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Hey guys,
I've posted here before about my engine "pinging", or "ticking", or "tapping". I narrowed it down to possibly a lifter tap last time, but I have some new developments. See the end of the post for a video with audio of the noise.
Background info:
My truck is a 1983 49 state 300-6, with a 1bbl carter yfa and all of the original equipment except no cat.
A recent compression test showed 185 psi from all cylinders dry except 160ish from #4 dry and 175 from #4 wet.
I have 50 psi of oil when cold, and 25(idle)-40(driving) when hot
I took a road trip from SC (sea level) to CO (6500 feet), and the elevation has changed some things. My engine was pulling 17 inHg at sea level, and it's pulling around 12-12.5 right now after some idle circuit tuning for elevation.
The main point of this post is:
My tapping noise went away completely after I reached high altitude. I figured the Rislone oil detergent I put in the crankcase must have finally done its job after 1600 clicks down the interstate.
One day, I decided to try and adjust my timing with a vacuum gauge to try to restore some performance. I advanced the timing a few degrees by turning the distributor counterclockwise, and the vacuum peaked around 13-14 inHg. The engine also idled a decent amount higher with advanced timing. But, when I went to drive the truck around the block, the tapping noise came right back, just as loud as ever!
I know that altitude has an effect on relative engine timing, due to the chemistry of the air-fuel mixture and the speed that it burns. So when I advanced my timing at 6500 feet, it seems it made it run like it did at sea level, tapping included.
My question to the forum:
What could be causing this kind of tapping under load, which would be induced by advancing the timing? Since it's spark related, I don't think it's a lifter tick anymore.
A note about EGR:
I read about a malfunctioning EGR causing detonation by raising the cylinder temperatures. I tested my EGR the other day by disconnecting the green vac line from WOT to EGR. At idle, the hose was not sucking at all. Even as I revved the engine up, the hose still didn't pull any vacuum. I then connected a different hose to the EGR valve and sucked on it with my mouth (no vacuum pump lol) to find it felt like sucking through an empty hose -- it didn't seem to hold the vacuum I created. This makes me think that I Might have a bad EGR, but I'm not sure what I'm supposed to expect.
The EGR valve may not pull a vacuum as not all were sealed units and needed a set volume of air flow to actuate them. This sounds like a lean condition regardless.
The loss of the cat can lean out the fuel air mix in the engine. The fact that the tapping goes away at higher altitudes is is sure fire indication of a lean fuel air mix, the higher the altitude the lower the air pressure and lower the amount of oxygen the engine inhales this effectively richens the fuel air mix and your knocking goes away. The easy solution is to swap the carb for an earlier one (pre 80 49 state) or swap for a Canadian spec one (pre 85). Many U.S vehicles in this era were on the ragged edge in terms of fuel air ratio for emissions reasons. So you either need to keep all the stock bits (including the cat) or modify it accordingly providing local laws will allow you too.
If the tapping noise is only under load, then you are correct it's most likely pre-ignition or "pinging".
Advancing the timing is a no-no if it brings on pinging. While it does give better performance, it's all a delicate balance from the factory with the factory setup. Part of that delicate balance is the EGR and also the cat.
The EGR working does help prevent pinging. Most of the Ford EGR's work on exhaust backpressure AND vacuum. You will never be able to bench test most Ford EGR's, because there is no exhaust backpressure to activate the valve. There is a metal valve inside the EGR that meters the amount of vacuum going to the EGR and the exhaust pressure controls this metal valve. You should be able to see a felt filter under the bottom edge of the EGR, this is were the vacuum sucks through when it is wasting the vacuum from the valve,. They did this so they can control the amount of EGR according to engine speed. More engine speed means more exhaust backpressure, which presses down more on the metal valve, which leaks less vacuum which opens the EGR more. Your cat being gone is going to affect this, essentially crippling your EGR, since there is less backpressure. It may work some, but not as it's supposed to.
You should have gotten vacuum on the EGR hose when you revved the engine, if the engine was fully warmed up. They do not want the EGR working when the engine is cold, so the vacuum line comes from the thermal vacuum switch. From there it goes to a ported vacuum source. The ported vacuum source only has vacuum when the throttle is opened (no EGR at idle) runs around to the thermal switch (no vacuum if the water is below 100 degrees) and then runs to the EGR. Those thermal valves do go bad, and I believe they still sell them in the store.
If you do not want to mess with the EGR system, you can tune it out. From my experience, you can leave everything as is and turn the dist base timing back till you get no pinging. What you will probably find when you do this, you will be down around 2 degrees or so BTDC, and the engine does not have any power and gets lousy fuel mileage. Turn it up and set it to spec, which is probably 8-10 BTDC, and it runs better, but it pings on light throttle. If you go ahead and mash the throttle the pinging stops. This is coming from the vacuum advance on the distributor.
What I ended up doing first was to disconnect the vacuum advance and plug the line going to the carb. I then kept advancing the initial timing till it pinged or it would not crank over very easy. On my engine this ended up being around 14 degrees BTDC. It ran so much better like this. Got great fuel mileage and you just touch the gas pedal and it responded. No pinging either. But I knew I was leaving some fuel mileage on the table because the vacuum advance was disconnected. So I started experimenting around with the vacuum advance, trying to make it adjustable. The factory will use the vacuum advance to advance the timing as much as 20 degrees. This is way too much on a modified system and is the reason it pings so bad at part throttle only. If you can get this cut back, you can use the vacuum advance.
The EGR valve may not pull a vacuum as not all were sealed units and needed a set volume of air flow to actuate them. This sounds like a lean condition regardless.
The loss of the cat can lean out the fuel air mix in the engine. The fact that the tapping goes away at higher altitudes is is sure fire indication of a lean fuel air mix, the higher the altitude the lower the air pressure and lower the amount of oxygen the engine inhales this effectively richens the fuel air mix and your knocking goes away. The easy solution is to swap the carb for an earlier one (pre 80 49 state) or swap for a Canadian spec one (pre 85). Many U.S vehicles in this era were on the ragged edge in terms of fuel air ratio for emissions reasons. So you either need to keep all the stock bits (including the cat) or modify it accordingly providing local laws will allow you too.
Interesting! I did not know that the cat was related to the air-fuel mixture.
A friend of mine did the exhaust work, and got rid of the old (plugged up) cat because he said it really chokes out carbureted engines and there's no emissions tests here. I wanted to keep the air pump, egr, and vac lines to keep it original, but I never expected that deleting the cat would cause a problem.
I believe you, but can you explain to me why the cat leans it out? Is there something I can plug where air comes in?
Is a pre 1980 carb still a carter YFA, or is that a carter YF? Could I also get the same effect by changing jets to a richer mixture?
Thank you for the information!
Originally Posted by Franklin2
If the tapping noise is only under load, then you are correct it's most likely pre-ignition or "pinging".
Advancing the timing is a no-no if it brings on pinging. While it does give better performance, it's all a delicate balance from the factory with the factory setup. Part of that delicate balance is the EGR and also the cat.
The EGR working does help prevent pinging. Most of the Ford EGR's work on exhaust backpressure AND vacuum. You will never be able to bench test most Ford EGR's, because there is no exhaust backpressure to activate the valve. There is a metal valve inside the EGR that meters the amount of vacuum going to the EGR and the exhaust pressure controls this metal valve. You should be able to see a felt filter under the bottom edge of the EGR, this is were the vacuum sucks through when it is wasting the vacuum from the valve,. They did this so they can control the amount of EGR according to engine speed. More engine speed means more exhaust backpressure, which presses down more on the metal valve, which leaks less vacuum which opens the EGR more. Your cat being gone is going to affect this, essentially crippling your EGR, since there is less backpressure. It may work some, but not as it's supposed to.
You should have gotten vacuum on the EGR hose when you revved the engine, if the engine was fully warmed up. They do not want the EGR working when the engine is cold, so the vacuum line comes from the thermal vacuum switch. From there it goes to a ported vacuum source. The ported vacuum source only has vacuum when the throttle is opened (no EGR at idle) runs around to the thermal switch (no vacuum if the water is below 100 degrees) and then runs to the EGR. Those thermal valves do go bad, and I believe they still sell them in the store.
If you do not want to mess with the EGR system, you can tune it out. From my experience, you can leave everything as is and turn the dist base timing back till you get no pinging. What you will probably find when you do this, you will be down around 2 degrees or so BTDC, and the engine does not have any power and gets lousy fuel mileage. Turn it up and set it to spec, which is probably 8-10 BTDC, and it runs better, but it pings on light throttle. If you go ahead and mash the throttle the pinging stops. This is coming from the vacuum advance on the distributor.
What I ended up doing first was to disconnect the vacuum advance and plug the line going to the carb. I then kept advancing the initial timing till it pinged or it would not crank over very easy. On my engine this ended up being around 14 degrees BTDC. It ran so much better like this. Got great fuel mileage and you just touch the gas pedal and it responded. No pinging either. But I knew I was leaving some fuel mileage on the table because the vacuum advance was disconnected. So I started experimenting around with the vacuum advance, trying to make it adjustable. The factory will use the vacuum advance to advance the timing as much as 20 degrees. This is way too much on a modified system and is the reason it pings so bad at part throttle only. If you can get this cut back, you can use the vacuum advance.
Yeah, I figured the pinging was no good; I retarded the timing back to its default for now so that it runs smooth.
As I said to matthewq4b, can you explain to me how the cat affects the air-fuel mixture? As far as backpressure goes, could I install a more restrictive turbo muffler to get that back or is that something specific to cats?
When I tested the EGR vacuum, the engine was fully warm. The hose going to the EGR comes from a connection on the front of the carb labeled "WOT", and tees into another line going to the temperature switch, which I replaced half a year ago ($$). This hose didn't pull any vacuum at any point in time. I might have to try again after driving around a while, or put my gauge on it. But my finger felt nothing.
I would like to fix it rather than tune it out, but I'll try to do what I can for now.
You're right about the vacuum advance -- I hear less ping on heavy throttle, but I always figured it was because the engine noise was louder than the ping.
I already have done some research on my own and I saw people with GM cars talking about running no vacuum advance or ported advance. My distributor has a funky setup with a manifold vacuum source and a ported one that connect together into the advance port.
I think that I will run no advance for now and see how it does.
First priority is not to blow the engine up by raising cylinder temps and scoring pistons. I'll take that even if I have to lose some power and mileage until I can permanently fix the problem.
Thanks for the help as always!
As long as you hear no pinging, then you will have no engine damage. As soon as you hear any pinging, you need to address it. Letting it ping for a long period of time can cause some damage to the pistons.
Like I said, the EGR works on exhaust backpressure. This backpressure comes from the cat as well as the rest of the exhaust. The more you free up the exhaust, the less backpressure, so the less EGR flow you will have.
A free flowing exhaust can also scavenge the cylinders better, in other words cleans them out better, letting more air in and out. This is great for power when fuel is added also. If the carb jetting is kept the same, it can run a little bit lean, but in the real world I haven't seen any major problems from this. But it does point out how the factory engine setup is looked at as a complete package, and lots of things affect other things.
A baffled muffler would certain help things some, and probably also help neighbor relations. If there is something I hate, it's the sound of a six with a glasspack. Sounds like a ricer.
As long as you hear no pinging, then you will have no engine damage. As soon as you hear any pinging, you need to address it. Letting it ping for a long period of time can cause some damage to the pistons.
Like I said, the EGR works on exhaust backpressure. This backpressure comes from the cat as well as the rest of the exhaust. The more you free up the exhaust, the less backpressure, so the less EGR flow you will have.
A free flowing exhaust can also scavenge the cylinders better, in other words cleans them out better, letting more air in and out. This is great for power when fuel is added also. If the carb jetting is kept the same, it can run a little bit lean, but in the real world I haven't seen any major problems from this. But it does point out how the factory engine setup is looked at as a complete package, and lots of things affect other things.
A baffled muffler would certain help things some, and probably also help neighbor relations. If there is something I hate, it's the sound of a six with a glasspack. Sounds like a ricer.
Alright, I'll try disconnecting the advance today and see if I can get it to pull more vac without pinging!
Unfortunately, it's been on-and-off doing this tick ever since January of this year. Hopefully I didn't cause too much damage; either way I'll probably rebuild the engine in the next couple of years.
For the exhaust, I'll try to get something better on there. Right now I have a very quiet muffler on there. A cat would be more expensive than a turbo muffler but it might be worth it; I don't want it to sound obnoxious.
Plus, I see a lot of value in keeping things stock.
I have some friends who are into old cars and trucks and many of them like pulling all the emissions and feedback junk off, despite my best recommendations. It always just seems to cause more problems in the long run when you mess with it.
Alright, I'll try disconnecting the advance today and see if I can get it to pull more vac without pinging!
Unfortunately, it's been on-and-off doing this tick ever since January of this year. Hopefully I didn't cause too much damage; either way I'll probably rebuild the engine in the next couple of years.
For the exhaust, I'll try to get something better on there. Right now I have a very quiet muffler on there. A cat would be more expensive than a turbo muffler but it might be worth it; I don't want it to sound obnoxious.
Plus, I see a lot of value in keeping things stock.
I have some friends who are into old cars and trucks and many of them like pulling all the emissions and feedback junk off, despite my best recommendations. It always just seems to cause more problems in the long run when you mess with it.
As noted by Franklin when you free up the exhaust or even the induction system you will lean out the fuel air mix and if the calibration of the egr egr valve relies on some back pressure to function it will not function properly either.
The YFA was introduced in 78 IIRC, The YF will also be a direct bolt on.
Yes the above noted applications are still YFA Carbs and will be direct bolt on. Since your truck is not a an O/D truck it leaves many more options for a carb an O/D truck is pretty much limited to a Canadian spec carb.
These carbs will have the added advantage of providing more power and potentially better fuel economy. You will have to let me know if the EVAP system still in place or removed. As the carb can be had with EVAP or with out. The cheapest solution at this point is to just replace the carb, plus it leaves you open for future modifications. You could rejet the carb also the YF uses standard carter jets as used in the AFV and AVS but then you are still stuck with the stock fuel curve which was not great in these late carbs.
With the emissions system being mechanical on these vehicles it is designed to work hand in hand with all the other parts. Change or remove something and you may throw stuff out of whack They were designed for emissions above anything else with economy and power taking a back seat. Fortunately the fix 80% of the time is a simple carb swap. In some instances if may also mean a dist recurve but neither are difficult ot do. In all cases you will end up with a smoother running more efficient more powerful engine.
Since you are not in a state were emission testing is not a concern and retaining totally stock appearance is not a concern the easy solution is to disable the emissions equipment instead of trying to make 30 year old equipment where parts are no longer available or costly to function as intended. Regardless do NOT throw out the original equipment as it is in demand valuable for those that have no choice due to legislation to retain this equipment in operating order.
As noted by Franklin when you free up the exhaust or even the induction system you will lean out the fuel air mix and if the calibration of the egr egr valve relies on some back pressure to function it will not function properly either.
The YFA was introduced in 78 IIRC, The YF will also be a direct bolt on.
Yes the above noted applications are still YFA Carbs and will be direct bolt on. Since your truck is not a an O/D truck it leaves many more options for a carb an O/D truck is pretty much limited to a Canadian spec carb.
These carbs will have the added advantage of providing more power and potentially better fuel economy. You will have to let me know if the EVAP system still in place or removed. As the carb can be had with EVAP or with out. The cheapest solution at this point is to just replace the carb, plus it leaves you open for future modifications. You could rejet the carb also the YF uses standard carter jets as used in the AFV and AVS but then you are still stuck with the stock fuel curve which was not great in these late carbs.
With the emissions system being mechanical on these vehicles it is designed to work hand in hand with all the other parts. Change or remove something and you may throw stuff out of whack They were designed for emissions above anything else with economy and power taking a back seat. Fortunately the fix 80% of the time is a simple carb swap. In some instances if may also mean a dist recurve but neither are difficult ot do. In all cases you will end up with a smoother running more efficient more powerful engine.
Since you are not in a state were emission testing is not a concern and retaining totally stock appearance is not a concern the easy solution is to disable the emissions equipment instead of trying to make 30 year old equipment where parts are no longer available or costly to function as intended. Regardless do NOT throw out the original equipment as it is in demand valuable for those that have no choice due to legislation to retain this equipment in operating order.
Good sounding advice.
I'm not going to go as far as to replace the carburetor yet, since mine is only eight months old (remanufactured). I will do it if I don't have any other options, though.
Just got back from driving around and messing with the timing. I had some ping on the way out, then I stopped, disconnected and plugged the vacuum advance, and turned the distributor pretty far counterclockwise by hand.
I used a vac gauge to get it to nearly 14 inHg at idle! The truck drove fine, and felt more powerful at low revs. But it felt marginally less so at high revs, because the timing is more retarded than it would have been with the vacuum advance connected. The starter took a second to actually turn the engine over, but it fired up. If I have more problems starting I will retard the timing.
If I recurved my distributor, I might be able to make it advance less than the stock one did, and then I could use my vacuum advance properly without getting ping and without retarding the timing. Can I recurve my stock DSII distributor or do I have to convert to MSD or something?
You're correct, I don't have O/D, neither do I have A/C. It seems to have EVAP; there's a purge valve in front of the carburetor and a canister below the air intake by the grille. Before I try to take the emissions off, I want to figure out what goes where and which things I'll have to plug or replace.
For now, I'm going to see how it continues to run without vacuum advance. The idle is also higher than I would like it to be, and the curb idle screw is fully backed off. I think I have a vacuum leak or two to track down.
Good sounding advice.
I'm not going to go as far as to replace the carburetor yet, since mine is only eight months old (remanufactured). I will do it if I don't have any other options, though.
Just got back from driving around and messing with the timing. I had some ping on the way out, then I stopped, disconnected and plugged the vacuum advance, and turned the distributor pretty far counterclockwise by hand.
I used a vac gauge to get it to nearly 14 inHg at idle! The truck drove fine, and felt more powerful at low revs. But it felt marginally less so at high revs, because the timing is more retarded than it would have been with the vacuum advance connected. The starter took a second to actually turn the engine over, but it fired up. If I have more problems starting I will retard the timing.
If I recurved my distributor, I might be able to make it advance less than the stock one did, and then I could use my vacuum advance properly without getting ping and without retarding the timing. Can I recurve my stock DSII distributor or do I have to convert to MSD or something?
You're correct, I don't have O/D, neither do I have A/C. It seems to have EVAP; there's a purge valve in front of the carburetor and a canister below the air intake by the grille. Before I try to take the emissions off, I want to figure out what goes where and which things I'll have to plug or replace.
For now, I'm going to see how it continues to run without vacuum advance. The idle is also higher than I would like it to be, and the curb idle screw is fully backed off. I think I have a vacuum leak or two to track down.
And just cause you have remn carb does not mean it is right. What brand of reman is it? Some are complete crap.
And bottom line you are not going to be able to make this work unless you replace the cat or the carb. With ethanol laced fuel a missing cat and potentially non functioning EGR valve you are running lean and no amount of dickering with the timing is going to fix that. You need to address that before you do anything else. Keep messing with it and you will end up taking out a valve or worse eventually.
Sort out the fueling issue then do the timing. You will never be able to get the timing to good spot until the fuel issue is fixed.
You should set the timing to factory with a light with the vac advance disconnected, quit guessing. You can not use intake vacuum to set an emissions engine especially since you have no idea what is working or not.
Post a pic of the emissions sticker and we can tell you what can go and what can stay to keep the EVAP functional.
And just cause you have remn carb does not mean it is right. What brand of reman is it? Some are complete crap.
And bottom line you are not going to be able to make this work unless you replace the cat or the carb. With ethanol laced fuel a missing cat and potentially non functioning EGR valve you are running lean and no amount of dickering with the timing is going to fix that. You need to address that before you do anything else. Keep messing with it and you will end up taking out a valve or worse eventually.
Sort out the fueling issue then do the timing. You will never be able to get the timing to good spot until the fuel issue is fixed.
You should set the timing to factory with a light with the vac advance disconnected, quit guessing. You can not use intake vacuum to set an emissions engine especially since you have no idea what is working or not.
Post a pic of the emissions sticker and we can tell you what can go and what can stay to keep the EVAP functional.
.
It's an Autolite brand carburetor, made in Canada, with electric choke assist. Greenish in color.
I'll try to get my hands on a real timing light soon, it would be good for me to set it right.
If I end up deleting the emissions, then I'll probably change to an earlier, simpler carburetor. If I end up fixing everything, I'll put a cat or restrictive muffler on it to complete the closed-loop system.
Autoline is a reputable rebuilder an one of the better ones.
This is a feed back system and I presume the system is not functional. Then you have no idea where the carb was last set to by the EEC it could be set to max lean. The feed back carb is going to have to go that is non optional unless you are going replace all the missing emissions equipment. And the carbs I listed are earlier non emissions carbs.
So you need to decide what you goiing to do.
To leave the EVAP in place in this application is pretty straightforward. Once you swap the carb. Remove everything traced in red.
You will also be able to remove the air pump and its associated plumbing since the cat is gone there is no need for it any way.
And all the associated EEC wiring and ECU can be removed also. Should clean things up under hood quite a bit.
Autoline is a reputable rebuilder an one of the better ones.
This is a feed back system and I presume the system is not functional. Then you have no idea where the carb was last set to by the EEC it could be set to max lean. The feed back carb is going to have to go that is non optional unless you are going replace all the missing emissions equipment. And the carbs I listed are earlier non emissions carbs.
So you need to decide what you goiing to do.
To leave the EVAP in place in this application is pretty straightforward. Once you swap the carb. Remove everything traced in red.
You will also be able to remove the air pump and its associated plumbing since the cat is gone there is no need for it any way.
And all the associated EEC wiring and ECU can be removed also. Should clean things up under hood quite a bit.
Thank you for taking the time to do this!
I didn't know this was a feedback system! I guess that explains why I have manifold AND ported vacuum advance...
It sure would be a lot simpler and cleaner without all those vacuum lines, but I have a few questions:
What are you referring to as the EEC/ECU? I have a DSII box on the fender, and a voltage regulator on the other side, but I've yet to actually see a computer or a diagnostic port anywhere.
What exactly defines the point between a feedback carb and a non-feedback carb? Theoretically, if I plugged all the ports on this one except for the basic functions, and did some re-tuning, would it work the same or is there something beyond that? I'm asking this because I always read about the '84 and up computer and sensor models and assumed those were "Feedback" and therefore mine was completely "Non-Feedback". Thank you for helping me understand.
Let me know if you want any other pics of underhood connections.
Thank you for taking the time to do this!
I didn't know this was a feedback system! I guess that explains why I have manifold AND ported vacuum advance...
It sure would be a lot simpler and cleaner without all those vacuum lines, but I have a few questions:
What are you referring to as the EEC/ECU? I have a DSII box on the fender, and a voltage regulator on the other side, but I've yet to actually see a computer or a diagnostic port anywhere.
What exactly defines the point between a feedback carb and a non-feedback carb? Theoretically, if I plugged all the ports on this one except for the basic functions, and did some re-tuning, would it work the same or is there something beyond that? I'm asking this because I always read about the '84 and up computer and sensor models and assumed those were "Feedback" and therefore mine was completely "Non-Feedback". Thank you for helping me understand.
Let me know if you want any other pics of underhood connections.
Feed back carbs were used in 83 and your emissions sticker lists TPS adjustment. So does your truck have a O2 sensor if so it is EEC controlled. And not all feedback systems used EEC distributors. And you mentioned closed loop that only applies to electronically controlled systems.
What carb exactly did you get. A part number would be helpful.
Feed back carbs were used in 83 and your emissions sticker lists TPS adjustment. So does your truck have a O2 sensor if so it is EEC controlled. And not all feedback systems used EEC distributors. And you mentioned closed loop that only applies to electronically controlled systems.
What carb exactly did you get. A part number would be helpful.
Understandable. Almost 100% sure I don't have an O2 sensor or a TPS. All of my junk is vacuum controlled except the ignition module itself.
I'd bet the TPS adjustment is referring to the California models, which did have computer control. They probably printed the same adjustment sections for all trucks.
Hold on. According to your sticker, you do not have the feedback system, no ECU (Engine Control Unit or Engine computer). The engines with the computer had no vacuum line to the distributor, it was all computer controlled. So you are good there.
As far as the timing thing, this is were Matthew and I have different approaches and disagree a little, we have had this discussion before. I am for the quick get er done type of timing without taking the distributor apart several times to recurve it. His method really requires this, and you can plan on doing this later if you like, but right now with some adjustments, you can get by and have a little better running engine.
Basically, you want as much timing as the engine can tolerate at all times and all conditions without pinging. This gives the most power and best fuel mileage.
The factory runs the initial timing too low, and uses too much advance in the vacuum unit. To get more timing in the lower rpms you can take a lot of time and experimentation re-curving the dist to make it advance faster at lower rpms, or you can twist the distributor around like you did to give more initial advance. When you do this you are just roughly moving the lower rpm curve up.
Whatever method you use, you are not going to be able to use the vacuum advance unit like it is stock. Whether you use Matthew's method of re-curving, or my method of just whole hog moving the initial, the factory vacuum unit advances the timing too much after that, and you will always have pinging, especially if the EGR is not working. So don't try to hook it back up unless you figure out how to adjust it. Some of the factory units did have some adjustment to them.
You made a comment in one of your previous posts about not having enough timing at the higher rpms without the vacuum advance unit connected. This is only true if you are at part throttle. If you are pulling a hill and have the carb wide open, there will be little to no vacuum advance anyway, your vacuum reading will be very low in this situation and it will not pull on the advance unit and advance the timing any. If you want to test this, find a plugged nipple on the intake, get a long hose and hook your vacuum gauge up and tape it to the windshield. Go for a ride and see what the vacuum is under different conditions. You will see how the advance operates since it is directly related to the vacuum levels of the engine.
07-12-2018, 08:03 PM
