Rich or Lean - I am confused

bj · Post by bj » Tue Oct 21, 2008 4:18 pm

I received some new genuine kehien jets and tried them out. I put in a 115 main and a 35 slow jet. Before I had a 120 and 40. I made sure that the float wasn't hanging up on anything also. It wasn't.

With this new setup it ran still rich, but better. The plugs still fouled, but not nearly as bad. Acceleration and constant power is pretty good, better than ever. Unfortunately it created a new problem. It idles high even with the idle spd screw all the way in. The air screw at 1 1/8 turns out.

I tried raising the float to 27.5 mm instead of 26.5. That seem to have a negative effect. Acceleration is now a little choppy. The plugs still fouled though.

One thing (of many) that I don't understand is the way the airscrew behaves. In the other old hondas that I have, as you back it out, rpm rises until it reaches a point at which it backs down. I thought that this was because at you back out the airscrew, it leans the mixture. You are finding the best mixture by adjusting this.

With this bike, rpm is highest when the airscrew is all the way in. Rpm drops steadily as you back it out.

Why? And why am I having this new problem with a high idle?

Still confused and frustrated,

Thanks,
Bryan

PS......My other bike is just about done and almost ready for this engine, but I really would like to figure this out before I put it in my nice "new" shiney bike.

CliffC · Post by **CliffC** » Tue Oct 21, 2008 4:29 pm

Bryan, I may be wrong, because its been a long time, but I believe what you are adjusting out and lowering the idle is the idle adjustment screw not the mixture screw. Cliff C

bj · Post by bj » Tue Oct 21, 2008 5:06 pm

Thanks,

You got me thinking some more. I went and got my other carb to play with the throttle screw and look at its effect on the slide.

HUGE REVELATION!

I had the 2 screws mixed up! If you look at the honda parts fiche, it appears (to me at least) that they have missed labeled the 2 screws. I am I looking at this correct? #19 is labeled as the air screw while it is actually the throttle stop and vice versa for #20.

Also,

Esteve....I was re reading one of your replys and I think that both ca72's and ca77's are supposed to have the floats at 26.5.

As always,

Thanks, I really appreciate all of your help and insights.

Bryan

bj · Post by bj » Tue Oct 21, 2008 9:45 pm

Check out these plugs!

That was it! I can't believe that I had the screws mixed up. I should have look more closely at the function of those 2 screws. I simply looked at how they were labeled in the parts fiche and went by that. I think that the fiche shows the round bowl version while mine is the square bowl type. Maybe that accounts for the incorrect labels. Who knows.

At any rate. I moved the needle clip back to the middle and reset the floats to 26.5

Turned out the air screw 1 1/8 (the screw on the left!) And set the idle just enough to lift up the slide a bit.

Man, what a difference. The bike was quick, and ran perfect.

And finally, after about a 4 mile ride, I pulled the plugs. Sweet! No soot. Maybe even a touch on the lean side.

115 main and 35 slow.

Thanks, I was so happy I started jumping up and down.

Bryan

e3steve · Post by **e3steve** » Sat Oct 25, 2008 2:44 pm

Nice going Bryan. I'd agree, looking at those pics, that it looks a touch on the lean side. And the float height for a PW26 carb is 22.5mm from the lip. 26.5mm is the height for a PW22 (247cc).

Take the carb off again, set the float at 22.5mm, re-assemble and take a ride. If, after a few miles, the plugs aren't a sandy, beige colour, then lift the needle a notch and ride again. That 115 mainjet may be a tad small, but I reckon setting the float height correctly, thus raising the fuel level closer to the throat and increasing the level at which the fuel rests within the mainjet (needle-jet) pick-up tube, will help overcome the weakness. Don't run the mixture lean; the resultant overheated combustion could prove tragically fatal for the pistons (holing) or exhaust valve seats (burning).

LOUD MOUSE · Post by **LOUD MOUSE** » Sat Oct 25, 2008 4:21 pm

With a 115 main jet ya can bet you are far to lean.
Install a 135, set the float and adjust the screws and ya won't hole a piston. ...........lm

bj wrote:Check out these plugs!

That was it! I can't believe that I had the screws mixed up. I should have look more closely at the function of those 2 screws. I simply looked at how they were labeled in the parts fiche and went by that. I think that the fiche shows the round bowl version while mine is the square bowl type. Maybe that accounts for the incorrect labels. Who knows.

At any rate. I moved the needle clip back to the middle and reset the floats to 26.5

Turned out the air screw 1 1/8 (the screw on the left!) And set the idle just enough to lift up the slide a bit.

Man, what a difference. The bike was quick, and ran perfect.

And finally, after about a 4 mile ride, I pulled the plugs. Sweet! No soot. Maybe even a touch on the lean side.

115 main and 35 slow.

Thanks, I was so happy I started jumping up and down.

Bryan

bj · Post by bj » Sat Oct 25, 2008 7:13 pm

Thanks Guys,

I am going to be very careful about running it too lean.

LM

You don't think a 135 main would be too much for a CA77? In Silver's restoration guide, he states that the pw22 takes mains ranging from 90 to 125.

I am in the process of putting this motor into my project bike. I think I will put a 120 or 125 main in and see how it goes.

Bryan