GTR Briggs 37 EFI (60hrs)
BPS Heads (40hrs)
BPS Neptune Tuner (Preprogrammed for the heads when purchased from BPS) (40hrs)
VooDoo Exhaust

Last two trips out I’ve been getting stuttering and stalling while throttling up from idle to full throttle.
If I squeeze the throttle wide open from idle it will stutter and hiccup pretty bad.
If I ease into wide open throttle the stutter is not as bad.
Once on plane and running wide open it runs great.
I was able to duplicate the stutter/hiccup/stall on the trailer as well.
I noticed a higher than usual backfire/popping coming from the exhaust while replicating the issue on the trailer.

Check list so far:
Fuel Filters are new
Fuel pump is pumping as it should.
Valves checked .005
Plugs look good

Reallly appreciate any advice or tips.

Have you done a leakdown?


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Check your intake gaskets where they bolt to heads for a vacuum leak. Im confused on the neptune because all the 4400 engines ive seen have bone stock factory tunes in them for their heads only engines

Did you have the issue prior to installing the exhaust?

Mods including exhaust have been on for 40+ hrs with no problems.
Going to replace the wiring harness as it is a 2015 37EFI.
Will see if the harness swap helps.

40 hours is like a week at the camp. alot can go wrong in that time, especially with a grenade motor.

will c has great advise, start at the basics and work yourself up.

good luck.