# Thread: New Mikuni Pop off Chart.

1. ## New Mikuni Pop off Chart.

Well, it is not actually new. Just want to add information about the stock 1.2 needle. For some reason I can't find a stock n/s psi reading on any of the forums. Some said 85psi some say 65 psi. so I decided to take my own reading.
I done the test on 3 carbs for my Yamaha SUV. and tested the pop off for atlease 20 on each carbs. The number in the chart is the closest numbers I got, also, I don't have the black spring. so no reading on that. If anyone can help me fill that in it will be perfect. I also highlight the Green reading as it is the stock setting for a gp1200 engine with stock frame arrestor. Again, my carb is old and it might not be accurate, so please if you have the more accurate reading please let know and I will change the chart. Thanks

BTW, base on the reading, I will guess the black spring should be arround 55 PSI.

2. sweet!

3. no one have the black spring for input?

5. I'm going to add my \$0.02 to an old thread. Engineers know this as a sum of moments problem, but w/o trying to do that problem we can also look at it as an interpolation problem.

Example: For the 1.5mm seat, if we didn't know what the pop off for the black spring (80g) would be, we could interpolate it. The 80g spring is half way between the 95g and 65g spring. So the pop off pressure should be about half way between the two (43psi and 32psi). That tells us the pop off should be 37.5psi. The manual says 38psi. So that checks out.

That means the black spring (80g) with a 1.2mm seat should be 56psi.

 Pop off Pressure (psi) Needle Valve (mm) 1.2 1.5 2 2.3 2.5 65g 47 32 18 15 12 80g 56 38 21 17 14 95g 65 43 25 20 17 115g 85 56 32 22 19

Another alternative is to do graphical interpolation. This is more appropriate if the plot of data were non-liner (not a straight line).

You can see the open points are the predicted values based on linear interpolation. It seems to work graphically also.

Or someone could measure the darn thing... I don't have a black spring, but I'm not really interested a lower pop-off either.

Cheers,
Matt

6. ## +1 by:

7. You must be a Mechanical Engineer We use Excel A LOT and Sum of the Forces & Moments in X,Y,Z are tattooed to my eye lids!!!! Good job on the graphs!

8. Civil. I see you noticed the ugly default excel x-y scatter format

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