Timing
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Thread: Timing

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    Opeler Conaero's Avatar
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    Timing

    I just bought a gas analyser and a new strobe light I can punch the advance retard into.

    Running a stock 1.9 with unleaded head and fuel, Weber carb and electronic points/ignition in the dizzy, what should I be setting the advance or retard timing too?

    Zero and line the TDC marks up or should I be building in some adjustment?

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    Carbureted engines at 6į advanced and fuel injected ones at 10į advanced initial timing.

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    OpelGT.com ‹bermoderator kwilford's Avatar
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    Quote Originally Posted by CommodŚren View Post
    Carbureted engines at 6į advanced and fuel injected ones at 10į advanced initial timing.
    Yep, that sounds reasonable, but the most important figure is maximum timing advance. Typically that is between 34 and 36 degrees, although a number of factors can enter in: fuel octane, compression ratio, cam design (advance, duration, overlap, etc), and more.

    The "shape" of the total ignition advance (how if any vacuum advance is allowed and at what vacuum and rpm, and the shape of the mechanical advance as it relates to rpm) is also very important, and is also affected by the factors above.
    Keith Wilford
    Finishing up a bare-metal, nut & bolt rotisserie restoration of my '71 Opel GT

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    Senior Member The Cub's Avatar
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    It depends on what distributor you have I have a 1972 that has 28-32į Of total mechanical timing, If you have a 1969-70 distributor you can add possibly 2-4į more. I hear that 6į is good from most people. If I ran 6į at 850 rpms I run 38į total at 4000 rpms when itís all in, as my distributor is 32į of total mechanical timing, I get way too much detonation with that much advance on my GT. If you have an earlier distributor you may be running as much as 38-42į of total timing. The book calls for 0į @ 850-900 rpms. Total timing is what Iím after and just let the timing at idle fall wherever it lands. It takes a little guts to get near an engine thatís running at high rpms, you can either get someone to help or do like I do first buy a timing gun with an adjustable dial and just put a spacer/piece of wood or something between the adjustment screw and stop on the carburetor throttle, set at 4000 rpms (all mechanical timing should be in by then) then set up the total to anywhere from 34-38į. I found 34į to work best gas mileage wise and performance is great too, at least thatís the happy spot for mine, a lot of people like 36į it seems. Hereís some excellent information below from Rally Bob on early OEM distributors. Before I got into all this I used to just take it out on the road and stomp on it heavy at 2000 rpms in 4th gear, moving the distributor up until I heard any pings then get out and back it off until the pinging disappears then tighten the bolt and then, off to the races!

    Bob's list below
    1968 - 32-36.5 mechanical advance
    19.5-22.5 vacuum advance
    51.5-59 degrees total

    1969 - 32-36 mechanical advance
    11.5-14.5 vacuum
    43.5-50.5 degrees total

    1970 - 32-36 mechanical advance
    11.5-14.5 vacuum
    43.5-50.5 degrees total

    1971 - 28-32 mechanical advance
    7-10 vacuum
    35-42 degrees total

    1972 - 28-32 mechanical advance
    7-10 vacuum
    35-42 degrees total

    1973 - 28-32 mechanical advance
    1-5 vacuum
    29-37 degrees total

    1974 - 28-32 mechanical advance
    1-3 vacuum
    29-35 degrees total

    1975 - 25 mechanical advance
    5 degrees static timing
    No vacuum advance unit
    30 degrees total
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    Member Dmcbrass's Avatar
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    Quote Originally Posted by The Cub View Post
    It depends on what distributor you have

    Bob's list below
    1968 - 32-36.5 mechanical advance
    19.5-22.5 vacuum advance
    51.5-59 degrees total

    1969 - 32-36 mechanical advance
    11.5-14.5 vacuum
    43.5-50.5 degrees total

    1970 - 32-36 mechanical advance
    11.5-14.5 vacuum
    43.5-50.5 degrees total

    1971 - 28-32 mechanical advance
    7-10 vacuum
    35-42 degrees total

    1972 - 28-32 mechanical advance
    7-10 vacuum
    35-42 degrees total

    1973 - 28-32 mechanical advance
    1-5 vacuum
    29-37 degrees total

    1974 - 28-32 mechanical advance
    1-3 vacuum
    29-35 degrees total

    1975 - 25 mechanical advance
    5 degrees static timing
    No vacuum advance unit
    30 degrees total
    I’ve never been able to understand why the advances decreased with later motors. This seems backwards. The early engines had higher compression which would create spark knock at lower advances.
    Anyone understand what Opel was doing with this?

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    Opeler dcm013's Avatar
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    1969 and 1970 (high compression ratio) required premium fuel. Back in the day, my 69 would ping even on premium if I bumped up the timing much.

    1971 and beyond, with lower compression ratio, were designed to run on low lead/no lead regular.
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    Quote Originally Posted by Dmcbrass View Post
    Iíve never been able to understand why the advances decreased with later motors. This seems backwards. The early engines had higher compression which would create spark knock at lower advances.
    Anyone understand what Opel was doing with this?
    As said above low lead fuels drastically decreased octane, but it was more an emissions thing. Advanced timing gives more Nox emissions in particular. Any knocking or misfiring can give massive Nox emissions too. Lowering the advance a couple degrees likely allowed Opel to pass the Clean Air Act Amendments of 1970.
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    Pedal Smasher Autoholic's Avatar
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    How your vacuum advance is configured also comes into play here. There is a difference between manifold vacuum and port vacuum. Manifold vacuum is highest when the carburator butterflies are closed. This is a crude way to detect load because of that, idle is no load and letting off accelerator when driving is no load. That means manifold vacuum will be present during engine braking, so the timing will be advanced beyond what it normally would be at a certain RPM. If this results in the combustion pressures getting close to peak before TDC, then it will fight the engine turning over and help with engine braking, just hopefully not engine breaking. *Port vacuum is highest during WOT* -WRONG, see my edit below. So, this is a crude means to detect throttle position. When the butterflies are closed, there is zero port vacuum. As they open, it increases and then decreases.

    This means manifold vacuum advance needs to be taken into account at idle timing, which may require less initial timing advance. Port vacuum advance needs to be taken into account for idle timing requirements. In the early days of emissions control, manifold vacuum was often used to retard and port vacuum used to advance. I believe this is how Opel setup the distributors on the GT for some of the years. To me, it would make more sense to use manifold vacuum for advancing the timing and port vacuum to retard timing. Or am I wrong here? - bad thought process on port vacuum at WOT, already know that was wrong.
    Last edited by Autoholic; 04-14-2019 at 12:08 AM.
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    Senior Member The Cub's Avatar
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    Quote Originally Posted by Autoholic View Post
    Port vacuum is highest during WOT.

    I always enjoy reading your posts and you may have been involved with this ďported vs manifold vacuum advanceĒ discussion a long time ago? You always have a very interesting perspective on topics. Iíve read that both or either manifold and or ported vacuum advance drops off altogether at WOT, I donít have any test instruments to prove this but the theory makes sense therefore itís always been my belief that thatís true. I recommend reading this post, the first one that comes up on Google if you type in ďported vs manifold vacuum advanceĒ heís a little bombastic but a fun read (the first reply to the originators question is very interesting reading)
    https://bangshift.com/forum/forum/ba...vacuum-advance
    Iím very intrigued by the ignition timing subject altogether. When I was toying around trying to get more advanced timing at idle (without modifying my total mechanical advance, I do intend on doing that in the near future), I tried the manifold vacuum advance, it did the trick and got me up to 850 rpms at idle with the well sought after 6-13 degrees initial advance, my 32/36 set up correctly with zero vacuum on the ported connection so I drove it around for a couple of tanks and didnít see an improvement on gas mileage and then began to dislike the excessive advancement on high to mid RPM deceleration so I moved my vacuum advance connection back to ported. So many good points were made in that post about running cooler at idle etc with the manifold advance (and how many of us have the problem of running too cool at idle)? and I remember those rediculous smog pumps. I still believe thereís a good argument to be had either ported or manifold. I do believe however that full ignition advance is in above 4000 RPMs at part throttle with with either connection to the canister. In my case somewhere between 34-42 degrees total using partial vacuum advance at that point, then would be dropping down to 34 degrees at WOT. So as not to confuse the original post 2 degrees advanced is where my ignition timing falls at idle with my distributor, that seems just about right. One more spot on post on the subject from GT Jim (post #12) and a lot more good information after that:
    https://www.opelgt.com/forums/1b-ign...k-advance.html
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    Pedal Smasher Autoholic's Avatar
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    Tom, I've read that thread about manifold vs port vacuum before. There are some interesting YouTube videos where guys will show port vacuum advance vs manifold vacuum advance on old engines. One that's worth watching even though is gets a bit long-winded is below...



    The Cliffnotes version of the ~12 minute video is a guy starts his engine on ported vacuum and it idles at around 900 RPM. Then he switches it to manifold vacuum, takes out some initial timing and then it idles around 1100 RPM, without any adjustments to the carb. The take-away is that now the carb can be tuned to back off the idle set screw, to bring the engine back down to acceptable idle RPMs. Less fuel will be consumed at idle if you're using manifold vacuum.

    Port vacuum was not created as an emissions control feature like many believe. In the early days of emissions control on carburated engines however, it became common practice to use port vacuum advance and often manifold vacuum retard if the vacuum canister had 2 ports. Manifold vacuum retard would cause the engine to have less timing at idle, delaying the spark which would result in higher EGT's. Increasing exhaust gas temps would burn more hydrocarbons. Cars ran like crap, but they met emissions requirements. Emissions were improved if the car also had an A.I.R. system.

    I was wrong about port vacuum being highest at WOT. In some ways, theoretically it should be since the carb will draw the most air in at WOT. The lack of any meaningful restriction however results in zero port vacuum at WOT, since the engine can hopefully pull all the air it needs through the venturi. Port vacuum will be present off-idle, when the butterflies are starting to open and then incrementally drop off as you increase throttle position. Because of this, if you got any vacuum readings at WOT then your carb is actually choking your engine's air flow requirement at WOT. The engine needs more air than it can get through the venturi, so it's trying to siphon air through the port vacuum orifice. You don't want that at WOT. So, port vacuum only comes into play off-idle / partial throttle and never at idle. One way to verify that the carb is strictly on the idle circuit when tuning it, is to measure port vacuum. It should be zero when the butterflies are closed.

    Some people will say you should always run manifold vacuum and forget port vacuum. I believe everything has a purpose. You'll need higher initial timing if you run port vacuum compared to manifold vacuum in all likelihood, for the engine to idle properly. The engine really doesn't care how the timing advance is controlled, at any given RPM it will operate with the most efficiency at a rather specific spark timing. This is why EFI is so great, it can control how much timing is needed to an exact science and take a bunch of information into account to know how much is needed.

    I've made the needed edits to my previous post as my brain is functioning better today than yesterday. Sorry for the incorrect info and thought process, I was tired and drinking. So, not very conductive to technical discussions.

    I am still wondering if there would ever be a useful case to use port vacuum to retard the timing... I can't think of any. I could see a useful case to have both manifold and port vacuum advance...
    Last edited by Autoholic; 04-14-2019 at 12:54 AM.
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    Pedal Smasher Autoholic's Avatar
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    I could use some help with some information related to ideal timing vs RPMs. What is the ideal timing advance in relation to RPMs? I know engine load is needed but if you're running a dizzy and a carb, EFI is off the table and pretty much so is taking engine load into consideration in a measurable way. How would you know if the advance curve for a dizzy is suitable to your engine?

    MegaSquirt has a very detailed page on all of this. It's pretty easy to understand if you understand chemistry and have a basic understanding of spark timing and how engines function. Looks like the best way to resolve this would be to do a bunch of calculations for the CIH.

    http://www.megamanual.com/begintuning.htm
    Last edited by Autoholic; 04-14-2019 at 12:53 AM.
    "Autoholism is an incurable addiction medicated daily with car porn." ~Zeppi

    1973 Opel GT project car - Plans: 2.5L CIH, Weber 38 DGAS, Getrag 240, Lowered 1", Watts link, exterior color - Rainforest Green Pearl, interior color - tan

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    Senior Member The Cub's Avatar
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    I was surprised to see you had made that comment, your knowledge is way past what I know Joseph thatís why youíre posts are usually the kind I learn from if I keep digging. Well that explains it anyway Iíve definitely had some days where too many brain cells were gone, heck I still do and I donít even need the booze etc. anymore for an excuse LOL. The bottom line is that the vacuum signal you use is simply another way of tailoring the ignition curve to match the engine's needs. I had a ton of initial advancement on my low compression 1.9 and it was almost impossible to get a ping even with our crappy 87 California E-10 gas. It looks like this Joe in the video was doing pretty much what I described in my last post using the vacuum advance to bump up his idle speed and adding more advance at idle with a slight difference I run my afr in the 12-13:1ís (depending on heat soak) if I tried tuning my mixture screw into the 14ís it wouldnít be pretty once heat soak started with stop & go Iím in the 15ís & sometimes 16ís. More than one way to achieve initial advance, Iíve come to the conclusion that limiting my total from its current 32į down to 20-25į or so is the best way to get more advance at idle and stay with the ported vacuum advance as long as the 2.0L can accept the early aggression. Unfortunately the distributors I have arenít the kind that are easy to limit the total travel of the weights I need to completely dis assemble the dizzy to properly weld in an adjustable set screw to adjust as needed. Iím intimidated by removal and re installing that ridiculous clip inside the top of the shaft to achieve complete dis assembly. Anyway not to hijak Mathews thread I just wanted to throw out a warning of possible over advancement if the higher compression engine is being used on the post. 0- 2į at idle is the limit on my CIH otherwise itís into detonation when the mechanical is all in at WOT. Iím even thinking of backing off another degree or two.

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    Pedal Smasher Autoholic's Avatar
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    Well, you bring up others considerations that need to be taken into account when figuring out the timing. Climate is important because this impacts air density, as does elevation. So, what works in Miami for timing will not work in Denver just based on the density and temperature of the air. You also brought up heat soak. On engines where this becomes an issue, a lower temp 'stat will help. Also, the type of fuel has to be considered. If you're starting to ping because the engine is getting too hot, a higher grade fuel is needed. Running E85 can help with this, because it burns colder than gasoline. So, while running E85 will suck on fuel economy in a carburated vehicle, it could help with getting the engine to run colder. It also has a much broader range for acceptable AFR under normal operating conditions and can resist higher cylinder pressures. Because you'd be running a completely different fuel that has different flame speeds than gasoline, different timing is needed.


    Getting into spark timing pretty much forces us to consider every other aspect of the engine. I'm still digesting the info in the MegaSquirt link and I keep saying 'well, ya, duh that makes sense'. It's a good starting point to figure out what might work for timing as you setup an engine for the first run after building it. I'll be the first to say I don't know enough about what makes for an optimal running engine, so, I like topics like this.
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    Senior Member The Cub's Avatar
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    Quote Originally Posted by Autoholic View Post
    Well, you bring up others considerations that need to be taken into account when figuring out the timing. Climate is important because this impacts air density, as does elevation. So, what works in Miami for timing will not work in Denver just based on the density and temperature of the air. You also brought up heat soak. On engines where this becomes an issue, a lower temp 'stat will help. Also, the type of fuel has to be considered. If you're starting to ping because the engine is getting too hot, a higher grade fuel is needed. Running E85 can help with this, because it burns colder than gasoline. So, while running E85 will suck on fuel economy in a carburated vehicle, it could help with getting the engine to run colder. It also has a much broader range for acceptable AFR under normal operating conditions and can resist higher cylinder pressures. Because you'd be running a completely different fuel that has different flame speeds than gasoline, different timing is needed.


    Getting into spark timing pretty much forces us to consider every other aspect of the engine. I'm still digesting the info in the MegaSquirt link and I keep saying 'well, ya, duh that makes sense'. It's a good starting point to figure out what might work for timing as you setup an engine for the first run after building it. I'll be the first to say I don't know enough about what makes for an optimal running engine, so, I like topics like this.
    Iím glad to hear what you said about E85. It will also require rejetting and different afr values, stoic is much richer (9.765:1) not sure if the heat range on the spark plugs should be lowered as well? I didnít think our engineís were equipped to handle it. It seems like the direction that this world is headed and I thaught it meant curtains for us carbureted folks so thatís good to hear what youíre saying. Iíve read that people use it for racing but know very little else. Itís not the methonal that has a low boiling point itís all the other crap the gas companies add that causes the low boiling point with our pump gas. It is a water collector though on the downside along with the other drawbacks you mentioned. Back to ignition timing, Iíve found an on line company that sells a huge assortment of springs that can be used for changing distributor curving. The mechanical/vacuum advance timing thing makes my family or wife happy because itís cheap entertainment and being critical to performance is a reward I get. The plan is in place to bring down the under the hood temperatures to battle the heat soak by removing the stock exhaust intake etc. next month (not a low budget project), that helps no matter what. I downloaded the link to the megasquirt site too, it looks like a good read. Finding the right mechanical curve is a compromise at best compared with a computerized fuel injection set up but fun stuff anyway.

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    Pedal Smasher Autoholic's Avatar
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    Tom, could you please share a link to the company you found for different dizzy springs?

    To run E85, or any alcohol fuel, in an engine that wasn't originally meant to run alcohol will involve replacing anything that touches fuel and isn't compatible. The carb will have to be rebuilt just to make sure. The float in your Weber is probably rubber, you'd need to get a copper float replacement from Redline or Webcon. The fuel lines will need to be replaced too unless you know for a fact that they are good to use. Gates Barricade is one inexpensive option I've found that has been engineered to run pretty much any modern fuel you can find at a gas pump.

    As for vapor lock... I believe and some day will test for myself, that the fuel line routing needs to be changed. If you ran a hard line from around the area of the mechanical fuel pump, mounted on top of the support beam that covers the brake push rod, up to the radiator support and then up and over the radiator to the passenger side...this would help keep the fuel cold. You could probably fit a hard line in the crease by the top of the radiator. Then, have a fuel pressure regulator at the end of this hard line. From the regulator, like a Malpassi unit for example, you would run a soft line to the carb. This setup does two important things for a carburated fuel system. 1, it keeps the fuel from hugging a hot engine and should remove a lot of heat from the problem. 2, a fuel pressure regulator helps keep fuel pressure consistent at the carb and should improve fuel consumption by eliminating pulses. If you also ran a ceramic coated header and maybe did a few other things to shield heat like ceramic coating the carb and intake manifold, I think you could get rid of vapor lock and hot start issues while still running a mechanical fuel pump.

    I haven't tested any of that yet and it will be a few years before that happens as I plan to do a full rebuild. Bare metal repaint, whole enchilada. But, this is my plan. I want to run a mechanical fuel pump, water choke, manifold & port vacuum advance if I can figure that out, and viscous fan clutch on the later CIH fan setup. The only electrification would be to run one of the Petronix Ignitor systems in the dizzy. So, I have to find ways to make it all happen old school. Oh, and the crazy side of me wants to create a Varicam mechanical valve timing cam sprocket for the CIH and have Rhoads Lifters modify a set of hydraulics. So, variable lift and variable valve timing using strictly mechanical methods. We'll see if that happens, but I've already done a bunch of CAD work for the Varicam.
    "Autoholism is an incurable addiction medicated daily with car porn." ~Zeppi

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    Opeler Conaero's Avatar
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    Thanks guys, plenty to play with there but I will go for 6 deg advance at idle with the vacuum plugged then have a look at the full advance at 4k rpm.

    Does anyone know off the top of their heads what the mixture setting is, 2 seems to stick in my mind.

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    Senior Member The Cub's Avatar
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    Quote Originally Posted by Conaero View Post
    Thanks guys, plenty to play with there but I will go for 6 deg advance at idle with the vacuum plugged then have a look at the full advance at 4k rpm.

    Does anyone know off the top of their heads what the mixture setting is, 2 seems to stick in my mind.
    Anywhere between 3/4 and 2 turns out from bottom is normal. 2 turns out should get you going, do not be shy if it needs to be backed out more it just probably means you need a larger idle jet, very common these days and all of the Jets can be replaced without removing the carburetor. Be sure there is a gap between the choke adjustment screw and the stop with a fully warmed up engine before adjusting Iíve made that mistake before. My 32/36 has a 60 idle jet (probably what you have, thatís what comes in most of them and can be changed) I have mine backed off 1 full turn out from bottom, to demonstrate that carburetors arenít all the same, I also have an older 32/36 that likes 2 full turns out from bottom on the same engine and requires a larger 65 idle jet. Iíve got my idle speed screw a little less than 2 turns in after contact, on my older 32/36 1 1/4 turns out from contact on the same engine, different size idle jet, in my experience new carburetors adjust differently that older carburetors that have some throttle shaft wear. After your engine is warm start turning the mixture screw in until you hear a stumble then back it out until it starts bogging. Somewhere in between is where you will find the best spot, just tune by listening. To set it up properly your idle speed screw should be less than 1 1/2 turns in after the screw makes contact with the stop. Otherwise if itís to far in thereís a progression circuit that will start adding additional gas to your mixture,and you might experience engine run on after you shut down the engine. Tune your mixture screw as described above, get it running as good as possible then if you have to and your idle is too low go ahead and turn the idle speed screw in to get to your 8-1100 rpms, wherever you like it, you can buy an idle cut off solanoid that helps with the engine run on if you have to tune out of specs. Mine is idles nicely at 750 rpmís. I have my idle speed screw in a bit too far with a very smooth idle but donít get engine run on because my idle speed is so low. Iíll attach a good link, I didnít box myself in, I allow myself a little room to adjust outside of the parameters a little if needed. If you can stay within the guidelines attached then your dynamite. If you are less that 3/4 get a smaller idle jet if youíre more than 2 turns out get a larger idle jet, if youíre close go up or down in 05 increments that usually gets it, if youíre way off Iíve used as high as a 70 or 75 before, I havenít successfully gotten anything lower than a 50 to work well, a 55 has worked nicely for me before. Hereís the official link, hope all goes well, HTH:
    Weber CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT

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    Senior Member The Cub's Avatar
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    Quote Originally Posted by Autoholic View Post
    Tom, could you please share a link to the company you found for different dizzy springs?
    Iím more than glad to, take a look at post 23. Itís simply amazing what you can find on the internet.

    https://www.opelgt.com/forums/1b-ign...-timing-2.html
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    Opeler Conaero's Avatar
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    Another question before I delve into this, can you set the timing marks up on the front pulley or another location as setting the timing off the flywheel is difficult with a cold engine let alone a hot one?

    Would it be an idea to set the flywheel mark to TDC then replicate the marks on the front pulley?

    Stupid idea or not?

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    Quote Originally Posted by Conaero View Post
    Another question before I delve into this, can you set the timing marks up on the front pulley or another location as setting the timing off the flywheel is difficult with a cold engine let alone a hot one?

    Would it be an idea to set the flywheel mark to TDC then replicate the marks on the front pulley?

    Stupid idea or not?
    I have done that on every Opel GT that I have the opportunity to do it to
    Keith Wilford
    Finishing up a bare-metal, nut & bolt rotisserie restoration of my '71 Opel GT

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