PMO E-tube, Main AC & Main Jet
 

Yep,

http://forums.pelicanparts.com/uploa...1555135558.jpg
(note - red circles are the PMO idle air correctors, stacked e-tube is being held up)

Gordo

Hey Gordo, Thanks for chiming in. Yea, I think I have sufficient information to intelectually do it again and maybe expand on it again, and, I ordered 60's and 165 mains so we will see what that does.

I agree that I think my issue is all in the idle to main transition, so any thoughts as to steps on that specific issue?

As you said and I know, the car was running fine prior to me getting it, so I think its more about set u vs replacing things.

I'm gonna take another crack at it this am as there is a cars and coffee I'm wanting to hit in the am...

I am interested in ordering a wide band and see a double set up from innovate but I have not really investigated to see if that is really the one to get.

Wow, hey Walt..... Its been some 10-12 years since I have been on this forum and its great to see you still here!

Oh, and Gordo, thanks, casue when I first did this last week, I had your page open during the full process...

So my granddad always says it takes a real man to admit his mistakes... So here I go...

I tried to rebalance everything this morning, including opening the air corrections to 1/8 of a turn (from in all the way) and bringing out the mixture screws to 2 1/2 turns out, from 2...

Better? yes, but not acceptable. took the hr drive to my cave, and decided to rebuild them one more time.......

Started disassembly and lo and behold, the drivers side carb was loosed to the intake manifold..... Not a ton, but enough for a real vacuum leak.....

Being I had already started the do over, I decided that although I may have found the issue, I needed to prove to myself that the carbs are clean...

took them completely apart again, double checked and yea, they are clean as can be.

Put them back on and just finished a 30 min run.

90% better, but still not where I want them to be as while they are a TON better (no backfiring, easy start up, smooth idle etc) I am still a bit flat in the 2600-3200 range.

It seems that right at the end of the idle circuit to the main circuit, something still off.\

Now, I have ordered 60's and 165 mains, up from my 55's and 160's, and although I had tried to high speed them, they are not here yet.... Not sure If I just need more fuel..

So, can any of you help me by explaining how and what happens when the carbs go from idle circuit to main circuit and what I can do to fix my little stumble?

Best and thanks so much for the advice!

Seeking Nirvana
 

Good to hear you have the basics worked out and running reasonably well. As mentioned, idle to main circuit transition (typically somewhere in the 2,5k to 3.5k RPM range) is challenging to make it smooth.

I recommend driving as is and waiting till you get a wideband to try to get it just right.

I originally thought my engine was running rich on the idle circuit, and richer with mains contributing during transition - until I got my wideband and realized my assumptions were 180° out... I found that the engine was stinking rich at idle & cruise, but leaned as it hit higher RPM's (still running largely on the idle circuit), with the mains transitioning / starting to contribute in higher RPM's (~3,600 RPM's) than I would have expected.

Rather lengthy to try to respond to your Q regarding how idle & main circuits work and interact. Great book that Performance Oriented / Paul Abbot / 1QuickS recommended "Weber Carburetors" by John Possini is a worthwhile read on Weber carbs, how they work and theories.

Gordo

Glad you are making progress. No worries, we all make mistakes. Its learning from them and moving on that is important.

raise the idle speed to about 2800, right in the middle of your flat spot. Try to adjust the idle mixture screws so that the car runs smooth. You may be able to get enough fuel through the 55s going another 1/4 turn out.

the emulsion tubes and air-correction jets will control the vacuum pull - and thus throttle % and load and rpm where the transition from idle to main circuit occurs. I would not make any changes until you have some data to support and point you in the right direction for changes to jetting.

I will say that typically jetting recommendation from Richard (PMO) for initial setup is really close to being correct. I would be slower to make changes to jets and more focused on fine-tuning what you have. IMO, just starting with 2.5 turns out is a starting point. You need to tune from there. We are all here to help make that happen.

LOL, progress can always be made when you make sure you tighten down the nuts....

Unless someone on here points me to another direction, on Monday I'll order the dual DLG-1 innovate wide band gauge setup, but it will take me a couple of weeks to get it in and going...

Great idea Jamie, to run it to the flat spot and then work the mixture screw there. Clearly there are one or two cylinders that are off in that flat spot.

The changes from 55's 5o 60's and 160's to 165 actually comes from Richard too (that's who I ordered them from) so being I won't get to it until mid next week, I'm guessing the stuff from Richard should be in...

Thanks everyone

If you'd have had CIS, there would have been lots of suggestions about air leaks! Not so often an issue with new carbs. So good that you found

My carb tuning is all on race motors, so I didn't pay much attention to coming off idle. My issues at first were coming off corners at tracks - dialing down the acceleration pump volume was what fixed that.

There are several books on Weber carb tuning. I can't find my copy of the fairly old one put out by Weber, but it has a good explanation of how this runs.

I used an exhaust gas temperature gauge to tune my carbs - because I used leaded fuel, and the car came with a dual gauge and wiring. I got an air density meter, and made a chart from different events and altitudes of main jet sizes which gave me the target EGT at various air densities. When I put the car on a chassis dyno, with an AFR probe up one of the tail pipes, it pretty much turned out I had it right, at least within 0.05 of a jet size.

Nowadays guys use a wide band ARR guage. For a street car you really don't need data logging, as you can find places to run at this or that RPM and see what that does. The main thing is to know if you are rich or lean where you perceive problems.

And you have PMOs. Didn't someone suggest you set up a phone call with Richard Parr? He figured out the quirks of the Webers, and did his best to fix them with the PMOs. He could tell you how he handled the progression from idle to part throttle. I can't imagine your carbs didn't come with a suitable emulsion tube and air corrector (which is mainly for high RPM operation). And you can't be far off with the idle and mains supplied. But do I understand you already talked with him?

If I might suggest something, since the engine seems to run fine at higher RPMs, maybe first you install just the bigger idle jet, and see what that does? Cut and try may work fine for you, though at this point you are pretty much guessing whether you are too lean or too rich. But bumping up the idle seems sensible, because it's influence pretty much goes away as the RPMs increase.

Hey Walt, as Gordo suggested I'm gonna drive it this week (well at least this am as I am off to the first cars and coffee this am) and wait for the dual wide band to come in. That said, thanks for teh explaination, as even knowing if the car is lean or fat, I do like to understand how it work and more importantly what to correct.

I do have PMO's and I did not speak directly to Richard, but went through Larry at Oil Analysis, as I thougth he might have parts and he is closer to me for shipping.

Larry spoke with Richard and Richard confirmed I was on the right path.

As the new Idle jet did not come in, I think I'm gonna wait for the DLG-1

So, knowing that an o2 sensor is 5 bucks, is it overkill to put a bung on each header pipe so I can dial down each cylinder individually?

Sounds compulsive, but once I get this dual wide band, it would be pretty simple.... no?

Bosch LSU 4.9
 

I think most, if not all wideband systems (gauges / meters / displays) use the Bosch LSU 4.9 wideband tailpipe sensor - which costs $65 and up. The sensor has a unique plug connector and draws power (to preheat) from the gauge (i.e. different from / not interchangeable with a cheap O2 sensor).

I used a single wideband with a single bung (left bank SSI bung) to help with configuring my carbs.

I primarily used the wideband to assess the carb configuration (i.e. jets) and changes - less so for making basic adjustments (mixture screw settings). My wideband (LM2) is configurable for 2 sensors, but I never felt compelled to add a second sensor (~$65) and sensor extension cable (another ~ $50).

Since the jets / carb config should be the same for each carb (ex. 55 idles, 160 mains in each throttle) - the basic results and outcome should be the same across left and right throttles / cylinder banks.

Dual wideband sensors (one in each header pipe) would enable you to confirm that your AFR's are consistent across the left / right cylinder banks, but in my opinion not necessary if you can adjust the settings per carb (i.e. idle mixture...) correctly / consistently. Dual widebands would also enable you to confirm that your acceleration pumps are contributing the same across the banks.

Some folks buy a single wideband setup, but have bungs on both headers - and move the tailpipe sensor from left to right to confirm consistent readings across both banks (vice buying a dual wideband system).

Bottom line - the choice comes down to how much you want to spend on the wideband setup. The DLG-1 that you were considering comes with 2 sensors (& extensions), and seems pretty reasonable at $400, but you can find single wideband setups in the ~ $135 and up range.

Good luck

You're looking at a 3 pin basic o2 sensor for $5. The cheapest I have found that has the plug connector for wide band is a motorcraft for my 2008 Ford Taurus X. I think they cost me $45 each. Just did a search and the motorcraft I have can't be bought for what I bought mine for two years ago. The cheapest is a Denso 2345097

I have highly modified Zenith TIN carburetors that came off a 1969-70 911T.

My carbs are about 50 years old.

Most significant was the change to transition ports to mimic a Weber IDA. Recently created a custom bellcrank profile to mimic the Weber hatchet.

I’ve use the dual O2 sensors to map what they do and why. And have developed my changes to help smooth out the operation.

One point on the O2 sensors, if you use EFI they are typically required for tuning and feedback. So integrating them into carb tuning is really backward technology flow. Use the new, to make the old even better.

lol, I'd prefer to day use new tech to make old tech new school

I have bungs in both SSI's on my car using one for regular monitoring plugging the other. I move the sensor from side to side occasionally by simply rerouting the wire harness/sensor from the tunnel to the bank/header im going to monitor.



for set up I have a second sensor so I have one in both header bungs and again switching the harness plug at the tunnel from side to side depending on which bank im working on. it is cumbersome, but effective. I just can't bring myself to purchase at $400+ for the system that monitor both sides in real time.

at one point I researched attempting to run both sensor at the same time switching from side to side via a switch. rub was if you do not keep power to the sensor it will become clogged and not work. I tried to find how to splice the hot wires to send current to both sensors to maintain them clean and working, yet being able to switch the data being sent to the gauge via a switch. roblem being in the end I was not smart enough to figure it our....;)

Yea, Juan, no question 400 bucks is a lot of money, but I tend to look at things as a time value of money. At what my time is worth (or what I pay others) compared to the cost of things... So a good $200 o2 sensor set up, plus bungs in at least both headers (still thinking that i may be easier to just put a bung in each header pipe as it will narrow down issues much quicker - hence time), then the time it takes not to just swap out a sensor from one side to the other after waiting for headers to cool down and going back out for yet another drive, then each time swapping back and forth, again....well, all of us will eat that extra $200 bucks up pretty quick

^^^ understood. im retired so ive got more time than money.....

LOl.... I typically work 7 days a week, so I have neither....

The normal place for the bung is just aft of the exhaust collector, so you are getting a combined reading from all three in the bank. At least that is what one does with SSIs or other decent headers. I don't know how one would deal with the stock SC exhaust, but does anyone keep that and go to carbs?

You won't find many, if any, who put bungs in each of the individual exhaust primaries. Way overkill, because as others are counseling you, it is easy to set up your carbs to behave equally. If you were a racer bent on the last tiny extra bit of power, you might put EGTs in all six (or some lesser combination) so you could account for the fact that the center cylinders run rich compared with the end cylinders due to the end manifolds being curved and thus longer. That is what makes Jenvy's or other full ITBs so desirable - all flow paths equal.

Once set up, what can change? Dirt/junk in some small hole somewhere. With a decent air filter, and good fuel filters, shouldn't happen.

You can deal with changes in air density, if you want to, with a single bung just fine. Not a big expense if you weld to add a second bung so you can swap sides. But how often do guys actually do that? And for regular driving you can find a combination of jets which will work well enough no matter where and when you are.

Be sure to use anti-seize on your sensor, and on any block off cap. There are ones which are safe for the sensors. I once neglected this, and stripped the threads in the bung getting it out.