Power valve and jets
 

We just rebuilt my carbs, they are Holley 850's. What power valves should be used in these carbs. The carbs are on 454 425hp chevy crate motors. Also what jets should be in them, right now they have 96's all the way around.

What model # are the carbs ? Its on the front right side of the choke tower. Generally...you should have a 125-65 power valve. I'd say (just my opinion) that the 96 jets are a little big. What intake are you running ? I'd prolly square jet it with 86's and read the plugs. As an all around easy way to get it real close...we run ours and keep track of the mph. Keep increasing jet sizes till the mph drops off...then back up 2 jet numbers. :drink:

The carbs are 80443's.

In my Merc manual it calls for 84's all the way around for the 850 on 440/460 cyclones.

The only number on the power valves in the rebuild kit is a 6 and I can't remember what the original had on it but the original is what we left in it.

Both carbs were very dirty(the boat had been sitting for years I was told when I got it). The problem I was having before the rebuild was that the engines idled between 1000 and 1300 all the time and had to run for a long time before they would run when shifting into gear. The hydraulic steering and tie bars on the transom was also black from the exhaust blowing on it.

This is what the Holley tech site says should be in it.
80443 850 (F)88,(R)96 6.5,6.5 4150 Marine

These are the power valves you need.
http://www.summitracing.com/parts/HLY-125-165/

The transom was black from the carbs most likely being too rich. You could leave the 96's in the back if you want..but I'd lower the fronts down. That'll prolly clear up the over rich condition at idle. Also...make sure the air bleeds are clean (gently blow them out).

This info should get you close sir. :drink:

The Holley site only says power valve. It doesn't say whether it's primary, secondary or both. I'm going to go out on a limb and say it's primary because of the big difference in jet sizes. A power valve is usually equal to 6-8 jet sizes of added fuel.

The only numbers on the power valves that came in the kit is a six, there is also a k do you think they are the 6.5's?

These are both 6.5's. Yours look like this sir ?

I will look again for the five but I only saw the six on them. I looked on Holleys site and they did not list a 6. Yes mine look like the one the left.

You should call holley and get the box stock setup for jets and PVs of the 850cfm marine carb. Almost certainly the PVs are 6.5s, but probably only in the primaries. If yours have them in the secondaries, block them. Then what ever the box stock jetting is add 5 to each and you will be close. So if it is 72p, 84s box stock, start with 77p, 89s. After you get that we can work on the idle mix setting and getting it to run on the idle circuit. Also make sure the airbleeds are clean as a whisle. I presume you did this during rebuild, but it deserves mention because it can corrupt all other tuning.

What do you mean by "block them"?

Replace them with block off plugs.

http://www.summitracing.com/parts/HLY-26-36/

If you have changed much in the Merc stock engines...like the cam then the Mercury stock PV size is likely not relevant. In most pleasure applications, if you elect to not use a PV then when at cruise you will likely be rich (black transom) and wasting $3+ gal gas.
The best way to set select a PV is by using a vacuum gauge. On the top end, we select the PV that will open at about 80% of the max RPM at WOT. As an example, if WOT is 5200 RPM, we would set the PV to open at approx 4200 RPM. This way you "go rich" only when you want a saftey net under high loads. This set up allows you to use much smaller primary and secondary jets...less fuel used for most of you boating hours.
At idle, you want to check that the PV you selected remains closed (PV size lower # than vacuum reading at idle). In most cases, this should not be a problem. If this is not the case, you will them need to some advanced tuning. Hope this helps.
Ben

Thanks

Dale
The number on the power valve indicates the inches of vacuum the the power valve opens (ie: 6.5 would open at 6.5 inches of mercury). I will try to check my holley book you may have a 6 power valve which would be close to the 6.5 i'm not sure if they made a 6. Do not try to reuse your old power valves as they are probably dried out, in addition one sneeze or back fire and it usually pops the diaphragm in the power valve. This would also explain the terrible idle and black (rich) transom.

some info ..... BT is correct about secondary PV

http://www.bob2000.com/carb.htm

The main jet sizes should have nothing to do with a rich condition at IDLE. It sounds like you need to clean out your air bleeds, and make sure your carb is actually using its idle circuit. While its idling, if you can turn in the mixture screws all the way in, and it will still run, you either have a blown powervalve, or your idle speed screws are turned too high. once you crank the idle speed screws up too high, the carb will no longer function using its idle circuit. it will pretty much idle like crap, stall, high idle speeds, etc. Pretty much anything on the carb that you can adjust with a screwdriver, is for idle only. Powervalves and main jets are for high speed circuit.

I like this thread! Getting some good info here.

Are the rebuilds just on your carbs or were the engines done also? If the engines sat for that long you need to do a compression test or crankcase vacuum check to see if the piston rings are still sealing. Anything you do to the carbs will be a waste of time if the engines arent healthy. Pumping oil out the tailpipes looks same as an overly rich condition.

Both engines compression was 150 across the board. The engines are stock crate motors. They are 454's 425hp.