Keihin PWK needle jet size? (not the needle it self)

[David v]

Hi there!

I?m just curious... I fitted a NEDJ needle instead of the standard N1EF in my AS2 in the 2011 Gas Gas EC300, and by eye, I could not tell the two apart. Measuring the diameter in every 5:th mm along the length gave this result in millimeters, starting at the thick part:

Edit: Got the 2.91 figure from Erhard and by that calculated the diffecence in gap where the fuel flows between seat / needle and added to the table.

N1EF NEDJ Diff (area in fuel gap)
2.70 2.74 0,04 (19.4% smaller)
2.69 2.73 0,04 (18.5% smaller)
2.69 2.73 0,04 (18.5% smaller)
2.64 2.65 0,01 (3.7% smaller)
2.55 2.57 0,02 (5.4% smaller)
2.41 2.43 0,02 (3.7% smaller)
2.28 2.29 0,01 (1.4% smaller)
2.07 2.10 0,03 (3.0% smaller)
1.79 1.85 0,06 (4.2% smaller)
1.53 1.57 0,04 (2.0% smaller)

At idle or very small throttle openings the difference is only 0.04 mm and that is a pretty darn small difference! Does anyone know the diameter of the hole that the needel sticks in to? It would be interesting to calulate the area difference.

Cheers!
/David

[Erhard]

Originally Posted by David v

Hi there!

I?m just curious... I fitted a NEDJ needle instead of the standard N1EF in my AS2 in the 2011 Gas Gas EC300, and by eye, I could not tell the two apart. Measuring the diameter in every 5:th mm along the length gave this result in millimeters, starting at the thick part:

N1EF NEDJ Difference
2.70 2.74 0,04
2.69 2.73 0,04
2.69 2.73 0,04
2.64 2.65 0,01
2.55 2.57 0,02
2.41 2.43 0,02
2.28 2.29 0,01
2.07 2.10 0,03
1.79 1.85 0,06
1.53 1.57 0,04

At idle or very small throttle openings the difference is only 0.04 mm and that is a pretty darn small difference! Does anyone know the diameter of the hole that the needel sticks in to? It would be interesting to calulate the area difference.

Cheers!
/David

The hole is about 2,91 +-0.2 due to my own measurement with test pin.

First of all:
Thanks a lot! This really prevents me from buying Suzuki needles NEDJ NEDW and so on. They all vary only in base diameter, tapered sections are fixed for those needles.
As you have shown, the tapered sections dont differ significantly. In the tapered section 1clip up or down changes Diameter more.

BUT:
The Base diameter of NEDJ is four sizes leaner than N1EF and equals N1EI (2,735) or N1EJ (2,745)..


To decide whether 0,04mm is signifcant, always consider the area of interest is the space between needle and bore:

Next question, do 0,04mm matter?
Yes and no!
0.04mm at Base diameter is very significant, as the Area for the premix Air/Fuel flow between Needle and the Bore is what matters. This is 2.9mm bore minus 2,74 vs. 2,70 Needle. Here Differences has to be calculated by Difference of Areas=Diameter^2*PI/4:
Result Difference 2,7 and 2,74 equals ~24%.
At the needle tip the same 0.04mm have far less effect. The same calculation leads to a difference of ~2% in the open flow area (1,57 vs. 1,53)

This is the reason all Needles are seemingly very similar at the start Diameter, but differ a lot in the tip. To change the flow at the needle tip significantly you need large diameter variation. For changes at the base it is much more sensitive.

Best regards,
Erhard

[Erhard]

For the geometry of N1Ex and NOZx Needles look here (at post #9):
http://www.thumpertalk.com/topic/810...eihin-needles/

Best, Erhard

[David v]

Thanks!

The 2.91 (I did use 2.90 for calculations) mm was what I was looking for, I double checked your calculation and if you compare the NEDJ to standard, the figure should be 19% leaner if you swap from N1EF to NEDJ. If you on the other hand swap back to N1EF from NEDJ it will be 24% richer...

19% is a lot. Let?s see if that fixes my problem, since I ride very slow (tough terrain and poor driver) the engine runs mostly just above idle. And if I get the engine to stop in the middle of av mud hole, it has been terrible to get started again! (Im guessing it is running rich and too cold = sparkplug full of sooth)
When cold it starts right up, but in the forest it takes a lot of cursing and kicking.

I also measured a N3EF needle. I?ll throw in that data if any one is interrested and also calculated the area diff in the gap that forms between needle and seat for each reading @ every 5 mm, if the seat is 2,90 mm. (Did the same to the NEDJ in first post) All compared to N1EF along the lenght:

N1EF N3EF Diff (area in fuel gap)
2.70 2.72 0.02 (9,7% smaller)
2.69 2.71 0.02 (9,2% smaller)
2.69 2.72 0.03 (13,8% smaller)
2.64 2.64 0.00 (0% smaller)
2.55 2.56 0.01 (2,7% smaller)
2.41 2.44 0.03 (5,6% smaller)
2.28 2.30 0.02 (2,9% smaller)
2.07 2.17 0.10 (10% smaller)
1.79 2.03 0.24 (17,6% smaller)
1.53 1.89 0.36 (20,3% smaller)

Everything is measured by a digital caliper. I guess that the reading can vary 0.01 mm from actual thickness, if some readings seem strange it is probably why. But it gives a good hint!

/David