.105 vs .106 Needle Jets

anything above idle is of course needle jet but not needle TAPER which is affected later by the groove position

acadian said:

which happens to be 90% of where most people ride 99% of the time

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IMO Cutaway dominates up to 1/4 and is where most people ride/cruise unless you are on the highway over 50mph (12-15hp).
small cutaway makes black plugs

If you are using your bike for road use, you can simply fit the largest specified main jets and forget them because most of your riding involves using between 1/4 and 3/4 throttle. When you set the idle, you need to lean off with the idle screws until you get a miss, then wind them back until you get smooth idle. That leaves you with the only tricky bit - getting the needles and needle jets right. The presumption is that you have set the ignition timing right for the fuel you are using, and you have not got flooding or fuel restriction. Flooding can be caused by incorrect float levels and also by vibration. If your carbs are rigidly mounted or touching the frame, you can get flooding. Also the choke arrangement can be faulty, if it is an enricher rather than an air obstructor. The needles and needle jets are critical, but they will never be right if you have fuel or air problems. Plug colour should only be used to set the main jests, but if they are rich, it usually does not matter unless you are racing.

Cylinder head is good. Just had the top end off less than 100 miles ago, to replace a leaky head gasket, and piston pin clips.
It had recent Kibblewhite guides and valves. We just put on new KIbblewhite red seals.

Will tear down and look again at the pistons/bores/oil ring tension and the oil pump also because it seems to wetsump very fast.

Before you lift the head, with carbs removed look at the Inlet guides, if they are dripping oil or wet with oil it maybe something simple like the valve stem seals popped off.

dynodave said:

anything above idle is of course needle jet but not needle TAPER which is affected later by the groove position



IMO Cutaway dominates up to 1/4 and is where most people ride/cruise unless you are on the highway over 50mph (12-15hp).
small cutaway makes black plugs

Click to expand...

When you raise or lower the needles, you don't affect the taper, you simply move it up or down. The rate of increase in the jet size due to needle taper, compensates for loss of vacuum, which determines how quickly you can open the throttle. If you us a 6D petrol needle instead of a 6F and grab a quick handful of throttle, you are more likely to get a gasp with the leaner needle. However, if you ride your bike like a two-stroke and feed the throttle on in a controlled fashion, there is often a power benefit in using the leaner needle.

I did notice white oil smoke on deceleration when watching your bike last Saturday night. Not much though. Actually it was par for the course typical of an old Brit bike

We found the problem... The PO had installed the oil ring expanders incorrectly, lacking in tension.

If its only done 4,000 then the bores will be scarcely run in..Am surprised that PO found it necessary to lift the barrel and replace or refit piston rings.. Maybe a factory error? But as a matter of course i would check the float needles to see if they are the brass rubber tipped upgrade or the original plastic which flooded..
The inlet guide oil seals will surely need replacing

The original owner from Texas swore up and down by the 4000 original miles. But we found it had been overbored .020 and the head had been redone with new KW guides and valves. Apparently there is high humidity where he lived and most of the bike had been refreshed after sitting so long.

After a brisk 50 mile Sunday morning ride, I tore it down and Ken's sharp eyes noticed straight away the oil ring expander overlap. This time, it did not smoke at all on the ride, surprisingly, but Ken said it smelled like a diesel truck! The plugs (Champion N4G) still fired and idled good but were by now oily and black!

Some time ago, I had replaced the brass/viton float needles with aluminum ones. I found the brass versions seem to always get sticky faster than aluminum, probably some chemical reaction with our fuel blend.