Jetting help - Fuel consumption

[webmaster]

What slide do you have?

Given that the n1ef isn't a great needle - it tends to drive folks to lean the pilot and crank up the idle to supply more fuel off the needle. (this is referred to pulling over).

One key thing you want drive for is to end up with a setting where you have the idle screw backed out so that the bottom (pilot circuit) and mid (needle circuit) are properly separated and can be properly tuned. Note that with the n1ef needle they aren't separated well and one symptom of this is the air screw doesn't have much effect and the idle screw can be cranked in to the point of coil bind on the tension spring - and even then it might not idle well...

So when you switch from the n1ef to n3eg (or when others switch to keihin straight taper needles - cek, ddk, etc. or JD jetting, etc.) In my opinion, you should back out the idle screw to lower the slide and needle to separate the circuits (pilot & needle) Running a leaner needle, and resetting idle, you typically go up one or two sizes on the pilot to balance things out. Note that this isn't going richer on the bottom - it's just making the pilot circuit supply more fuel and have less fuel come through needle circuit - to better separate these circuits.

With the circuits properly separated - it's easier to adjust, is less finicky to temp and altitude changes, and has a smoother transition from the low to mid - where it will typically burble then "hit" as it clears out with the "bad jetting".

Be sure to reset your air screw. Note that the air screw on this carb can be 2 and half turns out and everything is fine...

And given all of the above - check to make sure you have a #7 slide or leaner...

The carb itself suffers from a lack of sensitivity to adjustment that drives folks to jet it badly - this is one thing that RB-Designs resolves with his carb mods - he internally modifies the carb (inside the carb block) to fix this - this along with a slide, needle, brass and a thin divider plate to increase velocity at low rpms makes it work well across the rpms.

Others have mentioned having your combustion chamber shaped for optimal squish and compression - RB-Designs is the place to use for this service in the u.s. - best price and extremely high quality work.

jeff

[Jakobi]

Thanks for the additional info Webmaster.

Can confirm the slide is a #7. I have had a play with the air screw and the idle adjustment. While I haven't screwed them right in, after changing to the N3EG I had to turn the air in half a turn, and backed the idle back down a turn (it doesn't appear to be turned right in either)

To add to this, with both setups response was crisp and clean off the bottom end. N1EF felt to be too rich on transition from the straight to the taper (mid range) where it would load, burble, clear, and hit.

Would you suggest turning the air screw right in? If it still runs this would indicate I'm too lean on the pilot - correct? and would require a set richer. Is my understanding right?

One other thing. With the N1EF#1 the bike would not idle once warm. I never made any adjustments on the idle screw to try and resolve this. It idles perfectly with the N3EG#2 hot or cold

[Jakobi]

I think I see what you mean Webmaster.

I was tinkering around today. I now have the needle on clip 1 (which is perfect), but as you said. Both the idle screw (in) and Air screw (out) are at their max and don't make alot of difference.

I was under the impression I would have to lean the pilot circuit to get it to idle with the idle screw out. It feels quite doughy off the bottom and gets better as I lean the mixture.

Also, is it possible to change the pilot without removing the whole carb?

[webmaster]

On older models - you could :

1. Loosen the clamps on the carb (insulator and airboot) and rotate the top of the carb towards you.
2. You then have room to remove the slide.
3. With the slide removed - you now have from to rotate the bottom of the carb towards you with room to remove the carb bowl and access the jets.

I would assume you can do the same with the newer frame....

jeff

[Jakobi]

Originally Posted by webmaster

On older models - you could :

1. Loosen the clamps on the carb (insulator and airboot) and rotate the top of the carb towards you.
2. You then have room to remove the slide.
3. With the slide removed - you now have from to rotate the bottom of the carb towards you with room to remove the carb bowl and access the jets.

I would assume you can do the same with the newer frame....

jeff

That sounds like the plan! Should work! Thanks again

[Jakobi]

Nothing works

Go Richer on the pilot and it still just dies. Idles worse.

I found by leaning the pilot out it did help. I'm still having to turn the idle screw in considerably to get any kind of idle regardless of what pilot I use.

I'm going to stick to the 38 for now.

Do I need a needle with a leaner straight section? It came stock with a N1EF, i'm now on a N3EG. I like the profile of the N3 tapers better. Whats leaner than EG? EH?

[webmaster]

Did you turn down the idle adjuster screw when you installed the richer pilot jet?

I haven't used the n3eg - it is leaner than the n1ef? Yes?

jeff

[Jakobi]

Originally Posted by webmaster

Did you turn down the idle adjuster screw when you installed the richer pilot jet?

I haven't used the n3eg - it is leaner than the n1ef? Yes?

jeff

Yeah Jeff,

Its a bit leaner off idle, leaner again through mid, and then richens up onto the main.

I have found a level where I can get good idle adjustability with the 38 Pilot. The idle screw would be about 3/4's of the way in. Looking through the top of the carb you can see that the screw has taken up pretty much all the threading. Looking in the throat of the carb I hardly noticed the slide moving at all when making adjustments on the screw for the other 3/4's of adjustment.

Anyway, I have a nice idle now that lifts the front end cleanly off idle without any clutch, without any stalling. I can't complain.

Over all my whole setup is quite lean

38 P
N3EG#1 (N1EF#1 was burbly rich)
175 M

Tan plug, revs cleanly. Clip #2 wasn't as clean up to half throttle, but felt like it pulled harder from there.

Fuel wise, I used 6.5L to do 75km. (That was on clip 2)