Carb tuning
 

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

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?

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?

he is reading both.

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?

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

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.

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

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

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.

Also, Dan, I wouldn't plug the PV because to compensate for the huge PCVR's, youd probably have to run a monster primary main jet, to keep WOT AFR where it is. Then your primary light cruise at 3000-3500 will be pig rich.

You think like I do.... I was never a huge fan of tuning on a dyno and forgetting about it. Conditions change. I'd routinely be at the track just doing tuning passes on the car, get in 4th early and just run the whole rpm range while datalogging. You can't particularly see max power from timing that way, that was where the dyno did come in, but as for fuel, you can't get any better then real world conditions.

If you don't mind me asking because alot of it is still over my head, what's a general guideline you go by when setting up the carb. i.e. idle adjustment for x range, primary for y range, secondary for z range and how to dial in the power valve and throttle enrichment? I know every setup likes something different, and try as I may I've never found a really good breakdown on setting it all up.

joe,c&s sells the jets dan needs,6 sizes,4 of each size for 24 bucks,i agree with you on the sizing,go with whatever holley puts in the 850 metering block and it can be as even as efi,it is just a matter of drilling&tapping the metering block.i like the quickfuel carbs if starting new,they are boost referenced and are quality parts,and are fairly priced not to mention they look great.if you dont feel like drilling&tapping,make dan spring for 4 new metering blocks from quickfuel.

2 circuit and non boost referenced carbs? no wonder you beating your heads off the walls.....wait until you chop your props,,gonna have to do some more jetting....have you guys tryed 3.5 and 4.0 power valves?

Yes, the engine needs to be at operating temp, with no choke it will be a little lean and may not want to idle with first startup, but after it warm it will run like a champ. You may have to push the the accelerator arm by hand while warming up. Pumping the throttle with add more air and lean the engine even more

SKATERMAC,a blown engine with a air-fuel ratio of 14.7 at 6 lbs boost at full throttle will burn down in seconds,take that to the bank!

14.7 afr is the manufacture setting for the best possible emissions . A roots blown marine engine will more than likely puke when shifted into gear with a afr of 14.7 at idle.

And 14.7 while underway will for sure smoke pistons and or valves.

back when i was in high school[about 100 years ago]they thought and taught that 14.7 was the perfect afr,we sure have changed our way of thinking in the new world.

why on earth would you tune an engine so lean at idle that you need to pump the acc pump lever to keep it running,,just curious.

I said 14.7 at an idle his wot AFR will be 12.5. The info he posted to start with confirms this. Most stock carbs lean out under power someone spent a lot of time to correct that problem on his setup so why send him down the wrong road????
..

12.5 at wot with a non intercooled roots setup will be a recipe for a burn down. He needs to be quite a bit richer at wot . Us heavy vee bottom guys need to be able to stand on it for minutes, not seconds.

I agree if your running the wrong spark plugs and the timing is locked out. Running across Biscayne bay from Miami to Gilbert's at 150 plus takes a little more than a few seconds. If you tune the engines right you don't need 6 LB of boost anyway. Heat soaking an engine will kill any engine and fixing with to much unburned fuel will make it an oil burner in less 20hrs.

im not trying to be a diik but how many blown engines have you tuned with a air fuel gage?if he follows your tune up he will be on the road to rebuild,just saying!

I`m sorry man but the idle air circuit has nothing to do with primary or secondary jetting or any AFR numbers above idle. Ive got it as lean as it will go without dying when shifted and its at low 12`s at idle.. 14.7 aint happening.

Was hoping someone with some actual carb tuning experience would have chimed in (not counting Mild or Tkat of course) no biggie, we`ll get this figured out. I`m going to restrict the fuel dump thru the power valve at 4K and see what happens.

The advice I got from Nickerson today was to add a secondary power valve.. umm ok cause the primary valve fuel dump just wasn`t enough?? :picard1:



What in the world????

please tell me how your,or any boat can run for hours at 150 mph with less than 6 lbs boost.

Someone should tell Tatermac that he forgot to log off and now his 15 year old is giving out engine advice on the interwebs..:lolhit:

SKATERMAC,im always trying to learn,what engines do you have in your skater,and can you give some info,like what type of power adder and what your total timing is set at?

Im sure you would try listening

:QUOTE=ICDEDPPL;3988834]Someone should tell Tatermac that he forgot to log off and now his 15 year old is giving out engine advice on the interwebs..:lolhit:[/QUOTE]

well that is some funny chit right there:poopoo:

I think he is in the piston business

thats pretty much the answer i expected,im starting to think daddy is goint to be pizzed when he reads your posts after he went to bed.LOL:hitfan::confused:

i think i have seen his website BULLCHIT STROKIN PISTONS,WITH OUR PISTONS YOU DONT NEED NO STINKIN BOOST!

I am highly intoxicated at the moment, and this still smells like ****t.

Dan , lets shoot for 12.5 at wot. Mike and I need a winter project. Make sure you hold it pegged good, we need to upgrade heads while we're changing pistons out

I always wanted a 150mph skater that gets 25 mpg and passes the smog test

i know where we can get the pistons,lol.

150 mph with less than 6 lbs boost,his engine must have been built in THE MAGIC ROOM.

We all seen the movie but Please don't tell me he wrote the book to.

www.magicroombook.com

They where 1350 Sterling to start with. I use most of Mike's recipe. I run cams from Hollman Moddy custom ground. They are very small but will run to 7500 and idle at 700 rpm. My ignition system is fully programable it has boost retard, retard for curb idle (neutral) and i run a timing curve; 36 degree total. I run race stripped 10.71:1 Mooneyham blower at 1.1 over drive. Special surface gap sparkplugs. I tune with Innovative O2 AFR meters in the collectors. I run blower shop intercooler forward motion feed only. I have single stage waterpumps raw-water only at 150 degree water temps. Twin in line modified 1150 Holley 3 circuit carbs(power-valves front and rear) 80 Mains Squared .080 PVRC 4.5 and 5.0 above the blower with the intermediate and idle circuits this equates to a 112 main jets at full throttle acceleration 12.9:1 AFR

Well if i knew what i was doing maybe i could get big trouble into a lower et bracket,,it has 2 dominator carbe 4 stages od nos and more jets then yours , mike's and joes all put together and we manage to get it down the 1/4 mile race track in 6.87 seconds @ 210 mph..

http://i35.photobucket.com/albums/d1...psad298207.jpg

even with my glasses on i cant seem to find the blower belt,hell i cant even see the blower.