'72 GT Wideband jetting a 32/36 Weber - Page 3
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Thread: '72 GT Wideband jetting a 32/36 Weber

  1. #41
    Opel Intern Swiftus's Avatar
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    Quote Originally Posted by The Cub View Post
    Just want to thank you Jay, I contacted them and they were great people. One of their reps after taking with me at length on the phone, seemed very interested in the problem.
    Awesome! You're welcome for the tip and I am so glad you had a great experience.

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    Opeler The Cub's Avatar
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    Perpetual vacuum leak!

    Thanks to some good advice from you guys & having the new Wideband helps me see my AFR. I have made progress but haven't eliminated my GT’s vacuum leak yet. I'm convinced it's still located on the intake carburetor mounting area. The biggest reason I'm going down this path is I do get temporary short lived improvements by re gasketing this area.
    Yesterday I pulled everything apart and the rubber/fiber gasket material was gas soaked, pretty sure there's my leak. I removed and cleaned the studs, re surfaced the intake manifold, bottom of the carburetor, aluminum spacer & cleaned the phenolic spacer. I'm sure all of my mating surfaces are flat & true & clean at least to the naked eye. I used a piece of thick glass & emory cloth to surface, check and verify flatness on all surfaces including the carburetor mounting surface on the intake. It has be extremely close anyway.

    I put everything back together now using a 1/32" compressed fiber material made for intakes between everything but the carburetor & phenolic spacer.
    I finally used the 1/16” thick official weber carburetor mounting gasket Redline pt.# 99005.068 between the carburetor & phenolic spacer. I noticed that the same thing, it ran good at first until I got on the highway. I pulled it apart again to see what had the most gas soaking, the new compressed fiber material was soaked the Weber gasket was wet at the idle spots but totally dry around the perimeter sealing area. The Weber gasket seemed to be much more unaffected by the gasoline.
    So my solution at this point is to re gasket using 3 Redline Weber gaskets. Gasket, aluminum spacer, gasket, phenolic spacer, gasket, carburetor. I think the Redline gasket holds up better under higher volumes of vacuum force (higher RPM’s) a little thicker gasket 1/16” can't hurt either if there still are any imperfections. Even with the 1 time used Redline gasket back in place I can now pretty smoothly get it to 5500+ RPM's quicker with better throttle response.
    Even though it's better, it's too lean at highway cruise 14.5-16:1 @3500-5000 RPM's. The ride is okay though.
    I'd REALLY love to move on with the other things but I'm stuck with the good old vacuum leak. I've ordered the new gaskets and by next weekend I hope to have re gasketed and anticipate improvements. Does anyone know the approximate torque value I should be tightening the 4 nuts down to? 5,10, 15 ft. Lbs.? Less, more? I'm using a 13mm wrench cut in half and tightening as good as possible with the little stubby wrench. Maybe I'm not putting enough force on the base mounting nuts? I can't find anything on our site, a different site says 15 ft. lbs.? If anyone can chime in on the answer for the carburetor mounting nuts approximate torque value it sure would be appreciated. Thanks again in advance.

  4. #43
    7,000 Post Club My location wrench459's Avatar
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    Vacuum leaks will show up more @ idle than cruise with a wide band.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opeler The Cub's Avatar
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    [quote[/QUOTE]Second the afr at cruise is not right at all!
    The only time that I've went over 15:1 is under decel.
    Good luck and keep up the good work.[/quote]

    The car likes 11.5-12.5:1 at idle and purrs like a kitten. All the leaner #s at higher RPM's I've been posting follow at this idle mixture screw setting. When I try to lean it out at the mixture screw it starts sputtering at 13:1 going leaner it just gets worse. Everything I read says idle should be leaner? I'm just wondering if it will idle leaner and run better after I get the vacuum leak fixed? Any opinions on torque values for the mounting nuts?

  7. #45
    Opel Intern Swiftus's Avatar
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    Sounds to me like you need to start messing with the main jets rather than the idle circuit.

    Highway cruise and idle can definitely have similar vacuum levels, but your hope is that the vacuum leak is small enough that comparatively the throttle plates outweigh it when at cruise. That said, most highway cruise is probably done around 10 or 20% throttle.

    Do you know all of your latest jet sizes?

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    Opeler
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    I think that you covered this in earlier postings (Post #11).
    Excellent illustrations can't hurt in case somebody missed something.
    http://www.opelgt.com/forums/6a-engi...ml#post1226049
    Note: Bottom page 4 to check idle jet O-ring for leaks.

  9. #47
    7,000 Post Club My location wrench459's Avatar
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    It might be a good idea to check the "key-on-engine-off" A/F reading.
    They have been known to shift.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opeler The Cub's Avatar
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    Quote Originally Posted by Swiftus View Post
    Sounds to me like you need to start messing with the main jets rather than the idle circuit.

    Highway cruise and idle can definitely have similar vacuum levels, but your hope is that the vacuum leak is small enough that comparatively the throttle plates outweigh it when at cruise. That said, most highway cruise is probably done around 10 or 20% throttle.

    Do you know all of your latest jet sizes?
    Not a bad question since I've swapped the jets around more than once. This is what it has now.
    Idle: 50/55
    Main: 140/140
    Air: 165/160
    I richened the secondary up a little a few weeks ago. I talked to Redline tech support today he said 10-12 ft. lbs. on the mounting nuts should be fine & shouldn't cause harm to the base etc. I'm going to re gasket as mentioned, try that and see what my end results are. I get a consistent 14.8:1 key on with the engine off. Before starting the car.

  11. #49
    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by The Cub View Post
    .. I get a consistent 14.8:1 key on with the engine off. Before starting the car.
    Odd free air reading should be ~ 18:1.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opel Intern Swiftus's Avatar
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    Quote Originally Posted by wrench459 View Post
    Odd free air reading should be ~ 18:1.
    Agreed. However if still in the exhaust pipe, it is possible that there are enough fumes from previous running to cause it to drop. But yeah, I would expect a super lean number - like 1.5 lambda+.

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    Opeler The Cub's Avatar
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    Quote Originally Posted by wrench459 View Post
    Odd free air reading should be ~ 18:1.
    Again leaning on the side of caution. I've read not to apply voltage for very long to the wideband without running the engine. I re-tested it after reading your reply. The dial goes from 11-17 but it's range advertised as 10-20? The first couple of seconds I get a "P00" display then it defaults to "14.8", I gave it some time this time (15-30 seconds) and it went to I believe an over range display of "---" ? This was done on a start after engine was off for an hour or so so the residual fumes could clear the exhaust. Since I'm never driving under 11 or remember seeing anything 18 or above while driving I can't be sure. I'm going to contact the manufacturer today to find out what the display limit range is and what I should be seeing with this test? Worth looking into, thanks Dan.

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    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by The Cub View Post
    ... I'm going to contact the manufacturer today to find out what the display limit range is and what I should be seeing with this test?
    Good idea

    Here is the cal for my W/B


    Si vis pacem, para bellum "If you want peace, prepare for war"

  15. #53
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    Quote Originally Posted by The Cub View Post

    The car likes 11.5-12.5:1 at idle and purrs like a kitten. All the leaner #s at higher RPM's I've been posting follow at this idle mixture screw setting. When I try to lean it out at the mixture screw it starts sputtering at 13:1 going leaner it just gets worse. Everything I read says idle should be leaner? I'm just wondering if it will idle leaner and run better after I get the vacuum leak fixed?
    Two percent CO is good at idle.
    It took a feedback 'puter controlled carb's to go under 1% CO.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opeler The Cub's Avatar
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    I called tech support and they said that the range on my wideband is 10:1 to 18.5:1. In open air or fresh air in the exhaust stream it is normal for the gauge to read 18.5 and above. "---" according to the tech support at AEM. They also said it will not harm the sensor,they also said I can check the wideband as often and as long as I would like before starting up the engine cold without doing an damage to it. As far as voltage output I don't see any harm in checking that. I can adjust the idle screw rich & lean and try to verify voltage output to what theguage readings indicate. I'm changing my dash lights over to LED's. When I have my dash out I'll check that out. I think the voltage output numbers came with the wideband installation manual. I also believe there's a little calibration screw on the back of the meter if my numbers are off. I don't believe they are, it starts getting really unhappy at 14.5:1 to 15.5:1 (surging/sputtering). That sounds about right from what Rally Bob posted. I just re gasketed with some extremely helpful offline email advice from Charles. Vacuum leak issue should be solved. I'll need to give it some time first and re test, should know more in a week or so.

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    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by The Cub View Post
    I called tech support and they said that the range on my wideband is 10:1 to 18.5:1. In open air or fresh air in the exhaust stream it is normal for the gauge to read 18.5 and above. "---" according to the tech support at AEM. They also said it will not harm the sensor,they also said I can check the wideband as often and as long as I would like before starting up the engine cold without doing an damage to it....
    WOW who would have thought.
    I would keep another sensor on hand just in case the numbers don't match up.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opeler The Cub's Avatar
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    Jay I believe you are correct. I don't know why I seemingly got a day or so of better performance (AEM always indicated a lean cruise condition) but I'm sure that there's no vacuum leak at play anymore. I re gasketed using the Weber paper gaskets, copper spray between everything but the carburetor. The same exact order as I've previously mentioned 10-15 ft. lbs. of torque. Same lean condition @ cruise accompanied by the usual surging 14.5-15.5:1 and intermittently up to 17.5:1 or so. So here's the jetting history:

    Idle P Main P Air P Idle S Main S Air S
    55 140 165 50 135 160 Baseline to lean

    50 140 165 55 135 160 1st change to lean

    50 140 160 55 135 160 2nd change to lean

    50 140 165 55 140 160 3rd change to lean

    45 145 165 55 140 160 4th change Better but too lean, s surging

    60 140 170 50 150 160 5th change lean, surging @ cruise & accel

    Current:
    55 150 170 50 155 180
    Best ride so far
    Primary good, not sure about secondary. The primary is finally slightly on the rich side of where it should be I'm at 12.5:1-13:1 at idle, same on accel for the most part, highway cruise between 13-14.4:1 3500-4500 RPM, higher numbers on deceleration (lower than before).
    That's the good news, I'm afraid my mileage will not be very impressive. We'll see, keeping in mind I'm dealing with a fairly worn low compression 1.9 CIH. CIH's like fuel? (The "D" word) Fuel is what it's finally getting. I think the primary is close. I'm def fine tuning the secondary WOT is still 13:1 or so, I'd like it closer to 12.5:1 if I can get it there. I can try a 165-175 air corrector or a 160 main in the secondary?
    I'm still slightly perplexed as to why I'm so far off baseline jetting but I've read time and time again that there is no one recipe for jetting. I'll post up again when I get the secondary jetted a little better. Finally the great thing about this wideband is yeah if the sensor goes south and I'll be surprised if I'm one of the lucky ones since I use a little oil between changes, a new sensor can be purchased for around $80, certainly not the end of the world there. Don't have one on the shelf but since technology changes rapidly these days you may be right Dan, not a bad idea.
    kwilford and gt alex like this.

  19. #57
    7,000 Post Club My location wrench459's Avatar
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    Secondary air bleed might be a bit on the large size.

    Another trick is to use a fuel pressure regulator that bumps up the pressure at high rpm.

    The weber 32-36 fuel bowl is very low capacity.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Base line settings

    As I've got older I've found the more wide spread a belief is the more likely it's built on myth. You a have to question everything, sure take note of all that is said, but be selective about what information to believe. Some times I have found the answer from an unlikely source from general conversation (Maybe another topic or you dismissed it at the time) and not even known it, and only realized the importance of what was said after waking in the night with the answer. You are working your way through and getting results.
    You have done a great job keep up the good work

  21. #59
    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by The Cub View Post
    ...

    We'll see, keeping in mind I'm dealing with a fairly worn low compression 1.9 CIH....
    It might be helpful to Stop thinking about static compression and dwell more on dynamic.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Opeler The Cub's Avatar
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    Thanks for your support! And the education. Here's the scoop to date
    I want to document everything so if someone else gets stuck here he or she can see the process. Not so much that I know what I'm doing which I don't. This website is a wealth of information and I just want to contribute something to it.

    I found my GT in the doghouse again. For some reason after performing all of the carburetor surgery time & time again the next day it would drive better, then the Gremlins would show up. As of this morning no more surging & the numbers got better but after I took a longer drive on the highway I still got up as high as 17:1.
    Last night:
    Main: 150
    Main air: 165
    Secondary main: 160
    Secondary air: 170
    Results: my performance went down on the primary a little (like not breathing as well)

    This morning I tried changing just the air correctors:
    Main: 160
    Secondary: 170
    Results: not a significant amount of difference on the Wideband, it felt like it was suffocating on both primary and secondary. Real stumbly.

    Went to:
    Mains: 150/160
    Air: 170/180
    That was the best I'd had. Good in lower RPM range around 12.5:1 on acceleration but was still hitting the same numbers on the highway maybe a half .5 lower than before 13-13.8:1 on heavy acceleration and between 15-17:1 on light acceleration, it went back down to 12-14:1 when was backing off at part throttle. Still is running too lean in the higher RPM range.

    I was just about ready to kick the wideband & the new Weber to the curb
    Until; I figured I'm running out of jets what the heck, go for the highest number I had left in the box.

    My numbers finally came down!
    Idle's: 55/50
    Mains: 160/155 (didn't have another 160)
    Air: 180/170
    Idle 12.5:1
    Highway Acceleration between 12&13.5:1 mostly. Occasionally up to 14:1 almost never, maybe around tip in as high as 15 briefly (1 second) . Deceleration part throttle around 12.5:1. Between 12.5-13.5 WOT. Big difference! . Crazy stuff! By the way the snap crackle & pop is going away on my exhaust as well! I get to 5500 RPM's and there is still power? I've had this car for 30 years & NEVER seen this much upper RPM power! I think I'm finally in the ballpark! I guess my GT always wanted more gas, now I finally gave it some. I could probably go up another step on the main & could probably go up on the secondary. I hit the ceiling with what I jets had. I'll probably order more to have on hand, I think there may be some fine tuning still to be done. I'm in the green constantly now, unless the Gremlins show up again? I'm going to drive it the way it is for now and post back on line. Knock on wood, good enough to drive safely at this point.

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