Tom,
Sounds like your air flow is way out of sync. I've got a pair here in
front of me and I'll try to step though it. In a fairly large nut shell, here
it is.
First. On the shaft that the throttle cable hooks to there is an
adjustment screw. This is not the idle speed screw. It is a "service" screw
and we will get to it later. For now back it way off so that it is not
touching anything. Also make sure there is some slack in the throttle cable.
Second. Make sure that both throttle return springs are in place. If
you pull on the throttle cable the center shaft between the carbs should move
a little before either carb throttle shaft moves.
Third. Just under and forward of the manifold stud on the return
spring sides of the carbs is the idle adjustment screws. One per carb. If you
put your finger on the return spring lever and push down, then back off the
idle screw till the lever stops moving, then screw it back in till you feel
the lever move and then about two more turns. Do this to both carbs. This
will roughly set the idle balance.
Fourth. Using the unisyn check the air flow through both carbs. If the
idle speed is too high then back off the idle screw on the carb with the most
flow. If to slow tighten the idle screw on the carb with the least flow. You
want them to flow the same with a reasonable idle speed.
Fifth. Remenber the service screw that was backed out? Now tighten it
till the engine speed raises to 2000 rpm. Use the unisyn to measure the air
flows. The screw below the service screw on the rear carb linkage is used to
balance the high speed air flow.
Sixth. When the high speed is balanced, back off the service screw
untill it no longer touches. The only use for that screw is to raise the
engine speed to set the high speed air balance. Double check the low speed
air flow balance.
Seventh. At this point the high and low speed air flow should be
balanced and the service screw should be backed off. Now it is mixture time.
Carefully lift one of the slides being sure to stay out of the air flow. I
catch the bottom of the slide with a finger nail, a hook made out of a paper
clip would work also, just don't loose it into the engine. If the engine
speeds up when you lift the slide the mixture is too rich and the adjustment
on the bottom needs to be turned up, ccw from the top. With a little practice
you can push the slide down some. If you push it down and the engine speeds
up you are too lean. The adjustment needs to go down, cw from the top. Do
this with both carbs.
Eighth. At this point you may need to readjust the idle speed. Using
the unisyn to keep the low speed flow in balance, adjust the idle screws on
each carb to lower the idle speed . The high speed balance will not be
affected by this. At this point if you lift either carb slide the engine
speed should slow down as the engine runs on two cylinders. Raising the slide
all the way causes the mixture to go to dead lean, all air and no gas.
I tried to be brief but I think I covered it all. If anyone has
anything else to add please feel free to do so.
keith williams
>
> Now that the timing is right I am getting into setting up the carbs.
> Balancing them won't be much of a problem if I can get them both working
> at the same time.
>
> My problem is that no matter where I set the mixture on either carb,
> from full lean (up) to full rich (down) there does not seem to be much
> difference in the way they work. The back carb dramatically effects the
> idle if I lift the damper just a little, no matter where the mixture is
> set. The idle/air flow screw is backed out all the way.
>
> The front carb on the other hand has almost no effect on the idle when
> the damper is lifted. I have to lift the damper all the way to produce
> a mildly rough idling engine.
>
> Putting the Unisyn over the rear carb has quite an effect on the idle as
> does putting the end of the hose from the top of the rocker arm cover
> near the opening of the rear carb and drawing the fumes into the carb.
> I do get good air flow measured by the Unisyn on the rear carb. On the
> front carb I cannot get the ball to rise much at all without setting the
> idle quite high.
>
> At this point I have cleaned the dampers and changed their oil because
> they needed it. The needles are not worn anywhere and the dampers fall
> with a nice thunk.
>
> I have removed the float bowl covers. The floats themselves look very
> nice. No problem there. There is about 1 - 2 mm difference in the
> depth of fuel in the bowl. The rear is lower than the front. I would
> like suggestions about how to measure the float level. I understand the
> fuel should be about 23 mm below the top the the bowl. I assume that is
> measured from the top of the bowl without the cover. Since my fuel
> lines connecting the bowl to the fuel nozzle are clear (yes, they are
> gasoline grade fuel hoses) I could use them for level tubes and measure
> to a mark on the outside of the bowl. In that case I just need to
> confirm the 23 mm, or what the correct measurement would be.
>
> Tom
> 69 2000
> Portland
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