ICDEDPPL

iTrader: (1)

Trying to get these Nickerson 850`s to give me consistant AFR`s.
(540`s with 8-71blowers, 6psi)

After some tuning finally the midrange and idle is good to go:
12. 2 ish with a couple of lbs of boost at 3500rpm.

As soon as the secondaries start to open around 4000rpm it goes to 11... high 10 AFR

I believe the primary power valve opens, I also believe the power valve passages have been opened by Nickerson (not impressed by this) and it starts to dump fuel.. not enough air to burn it off..
At WOT its good at low 11`s.... just from 4000K to 4900 its pig rich dipping into the 10`s

I have tried:

Larger secondary air bleeds: Leaned midrange to high 12`s, no good
Experimented with different power valves... no luck
Dropped a few jet sizes but ultimately thats going to affect WOT AFR`s which are good.



I`m thinking of plugging the primary power valve and jetting accordingly to relieve that power valve fuel dump at this point....


Any input is appreciated

mike tkach

iTrader: (3)

drill and tap the holes behind the power valve and put screw in jets,roger at c&s carbs has been doing it for years,he can set you up with what you need.dan,i must ask 1 question,if you did not have the afr gage,would you know it has a rich spot?

Kyain

I'm very interested in some info on this as well too. I'll be going through this next season when I get out on the water so if you find anything not posted in here I'd appreciate it if you passed it along

Are you reading both banks on the o2 or just one?

mike tkach

iTrader: (3)

he is reading both.

ICDEDPPL

iTrader: (1)

Joe said the same thing Mike drill and tap the passages, then start jetting.. you`re right thou, I`d probably never know but now that I do it bugs me. ... is Roger local?

mike tkach

iTrader: (3)

no,do a googel search on c&s carbs,or i can give you his number.

Skatermac

Your carbs are setup right, the ARFs are too rich all the way though. Idle needs to be 14.7 in gear. Make sure your running a short ground strap spark plug no hotter than a 9. Make sure ignition systems working properly. After the idle is set your the rest will fall into place. Plugs will look like they came out of the box even after idling for and hour.

mike tkach

iTrader: (3)

so are you saying to get the idle at 14.7 and it will be right for everything else?

Kyain

He's pretty much on point with what I've targetted as far as a car setup. I've tuned many EFI systems (used to own my own shop, and I and another guy went through AEM's EFI classes and all) and we would always shoot for 14.7 no load and extremely light load up into the 15's for direct injected motors. We never looked for 12.0 or under until we were in boost, and even that was dependant upon conditions and actual load of the engine. Many times our targets under boost were not 100% optimal horsepower but what would keep the engine safe, i.e running richer to cool the cylinder and such.

In my mind tuning a boat SHOULD be easier then a car as your loads are pretty static compared to rpm in comparison to a car which needs response and power under all conditions, but I have ABSOLUTELY no experience with it whatsoever, and I've never touched a carb in my life to even have an idea as to just how close and perfect you can get them. I'm used to being able to command specific injection times dependant upon conditions, not for practically trying to control a fuel leak at all times.

I hope it's helpful but believe me, I as anybody would love a seasoned carb setup guru to walk into this thread and give a step by step lol. I'm still trying to find a USB port on mine and switching to EFI isn't in the budget at the moment with how much money I've already put out on this 540 build

MILD THUNDER

iTrader: (3)

Same thing I told him mike. His power valve channel restrictions are .0935. that is HUGE. At 3500RPM, he was pulling 8" of vacuum under the carb. At 4000, 0'' of vacuum. Somewhere in between there his PV opens, and his 02 reading goes from low 12's to 10's. I believe when the Power valve opens, that is causing his rich spot, rather than the secondaries starting to open. Rich afr means more fuel than air. In order to go from 12.2 AFR, to 10's, within a hundred rpm or so, its getting a large amount of fuel from somewhere. That somewhere I believe is the powervalve. Typical power valve channel passages on a 4150 style carb, are much smaller than his. The only carbs holley used those large restrictions is on a dominator. Which we all know were pretty much meant for one thing, WOT racing.

We all know when you plug a power valve, you have to jet up to compensate for fuel flow. What determines how much you need to jet up, is based on the size of the power valve restrictions. In otherwords, when the power valve opens, it can add 6 sizes worth of jet, 8 sizes, 10 sizes, 12 sizes, etc. If the power valve restrictions have been enlarged, then you will get a LARGE amount of fuel when the valve opens.

Your typical carb setups are usually 6-10 jet sizes larger in the secondary when the valve is plugged. Following this traditional setup on his carbs, netted a very rich AFR at wot. So it was recommended to Dan to put smaller secondary jets in to lean the wot afr. So now he is 2-3 sizes larger on the secondary, but has the rich midrange.

What I would do, is drill and tap the restrictions, and go back to what a standard 850 holley uses for size. Then, install larger secondary jets. This should clean the midrange issue, and still have a good wot AFR, and also much better fuel distribution. We don't want 75% of fuel coming from primaries, and 25% coming from secondarys on sideways mounted carbs. You then get into one bank running leaner than the other. Decreasing secondary jet is just band aiding the problem. Secondary fuel flow is proportional to the airflow thru the venturies. As airflow increases, so should fuel flow. Hence why as rpm goes up, AFR should go down (richer). Not leaner like his is doing. And ultimately, have a even amount of fuel coming from the primaries and secondaries at WOT. Just my opinion.

This is getting into a area most average weekend guys don't get into or talk about much. 10 Years ago this was unheard of here on oso. Nobody had/used widebands. The amount of fuel that can be changed thru small changes in the pcvr size is huge. Mike, you and I learned that when tuning those blow thru aerosol carbs. Next set of carbs hands down will be quick fuels, if you are into tuning them to work like EFI. Theres no need to drill and tap things, its already done for you. Air bleeds, PCVR's, emulsion jets, idle feed jets, etc. A properly set up carb should have no "lean' spots, and no "fat'' spots. It should be linear from idle to wot. And to get there, in a boat, you just cant do it without a wideband meter, on the water. Not a bench, and not a dyno. Theres much more to a carb then main jets, especially if you want it to have a EFI like fuel curve.