yeah i already had the rebuild it bug biting me in my neck, the poison spreading thru my body until it finally attacks and kills my wallet. lol
Its already on the list for later this summer, i was pulling motor anyway to put all new seals in it, and since i got it out i wanted to go ahead and swap out my tranny, then figured since that was out too i might as well tilt the front in and since i have that off i might as well put in new cab mounts and since i doing that i might as well sand blast the whole frame and reseal that and since i got it apart anyway i going to air bag it and switch out everything else and since i doing that well i might as well sand the body and paint it and finally since it is all apart anyway i might as well rewire the whole thing with a custom made painless wiring harness. whew !! talk about a project !, now not only do i have to do all that, now i gotta rebuild the engine too. "sigh " did i meation in the meantime i have to finish the building of the garage i want to do all this in ? lol
and i am perfectionist, i always figure i barely have the time to do it right the first time, and i damn sure dont have the time to fix it again later. so i want it perfect the first time. mightaswell commit myself to a rubber lined room somewhere lol

 

Just a thought, but--like 76supercab2 said there is some times a heatriser in the exhaust, if this stuck shut it could be causing some of the problems. Also with sticking with the simpler side, besides the cold passenger exhaust the symtoms kind discribe a timing chain problem. Good Luck buddy.

 

well if the compression test go well ( hoping ) i was thinking of replacing the timing chain, that has been on the back of my mind the last few days, and the only mightaswell that would come up is replacing the waterpump since it has to come off anyway and i got another one sitting on the bench anyway so mightaswell do it. oh no here comes the mightaswells afain lol

 

If the cylinder reads on the low side, do a "wet" test (squirt a small amount of oil in the cylinder and repeat compression test), if the pressure increases substantially,suspect bad rings or bore,other wise suspect bad valves and or seats....

 

Where did you hook up that new vacuum advance? I know the port on the carb is timed, so it doesn't advance at idle. I think they did this for emissions. This will make it sound rough. I always hook my gauge and vacuum advance up to actual manifold vacuum, and block off the port on the carb.

How's your PCV working?

If you have an air pump, this could explain the cold air coming out the exhaust?

You say you have the plugs gapped at 42. Do you have an aftermarket coil, or a stock one? I'd gap 'em at 32 and see what it does. Normally, if you go any bigger than about 35 you need an aftermarket coil. I'm thinking that it runs good on the freeway because the voltage is higher due to higher rpms, thereby allowing the coil to make enough voltage to get the spark through the gap. Accel makes a good aftermarket coil that I use on mine for about $25. You may consider picking one up.

I've had a problem with certain aftermarket replacement distributor caps and rotors, where the rotor was too small for the cap, and created too large an opening between the rotor and the cap. I'd check this, and if it's any more than about 1/16th of an inch, take it back and complain.

When was the last time you replaced points? I like to use the hollow point "blue streak" points, available at Car Quest. Be sure you replace the condenser when you replace the points. While you're in the parts store, get a dwell tach so you can accurately set them. They should be around 28-30 degrees of dwell. In a pinch you can use a match book to get 'em kind of set.

Good luck!

 

you have just made a ton of work for me kurt, #1 i think i will change the plugs back to 32, i have no idea why i set them at 42, total brain fart i guess. pcv is only about a month old and i checked the lines and they are fine, no air pump, and i havent replaced the points for a few months, i think i do need to set them again though.

like i said before she was running excellent before the back fire. the new carb and plugs were added after the back fire as well as the new exhaust. i havent had time to do a comporession check yet but i will get to that tommorow. thanks for all the ideas

 

"Where did you hook up that new vacuum advance? I know the port on the carb is timed, so it doesn't advance at idle. I think they did this for emissions. This will make it sound rough. I always hook my gauge and vacuum advance up to actual manifold vacuum, and block off the port on the carb."

It was not done for emissions. The ported vac on the carb is where vacuum advance is supposed to be hooked up, and always has been.

If you hook it to manifold vac, then you have max advance at idle, which decreases as you open the throttle. That's exactly backwards from the way it's supposed to be.

 

thats what i thought, i was sure i read that somewhere, i was looking it up before i replied to that part of it, thanks scroob

 

begining to sound familiar my first enigne rebuils started out as a valve job and kinda grew a lot

 

i once had a problem like that with a truck and found out that it was a valve by holding a dollar bill at the end of the tail pipe. if you have a bad valve the dollar bill will be sucked back in the pipe briefly. of course this will only work if it is an exhaust valve.

you may also have a a wiped cam lobe, hung lifter, or broke valve spring. the O ring from the exhaust is caused by reversion in the exhaust pipe. mabey you got one broke spring that needs to be replaced and that will solve the pob GOOD LUCK!

 

Bzzt. Wrong answer. Let me explain how vacuum advance works, and why.

Lighter, leaner mixtures, at part throttle and idle, are harder to ignite and burn slower. Therefore, more advance is needed to produce optimum engine output. Vacuum advance is the perfect solution, since at WOT you have very little, almost no vacuum in the manifold (with appropriately sized carb of course). The less dense the air in the manifold, the higher the vacuum. Now remember, the less dense the air / fuel, the longer it takes to burn, requiring more advance. Also, the way many carb's are set up, at part throttle the air / fuel mixture is leaner than at WOT. Leaner mixtures are also harder to ignite, also requiring more ignition advance. Again, the solution is vacuum advance.

Now the ported vacuum on the carb. This simply goes to a port slightly above the throttle plate. When the throttle is lifted off idle, the vacuum at the port shoots up to equal manifold vacuum. After this, it functions identically.

Ford was pressured to reduce NOx emissions. They wanted to reduce them at idle, so they needed to reduce cylinder pressures. How do you do this? Retard the ignition timing. Lower cylinder pressures directly relate to less NOx emissions. So they came up with timed vacuum for the vacuum advance, so that timing would be retarded at idle. Ignition retarded, NOx reduced, idle emissions test passed.

Now remember that leaner, less dense mixtures require more ignition advance. This applies at idle as much as part throttle. So, idle quality can be increased by running the vacuum advance straight to manifold vacuum, and blocking the port on the carb.

Sorry for the long post, but I had to make my point.

 

"Now remember that leaner, less dense mixtures require more ignition advance. This applies at idle as much as part throttle. So, idle quality can be increased by running the vacuum advance straight to manifold vacuum, and blocking the port on the carb"

So now you have a good idle and crap acceleration because of no vacuum advance.

I am sitting here right now looking at a Chilton's manual from 1969. On page 1352, when describing the Ford dual diaphragm vacuum advance distributor, here it what it says:

"The dual-diaphragm unit consists of two independently operating diaphragms. The advance (primary) diaphragm uses carburetor vacuum to advance ignition timing. The retard (secondary) diaphragm is activated by intake manifold vacuumwhcih provides additional timing retard during closed throttle deacceleration."

Most of the dual diaphragm units failed long ago, and were replaced with single diaphragm units. The proper place (as stated above) to connect the timing ADVANCE is to ported carb vacuum.

 

How is it going to have any vacuum to advance it with during acceleration? Where is it going to come from? At WOT, intake manifold vacuum = atmospheric pressure. Period. Where, I ask, are you going to get vacuum to actuate the vacuum advance at WOT?

Again, at WOT, you dont want vacuum advance because it would cause the engine to ping (if it was possible to have vacuum advance actuated at WOT, which it isnt). Centrifugal advance takes care of it there. You want increased vacuum advance to compensate for the leaner less dense mixture at part (or no) throttle.

 

well i found out today that when the engine was rebuilt 3 years ago they did a valve job and installed a new timeing chair, and they installed a cam that was from some kinda raceing package. the guy did not remember what the cam was though so i havent a clue. i went ahead and picked up a new timing chain kit, going to install that anyway since i was already planning on putting the new water pump on. i still havent had a chance to test the compression, i am sure to do that this weekend while i doing other stuff. i wouldnt think a valve job would go bad after only 3 years , the timing chain, i have seen them go quick. but i dont know, i will let you all know when i get it done this weekend., as for the vacumn advance i have it hooked to the carb. like i said the truck was running fine and full of power before the backfire, so i leave it there because that where it was then.

 

rusty70f100:

Vacuum advance is obtained from the carb port under acceleration by virtue of the air racing through the carb venturis. At the same time, the manifold vacuum drops, because opening the carb butterflies causes a "leak" in the vacuum that was built up.

You can verify this with a vacuum gauge.

Telling someone to hook the vacuum advance to a manifold port is just plain wrong. Any good car repair manual will tell you so - any good mechanic will tell you so. If you don't believe it, I suggest you go to any forum here (or on any other board) and ask.