Spark advance valve / vacuum question

[Anonymous]

The 66 inline mustang I recently purchased has an 1100 one barrel. The spark advance valve is not on the carb, and the vacuum line from the distributor to the car is non existent... The car has run consistently fine up until just recently when i posted about not getting any fuel into the carb (it gushes out of the line at the carb,but no flow into the throat).. My question is, is it safe to assume the dizzy the prev. owner put in is probably a later model such as a Duraspark?... Today I bought a rebuild kit for the carb. Do I need to find a spark advance valve and / or reconnect a new vacuum line from the dizzy to the carb, even though it ran fine before??... Im wondering whether to leave it as it was when i bought it

 

[BIGREDRASA]

If you can get it running without blowing up, rev the engine and check to see if the timing advances without the vacuum line. If it advances, then you have centrifugal advance, and it is a later model dizzy. That's for starters.

 

[cdherman]

Later 1100 carbs without the spark advance valve cannot be retrofitted with the valve without majot work. The casting will still have a hole, into which the spark advance valve would have been threaded. But the casting is raw, no threads etc. The internal passages are not drilled out either. According to ponycarbs, the later carb can be retrofitted by them, but major complicated.

And why bother, when so many other options exist? If the current distributor cap looks like a standard one, as opposed to the later duraspark which is distinctively larger, and "flatter", then you hopefully have a dual advance (vac and mechanical) distributor.

The dual advance dizzy that was used between after loadomatics is often referred to as a "thermactor" dizzy, as it arrived on the scene at the same time as the thermactor polution pump. They actually do not seem to have anything to do with one another, as far as I know. Just date of arrival.

If you pop the top off the dizzy, pull off the rotor (don't worry, it goes on only one way), you will see the top of the shaft. If its solid and sort of "D" shaped, then that would be the old loadomatic dizzy, which has only vacuum advance. The later dizzy will have a hollow, or "C" shaped shaft. You will find that the later C shaped shaft has some rotation in one direction (more than just your worn camshaft gear!!) That rotation is actually about 20 degrees and is the shaft rotating in the mechanical advance mechanism. It goes one way only, and springs back (springs are in there to counter the weights).

Hope this helps.

 

[Anonymous]

cdherman,

thanks...I will identify the dizzy tomorrow after my carb rebuild. Your advice on how to tell the difference was extremely helpful, I didnt know how to tell for sure..

 

[Anonymous]

Well, I couldnt wait till tomorrow...I checked my dizzy and the shaft is the solid "D" shape, which tells me its the old Load O matic...The carb has the "raw" advance spark hole with no threads....Now I get confused on this sometimes, but that means since it isnt an original 1100 carb (it's a Holley rebuild),with no supplied spark advance valve that is why the load o matic dizzy has been working fine with this carb like the prev. owner sold it to me ...?? does my question make sense?....If I had an original carb that actually had the advance spark valve, I would definitely had to have had the vacuum line hooked up from the dizzy to the carb,, yes? [/i]

 

[BIGREDRASA]

What it means is that your dizzy is not able to give you any advance. You will therefor improve your performance by finding a later model dizzy, maybe one of the later model electronic units, such as the Duraspark. If you do a search in this forum, you'll find lots of info on the transplant.

 

[Anonymous]

Ok, how about a Pertronix unit ?.....Would that be as beneficial as a Duraspark.?..... I cant find a 77-79 Duraspark for a Ford any where around here at the auto parts stores... I do have a buddy at a salvage yard, but if I get a Dura dizzy from a salvager, how reliable are they, relatively speaking, I know anything can be a lemon

 

[BIGREDRASA]

The Pertronix will only serve to replace the points. It will not do anything for your advance. Even a used dual advance dizzy with the Pertronix I or II should work better than what you have now. If you find a used dizzy, wiggle the shaft. If you can wiggle the shaft noticeably, the dizzy is worn out; otherwise, clean it up, oil it, and drop it in.

 

[Anonymous]

Cool... Thanks Tony

 

[cdherman]

The only advantage of the stock "thermactor" dizzy which will have mechanical and vacuum advance, is that it will look more original. By dropping in the Pertronix, you will have a pretty nice, stock looking electronic ignition setup. The duraspark setep is really good, relaible, and relatively cheap. But has more wires, an external box that needs mounting on the firewall, a larger, different looking distributor cap.

For my tastes, I went with the dual advance old style dizzy with Pertronix. But I like stock look in my truck.

Whatever you do, you will be better than having no spark advance at all, which is what you now have. Is the vacuum port on the carb plugged or blocked with something? Hope so, or you have had a nasty vacuum leak all this time too!!!!

 

[Anonymous]

Hey cdherman,

Well, the input where a spark advance valve would could is "raw"..it's there, but has no threads, so this is a later version of a Ford/Holley rebuilt 1100.....Now the vacuum advance - it has some sort of brass cap, or nipple shoved in there sideways..I gotta figure out how to pry it out, 'cause I sure cant figure out why whomever had it before me did this.
...And I am buying the Pertronix unit and an ignitor coil to go with it today

 

[Anonymous]

66Inlinestang,
Are you buying a new or different model distributor? I would not sink any more money into the loadamatic unless you absolutely want to retain the stock distributor. Odds are that even if you had it hooked up to a vacuum source, the diaphram in the vacuum can is likely leaking due to its age.
A later model distributor is much better, and easier to tune.
Doug

 

[Anonymous]

I guess my biggest problem in confusing myself is this...The distributor in the car now didnt have the vacuum line attatched to the 1100...in fact, the prev. owner cut it, it still has some length of vacuum hose he just laid over and shoved into the grill....I think i posted the fact that the car actually ran really well with it the way it is...Then my fuel flow stopped at the inlet into the carb... The distributor does have the solid shaft with a "D" shape... So, because the person I got the car from apparantly cut the vacuum away, and looks to me like he shoved something into the vacuum inlet at the carb, would that eliminate the dizzy being a load o matic ?...I should have had major idling, response issues...??? which i did not...

 

[Anonymous]

If it is a Loadamatic distributor, by disconnecting the distributor and plugging the ports, there is no means for the spark to advance with increasing engine rpm. Your engines response will be slower on acceleration and you may experience coolant temperature issues. With the distributor isolated, it is possible to advance the static timing such that you get a decent idle even without the vacuum advance contributing. And you can find an initial timing setting where the engine will idle and actually accelerate without pinging. However, engine response and fuel economy will not be anything near optimum. Without a functioning advance mechanism, the initial spark advance setting will work over a limited engine rpm range, top end acceleration will be very flat. As an example, the Briggs & Stratton Lawn mower engines do not have any provisions to advance the spark advance. However, the engine rpm is relatively low, something like 1800 rpm.

At this point, you need to get some sort of distributor hooked up with a functioning spark advance mechanism. Installing a Pertronix kit on it before making sure the distributor advance is functional may be a waste of money and a disappointment. A rebuilt distributor from Autozone for a 67 or 68 mustang will be very cheap.

 

[Anonymous]

Ok... Thank you very much for that advice...I think i was trying to get around a potential problem, and was probably going to magnify it...I will do that, upgrade the distributor so I can be sure of what I've got, and go on from there... Thanks again, advice well taken

 

[Anonymous]

Flat top end is my big symptom. I've got a '67 Load-o-Matic (verified last night). Trying to sort out dizzy swap stuff. Anyway, my advance works, theoretically. I pop the cap, suck on the the vac line and the advance moves. Could I have a vac leak at the carby? Would bad plug wires or coil exhibit similar symptoms?

Trying to get the stock set-up running right as a baseline before swapping parts. Otherwise, I could be chasing existing problems while trying to tune new parts.

Sorry to be threadjacking.

--mikey

 

[Anonymous]

66 Inlinestang, I was in error about using 67 distributor. You need the '68 and later distributor which is not the loadamatic.

Mickey, I would think that a bad coil or plug wires would manifest themselves as a miss at idle and or a break-up of the ignition system at higher rpms with multiple missed firings.

If you have the loadamatic, you must have the carb with a provision for the spark advance port for the loadamatic to function as designed. It also must have a functioning spark control valve. See Jack Collins post at the top of this forum for a good explanation.

A vacuum gauge would tell you if you have decent vaccum at idle, enough to function the vacuum advance at idle. Even if it is not leaking, the diaphram could be old and stiff, and not providing the proper amount advance. A dial-back timing light would show you how much total advance you are getting at say 3000 rpm. I do not have my shop manual handy where I could tell you what kind of advance the loadamatic should provide.

And as a reality check, the stock 6 cyl engine has a relatively flat top end response anyway; a better distributor may not improve that situation. But if you replace a non-functioning distributor with one that is working properly, you should see quite an improvement in the engine's pep.
Doug

 

[Lazy JW]

.... Without a functioning advance mechanism, the initial spark advance setting will work over a limited engine rpm range, top end acceleration will be very flat. As an example, the Briggs & Stratton Lawn mower engines do not have any provisions to advance the spark advance. However, the engine rpm is relatively low, something like 1800 rpm....

Actually, the little Briggs engines routinely run well over 3000 rpm. However, they could improve performance with some sort of spark advance. We used to gap the points wider for better top speed on mini-bikes, but they develop a nasty tendancy to kick-back when you pull the starter rope. Most older tractors with magneto ignition had no spark advance mechanism, but they usually ran at low speeds. They did use an impulse device that also retarded the spark while cranking to keep from breaking your arm.
Joe