Weird timing/ignition issue

[improbcat]

I've been fiddling with my Comet trying to get it running better and am having the oddest problems. I apologize that this is long-winded, but I'm trying to not miss anything.

It had a miss above idle that I couldn't seem to even locate, and generally ran a bit rough (the car shakes slightly at idle in or out of gear). All the plugs looked the same, and pulling any of the plug wires caused the same effect in the engine. It was suggested I might have a bad distributor (plus I had one of the obnoxious ones with the extra vacuum port for emissions). So I ordered a Cardone rebuilt unit.

When it arrived, I noticed it had about the same play in the shaft as the old unit (about 1mm vertically, and just enough horizontal to feel, but not enough to be able to measure with my calipers). It also has points where my old one had a Pertronix unit. I figured I'd stab it in anyway and give it a try.

I disconnected the vacuum to the advance on the distributor and used a vacuum gauge to set the timing (is about 10deg at a guess, can check if it is relevant. At the best I am getting 18-18.5Hg on the vacuum gauge at best and fluctuates less that 1Hg at idle. It responds the way a "healthy" engine should according to the vacuum diagnostics I found online. The misfire seems to be gone, but the engine/car still shakes slightly at idle.

When it gets *really* weird is when I re-connect the vacuum to the distributor, the engine immediately starts running noticeably rougher, and the vacuum gauge varies erratically between 18-21Hg. It sounds like there is suddenly a misfire and when revved it also sounds like it isn't running properly. I'm baffled as to how connecting vacuum to the vacuum advance could cause this.

So my questions:
Should the vacuum advance be connected to manifold vacuum, or to the port on the carb that doesn't have vacuum at idle?
Does this sound like a distributor problem, or elsewhere?
In general, anyone got any guesses as to what is happening?

EDIT: The engine is a 200ci out of a '71 Maverick. I just realized I failed to mention that.

P.S. Mustang1966, I haven't had the time/money to bring it to the shop you recommended, that is the next step if I can't figure this out.

 

[Explorer]

Hook the dizzy to ported vacuum and see what happens. Using manifold vacuum will automatically advance the timing soon as hooked up. While that is acceptable in some situations, I believe you need the ported vac.

 

[Lazy JW]

The diaphragm in the vacuum advance unit "may" be ruptured, causing a bit of a vacuum leak.
Joe

 

[improbcat]

Hook the dizzy to ported vacuum and see what happens. Using manifold vacuum will automatically advance the timing soon as hooked up. While that is acceptable in some situations, I believe you need the ported vac.

Huh, Hadn't thought of it that way, I'd figured it needed full vacuum to keep from advancing, I guess I got it backwards. I'll hook it up to ported vacuum tomorrow and try that.

The diaphragm in the vacuum advance unit "may" be ruptured, causing a bit of a vacuum leak.
Joe

Maybe. What is part of the weirdness is it actually runs better with the vacuum line to the distributor just unhooked and open than when it's attached to the distributor. Going to try hooking it to ported vacuum like explorer recommended and see where that gets me.

 

[Lazy JW]

I just re-read your original post and realized I skimmed through too rapidly the first time; you mentioned that you already have purchased a rebuilt distributor so it seems unlikely that the diaphragm would be bad.

Does the new distributor have two vacuum cans or did you purchase the "single advance" type?

Are you using the 71 carburetor? If so, ported vacuum is probably what you want to use.
Joe

 

[improbcat]

Does the new distributor have two vacuum cans or did you purchase the "single advance" type?

It is described as a "A-1 CARDONE Part # 302613 Point Type; w/Single Vacuum" and looks like this:

It looks just like the dual vacuum one i pulled out except with one less fitting for a vacuum line on the top of the advance.

 

[Lazy JW]

That unit should do fine. Carefully inspect the breaker cam; all of the lobes need to be smooth and uniform. The points need to be correctly adjusted and meeting square at the contacts; the coil must be connected with correct polarity (negative to the points).

Make sure the choke opens properly and the heat riser is correct. Also the PCV system.

Get it hooked to ported vacuum, re-set the timing, adjust the carb, then let us know what happens.
Have fun,
Joe

 

[Explorer]

The rear port was to retard timing for starting. Front port to advance timing. If you have your initial timing already set with vac lines plugged to carb, go on and hook up the ported vac. I fool with the Duraspark a lot on V8's, but never on a six and their diff carb setups. Waiting to see how it works.

 

[improbcat]

The results of today's fiddling:

First off, I found out my left motor mount has gone bad *again*, so ignore all previous comments about the engine shaking.

I connected the distributor to port vacuum, adjusted the idle mix screw and set the timing(in gear). I get the best vacuum at 12deg, but it only goes down 1 Hg at 10deg. I also threw a new set of plugs in as I had them handy, the old ones looked ok with only a slightly brown coating on the porcelain.

The engine is running relatively smoothly at idle, but above idle it starts to have a miss, that seems to get worse as the RPMs increase. the vacuum fluctuates about 1-2Hg in time with the misfire. The misfire seems *slightly* worse when the advance was hooked up than with out it, but not much.

 

[rbohm]

8) i think your ignition problem is a bad coil. but i also think you might have a carburetion or other fuel system issue as well.

 

[FalconSedanDelivery]

Unlike most here ( I 'll get flack for this but had to jump in on this one ) that think recurving a dist is buying a mr gasket 925d spring set and bending a tang , ive seen the thread on how to recurve a duraspark ( Ive done Hundreds of Dists ) and its a good artical , but Ive seen books on many things and read them, dosent make me an expert on most things but on Dists I am ,See the problem with most passed around info is that knowing What to do is NOT the same as knowing why your doing it, ok enough rambling , The Vacuum canister is allowing TOO much vacuum advance , Regardless if its hooked to ported or manifold vacuum source , ( although ported IS the 99 percent correct place ) ok here comes the flack again , LOL , if yours is like the unit pictured it is adjustable , How do I adjust it , insert a small allen wrench in the vacuum hose hole and turn it to , oh thats right unless you have the equipment AND BOTH the knowledge of How and WHY, It won't be right sorry other than telling you its not adjusted right and saying how , is as far as I am willing teach anyone on a forum.Why?It takes longer than I'm willing to type ( Years ) suffice to say that Reman units that you buy are rebult NOT taylored to any particular combo, I do it for a living I know this for a fact , please dont throw money away on a coil , or other componets , when what you need is your Dist Recurved.

 

[Frankenstang]

I was reading your post, and had not noticed what carburetor you are running?

EDIT: Are you sure that is not a pre 68 load-o-matic dizzy? My point is that carb & dizzy matching or mismatching could be an issue.

If it is a load-o, you'll have to have an SCV carb to give it a proper ported vacuum signal, and you mentioned that your engine is from a '71 Mav, and the old dizzy had two connections for vacuum which makes me think you don't have an SCV carb...which would mean that replacement dizzy (if it's a pre '68 load-o) is wrong for your setup.
Just my $.02

 

[Explorer]

Unlike most here ( I 'll get flack for this but had to jump in on this one ) that think recurving a dist is buying a mr gasket 925d spring set and bending a tang , ive seen the thread on how to recurve a duraspark ( Ive done Hundreds of Dists ) and its a good artical , but Ive seen books on many things and read them, dosent make me an expert on most things but on Dists I am ,See the problem with most passed around info is that knowing What to do is NOT the same as knowing why your doing it, ok enough rambling , The Vacuum canister is allowing TOO much vacuum advance , Regardless if its hooked to ported or manifold vacuum source , ( although ported IS the 99 percent correct place ) ok here comes the flack again , LOL , if yours is like the unit pictured it is adjustable , How do I adjust it , insert a small allen wrench in the vacuum hose hole and turn it to , oh thats right unless you have the equipment AND BOTH the knowledge of How and WHY, It won't be right sorry other than telling you its not adjusted right and saying how , is as far as I am willing teach anyone on a forum.Why?It takes longer than I'm willing to type ( Years ) suffice to say that Reman units that you buy are rebult NOT taylored to any particular combo, I do it for a living I know this for a fact , please dont throw money away on a coil , or other componets , when what you need is your Dist Recurved.

No flack from me, totally agree. My problem lies with remembering that not all people are running a Duraspark so point gap and dwell come into play with older style dizzy's.

 

[JackFish]

I'm not sure about your specific dizzy, but on the ds2, there are two options inside the distibutor for initial timing advance. Typically 13 or 18 degrees of advance, IIRC. Without tearing it apart you have no way of knowing which one was used by the rebuilder.

 

[FalconSedanDelivery]

In the Dist in Question , he comments that it runs better with the Vac unhooked , that points to an overadvancing of the timing ( Dwell and gap not withstanding ) , I have seen canisters ( Vac adv ) try to pull in anditional 30 degrees ( Dist degrees ) X 2 for crank = 60 , altough most pull in 8-20 , and that varies on the vacuum strengh applied,many things come into play , and to respond to another post above , there are at least 6 different dist cams for the Falcon 6 , some as little as 8 some as high as 20 , and combos inbetween , the rebuilders put in new bushings and other wear Items , but the curve , good luck , even aftermarket Dists need Recurved , there is NO One fits all setup , That why I am serious when I post , No its Not Rocket Science , BUT it does take Experience and tools ( I have 3 Sun Dist Machines at my Shop ) I wish him well

 

[Lazy JW]

....

No its Not Rocket Science , BUT it does take Experience and tools ( I have 3 Sun Dist Machines at my Shop ) I wish him well

I certainly envy your equipment and experience, and there is no doubt in my mind that your method is the best way to set up a distributor, followed up, of course, with rigorous dyno testing.

Myself having been born on the "other" side of the tracks, none of the above is gonna happen Be that as it may, I have been able to stumble along through life's school of hard knocks, and while I have made my share of mistakes along the way I have always been able to achieve results that have satisfied me even though I most assuredly did not wring the final ounce of power from my vehicles. And yet life goes on.

I am confident that the overwhelming majority of members on this forum are in the same boat as I; what we need is mutual support and workable solutions that the average motorhead can use to accomplish our modest goal, which is primarily to enjoy our vintage machines.
Joe

 

[66200i6]

Looks like it is time to start taking some measurments. With and with out vacuum advance connected to the distributor. Ask for some help from another backyard mechcanic and hook up your timing light and tach. Put together some scratch paper with a table of reading that you will be taking note of. With the vac advance disconnected and pluged run the engine while reading your timing. Start with "Stactic" reading or idel and then take readings at 500, 1000, 1500, 2000, ect. Up to the point of where you will be running. Next, use manifold vacuum source (just cause it can be read at idle) and connect to your distributor and run the same set of readings.

Now that you have this in your pocket you can tell what is going on. If the advance is indeed too high you will see it in your notes. Once its dialed in you can decide if you what your vacuum advance to be active at Idel or not (Ported inactive, Manifold active).

Have fun, Ric.

 

[Mercury Mike]

I certainly envy your equipment and experience, and there is no doubt in my mind that your method is the best way to set up a distributor, followed up, of course, with rigorous dyno testing.

Myself having been born on the "other" side of the tracks, none of the above is gonna happen Be that as it may, I have been able to stumble along through life's school of hard knocks, and while I have made my share of mistakes along the way I have always been able to achieve results that have satisfied me even though I most assuredly did not wring the final ounce of power from my vehicles. And yet life goes on.

I am confident that the overwhelming majority of members on this forum are in the same boat as I; what we need is mutual support and workable solutions that the average motorhead can use to accomplish our modest goal, which is primarily to enjoy our vintage machines.
Joe

Wow, Joe. There's a reason I always read your posts twice. =)

 

[The Plankster Prankster]

First off, I found out my left motor mount has gone bad *again*, so ignore all previous comments about the engine shaking.

when i was having problems with mounts, i took a brand new one, removed the reinforcing pin, and replaced it with a 1/2" grade 8 bolt with a locknut. there was a little trouble getting the bolthead to sit flush so it wasn't holding the mount off the perch, but worked it out and never had another problem

 

[improbcat]

First off, I found out my left motor mount has gone bad *again*, so ignore all previous comments about the engine shaking.

when i was having problems with mounts, i took a brand new one, removed the reinforcing pin, and replaced it with a 1/2" grade 8 bolt with a locknut. there was a little trouble getting the bolthead to sit flush so it wasn't holding the mount off the perch, but worked it out and never had another problem

That is my plan. I've basically been waiting for it to fail again to see if I needed to do this.