Have you checked the timing?

Jeff20b: Using the vac advance can really increase low end torque if you connect it to the proper source (ported vacuum, not manifold). I suggest you give it a shot, I think you'll like it.

 

While I have your attention, which tube on the carb spacer have you found to work for you?

 

OK, so I replaced the busted diaphragm, and routed the vacuum lines as the factory manual shows. My distributor is advanced as much as possible on the rotation, and my adjustable diaphragm is pulled all the way out, so the car is advanced as much as possible.

The car is completely normal, then when i hit around 3500 rpm i feel a slight sputter, After 4500 rpm Its noticeable. Sometimes it seems the car is misfiring, but then other times it will rev to 5500 rpm just fine. I am fixing to run dual inline fuel filters, so i can see the fuel going into the carburetor.

I'm open to all suggestions as i don't know how to set time, but am eager to solve my problem. thanks again everyone.

 

I ran the two fuel filters to the carb, and they show clean gas going in. and they show a good amount of gas going in. could it be a simple spark plug problem? Then why would it only sputter in some ranges under certain load? THIS ISSUE is eating me alive, because the car has so much potential I can't access. ):

Thanks again for everyones thoughts!

 

I believe it was the furthest one forward on the base of the carb. I'll double check when I get home tonight, but I'm pretty sure it was that one.

If not that one, then the next one back.

 

Why do you have the timing so far advanced? Was this set with a timing light?

When it starts to break up, are you hearing any noises (like marbles rattling around in a coffee can)? If so, that is an indication of spark knock/detonation, which means that you are too far advanced.

You really need a timing light to get it set correctly, and this would defiinitely cause your issues if set improperly. Old timers can set the timing by sound/feel, but that takes a lot of experience to get it right.

Do you have a timing light?

 

I do hear marbles!!! haha I like you kentetsu. And i don't have one. are they easy to use? literally when i try and make the car rev it sounds like the marbles and i avoid that always,because it sounds like it might be damaging. how do you generally set time on the 12a?

 

With a timing light. Can you borrow one? Or buy one, they're about 50 bucks for a nice one.

For now, try retarding the timing until you reach a point where you no longer hear marbles, and are no longer breaking up. If you are not able to get to a "happy place" with the timing, then go over everything and make sure the wires are all going where they are supposed to be.

One thing you should probably do is unplug the leading ignitor, then confirm that you no longer have spark on the leading plugs. This will verify that each ignitor is firing the system it is supposed to. While it may sound unlikely that your ignition could be reversed, it happens more often that you would believe.

 

Ok so after I posted I retarded the adjustable vacuum advance completely and it helped alot. My revs are just about to 5k without sputters, I haven't really spent time on the distributor angle, but i'm guessing there needs to be a close balance between both.
I appreciate the advice everyone, it seems i almost have my issue resolved. So i need to make sure i'm firing in sequence by pulling the lead igniter and checking the leading spark plugs(bottom?) I will have to ask some friends if they have timing lights. thank you everyone.(:

 

Adjusting the vacuum advance: you can only do that with the trailing vacuum pod.

What you need to do is turn the distributor, but just find a timing light first and it will make everything much easier...

 

ok, A friend of mine has a timing light, i have never used one, but he popped my hood and saw a tick on my front plate, but nothing on my pulley. he said we need two ticks or marks. whats up? Thanks again everyone.

 

The two marks are hard to see. Look with a flashlight while the engine is not running. You may have to bump the starter a little until the side of the pulley with the marks is visible. Once you find the notches put a dab of paint or fingernail polish on them. The mark closest to the driver side is for the leading ignition. You adjust by loosening the bolt at the base of the distributor and turning the distributor until the mark lines up with the pointer on the front cover. The trailing ignition is the adjusted by loosening the screw on the adjustable vacuum advance pod and moving the pod out or in until the second mark lines up. Timing light should be hooked up to L1 plug wire for leading and T1 plug wire for trailing.

From the 85 FSM.

 

Ok thanks guys, I will look a little harder with my shop light and see if i can figure this thing out. I will keep all posted.

 

Not to rant on ALWAYSWANTRX7's parade...but what if I'm having the same issue he is...only my timing is perfect? I also do not have the 'marble' rattling sound, just terrible misfire/stumbling at full throttle and also anything over 4k.

Fuel filters are new, pump is not. New cap, rotor, wires, plugs, coils, battery, grounds......

Maybe it's one of the carburetor related devices such as the shutter valve?

 

Go through the same troubleshooting steps we have provided the original poster. Probably start your own thread so that you can report on the results of each step...