302 idle and vacuum concerns

[afreejack]

This is an 82 302 with a T5 tranny in a 66 convertible.

The idle is quite rough to the point where I cant get it below 650 rpm without taking a chance on the engine stalling. Even with the idle speed adjusted at 700, when I start the engine warm after it has been sitting for a few minutes, it's is still VERY rough. After a couple of minutes of giving it some gas (keeping it around 1000 rpm or so) it will idle ok at 700.

This is what I've done:
New edelbrock 1406 carb and I've adjusted both the idle setting screws.
New distributer and timing has been set to about 10 degrees. Vacuum advance on the distributer is connected to the driver's side port (constant vacuum)
Have gone around and checked for leaks in all vacuum fittings and found none.


Using a vacuum gage, I found that the vacuum is about 13" at idle (set at 700 rpm for now). it does fluctuate between 14 and 12 (in time with the rough idle on the engine). When I give it throttle, the vacuum goes up to about 21" and stays steady (held it at 1500, 2000, and 3000 rpm and it stays about 21"). When I let off the throttle, the vacuum jumps up to 25' and then back down to 13" at idle again.

I did verify that the vacuum gage is accurate beforehand (I have access to a low pressure calibrator) and it is.

Any ideas?

 

[woodsnake]

Do you have a performance cam? Does it smooth out if you increase the base idle up to 800?
It sounds to me either like a vacuum leake, or what comes with a performance cam...

 

[PoppyMod]

This is an 82 302 with a T5 tranny in a 66 convertible.

The idle is quite rough to the point where I cant get it below 650 rpm without taking a chance on the engine stalling. Even with the idle speed adjusted at 700, when I start the engine warm after it has been sitting for a few minutes, it's is still VERY rough. After a couple of minutes of giving it some gas (keeping it around 1000 rpm or so) it will idle ok at 700.

This is what I've done:
New edelbrock 1406 carb and I've adjusted both the idle setting screws.
New distributer and timing has been set to about 10 degrees. Vacuum advance on the distributer is connected to the driver's side port (constant vacuum)
Have gone around and checked for leaks in all vacuum fittings and found none.


Using a vacuum gage, I found that the vacuum is about 13" at idle (set at 700 rpm for now). it does fluctuate between 14 and 12 (in time with the rough idle on the engine). When I give it throttle, the vacuum goes up to about 21" and stays steady (held it at 1500, 2000, and 3000 rpm and it stays about 21"). When I let off the throttle, the vacuum jumps up to 25' and then back down to 13" at idle again.

I did verify that the vacuum gage is accurate beforehand (I have access to a low pressure calibrator) and it is.

Any ideas?

I think your vac is low based on your know engine build. Unless you have a known HP cam, your idle at 700-800 should be smooth and the vac about 15-18", give or take a 50 RPMs. My highly modified engine idles at 800-900 with a vac reading of 17" and is connected to full vac.
The erratic idles needs to be investigated more. I know this carb well. Did you adjust the carb mix using a vac gauge? Also, tight lifter pre-loads will reduce vac. I would start with no more than 1/2 turn. Also, move the advance up a bit to 12 deg.
Just a few ideas. Good Luck!

 

[afreejack]

Appreciate the help.

I went all around the carb, manifold, etc.. looking for a vacuum leak and didn't find any. So all thats left for that is to pull the manifold and put in new gaskets?

I also forgot to mention that when I first started it up cold (choke engaged), the vacuum was about 17". (don't know if that helps)

I did bump the idle up to about 850 and there was virtually no change in the vacuum. I also tried advancing the timing (with the idle set back to 700) and didn't see any difference except the engine did run slightly smoother.

Based on info from the previous owner when I bought the car, I believe all he did was pull the engine out of an 82, changed the water pump to fit the 66 radiator and dropped it in this car. So I'm pretty sure it's a stock cam.

I did advance the timing a little bit to about 12. there was no change in the vacuum.

When I originally adjusted the idle mixture screws, I did it by RPM (didn't have a vac gage then) by opening them both 2 turns, starting the car, and adjusting them until I had the highest rpm it would go. I did double check them yesterday with the vacuum gage. When I turn the screws more than a quarter turn either way, the vacuum drops off below 11 and engine speed drops by over 100 rpm. I'm assuming that means they are set right (they are both opened the same amount - around 1 3/4 turns).

If there is a better way to adjust the idle mixture, please let me know (I went by the manual for the carb when I did it the first time).

I probably wont have time this week, but I'm hoping that maybe by this weekend, I'll be able to pull the valve covers off to take a look at the valves. For adjusting them, the only thing I need to worry about is the torque on the rocker arms right? If not, what else am I going to be looking for? Like I said above, I believe this is a stock 5.0 out of an 82 mustang with no modifications other than the water pump.

 

[2+2GT]

Sounds to me like you have too much cam to get t a good idle. Coupla ways to fix that. You can replace the camshaft, or for much less work and cash you could switch the one you have to Rhoads lifters. That'll give you variable valve action, increasing the vacuum at low rpm. Prob'ly give you better mileage and low-end torque, too.

 

[PoppyMod]

Appreciate the help.

I went all around the carb, manifold, etc.. looking for a vacuum leak and didn't find any. So all thats left for that is to pull the manifold and put in new gaskets?

I also forgot to mention that when I first started it up cold (choke engaged), the vacuum was about 17". (don't know if that helps)

This is normal as the choke plate creates an obstruction in the air intake.


I did bump the idle up to about 850 and there was virtually no change in the vacuum. I also tried advancing the timing (with the idle set back to 700) and didn't see any difference except the engine did run slightly smoother.

The engine smoothing out, is an indication it likes more advance at idle.


Based on info from the previous owner when I bought the car, I believe all he did was pull the engine out of an 82, changed the water pump to fit the 66 radiator and dropped it in this car. So I'm pretty sure it's a stock cam.

I did advance the timing a little bit to about 12. there was no change in the vacuum.

OK, based on the engine "smoothing", then leave it at 12.

When I originally adjusted the idle mixture screws, I did it by RPM (didn't have a vac gage then) by opening them both 2 turns, starting the car, and adjusting them until I had the highest rpm it would go. I did double check them yesterday with the vacuum gage. When I turn the screws more than a quarter turn either way, the vacuum drops off below 11 and engine speed drops by over 100 rpm. I'm assuming that means they are set right (they are both opened the same amount - around 1 3/4 turns).

OK, using the gauge, adjust for the highest vac at your idle RPM.


If there is a better way to adjust the idle mixture, please let me know (I went by the manual for the carb when I did it the first time).

The vac gauge with an AFR meter is ideal, but, the gauge alone is typically the the fine.


I probably wont have time this week, but I'm hoping that maybe by this weekend, I'll be able to pull the valve covers off to take a look at the valves. For adjusting them, the only thing I need to worry about is the torque on the rocker arms right? If not, what else am I going to be looking for? Like I said above, I believe this is a stock 5.0 out of an 82 mustang with no modifications other than the water pump.

Torque is not an issue, so much, as the number of turns from "zero" play. The important aspect, is to insure each cylinder's valve(s) is on their respective heel of the cam (insures valve is fully closed).


Few other ideas... before you remove the intake.
Have you ruled out a "fouled" plug?
Plug wire going to ground before the plug? (especially, if you meticulously have ruled out a vac leak.)
Have power brakes, check the line connection at the intake or a leak in the hose.
Snug down carb base nuts

The last resort is removing the intake.

Again, good luck!

 

[afreejack]

Plugs are new and when I checked them they were still good, verified the gap was correct. Brand new distributer and the dwell is at 27.8. (A friend recommended that I set the dwell to 29). I also picked up some spacers and routed the plug wires(new wires) to neaten them up and make sure they were not twisted around each other (crossing wires as close to right angles as possible) and not laying on the engine.

I don't have power brakes, and I did verify that there was no leak in the plug for that fitting on the carb. Reverified the carb was tight on the manifold when I was checking for leaks. Already had replaced the pcv and breather cap.

I'll put the timing back to 12 and keep it there for now and re-verify the idle mixture.

Also, would too much fuel pressure at idle be an issue for this (stock mechanical fuel pump)? I havent looked down the throat of the carb at idle to see if there is anything coming out of the main jets, but I will tonight. Would it be in my best interest to get a regulator anyway?

I'm trying to rule out all of the easy fixes before I have to take apart the engine. The wife is happy that I finally got it on the road and gave me a nasty look when I talked about tearing the engine apart.
(she knows that eventually I'll be rebuilding the engine, but she wants to be able to drive it for a while first)

 

[PoppyMod]

Plugs are new and when I checked them they were still good, verified the gap was correct. Brand new distributer and the dwell is at 27.8. (A friend recommended that I set the dwell to 29). I also picked up some spacers and routed the plug wires(new wires) to neaten them up and make sure they were not twisted around each other (crossing wires as close to right angles as possible) and not laying on the engine.

OK good

I don't have power brakes, and I did verify that there was no leak in the plug for that fitting on the carb. Reverified the carb was tight on the manifold when I was checking for leaks. Already had replaced the pcv and breather cap.

OK, good

I'll put the timing back to 12 and keep it there for now and re-verify the idle mixture.

Good place to start


Also, would too much fuel pressure at idle be an issue for this (stock mechanical fuel pump)? I haven't looked down the throat of the carb at idle to see if there is anything coming out of the main jets, but I will tonight. Would it be in my best interest to get a regulator anyway?

The Eddy's are quite happy with 5- 6 psi. Over doing it, will only serve to push the float needles off their seats and cause flooding. No typical affect on your issue.


I'm trying to rule out all of the easy fixes before I have to take apart the engine. The wife is happy that I finally got it on the road and gave me a nasty look when I talked about tearing the engine apart.

Yeah, they tend to get that way because the family budget suffers LOL. The good news is, intake gaskets are cheap, it is more of a pain in the patoot!

(she knows that eventually I'll be rebuilding the engine, but she wants to be able to drive it for a while first)

Good for her!It's good she takes' an active interest.

 

[horseballz]

afreejack,
1>How did the engine idle before replacing the carb?
2>Where was the vacuum for the old distributor coming from, manifold (constant) or ported Little or no vacuum at idle)?
3>What kind of spacer is under the carb, between it and the intake manifold?
4>How does it run driving down the road?
5>How old is the gas in the tank?
Just Askin',
Gene

 

[afreejack]

Gene,
The idle was never really any good. I have been replacing and fixing things since I got the car. It did have an electronic ignition setup (and the rat's nest of wires that goes with it) from a granada and a holley 650 carb on it. I found that the holley carb was basically a piece of junk and there were vacuum leaks, loose/misadjusted fittings, etc..., so rather than try to rebuild it (there were missing parts on the choke assy as well), I got rid of it and bought the edelbrock.
At the same time I was running into issues with some of the wiring (kind of expected with 40 year old wiring) and ended up buying a whole new harnes for it. At that time, I got rid of the electronic ignition and old distributer (and replaced the alternator with a one-wire). It's amazing how clean the engine compartment looked after getting rid of all the old spliced wires running averywhere.

Not sure about where exactly the old distributer vacuum was coming from. Basically, I just yanked off the carb and started from scratch. Everything I found talking about a points type distributer said to plug the vacuum advance into the constant vacuum port. (I haven't tried the other port on the passenger side of the carb yet. maybe I should...?)

There's nothing between the carb and manifold except a gasket. No plate or spacer.

Driving down the road, it feels good. Plenty of power, Quick acceleration, no hesitation when I put my foot to the floor. It's just that rough idle thats killing me. Sometimes I wonder if it's going to stall at a stop sign.

I'm on my second tank of fresh gas right now. just filled up last week.

Poppy: Regarding the fuel pressure. I'm just concerned if the pressure at idle is too high and if there is some dribbling from the main jets. (Something I'm going to look at next time I play with the car.)
Sometimes the wife's interest is "When are you going to be done tinkering with the car so I can drive it!" LOL

 

[horseballz]

afreejack,
First off, you'll likely NEVER be done tinkering!
1> How is the idle with the vacuum to the distributor disconnected from the distributor and plugged?
2> Is there a chance that there is a mismatch of the carb gasket to the manifold or the carb? Possible vacuum leak.
3> You really should have a properly fitting carb spacer, but I don't think that is the cause of your problem.
4> What kind of intake is it? Stock cast iron or after market?
5> Where is your PCV hose connected? If it's connected directly to manifold vacuum without any restriction that could a source of vacuum loss.
Keep us posted and we WILL help fix your issue.
Gene

 

[Az Pete]

I would try the ported vacuum source. You need to try both and run the one that is best for your setup. For most of my street setups, I run ported. Once the car is tuned with the vacuum disconnected, reconnecting it should not change the idle settings.

Did I miss how much total timing you have?

 

[woodsnake]

Also, try spraying some carb cleaner around and at each mating surface. I.E., where the intake manifold meets the heads, where the carb bolts to the intake manifold, etc...Check the vacuum hose on the distributor to make sure it is tight, and not cracked and breaking apart. You said the car does NOT have power brakes, right? So the only vacuum should be from the distributor to the carb, is that correct?
Vacuum leaks are pesky mo'fo's, it doesn't take much to really get your goat!

Also, how old is your timing gear set? Is that recently replaced to?

 

[afreejack]

I really appreciate the assist from everyone and hope to be able to pay it forward.....

Had a couple of hours this afternoon to do some playing and this is where I'm at now:

Reverified that there were no vacuum leaks. sprayed so much carb cleaner all over the top of the engine and carb that I wonder why it isn't clean enough to eat off of.

I advanced the timing to 12 degrees, readjusted the idle mixture screws and now I have about 13-14 inches of vacuum with the idle set at 650 rpm. With the vacuum advance connected, it looks like I have about 25-30 degrees of total vacuum at idle.

The vacuum advance is the only vacuum connection on the carb and the rubber hose is new. (replaced it when I got the new distributer) no cracks or breaks in the hose and I did make sure it's tight over the fittings.

When I disconnect and plug the vacuum hose from the distributer to set the timing, the engine idles VERY rough and drops to around 350 rpm. (I have to raise it up to about 600 to set the timing and then reset it back down after hooking up the vacuum to the dist.) I did switch to the ported vacuum on the carb and the engine idled like crap (very rough and very slow), but seemed to run ok when I gave it some throttle. From what I understood about the ported/constant vacuum, if you have breaker points, you should use the constant. Right?

The intake manifold is an aftermarket edelbrock (put in by the previous owner). I have a new oil cap/breather on the driver's side valve cover and a new baffled breather(pcv?) on the passenger side with a hose running from it to the bottom of the air cleaner (also an edelbrock 9 inch round, not the original mustang pan style). I didn't see a spot on the manifold for an actual pcv valve and that vacuum fitting on the carb is plugged. Should I have a PCV valve in the manifold?

I used the gasket that came with the carb and when I put it on the manifold prior to setting the carb on it, the fit looked right. (there are no leaks around it that I could find) I can look into a spacer as well. At least that's an easy thing to install.

I've thought about the timing gears and that they may be worn. I dont know how old they are but I'm not quite ready to take apart the front of the engine to get at them.

I keep telling the wife we got the car for her to drive around and look cool, and we got it for me to tinker with it.
She just doesn't like it when my tinkering interferes with her driving.

Thanks again all...

 

[woodsnake]

Is the vacuum advance plugged when you are making your initial timing adjustments?

 

[Az Pete]

Again, on all of mine, the idle would not change when the vac. line was reattached after setting everything.

If you meant to say you have 35-30 degrees of timing at idle, that is way to much in my opinion. That should happen once you speed up the engine. That is caused by the manifold vacuum being a constant pull and changing things before the engine is demanding the change.

Have you tried the ported vacuum? If not......try it.......I always run that unless on an extremely built engine, then it is either manifold vac. or no vacuum advance at all.

45 years playing with these old Fords and it comes down to a wrong setting so many times.....

 

[horseballz]

afreejack,
Az Pete is on the right track. Points or magnetic/electronic trigger makes no difference, ignition timing/advance is ignition timing/advance. From what it sounds like in your last post, I suggest you go ahead and set/check your timing with vacuum disconnected at specified idle speed and then hook your vacuum advance to the ported source and then adjust idle speed if needed. Idle speed should be 525-550 RPM in drive which should give 600 RPM or so in park. Your vacuum still sounds kind of low, unless there is a performance cam in there that you don't know about. I'm not sure what model intake you have (Performer or Performer RPM?) but I think you should try re-torquing your intake. Click here for the specs/instructions/tightening sequence:

http://www.edelbrock.com/automotive_new/misc/tech_center/install/2000/2121.pdf

Tightening sequence is VERY important to avoid cracking your manifold. If you don't have a torque wrench, you can get a fairly accurate, click type, 3/8" drive for about $20-$25 or 1/2" drive (now on sale) for $9.99 at harbor freight. If money is tight, I can post a link for a 20% off coupon to use on the 3/8", which is what I would recommend for the lower torque required for the intake. At those prices I would buy both so you can have one for precise low torque, such as intake manifold, spark plugs, etc. and one for higher torque such as lug nuts, etc. The trick to keeping these cheapos accurate is to reset to the lowest setting when done using them before storage to not stretch the springs inside. I wouldn't recommend them for daily/professional use, but they're pretty OK for the weekend tinkerer. Keep us posted.
Good Luck,
Gene

 

[afreejack]

I drove the car in to work this morning and it seemed like the idle was rougher than it was yesterday afternoon (82 yesterday afternoon, 65 this morning?), so it looks like I'm back to checking everything out again.

when I did all the timing checks, I disconnected the vacuum hose from the distributer and plugged it. I will try again and hook it up to the ported vaccum on the carb and see how that goes.

I'll take a hard look at the manifold and see if I can determine which one it is. I do have a good torque wrench that I picked up at autozone a while back when I was doing my clutch, so I can use that to check the torque on it. (I wouldn't be surprised if the previous owner just slapped it on and cranked the bolts down. He seemed like that kind of guy) Thanks for the link to the torque info.

 

[afreejack]

OK, did some more work on the car yesterday and this is where I stand:

Shifted the dist. vacuum hose over to the ported connection on the carb and reverified the timing to about 12 degrees (vacuum hose dosconnected and plugged). With the vacuum hose connected, the timing is still 12 degrees.

Readjusted the idle mixture screws with using both the tach and the vacuum gage (connected to the constant vacuum port). I also put a spacer plate in with new gaskets (no vac leaks around there).

Idle is set at 700 rpm. It does fluctuate between 690 and 720 and occasionally goes between 680 and 740. I did notice a little bit of a lope on the engine as well, but it isnt constant. The idle is still a little bit rough. the vacuum stil fluctuates between 13-14 inches. (When I tried to put the idle down to 600, the vacuum dropped and fluctuated rapidly between 6 and 12 inches and the engine was EXTREMELY rough)

One thing I did notice was that after I got the mixture screws adjusted and the idle set, when I took the vacuum gage off the (constant vacuum) carb fitting, the idle increased to 750 rpm. When I put the plug on the fitting, it went back down to 700. I would think that the open vacuum connection would cause the engine to slow down or run rough like it was a vacuum leak? Is this normal or an indication of something else?

When I drove the car, it did seem to respond a little bit better so maybe hooking up the dist vacuum to the ported connection was the way to go.


The manifold didn't have any number on it except "performer 289". After poking around on the net, I believe that it's a Performer 2121. I didn't get the chance to verify the torque on the intake manifold (I'll try that this afternoon if it isn't raining because I have to take off the carb and coil to get to some of the bolts with the torque wrench.) I did do a check on the ones I could get to and they were not all torqued to specs. (I didn't torque them, just checked to see if they would move). I'll update after I retorque it correctly.

 

[horseballz]

afreelack,
Normal for idle to increase a bit when you create that vacuum "leak" and normal for idle and timing to not change when hooking to ported vacuum (little or no vacuum at idle). It sure sounds to me as though there is at least a mild performance cam in your engine. Get your manifold torqued and see how that goes. After that, you might want to try bumping/advancing your timing another couple of degrees at a time until you get a little "pinging"/spark knock/rattle under acceleration/load or kickback on the starter when warm and then back it off just enough to stop the ping and/or kickback. Up to 16 or 18 degrees would not be that out of line for some performance cams. What you are really looking for is about 36-38 degrees total timing with vacuum disconnected. A timing light with a degree dial would be handy for checking this, (I'm assuming the timing mark scale on your damper doesn't go much higher than 20-30 degrees Before Top Dead Center -BTDC) but you could use a tape measure to measure how far 10 degrees is on your damper and then use a white crayon or white out to make a mark at 30 and 40 degrees to get in the ball park. I don't think you stated what kind of distributor you installed. It would be helpful to know at what RPM (with vacuum disconnected) your timing starts to advance and where it is at 1500- 2000- 2500 and 3000 RPM and at what RPM it stops advancing any farther (likely between 2800 and 3200). That would be your total advance, including initial timing PLUS the mechanical/centrifugal advance. Then for test purposes, move your hose back to manifold vacuum (with other plugged) to see how much advance your vacuum gives you. My late model 5.0 with a medium roller cam and longer (giving more lift) roller rocker arms, likes about 17-18 degrees initial (at 790 idle) plus 24 degrees mechanical advance for an all in total of about 41-42 degrees and then the vacuum advance is adjusted to give another 7-8 degrees on top of that. Your vacuum advance may be adjustable, depending on what distributor you have. Please let us know what you've got. It sounds like you're on the right track.
HTH,
Gene