302 idle and vacuum concerns

Az Pete · Oct 14, 2010

Sounds like you are getting closer. I would set the idle as low as you can before it starts getting rough.

Is this a man. tranny?

Did the hose for the vac. gauge fit everything tight? Yes, a vac. leak can increase the idle speed.

Be sure to re-torque properly..... That is to loosen the bolts and then torque to the proper setting. What you are doing is different than re-torquing after an install and torquing and then again after the engine is warm.

afreejack · Oct 14, 2010

Pete: It's a 5 speed and the vacuum hose is tight.

Here's what I did today:

Removed the interference and retorqued the manifold. Some of the bolts had less than 10 ftlbs of torque on them. They are all torqued to 20 now.

The distributer is stock.

Removed the vacuum hose from the dist. and took some readings for the centrifugal advance. These are going to be estimated because the water pump intake covers up the spot where the real timing marks are. (I had previously found tdc and marked that on the balancer) Today I went out there and measured the distance for 10 degrees (9/16") and used a sharpie to mark it where I can hit it with the timing light. (silver sharpie shows up very well)

With idle timing set at 15 degrees, and the vacuum hose disconnected and plugged, the centrifugal advance started to open about 1300 rpm. it was about 18 degrees at 1500 rpm, 23@2000, 28@2500, 32@3000 and was fully advanced at 3200 rpm at 34 degrees.
When I connected the vacuum line to the constant port, the idle timing went up to 23 degrees (8 degree vacuum advance?)

After doing all of that, I advanced the timing to about 17 and set the idle down to 680 (any lower and it gets rougher). the engine is definently a little bit smoother, and there is a fairly steady lope to it. (fluctuates about 10-30 rpm) The vacuum is at 14.5" and fluctuates about 1/2"(maybe because of the lope?)

I think you might be right that there is a mild performance cam in it and my neighber, who can over to see what all the noise was (I love my exhaust system), thinks the same thing.

Thanks again,
Jack

woodsnake · Oct 14, 2010

Any chance you can post an audio/video link of all this?
When you set your idle, be sure to give yourself some lee way, so that it doesn't stall coming to a stop light, or slow turns, like into a parking lot or something. Try and ajust your idle speed so that you get the most vacuum at idle, VS being concerned about a lower number, or about what the "book calls for". After 40 years, those numbers are good for a reference or starting point only, and not necessarily set in stone. I think somebody snuck a cam in there a few years ago, and didn't bother to tell anybody......

horseballz · Oct 14, 2010

afreejack,
First let me say that it is so easy to help folks like you who actually pay attention to the details of the suggestions we give. Good work Grasshopper! The last suggestion on this issue is to go head and bump your idle back up to 720-750 RPM to help ensure good hot start idle. It's not unusual for a carbed engine to have a slightly stumbly idle when started after only sitting off for 5-20 minutes, especially with no spacer under the carb to insulate it. You see, the engine actually gets a little bit hotter just after turning it off, as the cast iron block and heads hold a lot of heat and when you turn the engine off there is no longer water/coolant flowing through it or air flowing around it to remove the heat and the carb heats up from heat soak from the rest of the engine and also no air flowing around it. To confirm this, get the car/engine up to full operating temp by driving for at least 15-25 minutes and note the position of your temp gauge. Then after turning it off, wait 2 -3 minutes, turn the key on without starting the engine and check your temp gauge. It will likely be at least a little, if not significantly higher. I think the next thing you need to "tinker" with/address is your lack of a carb spacer and correcting your PCV setup, which sounds to be incorrect. We should probably start a new thread to deal with these issues, as this one is getting kind of long.
Happy Motoring,
Gene

PoppyMod · Oct 14, 2010

Another thought...
Have you ruled out the dizzy vac being good? I.E, when tested, it holds a vac? Of course the other way to test it is to connect it back to full vac. Start the engine attach a timing light and observe the timing advance. Maybe this has been ruled out. There have been so many helpful postings, I could have missed it.

horseballz · Oct 14, 2010

He says he's getting about 8 degrees extra vacuum advance.
Gene

PoppyMod · Oct 15, 2010

OK regressing.....the symptoms are "rough" idle and "low" vac reading...

Speed reading all of the input, it appears, or has been tried.....

1. checked all avenues for leaks and with none apparent. (both hard connections and soft (hoses)
2. checked and ruled out the PCV system
3. the advance mechanisms both, dizzy vac (no leaky diaphragm), and dizzy mechanical are working as designed (initial at 12, total "all in" by 3200, confirmed with timing light at incremental steps)
4. adjusted the carb using vac gauge and basic raw settings

Was the valve pre-load adjusted to 1/4 -1/2 (max)?
(I offered, if too tight, will produce a lower than normal vac, ; all other settings being inline)

After readjusting the pre-load...
Assuming a mild street cam has been installed, raise the base idle to 900. Did the idle quality improve?
And, no change in vac reading.

What was the action of the vac gauge at idle?
see: http://*******.com/index.php/topic,3020.0.html
We want a steady needle, even if lower than normal reading.

All of this producing no tangible results, I would pull the intake and check the cam lobe lift. If really adventurous, go through the cam degreeing process to see if some PO slipped a "mickey" in there.

With this being stated, I am running out, if not already, of potential ideas!
All of this is making me feel like this was a final exam question in a trade school test!

afreejack · Oct 15, 2010

Woodsnake, I'll work on getting something put up so you can listen.

Gene, the engine is definently hotter after sitting for a few minutes. I figured that was a normal thing since it's turned off, the residual heat rises from the cylinders and the fan isnt moving any air across the engine. I forgot to mention that I did go out and buy a spacer and put it in. Prior to doing that, I had a big problem with the engine idling after a hot start (it wouldnt even start unless I gave it some gas). That problem went away after putting the spacer on. It still stumbles for a minute, but it will start and run without touching the gas pedal.

As for the PCV setup, I'll see what I can find for diagrams and such and work on that. if I run into any other issues with that I'll start a new thread on it. (I can't believe that this one went two pages.) Same thing with opening the engine and checking the valves and cam (after all, the weekend is here and the wife wants to go for a drive).

Poppy, I did, at one point, have the idle up to about 850 and the engine ran smoother, with the vacuum mostly steady at about 16", maybe a 1/4" fluctuation or so. At 680rpm, the vac is about 14" with a 1/2" fluctuation. When I give it throttle the vacuum goes up to about 20-21" and is rock solid.

Driving it in to work this morning, it definently felt like I had more power and the acceleration was smoother.

You might feel like you are taking a test, but I feel like I'm back in class learning this stuff all over again!
I really do appreciate the help from all of you. Thanks again.

PoppyMod · Oct 15, 2010

afreejack said:
Woodsnake, I'll work on getting something put up so you can listen.

Gene, the engine is definently hotter after sitting for a few minutes. I figured that was a normal thing since it's turned off, the residual heat rises from the cylinders and the fan isnt moving any air across the engine. I forgot to mention that I did go out and buy a spacer and put it in. Prior to doing that, I had a big problem with the engine idling after a hot start (it wouldnt even start unless I gave it some gas). That problem went away after putting the spacer on. It still stumbles for a minute, but it will start and run without touching the gas pedal.

As for the PCV setup, I'll see what I can find for diagrams and such and work on that. if I run into any other issues with that I'll start a new thread on it. (I can't believe that this one went two pages.) Same thing with opening the engine and checking the valves and cam (after all, the weekend is here and the wife wants to go for a drive).

Poppy, I did, at one point, have the idle up to about 850 and the engine ran smoother, with the vacuum mostly steady at about 16", maybe a 1/4" fluctuation or so. At 680rpm, the vac is about 14" with a 1/2" fluctuation. When I give it throttle the vacuum goes up to about 20-21" and is rock solid.

OK, Good! It appears to me, the engine is liking 850-900 Rs, There is nothing wrong with that. Raising the idle will help with re-starts, as well. Adding the spacer will reduce any heat-soak by the carb and impending vapor lock, another good fix. That 16" of vac is looking more normal.
Now, this comment can cause all kinds of additional comments, but, I'll throw it out there anyway.
I'll say most all pre-emission era cars ran full vac to the dizzy. "Ported" didn't show up until "Federales" got involved. I have tried both, ported (1405 Eddy) and full vac (680 Holly XE series). I made best power and over-all drive-ability running "full vac". I am running "full vac" today with my dual Weber setup. So, it's depends on your setup and what your engine likes.

Driving it in to work this morning, it definently felt like I had more power and the acceleration was smoother.

You might feel like you are taking a test, but I feel like I'm back in class learning this stuff all over again!
I really do appreciate the help from all of you. Thanks again.

Another thought....
You can do some more "tweak" tuning by experimenting with the dizzy vac settings. If your dizzy vac is hexagon in shape, the timing can be adjusted as a much as 10 degrees one way or another. These settings will affect the mid-range. Considering a total of 36-38 ('m running 16 deg (initial), 4 deg (dizzy), with 24 mech, btw), you can try 14 intial, if it starts to ping drop the "dizzy vac" to 4 or 6 degrees. (I think i read it was "8")?
All of this means, there is more tweaking to further improve the engine's "happy place"
Happy Motoring!

horseballz · Oct 16, 2010

afreejack,
Does your new carb spacer have a PCV port on/in it? To do a PCV setup properly, you need to be connected to a restricted vacuum source. For example: I'm using a 1" Holley aluminum (still looking for a phenolic, for better insulation from heat soak, with a PCV port) carb spacer that has a 3/8" or 1/2 inch port in the rear that is pulling vacuum from beneath the rear 2 barrels of the carb through 2 approx. 1/32"-1/16" (the restriction) holes. This port is connected, by hose, to a late model (88-89) Mustang 5.0 PCV valve with 2 nipples using the small one (to increase restriction) and plugging the other. This PCV valve is then plugged into the top of the rear of one valve cover to gently suck oil fumes, etc. out of the crank-case system into the intake manifold and then cylinders to be burned in the combustion process. In the front of the other valve cover, a filtered air inlet is required to replace the "air" sucked out by the PCV. A filtered cap/breather is OK, however, I have a hose connected from that valve cover to the air filter housing, inside the filtered area. It doesn't matter which valve cover is sucked or which is the air inlet, but one should be on the rear of one valve cover and the other on the front of the other valve cover. The restriction is to reduce/control the amount of vacuum leakage that's created by the PCV, especially important on a low vacuum, big cammed engine. Please forgive the long dissertation, but this issue is often overlooked/misunderstood.
My $.02..errrr $.05 or $.06,
Gene

PoppyMod · Oct 17, 2010

horseballz said:
afreejack,
Does your new carb spacer have a PCV port on/in it? To do a PCV setup properly, you need to be connected to a restricted vacuum source. For example: I'm using a 1" Holley aluminum (still looking for a phenolic, for better insulation from heat soak, with a PCV port) carb spacer that has a 3/8" or 1/2 inch port in the rear that is pulling vacuum from beneath the rear 2 barrels of the carb through 2 approx. 1/32"-1/16" (the restriction) holes. This port is connected, by hose, to a late model (88-89) Mustang 5.0 PCV valve with 2 nipples using the small one (to increase restriction) and plugging the other. This PCV valve is then plugged into the top of the rear of one valve cover to gently suck oil fumes, etc. out of the crank-case system into the intake manifold and then cylinders to be burned in the combustion process. In the front of the other valve cover, a filtered air inlet is required to replace the "air" sucked out by the PCV. A filtered cap/breather is OK, however, I have a hose connected from that valve cover to the air filter housing, inside the filtered area. It doesn't matter which valve cover is sucked or which is the air inlet, but one should be on the rear of one valve cover and the other on the front of the other valve cover. The restriction is to reduce/control the amount of vacuum leakage that's created by the PCV, especially important on a low vacuum, big cammed engine. Please forgive the long dissertation, but this issue is often overlooked/misunderstood.
My $.02..errrr $.05 or $.06,
Gene

Hey Gene,

First, nice writeup!
You mention you're looking for a spacer with a PCV nipple. I have two immediate thoughts. One, the early mustangs had 1" aluminum 4 hole spacers with the nipple off the back and are still available from the usual vendors, I know this as I have an OEM.
Two, it's easy to drill and tap, then install an extended brass nipple. I did done this when I needed a full vac port for my Webers.

Ken

horseballz · Oct 17, 2010

Thanks Ken,
You said:
"Hey Gene,

First, nice writeup!"

Yeah, any excuse to just sit here being largely non-productive. I'm glad I don't smoke pot any more! If I did, I'd likely never even get up to go to the bathroom.

I already have a Holley 1" aluminum spacer that has a restricted PCV port, but am looking for one made out of phenolic (sort of a plastic resin type stuff) that would help insulate my Autolite 4100 from the manifold to reduce heat soak/vapor lock here in the 115 degree summer heat. I expect the heat soak/vapor lock issue to get worse next summer, once my AC is done and working.
Thanks Again,
Gene

PoppyMod · Oct 17, 2010

horseballz said:
Thanks Ken,
You said:
"Hey Gene,

First, nice writeup!"

Yeah, any excuse to just sit here being largely non-productive. I'm glad I don't smoke pot any more! If I did, I'd likely never even get up to go to the bathroom.

I already have a Holley 1" aluminum spacer that has a restricted PCV port, but am looking for one made out of phenolic (sort of a plastic resin type stuff) that would help insulate my Autolite 4100 from the manifold to reduce heat soak/vapor lock here in the 115 degree summer heat. I expect the heat soak/vapor lock issue to get worse next summer, once my AC is done and working.
Thanks Again,
Gene

Ah yes, I just noticed you out there near "sin" city. We've been there many times, once in June. That was the last time in June! We, normally, go in January or February now.
Anyway, phenolic would be your best bet with what you have in mind. If your ride is not a concours car, you could add an electric fuel pump, re-route your fuel line to the firewall, add a fuel block, then, come off of it to the carb. This get's line off the front of the engine.
Also, it's quite possible, that by adding an electric pump to work with your current mechanical will reduce any tendency toward vapor lock. Conatant pressure has a profound affect on mitigating vapor lock.
Just some more ideas to clog your brain.

Good Luck!

302 idle and vacuum concerns

Az Pete

afreejack

New Member

woodsnake

horseballz

PoppyMod

Member

horseballz

PoppyMod

Member

afreejack

New Member

PoppyMod

Member

horseballz

PoppyMod

Member

horseballz

PoppyMod

Member

Similar threads

302 idle and vacuum concerns

New Member

Member

Member

New Member

Member

Member

Member

Similar threads

Privacy & Transparency

Privacy & Transparency