Float needle and seat size question

[JohnnyO]

I was rebuilding my carbs today and removed the needle and seat assembly to replace them and noticed the size of the needle in the assembly I removed was larger in diameter than the replacement. I then noticed a "2.0" engraved on the side of the one I removed. I then blew air through them both and the old one allowed more air through than the new one.

I understand that the needle and seat assembly regulates the fuel to the float bowls and cuts it off when the floats rise.

My question is this: If I use the new, smaller needles and seats am I going to be starving my carbs of fuel? The old ones are in good shape and open and close perfectly so I could put them back in.

Is there a performance gain by using the larger or smaller needle assemblies?

Thanks,

John

[Zforce]

I would also like to know what is the largest size needle valve that will fit because I too have thought about the small size of the replacement needle valves that are availabe being a restriction. Just eyeballing, it appears the fuel hose to the jet nozzle is larger so a healthy motor could easily drain the float bowls causing high speed lean out and stumble above 4k rpm.

[Bruce Palmer]

Nissan needles and seats were 1.7 and 2.0. The needles and seats we supply are 2.0 as well. In theory you are correct but in practicality it's immaterial. The average guy driving a street car or even a track day car wont see enough flat out full throttle duration to even give the sense of float bowl levels being down.

The E-production Z the owner runs can do the front straight at Portland at say 7500 RPM and at the end of what is about 3/4 of a mile he feels that maybe the bowls are starving a bit. Once he's out of the throttle going into turn one the float levels catch righ back up.

So what I'm saying is that on the long course at Bonneville it would be a problem but for you guys on the street, it's about as big a problem as gravity on the moon. Yes it's different but until you get there it's not a problem.

Remember that fuel supply to the needles and seats are under pressure where everything else is gravity fed. A smaller needle and seat could very easily make up for any "potential" short fall just by remaining open longer.

And no we will not produce a he-man size needle and seat, so don't ask.

[JohnnyO]

Thanks Bruce. I don't need he man size but in my case I think that I will use the larger ones until they start sticking.

What exactly do you measure to get the 1.7 or 2.0?

John