Happened to notice something today. Y'all know I drop in here , like , a daily fix...and I just notice that debates are less frequent, some answers are are like 1,2 or 3 replies long and spot on.

Are there consensus's forming here? Have we all been elevated to a higher level of understanding through all the experience that a community like this brings to bear...?

( guess its a BIG THNX to all those BTDT types who care to drop in and share).

And not-for-nothing, and I excuse a 'learner' like myself from this comment, but the level of knowledge here beats almost any gearhead conversation I'd had 'live' , excluding those with just the upper crust, or the cognisetti of the motorworld. Top racers, engine builders, really in the know machinsists, some regular car guys with higer than average IQ's I guess....

Flippin' cool place to hang out.

Is that 'consensuses' or consensi'? smile.gif

I believe "consensus" is its own plural

I think you are right and think a big part of it is site management. We have excellent forum leaders and their efforts should be recognized. The members are intelligent, knowledgeable, and willing to share. I have been a participant for many years and this IS THE #1 SITE bar none!

I've been on other boards, particularly during my ongoing Olds 455 rebuild. There is no other site to compare to this one. Good info, minimum "junior high school superiority" head games.

Yeah, a lot of people are learning a lot of info. Even a hard-head like me.

Thanks, all! Especially Al and Dot, and the forum moderators.

Gene,

I am right with you. One of the benefits of entering questions and discussions is the ability of people to open up and present their experiences with others in an open but nonoffending manner. Much of this action is prevelated by the realism that geographical distance allows us to share ideas in a noncompetitive environment { typical male trait } much unlike you would experience in a local cruise night or a day at the races. Yes I have know some who would open up and share their research and information but as is typically the case when wrought with a competitive situation, males will become defensive of the "turf" including knowledge. It also helps that there are many professional engine and chassis builders that are involved.

I had a similiar discussion with a very good lifetime friend {been close friends since the 2nd grade if that counts} who also is like me - given a choice - we like old muscle cars. I honsetly could never see myself in a Porcshe. When I am finally done my '69, I might have close to the same amount invested. But you know what, I wouldn't give it up for anything.

One of my favorite TV shows was Home Improvement. Tim Allen {who is a natural car buff} managed to bring HotRodding into primetime reality. We have all benefited from it. No longer is wrenching looked upon as greasy motorhead pastime but good clean fun.

People ask me "How did you learn how to do that ?" when I show them my project '70. They see body work, paint, engine, heads, interior welding, etc... and I just tell them about Chevelle Tech and how I can come here and ask a question or a "How To?" and I get responses from some of the best in the business from coast to coast within 24 hours and usually alot sooner than that. This site is priceless and I thank everybody who is involved with it. I am doing this entire project myself, except the engine machining of course and it is only because of the folks who come here.. graemlins/waving.gif

I think you're right, Gene. The level of answers given is much higher. I think most here now have a good working knowledge of engines and most, of not all, of the theory down pat. Questions that use to elicit many answers that were, to varing degrees, off the mark, now get correct answers in the first or second reply.

There are sill a few fallacies floating around: like the vacuum point of a PV having an effect on idle quality, which it doesn't, BTW (just though I'd stir a bit of controversy smile.gif ).

Pat, I live that reality, I have a #105 in and it idles at 9.5-10". No problems. Lean, in fact. One problem with that 'fallacy' is that Holley promotes as a 'rule' to its tech lines as simple solution to pulling too much air through the venturis at idle. So, its a manufacturers rule.

I'll agree. There are some sharp folks on here.

I don't post much, but check in daily just to learn from others experiences.

Many other boards have a lot of members that post for no other reason than to see their name on their computer screen.

I had a guy argue with me once stating that Chevrolet never put dish pistons in 350's. I ended up deleting that board from my favorites.

Keep up the good work all!! graemlins/beers.gif

Hmmm... intresting thought Gene.... Well I'm still a relative newby here so I dont have the benefit of years of seeing this board develope like I have at other places ( non Automotive ).... Either way any forum/BB 's greatest assett are it's contributing members.... And there is a broad and varied base of knowelege here.Restoration experts , Transmission builders , engine builders , machinists , drag racers ,show cars , cam designers , auto parts people , hot rodders , history buffs , car nuts , ect ect ect from all over the world sharing what they know .... and we all are hungry to learn more!

BTW there is one way a power valve can effect the idle of a car.... But it has to have a ruptured diaphram to do it !!.... tongue.gif

I guess there are only so many ways to answer a question, I have often wondered why when a question was asked, why did it require Thirty guys to say exactly the same thing when the first Two or Three posts gave the answer in great detail.


Rocky

Originally posted by rocks66ss:
I guess there are only so many ways to answer a question, I have often wondered why when a question was asked, why did it require Thirty guys to say exactly the same thing when the first Two or Three posts gave the answer in great detail.


Rocky That is a case where the last 27 guys just wanted to see their names posted on the board. Kind of like people that love to hear themselves talk. :rolleyes:

Ok Pat explain to me how the power valve being open at idle doesn't enrich the idle circuit.

Originally posted by Mike Feudo:
Ok Pat explain to me how the power valve being open at idle doesn't enrich the idle circuit. ==
Not a carb pro but here is my limited understanding,,
The power valve is only supposed to feed fuel to the main or hi speed circuit, same as the main jets.
While both the size of the main jet & the power valve being open will effect the idle circuit very slightly because there is more volume of fuel in the main well it is almost negligible.
This is assuming you have the carb adjusted properly meaning the throttle blades closed enough not to be trying to idle off the main & transfer slots.

I'm not Pat, but I agree with him mostly. I don't think it will have a dramatic effect on idle quality. I've had a few experiences that make me think it can add slightly to the idle mixture. Not that I understand why it does. Because:

The PV restrictions are plumbed to the main wells which send there fuel through the booster venturi.
The main wells also get there fuel from the jets.
So if your not pulling enough air to start the booster venturi flowing fuel, your not using the main well. Meaning your using the idle circuit.

The idle circuit has it's own well and "jet". A fixed restriction that isn't visible in all models.

The Holley book by Dave Emanuel has good diagrams if you want to "see it for yourself"

Scott,
As I said, i'm not a carb guy, I know enough about them to send them to someone who knows what they are doing for most modifications but I believe if you look closely you will find all fuel passes through the main jets first assuming the power valve is closed.
As you go up in jet size or open the power valve you have more volume available for the idle jet or restriction you are referring to which in turn enrichens it ever so slightly but again, it is a very slight amount.
I have found this to be the case when plugging the secondary power valve on 4 corner idle carbs & going up like 8 jet sizes. The idle mixture seems to go a little rich.

The idle circuit gets its fuel from the main well. The main well is feed by the main jets and the PV. The PV acts like a third jet that opens only when the vacuum is low. The PV draws fuel from the bowls and delivers it to the main wells, exactly the same as the main jets. The main jets are always large enought to satisfy the fuel demand at idle. Since the PV is drawing from and delivering fuel to the same places as the main jets, the fuel level in the main wells remains the same as the level in the bowls. With the fuel at the same level, the fuel emulsion is unchanged. The mixture in the idle circuit is controlled after the main wells so if the main well level is unchanged the path the fuel takes to get there is immaterial. As 69LS1 so gleefully pointed out, a rupture in the PV will dump fuel directly into the manifold and this will cause a rich condition.

A simple physics experiment will demonstrate this. Take a container and put a water tight divider in it. Fill one side. The water stays on that side. Dump it out and put two 1/8" holes near the bottom to act as main jets and fill one side. The water will seek its own level on the other side and the levels on both sides will be equal. Dump it out again and put a 1/8" hole about 3/8" above the lower holes to act as an open PV. Put the same amout of water on one side. The water seeks its own level again and it is the same level as before. No matter how many holes you put in the divider, the water will go to the same level. Time is a factor, with the original holes it will take longer for the water to stablize. Since the idle circuit is way more than adequately feed by the mains, time isn't an issue. The only way the PV could effect the idle is if the mains could not adequately feed the demand. All of this would change if the fuel were being forced through the jets and PV. then the PV being opened would have an effect but this is not the case. Just as changing main jet size doesn't effect idle (unless reduced to the point of starving the idle circuit), opening the PV has no effect on idle.

graemlins/clonk.gif
I even looked at the picture again before I posted.
Completely missed the idle feed hole next to the PVCR. Need more sleep.

To clarify, when I first researched a few years ago, I couldn't figure out why the idle mixture changed with bigger jets when taking into consideration what Pat said. All I knew was I'd seen it happen. Went up two jets on the primaries and cured a part throttle surge on the 850dp. Had 2 small vac leak on the 383 and guessed too high on the PV # - 6.5. I could just hit the PV leaving a light since I had the vac leaks.
You could hear it in the exhaust note and feel it a little. Not that it cured the lean spot. No it wasn't pump shot related and I probably could've bandaided it with pump shot. But that wouldn't have fixed the white plugs. Found one leak from a slightly warped base plate. 2 gaskets cured it.
Ended up going to 76/82 on a 750dp w/RPM intake.
That got rid of the part throttle lean spot. I'd seen similar motors running 68-71 primaries.
Finally found the other leak. Brand new vortec intake that was .012 high in the middle. And I checked the ends on intial assembly after being warned by my machinist about a rash of warped Edel. intakes. Didn't think to straight edge it. :mad: I even greased the gaskets and checked for contact. :mad: :mad:

With a greater volume in the main well the idle circuit has more to draw from. Your analogy about the bucket has no meaning when the idle draw is controlled by vacuum not gravity. The difference is not great and if you get a power valve that opens way before the idle vacuum you can adjust the idle to the richer condition but why have a power valve if you do that.

I have seen cars idle very rich with a ruptured powervalve, when the powervalve is fine either sized correctly or incorrectly it shouldn't effect the idle at all from what I've seen. Hell plug it off and I bet it won't change the idle one bit. But a ruptured powervalve that will leak fuel through the powervalve to the vacume side of the valve and down through the baseplate orifice will definately richen the idle and part throttle.
To reflect on the original post, this is the best forum around, generally I think the guys that hold back performance secrets won't be here. The people here are helpful and continually looking to improve and learn, thanks for all the info shared. graemlins/beers.gif

Originally posted by Mike Feudo:
With a greater volume in the main well the idle circuit has more to draw from. Your analogy about the bucket has no meaning when the idle draw is controlled by vacuum not gravity. The difference is not great and if you get a power valve that opens way before the idle vacuum you can adjust the idle to the richer condition but why have a power valve if you do that. There isn't a greater volume in the main wells. They are a certain size and opening or closing the PV doesn't change that. The PV supplements the main jets to provide added fuel when demand is high. Since the jets can supply all the fuel needed at idle, adding another passage for the fuel to the wells has no effect.

Fallacy or not, my point that controversy remains is made. Most of the subjects on this board have had a consensus of sorts reached. Of course, there is still the subject of the proper suspension for launching a car smile.gif . Another controversial subject.

Again, I think the myth has been propogated by Holley, as a "one size fits all", i.e., if someone has too much primary opening,. or float level just a schooch high, the carb may be pulling lots of fuel through the boosters at idle and moreso with the PV open, so they make a simple rule up to avoid confusion.

Pat I have tried to come up with a reason why when you increase or decrease a Holley main jet you usually have to re adjust the idle circuit. Is it possible that the well really doesn't fill until the booster signals that fuel is needed because of air flow through the booster. I see your reasoning but my experience says it doesn't work that way. Holley definately is in the market of selling parts and tells you that just about everything in a stock Holley needs to be changed for racing.

I've not had to adjust the idle mixture after re-jetting. Never even thought about it. I spoke with my carb guru sometime back about this. When he went through my carb he left the stock 65 PV in even though he knew my idle vacuum is 6". He said it doesn't matter what PV is there as long as it stays open while at full thottle. The carb works fine with a PV having a higher vacuum point than the actual vacuum the engine makes. He explained it much the same as I went through above. As long as there is enough fuel for the idle circuit, it doesn't matter if the PV is open or closed.

Gene, I agree, and thank you and others for the help you have given me.

Pat and Mike. Thanks for debating that PV issue. I've learned something new today about PV's and carbs.

I don't claim to have the answer but I can tell you that every time I have gone from no PV to larger mains by 6-8 jet sizes I have had to readjust the idle mixture screws.
This is with the throttle blades closed to the bottom of the transition slots & has nothing to do with pulling fuel through the boosters.
Holley says it will make a slight difference & this has been the experience I have had.
Possiibly it has something with a bit more fuel being drawn through the bottom of the transition slots & not the idle circuit, don't know.
Just know in real life big changes in jet size seem to effect idle.
I will also agree with Pat that with small changes I see no difference that I have to adjust for. :confused:

My experience has been the same as wolfplace. A 1or2 jet sizes makes no or little difference in the idle quality. Pat a 6.5 power valve when you have 6 in of vacuum will make very little difference. It will start to open at 6.5(or should depending on how good the batch of springs Holley got)but will not just pop wide open. Far more people run into tuning problems with the idle transfer slots than with any other thing that can go wrong. Actually it really doesn't matter how you make your combo work as long as it works for you.