Some needle valves are different lengths or screw into the cover and stop at different heights....as you found

Yeah perhaps, but the new valves behave just like the old ones I took out. I couldn't get the long legged cap dialed in with the old tall valve body either.

I just find it interesting that to get the correct gas level in the glass bowl required that the black float be nearly touching the inside of the cap. If I were to use the static 12mm, 16mm inverted lid method I'm sure that there would be insufficient gas in the bowl during acceleration (stumbling). Those numbers might work if the needles were solid and not internally spring loaded. IMHO, the spring loaded 3 part needles are just not designed for an inverted static setting. Does anyone know if the original needles were spring loaded, or were they solid ?

Weighting the float could possibly be a solution to increase fuel height (and keep the float parallel to the roof at nominal)..... or cutting the high towers down and drilling new holes for the float pin.

Weighting the float could possibly be a solution to increase fuel height (and keep the float parallel to the roof at nominal)..... or cutting the high towers down and drilling new holes for the float pin.

Not sure how one would bond a weight to the plastic float in that environment, but its worth thinking about.

I like the redrilling idea, but I don't think the "towers" would need trimming down unless they interfere with the movement of the float.

You could open the float at the top, insert weights, then seal so nothing external to hang up.

You could open the float at the top, insert weights, then seal so nothing external to hang up.

It's the sealant that worries me in a long time gas environment.

Fuel level in the front bowl needs to be 2 mm lower than rear bowl. that's why the ears and valves are 2 mm longer (for the later 3-screw SU's) for the front carb. Then the fuel in both nozzles will be at the same level (the main thing).

Wonder if the 4-screws also ran longer nozzles in the front? The 72 FSM doesn't mention this change - wonder if Nissan engineers were embarrassed that they got it wrong with the 4-screws. Maybe the factory race team noticed the fuel level difference when they pulled the domes and checked fuel level in the nozzles. Easy enough to fix with a couple of washers, so maybe they passed it along to the designers who incorporated the change for the 3-screws. ???

Edited October 21, 201311 yr by Stanley

It's the sealant that worries me in a long time gas environment.

The floats are solid foamed EPDM stuff . Nothing to seal. If you really really had to add mass, just screw in a tiny screw or embed a tiny needle or metal shaving.

I'm also wondering about all this lovely static fuel height setting and imagining how this relates to the case when fuel is spritzing in the top and flowing out the bottom as the car runs. Here's hoping its kinda similar.

Edited October 21, 201311 yr by zKars

The floats are solid foamed EPDM tuff . Nothing to seal. If you really really had to add mass, just screw in a tiny screw or embed a tiny needle or metal shaving.

I'm also wondering about all this lovely static fuel height setting and imagining how this relates to the case when fuel is spritzing in the top and flowing out the bottom as the car runs. Here's hoping is kinda similar.

Ah I see, I didn't know they were solid, that makes a big difference!

Yeah I hear ya, with all of the fuel entering and leaving and the car going up hill/down hill over bumps, idling, accelerating, banking, etc. it's a wonder a float system works at all !

Early Spitfires had floats, German Messerschmitts had fuel injection. In -neg G moves, the floats raised and caused the Spitfire's engine to stop. To circumvent this, the Spits had to roll first before pursuing...... giving the Me-109 time to get away. Think of this when you pull high G turns, etc.

I think putting the float on a gimbal would help (or the long buffer hose (anti slosh tank) between the bowl and jet solution I mentioned in another thread) however Weber and Hitachi (flat top) addressed it by putting the jet smack in the middle of the float bowl.

Edited October 21, 201311 yr by Blue

Where do i purchase a new set of high quality needle valves for my 3 screws su carbs? 

Why?