Nitrous miss/pop at higher rpm

I am probably just not thinking this through right now but just got back from my first nitrous run (around town) and am getting a miss/pop at around 4800+ rpm. Is it not enough fuel or timing not retarded enough??? I am running a 125 hp shot and backed off timing by 5-6 degrees. My timing marks are off so cannot give an exact degree it is set at. Fuel pump is rated 8.1 psi but after turning the car off it holds at 6.5 on the dial so assuming that is what it is pumping.(dial bounces too much when running to read). I read nitrous should only need 5.5 psi.

383 engine - 750 Holley

Thoughts??? Bigger jets?? Back of timing?? Hope not bigger fuel pump b/c I just upgraded this one from 5 psi.


Update: Just took it out again and noticed greyish smoke cloud behind me while on the nitrous. Still missing and got what sounded like backfire/pop in carb again around 5k rpm. I hit nitrous at 3k and all works great up until around 5k.

What do you have for ignition system?

Just same as stock with coil and electronic distributor. Accel shorty plugs ACC-8197

Checked the plugs out right after a shot?

I ran out and got some 110 race fuel and advanced the timing just a little shy of where I started in the first place and no more smoke, no backfire and a little higher rpms but it will start to stumble around 5.5k now. Different from before though. That felt more like a miss. This actually feels like it is running out of fuel. I am going to give it another degree or two of advance if it can take it and see how that goes. If that does not work I'll probably have to get a bigger fuel pump.

I'm going to pull those plugs too and see what is going on. My guess is I am running lean up there

Running out of fuel at higher rpm with nitrous is a recipe for disaster. Always better to over fuel and work backwards from there. Get your timing marks accurate so you know where you are. If you've ever experienced a nitrous "BOOM" you'll know why timing and fueling are MOST important. If it is lean on the top end and you keep running the rpm up, you might want to invest in an engine diaper to catch the parts. Not preaching; the voice of experience talking...lol

1. GET a fuel psi gauge NOW before you do more guessing
2. DO NOT retard timing UNLESS you need to
3. If you aren't running the n2o side on it's own dedicated fuel line, then make sure you have a GOOD pump that can handle both the motor and the n2o system.

Continue doing what you are doing and you will wreck a piston shortly.

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