1968 Idle Going Lean

[robert campbell]

James, too funny!!

I was wondering what kind of smoke you blew in?? Whacky tobacky??

Rob

 

[p51]

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

 

[robert campbell]

I always block the cross over. This feature was for daily driver cars back in the days. Now that they are sunny Sunday cars this is no longer needed. These cars live a pampered life and are not asked to run on 20 degree days anymore where carb heating is necessary to prevent carb icing.

Rob

 

[p51]

I always block the cross over. This feature was for daily driver cars back in the days. Now that they are sunny Sunday cars this is no longer needed. These cars live a pampered life and are not asked to run on 20 degree days anymore where carb heating is necessary to prevent carb icing.

Rob

Thanks Rob. Sorta what I was thinking as well. Also with the alcohol added in the gas these days the fuel is even more volatile than back when the cars were manufactured. And if I ever do add throttle body EFI to the car, the intake exhaust cross-under would not help even on cold days.

 

[p51]

Dr Rob et al

So, I've gotten the intake manifold off (boy that sucker is heavy) and the mating surfaces on the heads and manifold cleaned up. Got some questions:

Q1: I noticed on one of the hold-down studs that oil had crept up from the lifter valley to the top of the manifold. Are you supposed to put something on intake hold-down bolts to seal them? If so, what do you use?

Q2: I noticed that on the manifold one of the carb stud bolt holes goes *into* one of the intake runners (!?!). I assume that is the normal situation for the stock manifold (is it?). So, again, what do you sealant do you put on the bolt?

Q3: I noticed that the water ports on the back of the stock manifold are not used. Is that standard for all 302 manifolds?

Q4: The manifold bolts need to be replaced. The ones near the water ports esp were starting to corrode. I was thinking ARP but they are 3x the summit racing bolts ($30 vs $10). Are they worth the extra money? Which bolts would you recommend?

Aside: I was hoping to see clear evidence of a break in the gasket that was causing a vac leak. Unfortunately, the gasket was all intact (no blow through) although in one place the "impression" of the gasket on the head/manifold was not as clear as elsewhere. So maybe that is where vac leak was....

Thanks
James

 

[robert campbell]

James,
I use PermaGasket Super 300 on all bolts that may thread into holes that are not blind and may need to be sealed. Especially on flywheel bolts for manual transmission cars. All early small blocks crank holes enter the oil pan lubrication. Available at any local car parts shop.

https://www.amazon.com/Permatex-80057-Super-Gasket-Sealant/dp/B000HBI9DM

Hope the effort solves the problem. All early small blocks do not use the rear cross over for cooling. Only the front.

Rob

 

[p51]

James,
I use PermaGasket Super 300 on all bolts that may thread into holes that are not blind and may need to be sealed. Especially on flywheel bolts for manual transmission cars. All early small blocks crank holes enter the oil pan lubrication. Available at any local car parts shop.

https://www.amazon.com/Permatex-80057-Super-Gasket-Sealant/dp/B000HBI9DM

Hope the effort solves the problem. All early small blocks do not use the rear cross over for cooling. Only the front.

Rob

Thanks Rob. The manifold is back on with the new gasket in place. Sometime tomorrow I'll put everything else back together and also do a little cleaning of the disti (since its out). Hopefully, by Tuesday I can fire it up and see if I fixed the problem... fingers crossed...

 

[p51]

James,
I use PermaGasket Super 300 on all bolts that may thread into holes that are not blind and may need to be sealed.

Rob

Quick question. Do the two front and two rear intake manifold bolts go into the water jacket on the stock 302 J-code engine heads?

Thanks
James

 

[robert campbell]

James,
They do not, but the thread sealer will not hurt a bit on all intake bolts.

I chase all bolt holes with a tap and run a die down all intake bolts. I use flat washers with no lock washers on the bolts. I do a 30 percent, 60 percent, 100 percent torque sequence on the bolts as per the recommended torque pattern. Sometimes I go over the final torque two or three times to ensure the proper torque is achieved.

Then I check the torque at least once a year if it is an aluminum intake. They will become loose and need to be re-torqued.

Rob

 

[p51]

James,
They do not, but the thread sealer will not hurt a bit on all intake bolts.

I chase all bolt holes with a tap and run a die down all intake bolts. I use flat washers with no lock washers on the bolts. I do a 30 percent, 60 percent, 100 percent torque sequence on the bolts as per the recommended torque pattern. Sometimes I go over the final torque two or three times to ensure the proper torque is achieved.

Then I check the torque at least once a year if it is an aluminum intake. They will become loose and need to be re-torqued.

Rob

Thanks Rob. Got delayed. Hopefully button things up this weekend... at least know if I was right or wrong about the vac leak.

 

[p51]

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.

 

[p51]

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/fel-ms901031/overview/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.

 

[robert campbell]

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

 

[p51]

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

 

[robert campbell]

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

 

[p51]

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

Rob

AFR gauge in the car...

https://www.amazon.com/gp/product/B0184TSI84/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

 

[robert campbell]

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

 

[Mosesatm]

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!👍

 

[p51]

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 :wink:. 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

 

[p51]

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" :wink: My German side is appalled that the liquid-filled gauges are (evidently) so poorly engineered