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

well that,s quite the story,those [special surface gap sparkplugs]must be magic.you say these engines were sterling 1350s at one time,what hapened to the psi screw blowers that they had before you put those monster 10.71s on top.how about giving the cam specs on those [hollman moddy]cams.id also like to know how much boost you are making at wot.12.9 afr at full throttle on a roots supercharged engine,keep dreaming,LOL.im calling bs on this one,i cant wait to see what joe g will have to say about your pipe dream story LOL.boost retard for curb idle,so are you saying that this magical engine idles in boost requiring the timing to be retarted?funny thing is you made a comment about not leading someone down the wrong road,anyone who tries to tune an engine with this recipy wont make it 1 mile down the road.are you a comedian because your story is funny LOL.

Well this thread went to $hit lol

Exactly, Best of luck on you quest. Steve M

so i guess you are done blowing smoke?:bsflag:

Dan, think of the carb as having 3 power circuits. Primary main, primary power valve, and secondary main. Primary mains are doing the work until 3500RPM. After that, the Power valve opens, adding fuel, and the secondarys come in, again adding fuel. In order to fix your rich spot, fuel needs to be pulled from somewhere. You cant pull primary jet, because you'd be lean at 3500. If you pull any more secondary jet, you'll be lean at WOT. So there lies a spot in the curve where there just is simply too much fuel being introduced. Powervalve circuit. If you remove fuel from there, and don't make any other changes, this will lean the wot AFR also. So, you would need to add more secondary jet.

So lets say you remove 4 jet sizes worth of fuel from the power valve circuit. You would then go up 4 sizes on secondary main jet, so your WOT AFR stays the same. So, you will go from a current setup of 88P/92S, to like a 88/96 Setup. Or 88/98 possibly. That is much more of a traditional jetting configuration, and fuel distribution will be better. Carb's can give very linear fuel curves. But they need to be set up properly.

Most people don't talk about power valve channel restrictions. When modified, they can have a huge effect as far as fuel changes. For example. Lets look at a holley #88 Main Jet. Drill size is .104. Now lets look at a #83 jet. Drill size is .094. So, theres a difference of .010 between the two. If I told you to pull 5 main jet sizes, youd expect a substantial change in AFR correct? Theres a lot more math to it, as you have to figure total flow area, etc. But as a quick guideline, reducing the PCVR by .010, would be like pulling 6 jet sizes worth of fuel from the overall flow. So you'll have to make that up if you want to keep the WOT afr the same.

To sum it up, lets go to the river, install a .010 wire in the pcvr's, and record the data. My guess is you'll prob end up with 88P/96S, no more 10's at 4000RPM, Better fuel distribution, and a safe wot AFR.



This is stuff we can talk about on the phone or at the dock. I am writing it here, that maybe it can help someone else out.

try 4.5 pvs

I second what Mild Thunder is telling you the two of you can tune your boat on the water, and he can show you how to keep it tuned the way you want it. You'll never fix it here on this board. If your ever in my neck of the woods I'll will do the same for you.

Damn good thread! Thanks MT²

I agree, MT just broke it down exactly how I should be looking at as to what adjustment do what, even if he didn't intentionally do it that way lol.

its in a bottle and fed into the engine by 25 jets and that is just the nos side..

He tried them. No change. When I put a vacuum gauge on the carb adapter under the carbs, at 3500RPM the carbs are seeing 8-9" of vacuum. At 4000, the vacuum drops to zero. So in that 500RPM window, pretty much any powervalve will either be closed, or open.

So measuring the jets it appears to be .001 difference between jet sizes.
I put a .013 wire in the powervalve passages, lets see what happens.

:thankyouthankyou:

wonder how far that would go in a single engine boat before it ran out of nos,or puked the drive?

i dont trust those jet charts or the number on the jets ,,i always use a pin gauge and at times i will correct the sizes with jet drills..

Anybody have knowledge of blow thru's? Don't mean to hijack your thread Dan but considering the turns this thing took already didn't think you'd mind.

I'm trying to figure out a stumble that almost always happens when the power valve opens. This happens at all loads, RPM's and any power valve used. I was going to change out the power value restrictors but my $1300 Carb shop carb came with less than the desired bleed type screws. Time to get the drill. Also, I can only get 1/2 of a turn on the idle mixture screws before it goes way rich at idle.

I was thinking or starting with the idle feed restrictors since opening the idle bleed really didn't change much. After this, and getting at least a 3/4 turn on idle mixtures screws go after the power valve restrictors. Any thoughts?

Yes, I know this is a car. but the Carb Shop guy is useless. "Didn't do it on the dyno"

on blow through you need jet extensions on the secondarys,,also see those 2 holes under the power valve,,those need to be slightly opened up if your jet is above 88 in size but dont go crazy..

What size are your pcvrs? And are you running a high flow 4 window powervalve?

sounds like the power valve channels may be the issue as well, try to find some stock holley metering blocks and swap those for a test....will know quick...Rob

I have a standard stock style power valve 4.5. I tried 3.5, 6.5 and 5.5 it did the same. Just followed the power valve rating . Size...not sure need to check that yet. I'm pulling around 10-11 inches of vacuum at idle.

He should still have vacuum at 4k rpm. Maybe its not a carb issue. The blower might be tired.

Have you tired a "Boost Referenced" power valve? I don't mean like where it gets its signal, but a actual powevalve modified so that it opens at a certain boost level, rather than vacuum drop. With the blow thru, a standard style diaphragm powervalve can be tricky. Opening too early, therefore causing a bog. If you set it up to say open at 3psi of boost, you may find that helps.

Absolutely wish I went that way vs. The carb shop crap. If I'm going to invest anyore than $200 bucks into this I just going to pull the trigger on a Holley fuel rail EFI sefup.

I just purchased a 4 window #6 power valve. It really feels like a initial lean out condition when opens. Having to run the black accelerator pump cam seems a little extreme for a big head, 238/248 solid roller, 327 cu engine

http://www.theturboforums.com/smf/in...topic=110547.0

You can make your own

Also, are you running an AFR gauge?

The way C&S does it, is they change the PV opening rate by using little shims behind the spring. Adding a shim makes the PV open later, removing them makes it open sooner (more or less spring tension). Easier than playing with a bunch of springs.

I will say this. My buddy had some pro systems blow throughs on his boat engines. In my opinion, they sucked. Fuel curve sucked, idle sucked, low speed driveability sucked.

I convinced him to get some C&S aerosol carbs, Fixx here talked highly of them. With the new C&S carbs, the Fuel curve we dialed in with the help of roger on the phone, was perfect. In the boat, they idle like stock 500EFI's, 600RPM in gear. These are 522ci that made well over 1000hp on the pump.

With the way your hat is positioned, keep an eye on those #1 and #2 plugs. Those will probably be the lean ones

Thanks for the well detailed link. Lord knows I have enough PV's to destroy to make one good one. This theory makes perfect sense.

Yes I have AFR gauge. Currently I have idle set at 14. Cruise at low RPM's with constant petal is 12.2 to 12.5 max. Moving through the PV opening it briefly goes way lean then drops 11.5. If i'm too low in the RPM's I can see 10.5. WOT is 12.5 to 12.8. To me, the WOT is a little high and cruise is a little low. I have re-jetted recently from 74P86S to 76P88S and had almost no change on cruise but brought my WOT numbers down from a scary 13.6. (had a couple lean-out pop backs at high RPM's ) My assumption tell me that it's cruising on the idle circuit. Subsequently, I may need to look at fuel restrickers also. Especially since I can't get turns on idle mixture screws which is probably complicating enrichment circuit.

Interesting note: on a full exhaust I tried 2 locations for the O2 sensor. One at the collector and the other 3 feet further down in the H pipe. The collector readings were actually very similar. Maybe a tad richer.

Do you have 4 corner idle setup? Have you tried closing the secondary screws, and opening the primary screws a bit more? Should richen the transition a little. This may help the stumble. IMO 4 corner idle just isn't needed on a mild street engine. Big compression, big cammed large port race motor, sure. Sounds like a lean stumble. Or possibly a larger squirter.

CSU's boost ref pv is adjusted with a screw that puts more or less tension on the spring to open sooner or later when boost comes in. I don't know if Kevin (at CSU) would sell one by itself but its worth a try. I have one of his carbs on my turbo (street) car and it's fantastic. His tech support is second to none as well.

Tried squirters, overall best ones are in. Closing the secondaries more- the problem is when you do that theirs is a slight delay in fuel. Subsequently, put it back the way Carb Shop had it set. Going to install the power valve tonight. If that fails I'll either make one or contact CSU to see if they will sell one. I really believe the pressure is causing a delay or a weird disruption to the enrichment circuit. Plus, I need to get the very light load AFR's higher.

After typing all this I do remember trying closing the front idle mixture screws all the way (open rears more) and had almost no stumble at all. Ran really flat though.

MT-Next time you make a run to Racine let me know. I have the first round. Andy

Sounds like a plan Andy. The power valve mod just may do the trick. Conventional valves just aren't designed for that situation . Good luck with it .

if your air fuel screws dont seem to do a thing then your primary idle screw is turned up way too far,,to get rid of a off idle stumble you need to use the secondary screw to raise and lower your idle..you want like a 1/4 turn o n the primary idle screw and no more that 1/2 a turn on a/f screws..the further out you turn them the more your eyes burn..and all the engine will do is load up the further out they are..

if the idle air circuit is not properly adjusted you will have a major stumble and it wont matter what pv or what jets you have or squirter or throttle cam you change its still going to do it..

Good info Mike. ICDEDPPL dan had a lean sneeze issue with his carbs. I went through both carbs, and reset all throttle blades and mixture screws to spec. Did some fine tuning on the water after. Long story short, it doesn't sneeze anymore getting on plane.

Idle mixture screw definitely make changes to the idle and AFR's. What i'm saying is that i can't turn them out any further than a 1/2 turn without the engine going "pig" rich. Actually, it idles very well. Very clean and smooth for the size cam it has. Those numbers were at .050.

Update-I installed the 4 window #6 PV and no change noted. Decided to change the primary squirter from 31 to 33. Same crap. Measured PV ports to be .065. Kevin from CSU .054 should be stock. He won't sell his PV alone. Steve Morris engines quoted $3300 for the fuel inject setup needed with initial programming. So....looks like I have a PV to make tomorrow. Time to get a friday buzz on.

you do have jet extensions ??? when the carb is under pressure it will push the fuel to the back of the carb and wont allow any fuel to the jets..they need to be extended to the middle of the float bowl to prevent this from happening..

also,timing?

what sparkplug?

what spark plug gap?? this is important..

are you using a boost referenced fuel pressure regulator??

Ok, back to original post question....where does your power valves pick up vacuum ?? different carb guys do that differently...last one I had used the vac connection on the carb that needed a line connected under the blower to operate correctly...just a thought....Rob

UPDATE:

.010 wire in powervalve passages didn`t stop the fuel dump completely but it helped to keep the AFRs out of the high 10`s at about 11.2@ 4300 I`m good with that. seems to be the same AFR all the way to 5200

me thinks if you go down 1 jet size all the way around,YOU WILL BE GOLDEN!

Dan, the wire installed in the PCVR helped. Leaned the midrange by about .5 from what your saying. (you were 10.8 at 4200 before?) I'd go up another .010 in wire size, then add secondary jet. This should get you in the 11.5 range at 4200, and 11.0 range at full kill. Your just pulling a little fuel from the midrange, and adding some on the big end that way. The .010 size I suggested earlier was just a starting point to see what it would do. I'm not that good to get it spot on for ya! lol

I wouldn't go much leaner at wot. Iron heads, overdriven blower, and no intercooler, its not worth hurting the engines for 1/2 mph gain. Mercury's 600SC, 800SC, 525SC, all ran fat. Probably much fatter than low 11's at wot. They didn't get the best gas mileage, but they also didn't blow up, and you could stand on them all day.

Here is a chart regarding the effect of power when it comes to air/fuel ratio. Granted they did this test on a sbc with a small blower, but generally it coincides from what ive seen on the dyno sheets.

You'll see that going from say 10.5 AFR, to 11.5AFR, you gain about 1% in power output. 1% on a 800HP engine is, well, 8HP. Looking at a couple dyno sheets from my engines, one pull it made 798HP at 6000, AFR was 12.8. Adding 2 jet sizes all around, next pull, it made 794HP at 6000, AFR was 12.2. Keep in mind this was on the dyno, and we left it with the 12.2 AFR jetting. The day we dyno'ed, it was early spring, cold out, and the dyno cell has excellent airflow. In the boat, Im much richer with that jetting.

When we ran it last I was 12.2AFR at 3500 (1psi of boost) this time around its around 12.8. I think a little more primary and a .020 wire might do the trick.
Not too concerned about a few HP, just want the motor to run on healthy