Tuning recommendation

[Trevorbm]

building a 701 this winter, cylinder and cases ported dual 38s 190 psi, pfp. Running stock air box chokes removed. 70 low 135 high. What should I aim for pop off? 42 (95g spring) with 2 screens removed? Or 35?(80g spring) taylor at tc freeride made a video saying 80g spring, with choke removal and am flame arrestors. Tia

 

[Pro-pulsion]

32-35 psi popoff with an 80 pilot and 135 main would be my starting point. It's all based on the response you get from the engine though. Get a few sizes of jets like 75 pilots, 77.5 and 80, and 132.5, 135 and 137.5 mains, this is considering you are running the oem intake manifold on 62t cases which needs higher popoff pressures and something a little stiffer for reeds like Boyesen Pro Series reeds. Every engine is different, porting changes things, chokes changes things as you have mentioned, flame arrestors as you have mentioned change things.

 

[Trevorbm]

32-35 psi popoff with an 80 pilot and 135 main would be my starting point. It's all based on the response you get from the engine though. Get a few sizes of jets like 75 pilots, 77.5 and 80, and 132.5, 135 and 137.5 mains, this is considering you are running the oem intake manifold on 62t cases which needs higher popoff pressures and something a little stiffer for reeds like Boyesen Pro Series reeds. Every engine is different, porting changes things, chokes changes things as you have mentioned, flame arrestors as you have mentioned change things.

Looks like I’ll have to guess and check for now. Stock up on jets and springs and test in the summer.

 

[Pro-pulsion]

It's the only way to properly tune, most people seem to have good luck with 75 pilots, 135 mains and 32-35 psi popoff but there are lots that those base settings didn't work for. On my 38's with a factory mod pipe, the Boyesen reeds mentioned above and some porting it preferred 32 pop, 80 pilots and 135 mains. Check out the carb database and see if anyone is running a similar setup for a starting point too, look at as many close options as you can to find a common thread with their jetting and engine specs, you might find a pattern that will get you closer to where you want to be.

Carburetor (specs) Database: SuperJet and Blaster 1 - X-H2O - Epicenter of Freestyle and Freeride jetskiing

 

[fastgtfairlane]

The hull you're running the engine in will make a difference too based on how well the engine breathes. Example- a buddy has a jet maniac ported engine with 38s bpipe, zeel, etc. Had it in a fx1 then swapped running gear into a tigercraft v3 with only a pole breather to allow air in. Also went from a 144 mag to OEM 155 pump. He had to completely retune his engine. Needed more fuel down low.