Super Jet Mod Pipe Stock Carb Pop Off Pressure?

[Pacer]

I'm trying to tune a superjet with a Riva RPM kit and chokes removed to install a primer. I Jetted the carbs to the factory pipe specs, and it had good top end, but was sluggish on the bottom. It was loading up at idle, so I put the stock pilot jet back in, and now it idles better, but not perfect. I tried adjusting the pilot, and changing the pipe settings, but it didn't help with the bottom end power. I didn't check the pop off, but figured it might be too high, so I installed 2.3 needle and seats with the stock spring. That gave it a little more power, but it feels like it should have more bottom end. I'm going to pull the carbs and check the pop off. Any idea what number I should be looking for with stock carbs and chokes removed?

Thanks

I know there are a lot of threads on this. I searched and couldn't find the answer.

 

[Mike W]

Do you have a pop off gauge that you can test your pop off with? If not then I would get one. Also, the Factory pipe specs are very close so I would revert back to that and go from there. I'm assuming since you have the rpm kit you're running the a/m flame arrestors? If running a stock f/a then pop off will need to be higher. Just for reference I'm running a/m arrestors.

My RN is having similar symptoms. It is running very well at higher RPMs but just off idle it is loading up. My pop off was at 32 psi and it was suggested by the engine builder that I raise it to 38-40 to see if it clears up. In doing so I found a leak coming from the pump side cover on the slave carb so you might want to check for that as well. I fixed the leak and I'm currently at 38 psi so I will see how it runs today.

 

[Vumad]

My Superjet...
stock motor (1 over for fresh pistons)
ADA head 37cc domes (170psi)
B-mod, don't recall screw settings
stock carbs, stock airbox w/ 2 screens
Lightened flywheel, stock ignition
12/17 concord prop, stock pump

Setup to hold WOT for racing but also okay for surf. It can load up a little if I spend too much time idling or going really slow in the surf but it is minimal and I didn't want it to blow up on the track. I think it works just great in the surf I think.

Main 140
Pilot 75
Needle 1.5
spring 95g
Popoff 42 (might need to go lower if you have aftermarket carbs)

I stuck a piston on the track with 135 mains, but I didn't leak test it so who knows. It runs great now.

 

[Mike W]

Mine responded very well to 38psi popoff today. Try a higher popoff than what a 1.5 n/s and a 95gm spring will give you. I cut 115 gram springs to achieve that popoff.