Idle RPM change in relation to bike angle

[Kivi]

Hi
When my bike is in normal riding position, it idles ok.
If bike is in downhill position (front wheel lower than the back wheel, for ~15cm), idle RPM decreases.
But if bike is in uphill position, idle RPM increases.

And

When idling, and I shut the peatcock to OFF, bike runs for ~2 minutes, and then shuts off (because of no fuel in carb). But, during this 2 minutes, the idle RPM constantly increases, gradually and slowly. So, if bike idled at, say 1500RPM, 1 min after I turn the peatcock to off, idle is about 1800RPM. I still don't have tacho, but is clearly audible that the idle has risen. And if I turn the peatcock back to ON, in 2 seconds idle returns to normal idle speed.

Is all this normal behaviour?
I am trying to solve the rich condition judging by sparkplug being very black.

[Kivi]

I would conclude this: If the fuel level in carb bowl decreases (after I shut off the fuel and if I rise the front wheel), the idle increases. And if the fuel level increases (when I lower the front wheel, the fuel level in carb bowl front increases), idle decrease.

Can this point to some obvious problem with the carb or is normal?

Carb is ShengWey PD1, 30mm with 42 pilot (from 40 normal) and 110main jet (changed from 98 by factory).

[deadwood83]

Jets are arranged front to back on your carb (with float hinge arranged front to back as well in most common carbs). WHen you tilt the bike front to back, the fuel level relative to the float hinge changes. This gives a different effective fuel level relative to the pilot jet (since mains are typically dead center) giving you a different idle speed due to mixture change.


In short, pretty normal. Just don't try to tune your idle mixture on a hill lol.

[Megadan]

If the rpm changes aren't very drastic (just enough to be noticed, but not several hundred RPM) then it is pretty normal behavior for the reason deadwood stated.

[TheChairman]

Have you had a look at, and adjusted, your float level?

In a case of extreme grade, you may see some changes but it should run relatively evenly during normal operation including on hills. This sounds to me like your float level is too low.

[Megadan]

Originally Posted by TheChairman

Have you had a look at, and adjusted, your float level?

In a case of extreme grade, you may see some changes but it should run relatively evenly during normal operation including on hills. This sounds to me like your float level is too low.

Easy to check.

For a PZ30 carb, with the bowl off and the carburetor inverted, the bottom edge (now top edge) opposite of the float needle should measure 14mm above the bowl flange.