Carb talk
 

Whats the preffered way to set up a marine carb as far as secondary opening. 40% left, 60% left or 1:1?

Also is there a point to powervalve in a boat. Boost referenced .. dumping 8-10 jet sizes of fuel because I hit 1# of boost (pretty sure thats how it works) seems unnecessary. It`s not a car where you hit the gas every other stop light and need that fuel enrichment.

To me (carb newb but fresh eyes) I`d set up a marine application carb with 1:1 primary/secondary and block off the powervalves. Tune it that way.

dan,the power valve stops it from being to rich in no boost running,when you start making boost you need to ritchen it up.the boost ref blower carbs[quick fuel]come with a 4.5 power valve and on my engines i did not need to change from that.with your a/f gage you will see a steady line almost the same from 2500 all the way up at wot.

I boost reference both primary & secondary, and have progressive linkage opening of the secondary butterfly's. Why would you not want the motor to tell the carbs what it needs??? I have a great fuel cure from idle all the way to WOT. There are times that my secondaries are just a little open and I m still pulling vacuum. To me blocking off power valves is going back to the stone age

Rookie boost referencing question . Do I run vac line from these ports on the carbs to ports under the blower in the intake and can I T them or do they have to be separate ?

http://i1243.photobucket.com/albums/...000_0118-1.jpg

i can see a drag car with no power valve and 8-10 jet sizes larger because it is either ideling or wide open but in a blown boat deal forget it.most of the time the boat engine will be in vacuum or low boost.

Very nice by the way...Yes you can tee them, I have all 4 of mine coming of my carbs tee'd into my vac/boost line going to my gauge on the helm.

Mike I totally agree with you on that

t them togeather and run one line under the blower in the intake manifold.DO NOT run the vac line to the carb adapters.

that is because us blown fountain guys think alike!

Thanks B wan .

Ok Mike , I guess the idea is to put the lines where they will see vac/boost . Love this blower you sold me !

it looks like you have shined it to a mirror finish,it should serve you well.

:D :party-smiley-048:

deep,have you consulted with any oil guru,s as to what oil you should run?:cartman::party-smiley-004:

Seems the cat has his tongue . :blahblah::angry-smiley-038::ernaehrung004:

Boost referenced power valves are not necessarily manditory, but I feel they are the better way to go. Blocking the power valve in most setups was strictly a drag racing trick in the day, because strip cars didnt see high vaccuum/low load scenerios. Yes, for the most part, in a heavy boat, most of the time you're on plane, the PV will be open, if its boost referenced. I dont see it as a nuisance, I see it as another fuel supply to the main circuit.

Boost referencing them imo, makes the tuning process easier. For the most part, you are eliminating the lean to rich problem that occurs when the power valve opens, when non referenced. Because loads vary in a boat, based on trim settings, how much fuel or how many people on board, one day your AFR at 3500RPM can be 12.0, another day it might be 11.5 depending on the throttle position at 3500rpm. Its not always identical throttle postition vs rpm. By having the PV referenced, its pretty much certain that your PV is simply gonna be open. Now you simply add/remove jet, or with the quick fuels, change the PV restrictor size to tune the fuel mixture. Carbs can meter fuel well based on the load/rpm when relying on the venturi effect. Throw a random fuel dump into the main circuit, and you start getting unstable fuel mixture. IE, rich/lean condition with a simple 10% change in throttle position.

While yes, blocking them is possible,you may find yourself having to run very large jets in the carb to get an acceptable AFR. Every carb is different. My 850 holley marine carbs came shipped with 88P, 96S with PV front and rear. If i was to plug the PV's, I'd likely have to go to 96P, 104S, to even things out. With that being said, I do think boost referenced PV's are much more important in a street driven blown setup. In marine, we rarely have a scenerio where we are cruising with 10+ inches of vacuum, and gonna mash the throttle to wot needing the instantaneous fuel. For the most part, on plane, they are open anyways. Unless you have a super light cat. But most Vee bottoms, your never really gonna see much MANIFOLD vacuum at cruise. With non referenced PV's, you can see high vacuum under the carbs, at cruise, where the PV can be open.

I would run progressive linkage, and power valve in the primary, as far as boost referencing, you need to put a vucuum gauge right under carb base and ck at different RPM's, I have run into some roots type blowers producing so much vacuum that power valves and vacuum controlled meetering rods will stay closed when they need to be open causing a very lean condition...

this is why the carbs need to get the vacuum signal from the intake manifold,under the carbs is not a true indicator of what the engines fuel requirement are.

I've seen that when too small of a carb is chosen for the application. Very common on the baby single carb blowers when guys are trying to make 700hp with a small roots blower and a single 750 carb they yanked off their small block, or some tiny flame arrestor/filter. The right blower/carb combo in a marine setup should never have 6+ inches of mercury under the carb. The old merc 525sc, 600sc, 800sc engines did not have boost referenced pv's nor did they have enough vacuum to pull a 6.5pv shut at wot.

Ok so non referenced you get a fuel dump at 4000rpm with boost referenced you get a fuel dump at 3000..(lets say) No matter where it happens it`s still 8 jet sized dump. What am I missing?
I don`t want to get dump at anytime I want a nice even AFR curve.

Dyno sessions don`t count, AFR is always gonna look pretty because it`s a WOT run from start to finish.

I think I need to talk with a carb engineer no one around here knows anything!:banned:

You get a fuel "dump" when the PV restrictions are oversized. The powervalve or power enrichment circuit is not rocket science. When its boost referenced you won't have a "dump" becauase you can tailor the amount of fuel the power valve adds easily on a quick fuel carb. The main reason not to plug them is, in my opinion, an issue at low speed when airflow thru the venturi is weak.

I agree with ya on the dyno thing!

Well I talked to an engineer, they know everything , he says you`re all wrong. Lets spend the next couple hundred pages arguing about it.
I`d like to start insulting people now, who`s first?

Borg's Your Dingleberry
 

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borg who?

I have a question for you guys, I think that everyone so far the has responded to this thread, has a roots blower with carbs that are mounted sideways. So, have any of you checked at what angle they are at while running wot or Idle????? Mine are at 6.7* at idle and at 7* at WOT (depending on water conditions). And it just happens to be that 7* is perfect angle of trust for my setup. Well that don't work out the best for the float levels. Believe me put angle finder on a float bowl and see how much 7* lowers the low sides of the bowls. Maybe it wont make much difference, but I bought 6 two inch carb spacers and am milling them at 7* so when I m at WOT or idle my carbs will be flat level & can set float levels right on. Also the stock car boys have special floats for going around left turns all there lives. They are wedged on the G force side. I was thinking of installing these also, for rough waters running, getting on plane etc.... What do you guys think??????

Mine are mounted sideways. I changed my stock fuel bowls out for the aluminum bowls with large sight glasses. What's nice about them is you can raise the float level to the top of the sight glass, which is towards the transom of the boat. With the stock style bowls you'll be spilling fuel way before getting them that high. With the stock bowls I'd set them to where they are level with the bottom of the float hole, install the float screw, then raise the float another 1/2-3/4 turn. Either way, I've never had an issue float level related.

Yes MT, I have the stock bowls and the way you described is exactly the way I did set them, but its still not perfect, so I opted for angle milling some carb spacers. I guess it can't hurt. its only money & time right??? LOL

Sounds like a cool project. Were you seeing anything negative from the float height setting ?

i have thought about doing that with my 38 with #6 drives and bam 1550 dry sump trannies.she sits low in the rear and the nose is way up there.b wan,wanna make 4 of them for me while you are at it?

Ya, once in a while when idling through a no wake & hitting others wakes... It would tend to flood a little (black smoke)...thinking it was coming through the back boosters. I didn't want to lower the floats cause I didn't want any fuel starvation at the WOT. So if figured angle plates & be done with it, the carbs will be level and close to perfect fuel level. It just at to cool to wash your rings down... Same thing probably happens when getting on plane. Although, my boat gets on plane without tabs in about the length of the boat.

I`m not sure there are too many days out there on Lake Michigan where the boat stays level at any degree. You might need to build a carb gyroscope.

:faint2:

Ah hell . :silenced:

I'll bet the engineer didn't tell you that bolting your carbs down with l-19 bolts is worth 50hp...

turning the carbs sideways was a trick drag racers cam up with years ago, when using center hung floats they are less effected by up and down motion(wheel stands, bouncing around coming down) so on a boat they help in this way to...now the angle deal I have seen spacers angle milled in inboards for this...I doubt will help much in app like this but who knows...

If the straight up and downs vent tubes could always extend them up or do the rubber tube deal...to make sure no fuel comes out of the vents into the throttle bores.

Also, in your new found carburetor site, there are cool vent tube and vent tube mods that may help.

Quick Fuel makes 1050 marine carburetor with J tubes 2 circuit metering 1.710 venturi M-4710 (can that one be used side by side)
Then there`s a street strip carb, fx4700
Drag FX 4710
FX 4710-2 .. 2x4.. that`s the side by side application?

so many choices..I wish someone would answer the phone over there.

They are probably at PRI. That is this week. Lots of other shops close down for this also.

They must be a smaller company than I thought.

Check out these bad boys:


http://www.silverbackcarbs.com/