Jetting and power valves
 

My other thread about my Demon 850s Kid’s died on the vine so I thought a new thread might be good.

I mentioned something about stepping up to 50cc accelerator pumps and I plan to make that change there.

What about adding secondary power valves and tuning it that way? I’ve read some older threads that show this may be beneficial for especially with heavier boats.

Current setup is 86/93 with a 8.5 pv and I’m getting a lean pop when starting to really get into it.

I would need to get vacuum readings throughout the rpm range to dial it in - is it worth it? Or just go with the primary and add the extra pump shot and some jet to the secondaries?

Are you monitoring AFRS while testing? What AFR is doing should give you direction of where to go with your carb calibration.To actually get a lean pop from jetting it would have to be very lean, not off a few jet numbers. Remember AE covers up temporary lean condition's caused by sudden throttle movement

I never liked the fuel dump of POwer valves. I can se their in cars but not on boats .
Blocked them off and only ran big jets. 102`s

I am monitoring AFRs while running.

The boat has only been out a couple of times. Had a good day just running around letting them break in some more. Cruise to about 4500 had AFRs in the mid 12s. We decided to go running in the bay after lunch… we had a lot of slop at the mouth of the Chesapeake and with the wind had a pretty good chop with rollers. I got on it a little harder and it popped at about 4700. I didn’t see what the AFRs were when it popped, and decided to head back in with the intention of doing more thorough testing the next time out.

I wasn’t rolling into the throttle hard. I was applying it very gradually so I was surprised that it popped. Guess it was under pretty heavy load.

But doesn’t that kill “economy” and also risk washing it down with fuel at lower rpm?

Can you observe or record fuel press at 4700 RPM? Fuel press may be dropping off?

I have used a GoPro to video fuel line mounted press gauge since I can't see it while running WOT. Always wanted a helm mounted fuel press gauge for this very reason.

is it spark related i have had that happen worth a look

I'm out of room on the dash, but the idea of installing fuel pressure gauges where I can see them while running is something that I've wanted to do. I can setup my GoPro to watch the pressure on the fuel rail. Probably a good first step.

I'm assuming that fuel pressure is good - I definitely have the right hardware for it, but it's possible a restriction coming from the tank could be an issue. I removed the anti-siphon valves from the tank but never really liked how how far the new fittings went into the 90-degree pickups. The fittings for the valves I took out seemed to be a little shallower. I guess I can put the old ones back in if I see a drop.

I can't completely rule out spark related issues, but then again both run really strong otherwise. I only heard it pop once and then decided to not press my luck, but in other high-load situations (like getting on plane), I haven't experienced anything that would lead me to believe that there was an ignition issue. I am running the stock coils from the old MPI setup - maybe they need the be refreshed just for piece of mind.

I really think it's fuel related.

My fuel map was much better and I didn`t notice any negative affects.
At lower speeds the carb pulls what it needs

Double check the float level, and possibly fuel pressure dropping of at rpm.