View Full Version : lean or rich?

05-09-2015, 02:38 PM
Hi guys making progress with my jetting and running in. Currently running 75 pilot tube with 73 pilot jet mixture screw 1 3/4 out 132 main jet on PHBH 28 my issue is when I shut / close the throttle it hunts on the overrun doesn't feel since, is this a symptom of to lean on the bottom end?

Forgot to mention I am running Boyesen dual stage reeds with stock Rotax manifold, with standard pilot tube of 62 and pilot jet 62 I could not get it to run at all. Boyesen do claim their reeds make it run lean on the bottom end. Also running aTYGA pipe.

05-10-2015, 06:15 AM
Sounds like it's lean to me. Wind the mixture screw in and test ride. See if it improves.

05-11-2015, 03:12 AM
Thanks Morad, I thought winding the mixture screw in makes it leaner? I'll give it a try.
I do have another pilot jet to try a 75 to replace the 73

05-11-2015, 03:25 PM
General rule of thumb is if the adjuster is in front of the slide (engine side) then it's a fuel adjuster.

If the adjuster is upstream of the slide it adjusts the air that is mixed with the fuel from the pilot jet.

Not sure what carb you have so I assumed....

05-12-2015, 02:17 AM
I have the standard 28mm Dellorto PHBH carb. I understood it was a fuel mixture screw rather than a air screw, surely winding it in will make it lean not richer? I'll give it a try in both directions to see if it makes a difference before I change the pilot jet again.

05-12-2015, 09:51 AM
Phbh 28:
fuel screw clockwise (in) lean. anti clockwise (out) rich.
Dellorto 34mm carbs are air screws and opposite.