Main Jet question

[95jersey]

When your bike is WOT, and I mean full WOT does the needle have any effect in relation to the main? My understanding is once your past the 80+% it is all about the main and needle taper would not effect fuel delivery?

So regardless of the needle you choose, would the size of the main be the ONLY factor to the amount of fuel being delivered at that throttle position?

[dANbOT]

Changing the needle has a mild to pronounced effect at WOT... how much depends on the differences between the needles you jump from / to.

Needle changes have ended in needing a different main, and sometimes pilot for me several times over the years. It's usually when I go to a whole new series or design of needle.

[95jersey]

Originally Posted by dANbOT

Changing the needle has a mild to pronounced effect at WOT... how much depends on the differences between the needles you jump from / to.

Needle changes have ended in needing a different main, and sometimes pilot for me several times over the years. It's usually when I go to a whole new series or design of needle.

I agree that the needle and main interact from say 1/8 - 3/4

No doubt that fattening up the main has an effect on low and mid as you are adding more fuel, almost like dropping a clip and opening up the area around the needle...and the same can be said for changing the needle and leaving the main, that you can have much more fuel (or less) at say 50% throttle due to needle tapper.

But it is my understanding that at FULL WOT, you are strait on the main and the needle is fully lifted out of the jet. This may only be at 90% or above throttle?

[Jakobi]

I'm not 100% sure how the main jet interacts with the nozzle - I haven't really looked into it tbh.

However, if you look at the relationship between the needle, the nozzle and the throttle position it's immediately clear that the particular needle shape/design/taper profile is what determines how much influence there is towards WOT.

Something like a Suzuki needle tapers off significantly coming to a very pointy tip. Obviously this is going to allow more fuel past the needle as it approaches WOT. In contrast, a Yamaha N3Ex series needle is quite thick and will restrict the nozzle to a larger degree.

[Jakobi]

Can clearly see the difference even with the naked eye!

[dANbOT]

Great example Jakobi!

On my CR250 I tried many different needles, a few of which were actually longer than the OEM and may not have ever cleared the nozzle. Needle choice has long been the starting point for jetting a smoker for me, since it affects everything else.

1-needle choice
2-pilot
3-main
4-adjust needle clip