

[jimmyg]

Sounds like you have it under control.

[aschn]

Engine is back together, carb is on, pipes are routed and welded.

I need to double check timing before I start the engine again. Compression was 125 psi each cylinder after re-assembly, so I should be good there.

I'm glad the pipes are done, because I was getting pretty sick of welding 22ga cones together(23 pie cut sections total), makes the .049" gusset tubes seem easy.

With the new pipes, new carb and top end job it should rip! I've read online that expansion chambers can boost power up to 40% on some two strokes. I'll have to see if I can get on a roller dyno and validate that claim.

[jimmyg]

Great stuff!

[K-fab]

Looks good.
You just tripled hp.

[LIDUNO]

Pipes look cool, are they equal length to the chambers? I don't know crap about exhaust, but I know people tune their pipes by moving the chambers further and closer to the cylinder. I assume you wouldn't want one cylinder hitting it's power band before the other?

[K-fab]

Those look to be the same. Look at the spacing between the cylinders - appears about the same as the offset of the exhaust end.

Shorter, fatter expansion chambers generally give more low end and longer, skinnier are generally for higher revs.

[aschn]

Pipes look cool, are they equal length to the chambers?

Yup, both pipes are equal length. I used a pipe calculator software to plot my cones and calculate the tuned lengths/cone diameters. The only thing I am unsure of is the stinger diameter (the smallest diameter at the very end of the pipe). The smaller the diameter, the backpressure is higher (more power +++) but EGTs are also higher (not so good for rings and pistons). I might open up the diameter on the ends so that I do not have to replace more pistons.

[LIDUNO]

Nice, waiting for video of donuts and drifting.