Super Jet Need help with tuning fresh rebuilt motor

[tor*p*do]

So, I have a 61x/61x, 46mm mikuni, ADA head, freestyle porting, MSD enhancer, B headpipe with C4 chamber, 1990 SN
First rebuild I started at 120 pilot and 150 main, detonated and burned a piston.
So with fresh rebuild, I went rich: 132.5 pilot, 165 main, 2.3 n&s, 80 gr spring, ended up at 1 turn hi and lo.
Runs, but it is rich and stumbles at top end. Plugs are dark and wet.
5 gallons through it without killing motor, which is a good thing.
It is hard to do plug chops on my lake due to long no-wake zones.
Do I go to 125/165, 125/155, 132.5/155 as the next step?
Thanks!

 

[Dorny119]

So if you do like 1/8 throttle for 30 seconds, then get on it a little, does it load up (sort of a bog, then accelerate feeling)? If it does load up, then go 125/155.. If it does not, and your bottom end hits hard, go 132.5/155.

 

[Vortex]

Did it detonate or seize last time? Different things. Deto looks like you hit the top of the Piston and dome a thousand times with s pick hammer and is due to uncontrolled combustion (bad fuel, wrong ignition timing, squish band problem, etc). Piston seizure is when you burned away the oil film between cyl and piston, usually because your cooling system was unable to transfer heat adequately.

If you have for example 200psi compression, a bpipe set to run hot, single cooling, and msd enhancer and you're going wide open that is your problem. A c4 chamber had more trapping pressure (think adding a super or turbo to a car engine) so its been recommend in the past to run lower compression, ex: 37cc domes instead of 35.

Sorry if I'm explaining stuff you already are aware of.

 

[tor*p*do]

 

[tor*p*do]

Running dual cooling

 

[tor*p*do]

So if you do like 1/8 throttle for 30 seconds, then get on it a little, does it load up (sort of a bog, then accelerate feeling)? If it does load up, then go 125/155.. If it does not, and your bottom end hits hard, go 132.5/155.

It only loads up if I grab full throttle.
Going to try 132.5/155

 

[Dorny119]

It only loads up if I grab full throttle.
Going to try 132.5/155

Sweet. Let us know how that goes!

 

[long beach local]

Have you tried adding more water to that C4 chamber? It Will actually help with detonation. I was told this as I am having similar issues running a TNT V3 pipe in my proforce race boat with 160lbs compression using pump gas. I went to a 125 single main jet on the pipe and I believe my problem is solved. I should’ve probably started my own thread but oh well. I know a guy who tested with factory pipe designing that style pipe back in the day and they had experienced deto issues but after adding more water problems went away. Don’t ask me why ,but it actually helped my jetting too although I am using the lay down pipe.

 

[tor*p*do]

So, talked to engine builder and he said try 120/160 with 17 psi pop off
I ran 125/165 this weekend, but pop off was a little high
Ordered 2.3 and 2.5 needle and seat and an assortment of springs to dial in the pop off
Running strong, plugs starting to show some brown, piston wash still rich

 

[Dartman]

Dude, that blowup doesn't look like detonation.
new engine and slighty lean maybe, you butted the rings, then blew out the top of the ring land, needed to file ring gaps a little looser when assembled