Hi Marc, further details might include:

- fresh rebuild?

- miles on your motor?

- anything newly done to the motor or exhaust or fuel tank?

And then is it grey smoke, or more with a bluish look to it?

You may be looking at something normal...or not!

Thx for the responses.  Harry and Carl-Erik

I did run this by Randy Walker who has done some top notch work on the bike more recently. 

The exhaust is more white grey not bluish. 
Engine has not had recent work on the top and bottom. 
Work was done on the transmission and clutch recently, doing well.

Miles on the bike, unknown. But a lot, belonged to Ben Chesney

Nothing new done on the motor, fuel tank or exhaust.

I will not adjust the oil pump anymore and will keep an eye on the oil level. 

Rebreather valve was recently fixed a few months ago.   When repaired the rebreather was heard as a wheezy sound.  This sound was heard right after  I attempted to kicked the engine over, but was unsuccessful in starting the bike. However recently I can not hear this rebreather sound.  

Spark plugs changed a few weeks ago and now appear with heavy carbon.  Both plugs look the same color and equal amount of carbonization.  This has happened over a few weeks of use. 

Bike rides well with good and strong acceleration through all gears. 

Also, was having trouble starting the bike, usually starts in three to four kicks.  So I had the carburetor cleaned  about a month ago (it was quite dirty) and right after cleaning it started easily with a few kicks.  However, again more recently having more trouble kick starting the engine.  

Questions:

1).  Could it be the petrol I am using?  (too much ethanol and or water)?  I use lowest grade regular at my local gas station.  Is there a particular brand, company or grade I should consider?  Should I be adding something to the petrol I put in my tank?

2).  May I ask, is the ventilation tube the same as the rebreathe valve?  When working should it make a wheezing sound?

3). If the spark plugs the same color (carbonized), does this rule out cylinder oil rings needing repair?   

4).  Could the problem may be with the oil pump needing work? To much oil returning to the engine?  

5). As the engine runs strong and accelerates well, does this rule out cylinder problems?


Thank you, for any responses,

I go on with other hints and tips for your other questions.

1) As you have had recently clean the carb and found dirt, I would remove the tank and clean it, petcock and line thoroughly however industrious and hard job that is to make good. Final rinsing can be done hose down with water, just rinse with denatured spirit or ethanol to soak up the last of the water. And then try with a tank of fresh premium gas without any additive. Preferably non ethanol. Or you can run the bike with an auxiliary tank that is clean, just for test purpose.

The engine should run just fine with lowest grade regular, it is just that lowest grade might be slush quality with whatever settlings that the petrol company wants to get rid of.

2) At the base of the breather tube is the rebreather valve, it is just a flat disc that is oscillating back and forth with the air flow that the pistons make when they go up and down. Normal is a pulsating or fluttering sound from the tube.

A wheezing or whistling sound signals that the disc is stuck. That is upsetting the lubrication system and needs fixing without delay. Just remove the tube and clean the seat and disc. No gasket, just a thin smear of (anaerobic) sealer or at the most a very thin paper gasket should be used between the tube and crankcase because the disc can/will hang up in the gap between the housing and crankcase (or cam cover), that the gasket makes. It can be fiddly but a dab of grease will hold the disc in place in the tube seat, at reassembly.

1928-29 engines has a second breather valve disc inside the cam compartment, the housing is different and they don't tend to stick. A gasket there must never be used.

3) Same colour plugs does not rule out ring problems, unequal colour would indicate problems with one cylinder. Today's ethanol blended gas does tend to show much paler/whitish deposits and not leave a clear colour based indication so diagnosis based on colour is a lot more difficult. Mistakes can be done taking white or transparent deposit for a lean carb setting or manifold air leak.

However, heavy (black) carbon on the plugs is always from oil passing rings or valve guides. Beige/brownish carbon on the plugs is more normal. If that turns to (greyish) carbon or clean wet plugs, that can indicate excess fuel. Something wrong with the carburetor or a poor magneto that is missing ignition because of weak sparks. I'd say it again, with the modern petrol it can be difficult to read spark plugs.

4) If the oil level is OK in the crankcase then there is no reason to adjust anything on the oil pump. There is very little or no service job that can be done on the pump. The -31 pump has a few more details that might need an overhaul.

5) I would do a leak-by test with compressed air as suggested earlier, that would expose worn rings or other leaks right away. A compression test will compliment the leak-by for a good diagnose. A weak magneto can make decent sparks at higher revs, so the engine might feel "strong" through the gears but hard to start.

Carl-Eriks suggestion about gas in the oil is a possibility. Seen it happen 3 times on runs,  excessive smoke also usually accompanied by oil leaking out from just about very possible orifice, as the oil gets thinned down by the gas.

Agree with likelihood of fuel entering oil compartment of tank.  Old original tanks are silver soldered.  Silver solder becomes brittle with age, making the seems susceptible to fractures., which allow fuel to pass into the oil tank.  
Test as Carl Erik suggested.