The jetting was from my last tests.
When my son did alittle trail riding and said it ran better on top with the lid on, I really got into the inertia/velocity thinking. With the lid on it is generating the most negative pressure, which not only raises the slid, but draws the fuel up the emulsion tube more. My next test will be to jet down. So your request to try a 150 may be very interesting.

 

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If the 150 is too lean it may be because of you radical carb mods. Let us know how it works.

 

I called a friend on the edge of town, that has a hay field just cut and he gave me permission to test. I just got to stay on the outside edge. I think that I was running too big a main jet to make up for not having the needle raised enough. The theory of setting the main before the needle may not be the best for this application. The stock or aftermarket needles are very aggressive, that is, they have an aggressive tapering angle.
I feel that everytime I raise the needle one groove, I have to jet down one size. This sharp angle must cause a change of flow even for the main jet selection.

Hope to have some results today, if it does not rain!

 

What make of jets are you guys talking about. Oldmanracing, I assumed the 195 is a dynojet size, and installing a 150 dynojet is very very small. I use 150's on LTZ400's with smaller cards. With a 180 dynojet I am getting a 14.5:1 air fuel ratio mixture on a stock DS at 5000 ft above sea level. Tuning it for power, I have to use larger than 180 main jets.

 

This last weekend:
Lid On / OS Tubes
195 Dynojet Main


I will have to see what sizes I have below Mikuni 165 - which is very close to a Dyno 175

Mikuni / Dynojet Jet Size Comparison

Flow rates based on size markings of Mikuni and DynoJet jets are not comparable. As a guide .. the chart to the left indicates equivalent sizes based on the diameter of hole in the jet.
Mikuni jets are chamfered on the inside opening at the threaded end and
Dynojets have a machined flat surface. Keep this in mind when using this chart. These physical differences will never allow an exact comparison.

This chart is intended to be used as a tool to assist you in making a more
accurate decision when selecting a jet size range or comparing tuning data where an opposing brand is being used.


DynoJet jets are marked according to the diameter of the hole in the
jet .. ie: DJ150 = 1.5mm and DJ175 = 1.75mm.
This is not true for Mikuni or most other OEM equivalent jets. This size
Mikuni jet, (N102.221 Super BN), is marked according to its' flow rate,
ie: 150 = a rating of 150 cc of fuel per minute.


Mikuni Dynojet
140 149.3
142.5 152.0
145 154.7
147.5 157.3
150 160
152.5 162.7
155 165.3
157.5 168.0
160 170.7
162.5 173.3
165 176.0
167.5 178.7
170 181.3
172.5 184.0
175 186.7
177.5 189.3
180 192.0
182.5 194.7
185 197.3
187.5 200
190 202.7

 

I'm talking mikuni jets on a stock needle so adjust accordingly.

 

Old thread but what would be the verdict here? Is it that on the dyno the open lid makes more power, but in real riding/racing situations the lid on gives the best lap times?