Carb jetting/power valves.
 

Ran some today and with cooler weather the jetting seemed to be a bit lean in cruise and into the secondaries.

Idle is rich but could have been the trans slots were a little more exposed. I closed the butterflies some and it seemed to be happier. Very snappy.

Cruise AFRs in the mid to upper 13s and pretty much stayed that way getting into the secondaries. I think we saw 14s here and there during cruise.

Jetting is 86/93 with a 4.5 pv.

Step up the PVs to 6.5s or more and see what happens? Increase jets a couple sizes?

What about removing the power valves completely and running 96s across the board?

Engines really begin to pull like raped apes beyond 3800.

Thoughts?

yes.

Glad to have the meters. Had I not, I wouldn’t have know about the lean condition during cruise. I cannot say for sure but WOT throttle testing would have had me looking at secondary jetting.

The engines have good power, oil and water temps around 170 (I think water temps are actually a little lower… the top hose from the stat shows 148), oil pressure 55-60 with 15w40. Engines appear very happy.

13s at cruise… thankfully I really didn’t go anywhere with it other than to test.

How many are running like this? Seems like a gamble. Or am I making too much of it?

What size carbs

Demon 850s.

Does it have one power valve on the primary side only? Or does it have one on the secondaries also?
Do you have a vacuum gauge hooked up to know how much vacuum is being pulled at idle, cruise, wot.

I have not run her wide open yet. Just going off AFR readings at the dash, idle through mode range. I did push a little and AFRs remained the same. Coming off say 3800 to 3500 my buddy said he saw 14.1.

Idle vacuum is right around 10 inches. Might be a little more since the timing has been dialed in. Next time we go out, I’ll measure.

*Edit*

Power valve in the primaries only.

Do you know if your cruise vacuum will be low enough to actuate the PV's? If so that will richen things up, as you want. And then if it's too fat at higher rpm, you can take out some jet from the secondaries.
My setup does a similar thing, as I increase cruise rpm my mix goes way into the 13's. But when I get on it, the thing takes off and the afr is perfect mid 12's. I'm probably going to do a richer primary jet cause that's literally where I cruise most of the time. But I'll also lean out the secondaries the same amount to try and keep a nice afr at big throttle openings.
AFR meter and vacuum gauge is the best way to observe.
Some twat saw my vac gauge at the ramp and thought it was funny. Ain't there for you buddy.

Stepped up the power valves to 6.5s which is original for the Demon 850. Not much of a change. I didn’t measure vacuum so it really was a shot in the dark. I will next time. The engines were running great and we were a little harder on them escaping this evening before coming in. I may leave them at 6.5 and add jet to the primaries as mentioned.

Powervalves in a boat never made any sense to me. If you`re going to dump 6-8 jet sizes worth of fuel all at once why not just increase the jet sizes accordingly and get nice even fuel map instead of a gas dump?
I could never get a nice even fuel map till I got rid of the power valves and just went bigger jets.

That was a thought earlier in the thread.

Definitely boat dependent as some boats are under a lot of load even while ‘cruising.’ A vac gauge can be a good friend here.

Not so common to see vac cauge in a boat with N/A engine, i wonder why. I have one in my fresh build.

Yep, I brought it with me but got lazy and just wanted to play a little. Hooking it up is a ***** too because all of the vac ports were plugged. I could have gone with the 8.5 and probably been good to go, but I didn’t want to overdo it.

That is pretty much what I saw yesterday. Port was a few tenths lean compared to starboard but pretty much exactly as described.

About the only place that power valves make sense in a "performance boat" application is during the "accelerate to planing speed" range. You know the one - you push the sticks up to 2,500 rpm and leave them right there. The boat pops up on plane, then runs on up to 3,500 rpm at the same throttle setting. As the boat comes on plane, you have low vacuum and higher cylinder pressures. Once she's up and running free the vacuum climbs.

A vacuum gauge along with an AF readout is very helpful in figuring out your jetting and PV sizing.

And for me, a 3400 rpm cruise without any opening of the secondaries is fine to see AF in the high 13 or even low 14 range if the boat is fairly light.

With Holleys though, if you are into the transfers at all at idle, you may need to drill a small hole in the butterflies. Idle circuit should take care of your idle. If you are into the slots, then you're compromising your off-idle mixture.

What qualifies as a “light” boat? I’m guessing a 31 footer weighing 8500-9000 pounds isn’t considered light, but maybe I’m wrong.

I’m seeing as described. Digging into it to get on plane and then they settle into about 13. I want to say that was on the primaries (after on plane) but I was trying to pay more attention to the gauges and the “Cape Henry Slop” vs stick position. Memory says that it felt like I was against the point where you have to push to begin opening the secondaries (it’s definitely noticeable). I don’t have a problem ditching the power valves if that’s the better way, but I need to really check the vacuum while running to be educated on the next step to take, if any.

Idle transition, I’m not into the transfer slots. Running against the outgoing tide to keep speed up in the no wake is a little rich but not too bad. If I need a little more air, I have the “idle-ez” that’s part of the Demon setup. So far so good.

Next weekend we will be working on the Cig to finally get that thing done, but I’m looking forward to more running/testing. The new power is really fun!

Yeah. While you are tuning it's very helpful to have a vacuum gauge to look at.
Setting idle mix is USUALLY 1/4 turn richer than max vacuum. On a 4-corner carb, adjust all 4 evenly. An HP series Holley has an idle air bypass adjustment thru the tapped hole where the threaded rod for flame arrestor screws in. Not sure which Demons do/don't have this feature. It's handy.

I have not seen the idle-ez do too much but I imagine that it's purpose isn't to flood the system with air. Instead, just a little bit of a vacuum leak to help lean out of the idle a touch without exposing the trans slots.

I like the carbs. Some crap quality out of the gate was seen, but I corrected it. They had some good ideas with the Demon, and it looks like they took some of it and applied it to the HP Holley carbs.