Carb, timing and vacuum question

[jimlj66]

A bit of background
1966 Mustang, automatic transmission, 200 6 engine, 1100 carb. California car now living in Wyoming at 6800' elevation. Still has the smog pump (all working as far as I can tell)

After I got the car running it had a BAD dead spot right off of idle. When I say bad it would kill the engine if you didn't have a foot on the brake and one on the gas while starting out. I did a carb rebuild and that took care of the problem, although I still have a slight hesitation off of idle that you don't really notice while driving but if under the hood you can hear it when you rev the engine.

I don't know the exact carb I have. There is no SCV on this carb. The hole in the carb for it was never threaded or drilled for vacuum. There is no tag on the carb but it did have a sticker on it with some rebuild shop in Ca. that had worked on it at some time. The sticker was mostly gone so I don't even know the name of the shop.

I have no Vacuum at idle to the distributor, but as soon as I come off idle I do. The vacuum line is coming from a port on the side of the carb, not the manifold. Is this normal?

I set the timing with a timing light to 14* btdc and the car ran ok, but not what I think it should. I then adjusted the timing by ear and it seems a lot better. I have heard you should use a vacuum gauge to set the timing, can anyone enlighten me on how?

 

[rbohm]

8) since the timing marks on the dampner are not always accurate, since the dampner ring can and does rotate slightly as the dampner wears, you can set the timing by using a vacuum gauge. you want to get the highest vacuum reading you can. take the car out for a run, and if you get detonation, back the timing down a bit until it stops.

 

[LaGrasta]

I too am dealing with a bit of this. My Holley 1940 carb has no SCV and I'm wondering if it should. When revving the engine with the timing light attached, I should see the timing mark advance, correct? Mine does not.

 

[rbohm]

8) yes, you should see the timing marks change as you rev the engine

 

[fordconvert]

A 66 would have come with a Load O mattic distributor (or didnt the ca cars have them?). Seems like chances are good the carb was swapped at some point and maybe the distributor was not. What you are describing with the vacuum line would be a typical ported vacuum source which is often how the factory did the vacuum advance with non load o mattic distributors. If you have a standard distributor it should work fine but if you have a load o mattic we may be onto your problem. With the vacuum line unhooked from the distributor throw your timing light on it and rev it up. If the mark moves you have at least a partially working standard distributor. If the mark does not move you have a stuck standard distributor or a load o mattic. Without a SCV you need a standard distributor. If you have a Load O now would be a good time for a Duraspark or DUI upgrade.

 

[LaGrasta]

If you have a Load O now would be a good time for a Duraspark or DUI upgrade.

I guess this is where I'm at. All these years I've been driving like this. UGH!
DUI is my first choice but seeing I haven't worked in over a half year, that's out of the question by at least $300! Since I already own the Pertronix unit and I'm very happy with that, what is my option for a non LOM dizzy? Or do I get an SCV carb and call it a day?

 

[ozconv]

The dizzys starting in 68 and ending in I believe the early 70s when the DS1 came on the scene had both mechanical and vacuum advance. The one I am planning to use is from I believe a 72 mavrick. Pertronix makes a module for it but it is not the same as the one for the load-0-matic so you will have to get a new one.

 

[fordconvert]

You should be able to get everything for a Duraspark 2 conversion for under $200 from just about any parts store. Let us know if you need more details on this option. A rebuilt dizzy is around $70 from the couple places I looked online. Junkyard and Ebay are also options.

 

[jimlj66]

A 66 would have come with a Load O mattic distributor (or didnt the ca cars have them?). Seems like chances are good the carb was swapped at some point and maybe the distributor was not. What you are describing with the vacuum line would be a typical ported vacuum source which is often how the factory did the vacuum advance with non load o mattic distributors. If you have a standard distributor it should work fine but if you have a load o mattic we may be onto your problem. With the vacuum line unhooked from the distributor throw your timing light on it and rev it up. If the mark moves you have at least a partially working standard distributor. If the mark does not move you have a stuck standard distributor or a load o mattic. Without a SCV you need a standard distributor. If you have a Load O now would be a good time for a Duraspark or DUI upgrade.

Thanks for the help. Please bare with me as I am a dope on this end of things mechanical. If I understand correctly, the load o mattic has no mechanical advance and a standard distributor does? If I have a standard distributor, the ported vacuum I have is the correct way it should be? If I switch to a Duraspark distributor, do I want ported or manifold vacuum?

 

[fordconvert]

You got it. The Load O has no mechanical advance so thats why it needs a special vacuum source, the SCV. A standard dizzy has mechanical advance and then usually also a vacuum advance. There are also 'dual' advance where the vacuum can has a second port on it. These were used for some of the emissions zones and years. Unless you had a dual one to start with and want to or have to keep the stock setup for emissions testing just get the common single one. I have read you can use the dual one and just leave the extra port open. Anything after 67 (including the 70's durasparks) would have left the factory running off ported vacuum. Some years and emissions zones may have had thermal switches to switch between ported and manifold vac depending on coolant temp. Which one should you use? Try em both and see what you like. I like manifold vac on all my engines including my 6 with duraspark. Some folks find ported to work better. Basically ported vac gets shut off when the throttle is closed. After the throttle is open they are basically the same. Manifold vac would be the strongest when the throttle is closed so you would get the most advance at that point. As soon as you open the throttle vacuum drops so your timing gets retarded. The debate comes in because if you are on manifold you have full advance. If you are ported and you stomp the throttle you get a quick blip of vacuum but usually not enough to move the advance. You will be working just off the mechanical till the engine catches up and builds some vacuum. If you are on manifold you would be running fully advanced and then when you stomp the throttle there will be a delay as the vacuum bleeds down before its tracking correctly with actual vacuum. I dont think this is too big an issue with the 1bbls and stockish cams because they always maintain pretty good vacuum. Where it is likely a problem is more aggressive cams and large carbs because they tend to be weak at idle to begin with and when you open a huge carb you loose whatever vacuum you had so that transition could really become critical. It also depends on if you drink Coke or Pepsi and if you like cats or dogs. Then you have to factor in if you live on the odd side of the street and were born on an even year....... its quite simple really.

Try em both. I have never had good luck using the PCV line. On my 200 I have the 3/8 steel line that comes off the log. At the end of it I have a T that goes the brake booster, transmission, and distributor. Been working great for 3 years now. Engine and duraspark are stock along with the 1100 carb.

 

[CZLN6]

Howdy Jim and all:

If your '66 is a Calif Emmissions equiped car, then you have a point distributor with both mechanical and centrifugal advance. It is designed to use a ported vacuum source from the carb. At your elevation you will need to use at least 14 degrees of initial advance- 16 may be better. Being a "C/E" car it will be down on CR as compared to the non C/E engines. It will also have a specific Autolite 1100 with no port for SCV and less CFM, 150 as compared to 185 on SCV carbs. The smaller capacity carb and lower compression are not what you need at your elevation. The automatic trans, with its torque converter will help with off idle power somewhat, but likely not enough.

Vacuum tuning both the initial advance setting and the low speed air screw on the carb will help you get the most from the combo. Be sure to tune the initial advance with the vacuum advance line disconnected and plugged. As rpms go up be sure to readjust the idle speed back to about 700 rpm. One you've achieve the highest vacuum setting with the least amount of advance, reconnect the vacuum line and move to the low speed air screw. Start by turning it in until the engine stumble, then slowly back it out until you achieve the highest idle rpm. Find the spot where the idle speed no longer increases and top there. Be sure to reduce the idle speed back to about 700 rpm.

Unfortunately, converting to a DS II will not significantly help with your power issues, since your stock distributor already has centrifugal advance. Getting away from points will reduce maintainance, but that can be adressed with a simple, and cheaper, Petronix Ignitor conversion. You engine has a large dish piston to reduce CR. Re-establishing a CR of 9:1, as opposed to the C/E 8:1 will be your biggest helper.

Keep us posted on your choices and your progress.

Adios, David

 

[LaGrasta]

I installed a SCV into my 1940 carb and the timing now advances when revving the motor. I retimed everything and have yet to take it on a long drive to really test the overheat situation. It makes sense that it will as the car will now have the correct timing at freeway speeds. I'll update again after I get a 20 miles drive in.