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

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    Opeler The Cub's Avatar
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    '72 GT Wideband jetting a 32/36 Weber

    I wanted to try the DGV when it was time to buy a new Weber. For my close to stock ‘72 GT, electronic ignition (Crane X-RAY-700), electric fuel pump (OGTS) mild cam re grind (see pic) The 32/36 seems to be the most sensible. Another two attractions to buy the DGV were:
    1) It has no vacuum channel from the bottom of the 32mm throttle plate, one less item on the vacuum circuit. I like to simplify the car to make troubleshooting those vacuum leaks easier. The only thing coming off of the tree on the intake manifold is the brake booster small stem is plugged for the retard on the distributor. The smaller valve cover hose is street waist.
    2) Curious with how the slightly different baseline jetting & the F6 emulsion tube would run. Here's what it has:
    Idle: 55/50 baseline (I swapped the idles so now it's 50/55) idle was too rich.
    Main: 140/135
    Air: 165/160
    Emulsion: F50/F6
    Everything else stacks up the same as on the DGAV's. I wondered how the F6 emulsion tube would work with more emulsifying holes towards the bottom spread out more evenly up the tubing? I saw an interesting YouTube clip https://youtu.be/1pkFSA_rRFI on modifying emulsion tubes, a little more than I'm ready for or need now. The location of the emulsification holes on the F50 are different than the F6. Interesting information if you watch the YouTube video anyway. My old DGAV’s would always lose power and sound leaner at 45k & up RPM's. My old theory was that it ran to lean.
    I've found on my new DGV as Rally Bob has stated in the past, the change in emulsion tubes (although jetted differently) is almost negligible. Still a harmless experience nevertheless. I've got plenty of F50's to use if I want to go back to one on the secondary.

    Wideband install:
    I installed my Wideband last weekend where the clock was, too bad the clocks on the GT's started to fail. I'd gladly have found another spot to mount the Wideband gauge (See pic). So here's what I've got. Right away with my new DGV my Wideband was showing me I was idling around 10.5 to 11:1 (way too rich) but to the ear sounded smoother at lean best idle. I read Rally Bob's post that idle should be around 14.2:1 other respectable posts saying 13.1:1 was good. I would have never known where my idle ratio was without the Wideband. I am now about to ¾ to 1 turn from bottom on the mixture screw and 1 ¾ turns out on the idle speed screw to achieve 950 RPM's. I gotta tell you though even though my idle sounded a bit rougher I'm at 12.6:1 now, my throttle response Is crisper than it's been in decades! On the downside cruise is way too lean between 16-18:1, I cruise & light acceleration mostly just after tip in on the first throttle plate. Tip in bleeps off the scale (above 18:1) Acceleration on first barrel between13 & 14.5:1 quick spike to 16 or worse on tip in for second barrel then right back between 13 to 14.5:1 to both barrels WOT. If I let back off where my primary plate is closed or just past tip in it leans out again, cruise sits around there?
    So I'm already running my idle jet at 50 I've never heard of anyone going down to a 45 but that's my next thought? I could go down to a 160 on my main air corrector first to see what that does? My idle is too rich, cruise too light & acceleration seems pretty good? I saw a good tutorial from Pierce Manifolds on the Weber carburetor set up https://youtu.be/fhYSo6u-Jm0 (at about 11 minutes including positioning of the idle mixture screw being critical in relation to the infamous tip in stumble. He claims that the best positioning for the mixture screw is 3/4 to 1 1/2 turns from bottom? I'd like to be 1 1/4 or more out but I'm not even 3/4 out now. It doesn't seem like I'm letting the mixture screw meter the fuel properly at tip in because I'm not far enough out from bottom? My old DGAV baseline jetted out of the box was 1 ½ to 2 turns out from bottom. I like Rally Bob’s way of jetting one barrel at a time, 32 mm for economy & 36mm for power. That would be the ideal set up. I thought that the Wideband would erase having to evaluate the spark plugs and be more accurate at dialing everything in.
    Final thaughts:
    I don't suspect I have any vacuum leaks. Engine is worn but compression is dead even on all cylinders dry. I like where my ignition timing is, I checked the vacuum advance & spring return both are fine. My only problem there is that the ball in the flywheel has rusted to the point where I would have to find it and hit it with a little white paint or something (pain in the rear to get to) to see exactly what I'm running it at. I've posted the cam card before but re posted if needed for jetting suggestion’s. I'm ready to jet away but perhaps I'll get a more accurate description of where my ignition timing is first. I'm not sure what to tackle first I'm open for feedback.
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    Just Some Dude in Jersey My location The Scifi Guy's Avatar
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    I've installed vacuum gauges in my GT's for 30 years, they're great for letting you know when a vacuum leak is starting. Generally, if you drive your GT every day, you can expect to need to tighten the intake/exhaust-to-head bolts about once a year, maybe every 6 months.

    As far as jetting your Weber, it's pretty tough to beat the almost 50 years of experimentation that has already been done with Webers on Opels. The standard accepted jetting guidelines work for 90% of most guy's set ups. Heck, I drove my old GT with a fresh out of the box Weber 32/36 for 18 years and 225K miles and I never jetted it and I always got 25mpg. All I had to do was tighten those bolts every 6-12 months. Ran like a kitten when I sold it.


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    I once took a 32-36 and modified the air horns.


    Also used the same top on a 38.
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    What's the best intake manifold set up for stock to resist vacuum leaks & the carburetor bowl gas boiling syndrome? I've tried Gil's suggested set up, works better than most. I've purchased a phenolic spacer tried that instead of the Felpro 60144 (the one Gil recommends). I'm having a back & forth private chat with Mr. Goin. I've been going gasket, heat shield, gasket, phenolic spacer, gasket, carburetor after reading some articles on the subject. In Southern California I don't want to do away with the heat shield but it Sure looks suspect as a possibility to being the main culprit for vacuum leaks. I like the idea of the vacuum guage install, that would get tee'd in to vacuum line going to the distributor? Correct?

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    Just Some Dude in Jersey My location The Scifi Guy's Avatar
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    In my experience, vacuum leaks were always at the join to the head. There's a thick gasket you can buy from OGTS that works really well, but the best thing you can do is to install the bracket that all GT's came with that stops the intake/exhaust assemblage from flopping around and basically pivoting up and down on that straight row of bolts. It looks like this:

    Exhaust to block brace 3.jpg

    Many times these have been removed and discarded.

    If my memory serves me correctly, the brace above grabs one of the bolts at the exhaust/headpipe union to the block.

    IMPORTANT FYI: You would think that the fix would be to keep those 6 manifold-to-head bolts really tight, but you can't do that because of the expansion of the exhaust manifold due to the heat. If you tighten those bolts as tight as you normally would tighten bolts that size, the expanding manifold will snap the heads off of the bolts, often flush with the block. Snapped off bolts can be a real mutha to extract from the head.
    Last edited by The Scifi Guy; 04-04-2017 at 10:58 AM.

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    Quote Originally Posted by wrench459 View Post
    I once took a 32-36 and modified the air horns.


    Also used the same top on a 38.
    Looks interesting. I've read that modifications like yours increases airflow. If you watch the Pierce Manifold vid this guy would argue otherwise. Did you notice any significant difference? What's mounted on the top? Is that for a blower, or part of the filter set up? I've never seen it before.

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    Quote Originally Posted by The Cub View Post
    Looks interesting... What's mounted on the top? Is that for a blower, or part of the filter set up? I've never seen it before.
    Mopar barrel intake blower hat.

    Yes, I did loose some t/q on the bottom-end, but that was not what I was after.

    RB left the primary tower alone and only cut the secondary side.

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

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    I realize that your trying to pick-up data points with the W/B..

    I'll add a chart if I may....



    CIH's likes fuel no doubt
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    Quote Originally Posted by wrench459 View Post

    RB left the primary tower alone and only cut the secondary side.

    Yup, but I also bored the secondary venturi out from 27 mm to 31 mm or so. That's where the real airflow gain is found.
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    Quote Originally Posted by RallyBob View Post
    Yup, but I also bored the secondary venturi out from 27 mm to 31 mm or so. That's where the real airflow gain is found.
    Kicks like a mule when the secondary comes in
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    Quote Originally Posted by The Scifi Guy View Post
    In my experience, vacuum leaks were always at the join to the head. There's a thick gasket you can buy from OGTS that works really well, but the best thing you can do is to install the bracket that all GT's came with that stops the intake/exhaust assemblage from flopping around and basically pivoting up and down on that straight row of bolts. It looks like this:

    Exhaust to block brace 3.jpg

    Many times these have been removed and discarded.

    If my memory serves me correctly, the brace above grabs one of the bolts at the exhaust/headpipe union to the block.

    IMPORTANT FYI: You would think that the fix would be to keep those 6 manifold-to-head bolts really tight, but you can't do that because of the expansion of the exhaust manifold due to the heat. If you tighten those bolts as tight as you normally would tighten bolts that size, the expanding manifold will snap the heads off of the bolts, often flush with the block. Snapped off bolts can be a real mutha to extract from the head.
    That is so true. When my engine got rebuilt the guy lost the bracket you showed me a picture of it (thank you for mentioning that) . I've re worked the head, exhaust & both manifolds, had side of head & manifold assembly re surfaced (back in '98) I installed this bracket you've mentioned from a '70 GT which I bought & canabalized for parts back then (the body was thrashed). I don't seem to have any issues there that I can find. I agree re torquing the manifold bolts that haven't been touched in almost 20 years could be trouble, unless you're checking or re tightening on a regular basis, the movement of those bolts on this engine could mean trouble. So on this subject I used a small stream of acetylene around the carburetor base & intake manifold to head areas this evening, I got no change in engine speed.
    I currently have, from intake up:
    1) 1/16" gasket
    2) aluminum spacer (I'm using it to get a better mounting surface on the intake, more surface area, note the small thin surface especially near engine side of manifold next to the mounting stud holes, see pic)
    3) 1/16" gasket
    4) heat shield (modified to match intake opening)
    5) .225" gasketed phenolic spacer, with a thin coating of Permatex's version of Hylomar in between everything except for under the carburetor. My experience has been that the carburetor cleaner washes away the gasket sealant, so I use acetylene. I also went back to the original Weber adapter for the OEM GT air filter with a modified cut out on top to allow better airflow to get cooler air instead of the box filter mount on top which is what I used to use. I'm still running way too lean. I'm seriously considering re gasketing under the carburetor? It's just running way too lean & inconsistent at or near tip in. I believe you are correct the baseline jetted DGV should be ballpark to what I'll end up with, as far as I know it's jetted for any 4 cylinder engine. I'm wondering if vapor lock causes lean running conditions? I get a little surging mixed in when it's running that lean. As you can tell I'm not as mechanically educated as you guys but I'm familiar with my GT and that's the extent of my knowledge at this point. I'm just glad that I found this web site.
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    Quote Originally Posted by The Cub View Post
    .. So on this subject I used a small stream of acetylene around the carburetor base & intake manifold to head areas this evening, I got no change in engine speed.
    Why not look at your AFR gauge instead of a rpm increase.
    The rpm's should have bumped up around the throttle shaft area.

    I look at the short term fuel trims BTW.
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    Quote Originally Posted by wrench459 View Post
    Why not look at your AFR gauge instead of a rpm increase.
    The rpm's should have bumped up around the throttle shaft area.

    I look at the short term fuel trims BTW.
    Quote Originally Posted by wrench459 View Post
    Why not look at your AFR gauge instead of a rpm increase.
    The rpm's should have bumped up around the throttle shaft area.

    I look at the short term fuel trims BTW.
    I did try to do that (not easy to do, it's mounted in the dash where the clock was). I'll try it again with someone looking at the guage while I hunt around again with the acetylene. This is all being done outdoors BTW I DEFINITELY WOULD NOT recommend this method in an enclosed garage or space. I work with Gas all of the time in the commercial HVAC industry and the first rule of thumb is to be extremely careful in enclosed spaces when working with gas. I also have my fuel lines routed away from my engine and am careful not to go near any rubber hoses containing fuel while using the acetylene. I don't want to turn this thread into a safety thread, I just wanted that out there in case someone else decided to use acetylene, propane or whatever instead of carb cleaner.
    Back to the subject at hand,
    I live at 2000 ft my car likes 12.5:1 idle what's pretty cool about the Wideband is when I drive 20 miles down towards San Diego the Bosh 4.9 sensor picks up on that, I'm consistently at 13:1 at sea level, pretty neat stuff. So when I have a helper help me run the test again, if it goes down below 12.5:1 I will have found a vacuum leak.
    On my latest jetting experiment, I tried the baseline jetting I had in my DGAV main jet-140, Air corrector-170 & Idle-60 to set the idle 12.5:1, idle mixture screw about 1 3/4 turns from bottom (good positioning) to get it there. My car didn't respond well. Throttle was less responsive, instead of modulating during cruise between 15:1 to 17.9:1 it did that & it went above 18:1 at times for 3-6 seconds, you couldn't hear the change with any sputtering or backfiring, but the Wideband sure picked up on it. I've re jetted back to the main jet-140, Air corrector-165 & Idle-50, Much better again, jetted pretty close to Otto's latest post, right now a 135 main seems to lean. I also checked the float level I adjusted it to 41mm-51mm. The 41mm is set before it seats just as shuts off the incoming fuel. My lean condition still exists but my surging problem disappeared for the most part. I've given some consideration to the fact that my engine has 150k plus miles on it and I probably am not going to reach peak performance numbers on my Wideband until I get the engine rebuilt.
    So that being said:
    The three things on my to do list are the lean cruise, the gas boiling 10 minutes after I shut the car off & even though I like where my ignition timing is, I see no harm in getting numbers on that also. I will use a separate tachometer, (my GT's tach has always been off a few hundred RPM's). I've also picked up some 1/8" phenolic gasket material. I'm going to gasket & sandwich the heat shield first, I'd love to put the heat shield on the shelf in my garage but I hear that it's pretty critical to have? Thanks for the advice Dan. When I'm re gasketed I'm going to get someone to help look at my Wideband while hunting for a possible vacuum leak. One last question I don't believe I'm harming my valves but I'd like a second opinion, if anyone wants to chime in. Am I ? I'm always between 12:1 & 14.8:1 when accelerating, lean conditions are when cruising (mostly highway) around 2500-4000 RPM's 70% of that time I'm under 17:1, less than 5% of the time it'll go red & above 17:1 but as currently jetted it says under 18:1. I'd definitely be more concerned if I was lean under acceleration. I've just acquired a pretty useful tool having this new Wideband, I just need to get educated on using it now. The data logging option is there, I'm not there yet, maybe some day who knows, it's pretty darn handy as is.

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    Quote Originally Posted by The Cub View Post
    The three things on my to do list are the lean cruise, the gas boiling 10 minutes after I shut the car off & even though I like where my ignition timing is, I see no harm in getting numbers on that also. I will use a separate tachometer, (my GT's tach has always been off a few hundred RPM's). I've also picked up some 1/8" phenolic gasket material. I'm going to gasket & sandwich the heat shield first, I'd love to put the heat shield on the shelf in my garage but I hear that it's pretty critical to have? When I'm re gasketed I'm going to get someone to help look at my Wideband while hunting for a possible vacuum leak. One last question I don't believe I'm harming my valves but I'd like a second opinion, if anyone wants to chime in. Am I ? I'm always between 12:1 & 14.8:1 when accelerating, lean conditions are when cruising (mostly highway) around 2500-4000 RPM's 70% of that time I'm under 17:1, less than 5% of the time it'll go red & above 17:1 but as currently jetted it says under 18:1. I'd definitely be more concerned if I was lean under acceleration. I've just acquired a pretty useful tool having this new Wideband, I just need to get educated on using it now. The data logging option is there, I'm not there yet, maybe some day who knows, it's pretty darn handy as is.

    First the fuel boiling issue is a hard one.
    Are you still running the stove pipe intake/exhaust system?

    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.
    Last edited by wrench459; 04-07-2017 at 08:39 PM. Reason: oophs went not when

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    Fuel Boiling

    Hi Tom,
    When I first got my GT it peculated the carby dry when parked after driving in traffic. I put a digital temp sender (connected to my fluke) on the top of the driver side foot well inside the engine compartment (the cool side ) and found to my amazement even though 25 deg C out side to air temp went from 40 deg C cruising to 70 deg C + once in traffic. I straight away made a heat shield full length of the exhaust manifold about 12 cm wide. It was straight on the intake plenum with gasket, then there was a 8mm heat in insulator on top then the carb. I remember, to fit it was not flat, and I put a cut in the leading edge so part could go under the thermostat housing.
    It also had a hole for a vacuum line.
    Long story but it worked.

    Alex

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    Just Some Dude in Jersey My location The Scifi Guy's Avatar
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    Carb Boiling

    Where I live, summers get really hot and steamy with no breeze. Over the decades I've tried everything: Heat shields, different carb and intake manifold set ups, jet coating the intake/exhaust, hood vents all over the place, various insulating spacers, giant radiators, multiple engine fans, electric fuel pumps, etc.

    NOTHING makes this problem go away on GT's. NOTHING. Apparently the situation isn't quite so bad with Mantas due to their larger engine compartments.

    The most effective methods I've found to diminish the effects of carb boiling are:

    1) Install an electric fuel pump. This allows you to refill the boiled out fuel bowl in the carb BEFORE you start cranking the engine. Turn the key to the Run position, wait 3-5 seconds for the sound of the pump to change, pump-pump-pump the pedal, engage the starter. Works flawlessly almost every time.

    2) Keep the engine fan, add an electric fan on a thermostat in front, possibly put it on a timer to run for a short time after shut down. This just helps you when you're stuck in traffic

    3) De-couple the intake/exhaust and get rid of the "stove pipe" exhaust manifold. Get what we call a "Sprint" stove pipe-less version of the stock cast iron exhaust manifold. Or get jet coated headers.

    4) Let the heat get out from under the hood! Probably the best thing you can do to reduce temperature at the carb when it's parked. This, however, requires you to go nuclear with your hood. I use the fiberglass Lenk hoods with the 2 big holes up front. I added extra holes and two vent areas(one above the carb, the other just for a balanced look on the other side of the engine) and I don't use the rubber strips around the hood.


    In my experience, heat shields don't do squat, or at least not enough to justify the inconvenience they cause when trying to get at bolts and such in that tight congested area.

    We've discussed in the past the concept of adding a carb cooling fan that would come on after shut down. Some cars even came with carb cooling fans right from the factory. Not many, but some. I'm 100% sure that if we could put carb cooling fans on our GT's, that could run for, say, 10 minutes after shut down, the boiled out carb problem would finally be cured. But, where to put one is the problem. No room. We've talked a bit about this subject, but no one has ever tried it.


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    [QUOTE=The Scifi Guy;1214122]In my experience, vacuum leaks were always at the join to the head. There's a thick gasket you can buy from OGTS that works really well, but the best thing you can do is to install the bracket that all GT's came with that stops the intake/exhaust assemblage from flopping around and basically pivoting up and down on that straight row of bolts. It looks like this:

    Exhaust to block brace 3.jpg

    Many times these have been removed and discarded.

    This one right?]
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    Quote Originally Posted by wrench459 View Post
    First the fuel boiling issue is a hard one.
    Are you still running the stove pipe intake/exhaust system?

    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.
    Yes, I have the stove type exhaust. When I read Charles’s G’s post from some time ago he said he has no boiling problems and he just uses a ⅛” gasket above & below the heat shield I went on a search (which wasn't real easy) & found a couple of products called Durlon 8500 (phenolic gasket material) & 8400 a good, more flexible material they say insulates just as well. I fabricated several gaskets. I think I've got enough space under the hood for close to ½” or so of gasket material. Since the Solex days of old I've always had boil off issues with the Weber's. We'll see what happens after I re gasket.

    After checking my ignition timing I was really surprised! All my readings were at 850-900 RPM’s at idle. No wonder I couldn't find the mark, it was off the scale. Not where I remembered setting it, It was so far advanced I couldn't see it. So I dialed it back so I could see it to a couple of degrees advance & tightened down the bolt & went for a drive. Not much difference on the AFR but I lost a ton of power! It almost didn't make it home. It ran way too hot & I had to go to WOT to make it up a graded hill that the car handles easily if I put my ignition timing back to where I had it. Using the vacuum method with my reading off of the intake manifold I was at 18” near TDC and 18.5” at my setting I have been driving it with lately probably 10 more like 20 degrees advanced, I made the marks on my distributor & timing cover since it was not legible on the flywheel (see pic). Something's definitely not right! I may be visiting my old thread I started with regards to my can timing? Almost 20 years ago I pulled the head I've had issues related to the mystery vacuum leak symptoms ever since, never was able to find anything. I must have gradually advanced my ignition timing over the years to this point. Could my timing chain have stretched that much? I'm able to keep up with any traffic situation as it is, would I be able to compensate with ignition timing enough to trick out the engine enough to get around as I've described if my cam timing has been off by a tooth? Going by the factory manual I lined up the cam gear as best I could after I pulled the head years ago. I'm still uncertain but there's 3 possibility’a, right?

    1)I still have a vacuum leak, one this bad should be easy enough to find, right I should almost be able to hear it? If you guys think it's still a good possibility I'll use the Wideband & acetylene combo previously suggested.
    2)Stretched timing chain?
    3)Stretching timing chain & or cam timing issue?

    I promise to come back to this thread to finish the Wideband jetting but it looks like I'm discovering some new issues here. I'd REALLY appreciate advice here guys!
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    Last edited by kwilford; 04-08-2017 at 04:20 PM.

  21. #19
    Just Some Dude in Jersey My location The Scifi Guy's Avatar
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    Quote Originally Posted by The Cub View Post

    This one right?]
    Yup, that's the one.



    In regards to engine timing, I've always done it by ear and, more importantly, by ride characteristics. For me, it's always been a balancing act between ease of starting and high rpm performance. Advancing the timing makes the engine start easier and there's lots of power, but a teensy bit too far and you get pre-detonation and that rattly valve sound. Retard too much and the engine is a mutha to start, but runs great.
    Last edited by The Scifi Guy; 04-08-2017 at 03:59 PM.

  22. #20
    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by The Cub View Post

    1)I still have a vacuum leak, one this bad should be easy enough to find, right I should almost be able to hear it? If you guys think it's still a good possibility I'll use the Wideband & acetylene combo previously suggested.
    2)Stretched timing chain?
    3)Stretching timing chain & or cam timing issue?

    I promise to come back to this thread to finish the Wideband jetting but it looks like I'm discovering some new issues here. I'd REALLY appreciate advice here guys!
    If the cam timing was late..the result will be a late closing intake valve.
    This will allow compression to flow back into the intake track.
    Hold your hand slightly over the carb..then rev it up.
    You will feel a large pull ..if you feel anything other..like backwards pulses... the cam is out of wack.
    The Scifi Guy likes this.

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

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