I have a low reading of 15-16 coming from the manifold (I think it's the transmission vacuum line at the back of the manifold). Chilton's says this is an indication of: "late ignition or valve timing, low compression, stuck throttle valve, leaking carb or manifold gasket."

My engine runs decent in neutral/park but when in gear it bogs down and sounds like a diesel and sometimes stalls. When I give it gas to drive away, it hesitates and then lurches forward several times almost as if I was driving a stick and sucked at it... It also stumbles at cruising speeds.

As far as my thoughts, I think I can rule out valve timing because I can't see a timing chain shrinking or stretching, but I may be wrong! I tried using a timing gun to check the timing, but something went wrong and the wires got really hot (dunno what happened, I hooked the black and red aligator leads to their respective posts on the battery and soon the wires got really hot. It was an old gun and there were no instructions). For now, I left the dizzy at the place it's always been. I'm still running points and still need to inspect them. I haven't checked the compression yet because I don't have a guage. I first thought it was my stuck throttle valve: I have to use two return springs to get it to return to the lowest idle. But I added that second spring months ago and I didn't have any problems until just a few weeks ago. And as far as the leaky carb or manifold gasket, I really don't know how to check those unless I just replace them entirely.
I've got a bit of work still to do on my own but I wanted to post my thoughts. As far as adjusting the timing, do you guys put the car in drive (and block the wheels) while you time the engine?

 

Sounds a whole hell of a lot like slipped valve timing to me,,, but you will want to make sure before you dive under that timing cover for no good reason!!!

How long since the engine was overhauled AND how many miles ago...

To test for a manifold leak, see if you can get the car to idle, and spray carburator cleaner around the intake and carburator base gaskets. do this outside, and have an extinguisher and a water hoseready in the remote chance of a hood fire.

Get a timing light that works, hopefully you have not moved your ignition timing since you started having problems,,, if the ignition timing is really retarded, then this is an indication of slipped valve timing, especially if you know it has changed since you started having issues.

IMO, compression would have to be pretty damn bad to effect engine vacumn toa largeextent...

You don't have a hot cam in there right? if you do, you might be chasing your tail...

BTW... newer timing chain sets seldom do slip, but your car had a nylon coated cam gear from the factory, these do fail routinely, in my experience at about 80K to 110K miles without exception. If yourengine has not been rebuilt, or has been rebuilt as late as the late 1980s, you may have these nylon coated gears.

 

I forgot to mention that I put carb cleaner in a spray bottle and sprayed teh base of the carb but didn't notice anything. I didnt' spray down towards the manifold seam though. I will try that tomorrow.

I have receipts for the engine rebuild done in '03 by the second owner before me. At the top of the receipt it says "this ticket contains parts for a : '68 Ford Mustang V8-289...SP MKP-653D". When I first got the car I thought this meant that the PO put in a '68 engine into my '66. But then I wondered if the shop thought my car was a '68 which would mean that it still has the original engine...maybe I'm just being hopeful. But I don't see a mileage anywhere on the receipt so it's safe to assume this is not the stock engine. Either way, it was rebuilt in '03. Among other things, it was bored and honed, reconditioned rod set, valve job, set valve stem height, installed guide set... The PO paid around $2k for the work.
I really don't know what kind of cam is in there either. The engine looks mostly stock so it wasn't suped up to my knowledge.

 

Two points,,, the first is, if the engine has a warmer cam than stock, the vacumn will be lower than the specs published in the service manual, if this is the case you may be chasing an issue that is not an issue, or at least not the issue that is causing you greif...

The second point is that if the engine was rebuilt in 03 I think it is near about impossible for the rebuilder to have used nylon coated gears, this being the case, I am all but certain that your valve timing is ok... good news.... (where would anyone get nylon gears in 03 ???)

A third point that Ijust thought of,is that the carb or brake cleaner you use needs to be very flamable,,, use an arosol type of cleaner....

<<you do have good oil pressure right???>>

 

Timing chains can stretch, but with good quality new designs, it is very uncommon. As far as cam, yeah, my engine idles fine at 800rpm with 13" of manifold vacuum but if it had a cam, you'd hear a bumpy idle I imagine. They may have reused a stretched chain, or it looked ok and subsequently stretched and jumped a tooth on timing. Definately check your points and set them properly, if ignition is off then that could be a problem. Also, when it idles, if it idles kinda rough try whacking the carb body with the butt of a screwdriver, if the idle cleans up then you have trash in the carb and it needs a rebuild. Also what is your idle speed at?

 

Good point on the spray bottle, it must be an areosal type. I simply put seafoam carb cleaner in a hairspray bottle. Not nearly fine enough! Oil pressure seems fine. But is it normal for it to go up high when driving at various speeds? I know it's rpm driven, but my dial seems to fluctuate at times.

 

Oil pressure will rise with RPM, and drop with engine heat, that is ok, usually reading in the high end of the guage is good....

Low oil pressure could cause the lifters to collapse, and effect vacumn, but pressure is good, so not an issue...

 

Good question. My 66 Mustang is doing something very similar. The engine idles fine, but when you start driving it sputters, and then goes (most of the time). The sputtering seems to get better as it warms up. We're thinking the vacuum advance hose maybe too big, so I'm going to get a new one of those on. We think the timing may be off as well, so we're going to try and mess with that as well (hopefully get an electronic ignition soon). I'll follow this topic to see how you fix your problem. Who knows, it may work on mine too.

 

It's scary but I don't know how fast my engine runs ever! It's crazy by today's standards to not have a tach standard in the dash. Can you buy diagnostic tachs for not too much money? I'm not gonna put one in my car, but I'd like to have one I can slap on (however that is done, can someone enlighten me?) so I can set idle and such.

 

Dwell Meters / Tachometers used to be available at most any auto parts store, I have not seen one in a while, but I have not been looking either.. I imagine you can get one for a good price at AutoZone Etc. and Get a timing light,,,,