Hey all, I've got my bike back together and have had it out for some test rides. She seems to run ok, except for when starting off from a dead stop, it feels like it lacks power- you really have to rev it a feather the clutch to get it going. It idles and if you blip the throttle it will rev up without any hesitation, but as soon as you let the clutch out, it falls on its face.
I had it it tuned and running very well when it was last used regularly. I had the carbs all apart and cleaned. All the jets are genuine Keihin and I resynced the carbs after reassembly. I'm not sure if the air screws need a tweak (I removed them, and I put them back at one turn out.). The Honda manual is cryptic in how they describe the adjustment- feeling the pressure of the exhaust from the muffler with your hand...
Dumb question, but which way turning the air screws richen the mixture? Being an air bleed, I would expect turning it in would decrease the amount of air and richen the mixture. It's been so many years sine I've worked with these carbs I've forgotten some of the finer points. Thanks!
Hi, Jonesy!
Turning the screws only works over the range of 1/2 turn to 1.75 turns: beyond that the mixture does not change any further. If your carbs are the 1969-1976 type of the "K" bikes, the setting is 1.0 turn out, within 1/8 turn either way max.
That said: if the spark timing is too far advanced at idle, the bike will falter when pulling away from a stop. This also happens if the float levels are slightly low: you can test this item by backing those air screws out 1/8 turn more than where they are now, and trying a ride. If it gets better, the floats are marginally too low. This happens with the modern too-stiff springs in the new float valves we are all getting during rebuilds: I solve it by setting the floats slightly richer, like 24-25mm instead of the stock 26mm in these early carbs.
Turning the screws IN makes it run leaner, just like most old-time cars. Turning them out makes them richer. If you go too far inward, it pinches off the air to the idle jet more and more until at about 1/8 turn the air stops and the fuel cannot percolate at all (and will not mix with air, so it also will not burn): this can then make the engine rich (and plugs wet) if the idle is then held at about 2000 RPM to make it stay 'lit', so people get confused about these screws and how they work as the result.
Much of the confusion about the In-vs-Out screw mixture seems to come from the old Honda manuals that stated, "...adjust rich by turning screw in...", which, if properly translated, should have read, "...if rich, turn the screw inward...". This was typical of the Jinglish translators of the 1970s. Most of the Honda manuals after 1985 or so got it right.
