Started to make adjustments to the SU needle last week, but its hard to see what’s happening, so I borrowed Wayne’s exhaust analyzer to check the mixture.
I Noticed that at lower rev’s it was running very rich and at high speed it was still lean I think. It’s a bit hard to say as the readings are very erratic, but I think that’s what it was.
So I adjusted the low speed mixture with a screw on the carb, and adjusted the needle a bit more to give me more fuel at higher speeds.
After installing the needle back in the SU carb, I was thinking “I don’t really know how far the piston goes up at full throttle, I need to find out somehow“. This is so I know where to make the needle thinner, to get more fuel.
And that’s when Brian, showed up, he’s in our club. He loves photography, so with his massive tele-lens he made some great photos. Thanks Brian!!
As you can see the piston is up, about 60% or so. This is at full speed ! 🙂
Now if you do the calculations, the carb has an 2″ opening, the engine has an 1.5″ opening, that means that the carb needs to open 56% to get all the mixture into the engine, so that’s looking good.
Just not sure yet if that’s a good thing or bad. Doesn’t matter I suppose for the fuel / air mixture ratio.
I think its still running a bit rich at low speed now and about 14% at high speed which is what is required, so maybe that’s it.
Here is me looking at the rev counter and the exhaust analyzer:
So at the moment, the engine is running really nice, and people say it runs a lot nicer, so that must be good, just not sure if I have more power….