I changed to a 75 shot, and hit the spray with about 1000psi. The car will start off strong once the nitrous starts spraying, and then after about 2 seconds it will get pig rich, start popping through the exhaust and shooting clouds of smoke out the back. I had a friend behind me when I hit it telling me it was shooting smoke. What could cause it to suddenly richen up like that?

 

Do you have the correct jets in for a 75 shot??

 

yeah check your jets first. what plugs do you have?

 

Yeah they are correct. It did it with the 100 also. I have TR6's gapped at .035.

 

Sounds like you may need to drop to maybe one size smaller on your fuel jet.

Are you pullling any timing?

 

What kit do you have?
What jets are you running?

 

I have a Harris Speed Works kit. I am pulling 5 degrees through my Mallory 685. My n20 jet is .044 and my fuel is .026. I was thinking about a using my 100 n20 jet with my 75 fuel but I am not sure if that will be to lean or not.

 

i would not try that...i think you need to look into your ignition system, plugs wires ect, go out at night and look for arcing...tr6 you can gap down to .30 might try somehting closer to that...

might just need to heat tht bottle more evenly

 

sounds to me like uncombusted fuel due to missing

What is your gap set at? how old is the coil?

 

Gap is .035. Coil is the same one that was on it when I bought the car a year and a half ago. I checked for arching plugs/wires, and they all looked fine.

 

My take on this.
You will be a little rich for 75 shot with those jets., but not pig rich.
Depending on fuel pressure, if around stock pressure you should be using around a 24 fuel jet for a 75 shot. This is from NX though.
The jet sizing should be pretty close, if the pressure is the same.
NX for a 75 is 41N-24F.
Looks like harris is a touch bigger on the nitrous jet.
Since you have the Mallory ignition, look into shielding the small wires going to the coil. This has been a problem on a couple of cars running upgraded ignition.
The 685 in my car did not like my wires. I chased the same thing you did for about 3 months. Changed from my Taylor wires to MSD and all was solved.
I would not gap down any further. .035 is fine for the bottle.