They are not boost referenced. I'm thinking this is something I should do!

Remove the rear powervalves asap for a starting point. Your dumping fuel for sure. Then work your way down on jets from there. I have 84P/92S with 8.5PV in primary only. 468's, Dart heads, B&M 420's at 6psi. Holley 850 carbs.

Not necessary. I prefer it, but not totally necessary. Your best friend on these setups is a wideband 02 sensor setup. Have a bung welded in your dry tail, and you can get a NGK Powerdex wideband. They are great quality and affordable compared to some others.

http://www.amazon.com/NGK-Powerdex-A.../dp/B0018MUNTM

We have tuned quite a few carbed blower setups using widebands, and its amazing the ''holes" you can find in the fuel systems from idle to wot. Its really an invaluable tool, that will not only help keep the engines in a better state of tune fuel wise, but also save money on fuel consumption. You probably wouldn't believe the amount of blower engines out there with AFR's in the 9's running way rich, or in the 12's borderline hurting things. Plus it really helps speed up the tuning process.

Thankyou. I'll order four power valve plugs tonight.

Hey Tom, I get all my carb stuff from these guys. Fantastic pricing and good shipping.

http://www.allcarbs.com/detail.php?p...&ctgn=39&stt=5

http://www.summitracing.com/parts/hly-26-36/overview/

Hey mild just a question . But do you have to run power valves on blowers or just even jets all corners? Also I have cmi headers how would I put a wide band meter bung in those. The water comes out right on the ends. Or can it be done?

You can run powervalves. Whether or not you boost reference them is up to you. Is it mandatory, no. You can tune around them. The reason a lot of guys boost reference is in fear of the vacuum on top of blower/under carb, can suck the PV closed shut. This is really not an issue on a marine setup running low boost. Mercury did not boost reference their carbs on their supercharged engines.

The problem not running powervalves, is you'll have to run large main jets. For example, lets say you were running a jetting combo of 82/92 with a pv in the primary. To remove and plug the PV, you would have to step the primary main jets up from 82, to say, 88 to as much as maybe 96, depending on the size of the power valve channel restriction. I've seen some aftermarket carbs with huge power valve channel restrictions, which is basically like a jet size. Also, you lose some tuneabilty as by not being able to tune for a light load situation where the power valve is closed, keeping the air fuel ratio in a leaner state. The only time i would consider plugging all the PV's is for a drag car or drag boat for the most part, where there are two throttle positions, idle and WOT. IMO i would leave at least a primary power valve in on a typical progressive linkage carb. If using 1:1 linkage, I would use front and rear pv.

When it comes to tuning in the boat, the primary main jet should be sized for low speed light load cruise AFR. The PV circuit should engage when the load is increased as to when you start getting into boost. Heavy boats will want a PV that opens sooner, light boats will want it later from a rpm standpoint. Secondary main jet should be tuned from when secondarys begin to open and to wot. If you carbs are boost referenced, the pv circuit will almost always be into play unless you have a really light efficient boat that will cruise in vacuum. For a boost ref pv to stay closed while on plane, your gonna need a low number, like a 2.5. pretty much your primary main jet tuning will be from low rpm to where the secondarys open, for desired afr. If AFR needs to be adjusted above the point of when the secondarys are open, add or remove secondary main jet, so you can keep your cruise afr where you want it. A 800HP supercharged engine in a 38 Cigarette might need a different setup than a 26ft cat.

Yes, you can install bungs in your exhaust tails esp if they are dry. Many of us have them installed. I would probably skip the boost referencing, run a PV in the primary only. Start with a high number PV like a 10.5 and go out and start tuning. Install a vacuum gauge in the baseplate of the carb adapter (most have a 1/8Th NPT plug you can replace with a nipple). Record RPM/AFR/Vacuum readings throughout the curve. The vacuum readings will tell you what your power valve will be seeing. Adjust from there.

This kind of tuning is nearly impossible on a dyno. While i don't think it replaces the need to dyno by any means, I think it is a useful and valuable tool, that will pay for itself. Most engines are dyno'd in a full state steady wot pull, and cannot duplicate different load/rpm scenerios in the boat. While its also a good idea to evaluate spark plugs, tuning off them alone, imo, is 1980 stuff. Todays unleaded fuels can make reading a plug difficult. I may be inexperienced in that area, but i cannot tell a difference between a plug held at WOT at 11.7 AFR and another one held at 11.3AFR. Some experts look at porcelain for jetting, some look at the base ring on the threaded body. Some look at heat marks on the ground strap for ignition lead, some look at it for plug heat range. Who is correct? I mean i can look at a plug and say "that's rich", or "that's too lean", but i cant pinpoint it to where i can say, 'yup, that plug there was running at 12.5 AFR, and that one over there, ya, that one was at 12.2"

Some may look at this kind of tuning as a waste of time and unneccesary. The way i look at it is this. If I put an engine package together, and spec a cam with .650 lift, i want .650 lift, not .620 lift. If I order cylinder heads with 2.25 valves, i want 2.25 valves, not 2.19. I want 8.5:1 compression not 8.25:1 compression. My thoughts are by guesstimating at your fuel curve, will leave performance results on the table, no more or less than the examples i gave. We don't cut corners on engine specs, but are willing to cut corners on tuning the engine?

More good solid advice. Thanks MT for taking the time to provide VALUABLE insight and staying on point as usual.

Eliminatorshane - We installed bungs in all four of my CMI tailpipes right after the joint. So far no issues with the O2's getting wet and they have provided great information.

Quick question, I had bungs welded in my tails at the end of last season, I want to set my carbs up. Everything is working well but I'd like to dial in my Afr, what's a good ratio to shoot for on some mild blower motors? From what I've been told 12.5 is the gold standard for n/a motors, but blowers should run richer than that? Just asking because I've never got a straight answer on that. If it helps, carbed hp 500 with 177 blowers and sport tube exhaust and aed boost referenced 850's

I would keep that thing as rich as possible with those tiny blowers on a 9:1 502 with iron heads with a single carb. Prob like high 10's and hope it lives . I would not try running more than about 4psi with it . Do u have intercoolers?