Well guys it's a fact....

jbruney said:

I thought I'd mention this discovery because the choke was never needed until this recent jet replacement for the old ones looked like new, so left them alone. I replaced them on a lark because of failing performance with them being the final option prior to new carbs. I thought the richness to be a fact of life, and almost tossed those choke slides last time the carbs were down..... Now I find the choke is the only method to get the beast started & running when cold after these many years.... Do you realize how much kicking/swearing/sweating & wondering what was gone wrong this old man went through before using the 'never used' choke lever? It was not a matter of what was wrong, but one of what was now right. I ponder the number of other old fools overlooking the obvious that just roll these machines to the back of the shed to become forgotten bundles of rust because they give up after a bit of adversity.

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I’ve been a firm believer, that modern fuel (even NON ethanol) has been of lower heat energy content per volume. OP’s experience aligns with it.
Anecdotal?
Coincidence?
Maybe.

Also, early season cold snap and seasonal vapor pressure fuel blending still in summer mode, not to be discounted.

Yesterday morning at cranking time it was almost 55F. Air screws are out at 1 1/2- a tad right where she like it for smooth idle. 87 @ pump no good & it doesn't really care for the 93 pump so 89 octane is smoothest all around for the garbage gas..... It does take a solid 5 minute to warm up enough to drive off without spitting, so the choke needs to be on and she lets you know when to turn it off by getting a bit sluggish. I feel as if riding a different bike now.

I was quite amazed at the difference new needle jets made. Soft brass and hard steel along with the engine vibrations is just tough on them. Slides were ok.

My bike is choke delete. I brought up the possibility of adding them back and got mixed reviews. Some saying yes, they help on cool mornings to others who about questioned my manhood at the thought of putting chokes in. Another told me my idle mixture was too lean and my bike would stumble with that adjustment; not true on my bike.

Anyway, since the season is coming to a close I'll put up with keeping it running for a couple of miles and maybe put chokes in over the winter. It's running so well I hate to mess with success though. Starts well and rides off just fine in the warm weather.

Tornado said:

Guess the jets/needles had some wear leading to enrichment, sufficient to not require choke.

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He first thing to do when you buy any old bike is replace the needle jets.

Fast Eddie said:

Well, I’d chalk it up as a success if o were you. I know a lot of us do manage without chokes on old bikes, but really a carbureted engine SHOULD need a choke of some kind if the mixture is close to correct.

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If you are running too rich on the needles, you are often not aware of it. All that happens is the motor becomes slightly sluggish. If you ride on public roads, that does not usually matter much. The idle circuit only affect the region below quarter throttle and usually gives no trouble unless a jet gets blocked. However needles and needle jets are critical if you want top performance. It is usually normal to have the main jets slightly too rich, so you don't burn anything when you fang the bike.

acotrel said:

If you are running too rich on the needles, you are often not aware of it. All that happens is the motor becomes slightly sluggish. If you ride on public roads, that does not usually matter much. The idle circuit only affect the region below quarter throttle and usually gives no trouble unless a jet gets blocked. However needles and needle jets are critical if you want top performance. It is usually normal to have the main jets slightly too rich, so you don't burn anything when you fang the bike.

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I agree Al. But, if yourun the needles too lean on the road you’re highly likely to seize up or hole a piston or both...

With experience, you should know when you are too lean by the way the bike performs. If you put the clips in the top notch of the needles, the bike should almost be imp[ossiblr to ride. If that does not happen when the needles are lowered right down,, the needle jets are too large. Also the taper on the needles affects how fast the throtlle can be opened without the motor gasping. You probably should need to feed the throttle on, rather than whack it open. As you open the throttle, you lose vacuum at a rate which is determined by the port size. The taper on the needle compensates for that. If the taper is too quick, the mixture richens up too fast and you accelerate slightly slower.
On my bike, the carbs are 34mm Mk2 Amals. I use 6D Mikuni needles which are the leanest. It means I am forced to feed the throttle on in a controlled fashion - as you would with any two-stroke. Admittedly, on a race circuit, you don't usually sit at one throttle position for long periods, even on really big circuits - unless it is wide open - and the main jets take care of that.
You need to be sensible and careful if you are looking for best performance. The sweet spot is not far away from destruction. I am luckt because I use methanol fuel which hides-up the tuning errors. It copes with slightly too rich, very well. But with petrol, you have a real problem. If the needle jet is a quarter of a thou of an inch too large, you will run slower. When you use methanol that quarter of a thou becomes half a thou.

If some guys tuned two-strokes the way others tune Commandos, their motor would not even start and run. That is how I learned to tune my 850. I am not joking or bragging when I say it is quick, it actually surprises me. In the last three races in which it raced, it was right up there with the 1100cc methanol-fuelled CB750s - even on the long straight bits of the circuit. It should not be able to do that - they are not slow.

If I ever race again, it will be with the six-speed gearbox. I still have a need to do that one day.

I find it quite interesting that in the Youtube videos in which modern bike are road tested, the riders often blip the throttle several times in each gear as they come up through the box. One nice controlled squirt in each gear is probably a better way to go. If you whack the throttle open, you usually accelerate slower.