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Old 07/08/2018, 07:38 PM   #31
p51
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Just an update - in case anyone is interested and for reference if anyone else runs into similar problems

I replaced the intake manifold gaskets and I still had the problem of the idle going lean after the engine had heated up. So I went back to the theory that the lean AFR was too little fuel rather than too much air (via a vac leak). This seemed to be confirmed when, again, I noticed the idle fuel pressure dropping (from 5.5psi to 4psi) after the engine heated up.

I had already routed my fuel lines away from the engine as much as possible (a lot better than they had been routed previously). So...

My first guess was the mechanical fuel pump - the idea being maybe a tear in the diaphragm that (for some reason) was partially failing when hot. Since these are pretty inexpensive I just replaced it. It wasn't the problem. I also checked the fuel line to the tank for any possible pinhole leaks (used my Mityvac for that).

My second guess was that maybe the Holley fuel regulator was being affected by the heat - it is only ~1.5" from the manifold and does get hot. Given I had a new pump spec'ed at 5.5psi to 6.5psi (which won't overcome the Edelbrock carb needle and seat) I just removed the regulator. That *seemed* to fix the problem (the jury is still out, but so far, so good). I also found a comment on-line that Holley regulators are sensitive to heat and "drop to 3psi when they get too hot". I opened up the regulator and there were no issues with any of its components (eg no holes in the diaphragm, etc) so I have no idea why it decided at this point to start acting up.

Some more test drives scheduled this week to see if this does, in fact, solve the issue.

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Old 07/08/2018, 08:17 PM   #32
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Looks like the Fel-Pro gasket set I'm getting for my stock, cast iron, intake manifold has optional exhaust cross-under (which is used to warm the carb for cold weather starts) block-off plates...
https://www.summitracing.com/parts/fel-1250s3

Any recommendations on whether to use these block off-plates or not with a stock manifold?

Note, I already have a phenolic spacer under the carb that seems to have fixed any fuel boiling issues.

Thanks
James
One other note. If you are working with stock J-code 302 heads, IMO the Fel-Pro gasket above is not the one to use even though Fel-Pro states that it will work on stock J-code heads. This gasket appears to be a universal fit gasket and supports larger water ports than on the stock heads. I installed it, filled the radiator with coolant and did a pressure test. It started leaking at ~9psi in two corners.

BTW: Turned out there were some comments about this gasket on the summit racing reviews that I had not read until (ahem) after the fact. I had bought mine at OReillys and thought that the "more expensive" = "better"

So I went back to the standard Fel-Pro gasket for stock heads
https://www.summitracing.com/parts/f...view/make/ford

On this gasket, the water port openings match perfectly with the stock heads. Did the exact same assembly procedure. When I pressure tested the coolant system (at 16psi) it held pressure for 30min (as long as I tested it).

This makes me wonder how many people install these gaskets, don't pressure test the coolant system, drive around for (possibly) months until one day it gets just hot enough that they start leaking.

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Old 07/08/2018, 09:19 PM   #33
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James,
My thoughts on fuel pressure affecting the AFR at idle would be slight or non-existent at best. The float bowls would be full with 2 pounds as well as 7 pounds at idle. Under full throttle on a dyno fuel pressure may affect the AFR ratio.

My guess is engine compartment heat and the humidity in the air. As long as the engine idles smooth, I find AFR ratios nothing to be concerned about. As long as vacuum is good and idle is fine, not to worry!

I will look at the Mr. Gasket intake I recommended, and it may be for an open water passage vice the l shape one of the earlier heads.

Rob
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Old 07/08/2018, 11:18 PM   #34
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Originally Posted by robert campbell View Post
James,
My thoughts on fuel pressure affecting the AFR at idle would be slight or non-existent at best. The float bowls would be full with 2 pounds as well as 7 pounds at idle. Under full throttle on a dyno fuel pressure may affect the AFR ratio.

My guess is engine compartment heat and the humidity in the air. As long as the engine idles smooth, I find AFR ratios nothing to be concerned about. As long as vacuum is good and idle is fine, not to worry!

I will look at the Mr. Gasket intake I recommended, and it may be for an open water passage vice the l shape one of the earlier heads.

Rob
Rob

That's exactly what I originally thought... that as long as there was any fuel in the float bowls it should be fine. The car should idle the same. But there does seem to be a correlation between the lean AFR and the low fuel pressure. Every time the the idle AFR went lean, the fuel pressure had dropped (from ~5.5psi to ~4psi or less). And when the AFR leans out the idle gets really rough and the car sometimes stalled. We're talking about an AFR > 18, sometimes 25.

Finally, when doing some research on carbs I came across the following from Wikipedia...
"Even temporary disruption of fuel supply into the float chamber is not ideal; most carburetors are designed to run at a fixed level of fuel in the float bowl and reducing the level will reduce the fuel to air mixture delivered to the engine."

Frankly, I don't understand why this would be true. Any air pressure is vented and I wouldn't think that the different levels -> weights of the fuel in the bowls would make a difference.

Another weird thing is that I have Wix fuel filter and you can see the gasoline. One thing I did was move it to after the pump (in case that was causing a problem). It fills up part way (~1/4) but there is always air in the top... and the engine seems to run fine in that condition (?!?). Maybe that's why its called "Wix" because it "wicks" the gasoline to the top of the filter (??)

Regarding vacuum, with an initial timing of 13, if I use manifold vacuum to control the vac advance (I know, I know...) I get a nice steady 18" of vacuum at ~825RPM. If I remove the vac advance at idle it drops to 15" adjusted to the same RPM and flutters +/-1". That's why I was thinking I had some sort of vac leak... either manifold to lifter valley or possibly worn valve guides were my guesses. The other possibility (?) is that the cam is not stock, but I don't know how to figure that one out.

Right now I just want to get back to where the car was ~3 weeks ago when it was idling smoothly. After that I plan to see if I can figure out where this 15" with flutter is coming from.

Also, just to be clear, I wasn't complaining about the gasket you recommended. Both gaskets I tried were Fel-Pros. This is the first time that Fel-Pro has let me down... disappointed and slightly poorer, but lesson learned.

James

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Old 07/09/2018, 10:04 PM   #35
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James,
The drop in fuel pressure under idle conditions should not have any affect on the amount of fuel in the float bowl. The fuel level is controlled by the float in conjunction with the needle and seat. Under full throttle a fuel pump may not keep up with fuel demand, but not very likely. Wiki tends not to be a very reliable source of info.

It is normal for a clear fuel filter to not be completely full at any time.

Timing will affect vacuum. A drop from 18 degrees to 15 degrees will drop vacuum accordingly. Yet, your engine should run at 18 inches of vacuum based on your cam and its cam timing as set by a degree wheel.

Carburetor adjustments, timing, or vacuum leaks as you know will affect engine idle. I would focus on engine idle and not worry about AFR readings.

Are you using an "exhaust sniffer" for your AFR readings.

Rob
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Old 07/10/2018, 01:26 AM   #36
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Quote:
Originally Posted by robert campbell View Post
Are you using an "exhaust sniffer" for your AFR readings.

Rob
AFR gauge in the car...

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

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Old 07/10/2018, 09:04 AM   #37
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James,
I re-read your post and realized that I said degrees of 18 and 15 when you were speaking to inches of vacuum. My bad. Certainly with a non-ported source you are running a ton of advance at idle with 13 degrees initial. My guess would be as much as 22 or more.

My suggestion is to try setting the initial up to about 15 or 16 and use a ported vac advance source to see what happens. You may be surprised.

Using a constant vac source makes your idle timing dependent on the vac source and klevel. Any fluctuation in vacuum will result in loss or gain in idle speed due to timing variations. You have two variables working at the same time. Using a ported vac source eliminates the vacuum loss or gain on ignition timing. This is one reason why nearly all 60's cars used ported vacuum.

My guess is with your near 22 degrees of advance at idle your carb must almost be completely shut at idle. This will cause a mis-alignment of the throttle plates and the transfer slots in the carb that support the idle circuit. If you go to a ported vacuum source my guess is your idle will be to low and you will need to screw the throttle stop screw and open the front plates. This will make you re-adjust your mixture screws to achieve the best idle. I normally set an Edelbrock at two turns out as a start point.

Yes, I know we have been down this road. Try it! Whatcha you got to lose!!!

Rob
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Old 07/10/2018, 11:39 AM   #38
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Quote:
Originally Posted by robert campbell View Post
James,
I re-read your post and realized that I said degrees of 18 and 15 when you were speaking to inches of vacuum. My bad. Certainly with a non-ported source you are running a ton of advance at idle with 13 degrees initial. My guess would be as much as 22 or more.

My suggestion is to try setting the initial up to about 15 or 16 and use a ported vac advance source to see what happens. You may be surprised.

Using a constant vac source makes your idle timing dependent on the vac source and klevel. Any fluctuation in vacuum will result in loss or gain in idle speed due to timing variations. You have two variables working at the same time. Using a ported vac source eliminates the vacuum loss or gain on ignition timing. This is one reason why nearly all 60's cars used ported vacuum.

My guess is with your near 22 degrees of advance at idle your carb must almost be completely shut at idle. This will cause a mis-alignment of the throttle plates and the transfer slots in the carb that support the idle circuit. If you go to a ported vacuum source my guess is your idle will be to low and you will need to screw the throttle stop screw and open the front plates. This will make you re-adjust your mixture screws to achieve the best idle. I normally set an Edelbrock at two turns out as a start point.

Yes, I know we have been down this road. Try it! Whatcha you got to lose!!!

Rob
Excellent points. Even I understood them!👍

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Old 07/10/2018, 11:58 AM   #39
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Quote:
Originally Posted by robert campbell View Post
James,
I re-read your post and realized that I said degrees of 18 and 15 when you were speaking to inches of vacuum. My bad. Certainly with a non-ported source you are running a ton of advance at idle with 13 degrees initial. My guess would be as much as 22 or more.

My suggestion is to try setting the initial up to about 15 or 16 and use a ported vac advance source to see what happens. You may be surprised.

Using a constant vac source makes your idle timing dependent on the vac source and klevel. Any fluctuation in vacuum will result in loss or gain in idle speed due to timing variations. You have two variables working at the same time. Using a ported vac source eliminates the vacuum loss or gain on ignition timing. This is one reason why nearly all 60's cars used ported vacuum.

My guess is with your near 22 degrees of advance at idle your carb must almost be completely shut at idle. This will cause a mis-alignment of the throttle plates and the transfer slots in the carb that support the idle circuit. If you go to a ported vacuum source my guess is your idle will be to low and you will need to screw the throttle stop screw and open the front plates. This will make you re-adjust your mixture screws to achieve the best idle. I normally set an Edelbrock at two turns out as a start point.

Yes, I know we have been down this road. Try it! Whatcha you got to lose!!!

Rob
Rob

Thanks. You're correct. At idle with vac advance hooked to manifold I get 13* + 15* = 28* which is, BTW, exactly what I would get once I cracked the throttle with the vac advance hooked to ported vacuum. So the only difference is that I already have the advance engaged at idle. And you are spot on in that the engine is much more sensitive to vac fluctuations with manifold when the vac drops below ~14" (above that the vac advance is full on so any fluctuations in the range 14"+ vac has no effect... I checked this using my Mityvac hooked to the vac advance). It is also true that with the large advance at idle the idle screws are only out about 1 turn and the throttle plates are more tightly closed... all making the engine more sensitive to changes to fuel and air vs using ported vac (the upside being better fuel economy and a cooler running engine). To your suggestion about trying ported vac hooked to the advance... to be clear, *I have already tried it* (previous to this current issue) with an increased initial timing of ~15* and, frankly, my engine runs better with manifold vac... that is the main reason I use it. Having said that, I still think that there is some fundamental issue that the engine has always had with a vac leak (not external). With no vac advance at idle and ~12* initial I get 15" of vac with +/-1" flutter... the upside is that that it sounds like I have a more radical cam . Assuming that the cam is stock (?), I should be getting ~18" vac steady even with 10* idle advance. As the idle advance increases (keeping the RPM the same), the vac goes up and the flutter stops... all consistent with a vac leak. And that is why (I think) my engine seems to "like" manifold vac vac advance... it's covering up/correcting for this internal vac leak.

As usual, thanks for your insight/input. Always appreciated.

James

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Old 07/10/2018, 11:13 PM   #40
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It's looking more and more like the issue was some sort of vapor lock in the Holley fuel regulator (which was placed horizontally just about 1.5" above the intake manifold and was getting pretty hot). I took the regulator out and went for a shakedown drive today. The fuel pressure stayed at a constant ~5.25psi regardless of temp (no dropping to 4psi). Idle AFR was in the range ~13.5 (cold) to ~15.5 (hot restart), ~14 when driving around. No rough idle or stalling. After driving I let the car sit for ~20min to heat soak. No issues on restart.

So there appears there were two problems:
(1) The vac advance canister was not holding vacuum (albeit, it was a slow enough leak that it may or may not have been causing part of the issue) and...
(2) The Holley fuel regulator was "vapor locking". Why it started doing this recently (after working nicely for years) is a mystery. I opened up the regulator and the diaphragm looked ok under a magnifying glass. I did notice, however, that the screws to the top part of the regulator seemed to not be as tight as they could be. It is possible that they had loosened over time (engine vibration?) and when the regulator was heated the gasket between the two parts was not sealing perfectly allowing the pressure to drop inside the regulator and, viola, vaporized gas in the line. But there were no gasoline leaks so... ???

For reference, this is the regulator I was using. Simple operation. Seems well enough made... I am not complaining about it...
https://www.summitracing.com/parts/hly-12-803

One other side note. During my investigations, I read on a number of forums that fuel pressure gauges that are liquid filled are not accurate when exposed to heat. The idea behind a liquid-filled gauge is that the needle doesn't bounce around as much but it turns out the heating of the liquid can affect the gauge readings significantly (!?!). Air filled ("dry") gauges are apparently a better choice (~general consensus). Interestingly, in general, dry gauges are cheaper than liquid-filled... another example where "more expensive" is not necessarily "better". If true, the Scot in me is pleased by this "cheaper" = "better" My German side is appalled that the liquid-filled gauges are (evidently) so poorly engineered

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Old 07/11/2018, 02:06 PM   #41
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Quote:
Originally Posted by p51 View Post
Rob

Thanks. You're correct. At idle with vac advance hooked to manifold I get 13* + 15* = 28* which is, BTW, exactly what I would get once I cracked the throttle with the vac advance hooked to ported vacuum. So the only difference is that I already have the advance engaged at idle. And you are spot on in that the engine is much more sensitive to vac fluctuations with manifold when the vac drops below ~14" (above that the vac advance is full on so any fluctuations in the range 14"+ vac has no effect... I checked this using my Mityvac hooked to the vac advance). It is also true that with the large advance at idle the idle screws are only out about 1 turn and the throttle plates are more tightly closed... all making the engine more sensitive to changes to fuel and air vs using ported vac (the upside being better fuel economy and a cooler running engine). To your suggestion about trying ported vac hooked to the advance... to be clear, *I have already tried it* (previous to this current issue) with an increased initial timing of ~15* and, frankly, my engine runs better with manifold vac... that is the main reason I use it. Having said that, I still think that there is some fundamental issue that the engine has always had with a vac leak (not external). With no vac advance at idle and ~12* initial I get 15" of vac with +/-1" flutter... the upside is that that it sounds like I have a more radical cam . Assuming that the cam is stock (?), I should be getting ~18" vac steady even with 10* idle advance. As the idle advance increases (keeping the RPM the same), the vac goes up and the flutter stops... all consistent with a vac leak. And that is why (I think) my engine seems to "like" manifold vac vac advance... it's covering up/correcting for this internal vac leak.

As usual, thanks for your insight/input. Always appreciated.

James

James,
Cam is a wild card here. Your engine should idle just fine with only 12 to 15 degrees of initial. 28 degrees is way to much at idle.

I have pointed this out before, but as you step on the throttle with "manifold" vacuum to the vac advance, you actually lose advance due to the loss in manifold vac. With ported vacuum when you step on the throttle yes, the vacuum starts to bring in the vac advance, but in a gradual method. Just as the engine demands it and just how the engineers designed the distributor curve to work for basically stock engines.

When you mash the throttle with your setup you actually have an immediate loss in advance of 15 degrees. Amazing that you do not have some sort of a flat spot. With ported vacuum the centrifugal starts to pull in and if you dial in 15 to 16 degrees of initial and use ported vacuum, the engine starts from a better spot.

Hate to say it again, but you need to try 16 degrees of initial, ported vacuum, and readjust your carb to this setting. I am truly convinced it would run a lot better!

What have you got to lose? At 28 degrees of advance at idle I would love to see a dyno pull curve from idle to full throttle. Your engine would fall flat on its face right off the bat and then finally catch up at around 2,500 rpm.

Rob
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Old 07/11/2018, 06:28 PM   #42
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Quote:
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James,
Cam is a wild card here. Your engine should idle just fine with only 12 to 15 degrees of initial. 28 degrees is way to much at idle.

I have pointed this out before, but as you step on the throttle with "manifold" vacuum to the vac advance, you actually lose advance due to the loss in manifold vac. With ported vacuum when you step on the throttle yes, the vacuum starts to bring in the vac advance, but in a gradual method. Just as the engine demands it and just how the engineers designed the distributor curve to work for basically stock engines.

When you mash the throttle with your setup you actually have an immediate loss in advance of 15 degrees. Amazing that you do not have some sort of a flat spot. With ported vacuum the centrifugal starts to pull in and if you dial in 15 to 16 degrees of initial and use ported vacuum, the engine starts from a better spot.

Hate to say it again, but you need to try 16 degrees of initial, ported vacuum, and readjust your carb to this setting. I am truly convinced it would run a lot better!

What have you got to lose? At 28 degrees of advance at idle I would love to see a dyno pull curve from idle to full throttle. Your engine would fall flat on its face right off the bat and then finally catch up at around 2,500 rpm.

Rob
Rob

I appreciate your passion about this vac advance issue but I am not at all sure you even have looked at the magazine articles/papers I posted about this... one by a GM engineer who was the Viper plant manager when he retired. His explanation about how vac advance works is clear and concise. It is also clear on at least one of the reasons why ported vacuum was introduced. And there is another guy who graphed the vac advance of ported vs manifold vs throttle opening... the advance curves pretty much followed each other with the only exception being at idle. So, again, once you crack the throttle and the ported vac port is exposed to the manifold vacuum, the canister advances the timing exactly the same as it would with manifold vacuum. Here is the graph...
http://www.gofastforless.com/ignition/vacuum_chart.jpg

Here is the post that refers to the graph
http://www.gofastforless.com/ignition/advance.htm

But regardless of the articles/papers/internet posts, I think you missed the following in one of my replies above...

"To your suggestion about trying ported vac hooked to the advance... to be clear, *I have already tried it* (previous to this current issue) with an increased initial timing of ~15* and, frankly, my engine runs better with manifold vac... that is the main reason I use it."

Until I figure out why I have that low vac w/flutter (this is without the vac advance hooked to any port, just an initial timing of 12') there is no reason for me to retry ported vacuum because I would get the same result I got when I first tried it. If there is anything you and I can agree on its got to be that trying the same thing multiple times and expecting different results is a sign of insanity

James

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Old 07/11/2018, 07:04 PM   #43
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All very interesting - But - I'm a simple man, preferring to keep things simple. My vision of performance upgrades for a 289 consists of a 4 BBL intake & carb, no more than 500CFM. (A basic 289 can't suck more air than that, so any more is a waste of $$.)
A 302 already has a 4BBL set up, so the only improvement there would be a Pertronix II ignitor & coil.
Accurate tuning will give the small block all it needs for proper operation.
Our GT/CS's are a unique Mustang, and I choose "not to confuse their identity" as a friend of mine used to say.
Although I DO make some modifications (Mini Tach, AM/FM radio, gold CS striping), only an MCA judge would know it. Even a Mustang enthusiast, let alone a casual observer doesn't know enough about the GT/CS to recognize minor alterations.
Well, that's the old man's opinion. Anyone wishing to build a 400 HP 289, be my guest. Just not my cup of tea.

Neil
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Old 07/11/2018, 10:12 PM   #44
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Rob

I appreciate your passion about this vac advance issue but I am not at all sure you even have looked at the magazine articles/papers I posted about this... one by a GM engineer who was the Viper plant manager when he retired. His explanation about how vac advance works is clear and concise. It is also clear on at least one of the reasons why ported vacuum was introduced. And there is another guy who graphed the vac advance of ported vs manifold vs throttle opening... the advance curves pretty much followed each other with the only exception being at idle. So, again, once you crack the throttle and the ported vac port is exposed to the manifold vacuum, the canister advances the timing exactly the same as it would with manifold vacuum. Here is the graph...
http://www.gofastforless.com/ignition/vacuum_chart.jpg

Here is the post that refers to the graph
http://www.gofastforless.com/ignition/advance.htm

But regardless of the articles/papers/internet posts, I think you missed the following in one of my replies above...

"To your suggestion about trying ported vac hooked to the advance... to be clear, *I have already tried it* (previous to this current issue) with an increased initial timing of ~15* and, frankly, my engine runs better with manifold vac... that is the main reason I use it."

Until I figure out why I have that low vac w/flutter (this is without the vac advance hooked to any port, just an initial timing of 12') there is no reason for me to retry ported vacuum because I would get the same result I got when I first tried it. If there is anything you and I can agree on its got to be that trying the same thing multiple times and expecting different results is a sign of insanity

James
James,
Read them all. Vacuum flutter at 15 inches is common with more overlap due to a "hotter" cam. Good look on your quest. My thoughts is that if your car was in my garage I could tune it to run far better than it does currently with far less than 28 inches of advance at idle. Even a full on race motor does not have that much advance at idle. Personally I feel that your throttle plates are far to closed to support the extreme amount of advance at idle. With far less advance at idle would allow proper alignment of the throttle plates to the transfer slots and a much better idle signal. This would improve your AFR ratio at hot idle.

Sorry to say this but it is my feeling that you have not went the full mile to adjust your combination to work with ported vacuum.

Good luck, but you seem to think that the engineers that designed your engine, and all engines in the 60's, did not know what they were doing. A couple articles by others may or may not be true. In a high performance world, they may apply. And trust me the high performance world is my wheelhouse.

I have a suggestion and that would be a dizzy with no vacuum advance!

Rob
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Old 07/12/2018, 01:09 AM   #45
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...I have a suggestion and that would be a dizzy with no vacuum advance!

Rob
Hmmm... no vacuum advance at all?... Interesting. Now that is what I call a compromise

And just to be clear, I think my cam is a stock cam. The rest of the engine is stock (eg heads, intake, etc) and when dynoed it pretty much matches the power put out by a stock 302... ~200HP at the wheels.

Anyway, it looks like I figured out my "leaning out" issue and am back to how the car was running ~4 weeks back. Again, thanks for the advice/help with the intake manifold. fuel filter (I had always wondered if air in the fuel filter was a problem), etc

James

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