Is the vacuum advance active at idle? The supplied vacuum come from the charcol/carbon/evap cannister. The advance works i checked and watched distributor move when under human vacuum .My timing is way off and the distributor is adjusted to the max. i checked mechanical timing and all looks good, Its all very confusing when it comes to charcol cannister. car starts and idles fine but sometime loses power while slowing and taking a turn. I can adjust timing when i run line directly from manifold to vacuum advanced port. its all very frustrating..
1976 vacuum advance at idle (800 rpm~)
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distributer uses ported vacuum so should be non existent when throttle plate is closed (idle). the timing should be set with a timing light, about 10 degrees BTDC at 800. This should happen with the ported vacuum line connected (remember no vacuum at 800 rpm) and the distributer set in about the middle of its range (see the slotted mount for the distributer). If you have to resort to extreme measure to get this to happen you may have a mis aligned dist drive shaft. check the FSM for how this should look, you will need to remove the distributer and look at the drive tang to make sure its aligned properly. while you are at it confirm the plug wires on the correct location on the distributer cap.
here are photos of my engine @800rpm~ distributor is all the way in one direction and tdc mark is off.
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so moving the distributer to the middle pushes that TDC mark even further off the scale correct?
You should check to make sure your TCC marking are actually correct, use something to slip down the #1 plug hole, something that will allow you to actually see the piston coming up on TDC like s plastic straw. Put a wrench on the crank nut and rock it back and fro to see if the TDC is correct to the markings. Its possible the flywheel damper notch is incorrect.
IF the TDC ,markings are correct you should check the dizzy drive per the FSM, should be set to approx. 11:30, the FSM will explain this.
You should check to make sure your TCC marking are actually correct, use something to slip down the #1 plug hole, something that will allow you to actually see the piston coming up on TDC like s plastic straw. Put a wrench on the crank nut and rock it back and fro to see if the TDC is correct to the markings. Its possible the flywheel damper notch is incorrect.
IF the TDC ,markings are correct you should check the dizzy drive per the FSM, should be set to approx. 11:30, the FSM will explain this.
yes moving to middle makes it worse. the timing mark you see was created when i adjusted cylinder 1 to tdc. there were no factory marks that i could see. rotor pointing to piston 1. I removed the valve cover and the (-) and the (v) were correct. -v not v-. ive notice there is no ported vacuum coming from the charcol filter which feeds the distributor. i know i can adjust timing when i apply direct manifold vacuum to advanced vaccum on distributor. Im not sure if that's the way to go. T off manifold to feed distributor. or do i have a bad charcol cannister?
also i checked the camshaft and cylinder 1 had "rabbit ears" measured clearance under inlet and exhaust feeler gauge moved freely i think that indicates valves are closed.
i thought that was a fixed position and keyed from the oil pump. could there be that much slop to cause a change in the timing?
You are assuming the oil pump shaft is installed correctly. that is not a good assumption. It is easy to get off a tooth when installing the pump shaft/dissy drive shaft when re installing said shaft. The spiral cut gears can be a bit of a challenge to nail it right the 1st time. To check you need to confirm the drive to the dizzy is set to 11:30 when looking at it with the dizzy off. This is at TDC. another trick to check is to use a screw driver and hold it over the opening where the dizzy stabs in, align it with the drive tang, the screw driver should NOT align with the mount holes but rather be off set so it falls on the side of the holes. Hard to explain, I may have a video, but you can see it in the FSM.
i think ill take a closer look to see if i can find factory timing mark and hoping they are close to the one i created. im also going to lift off dizzy and make sure it is keyed correctly if not ill drop oil pump and jimmy it around to get correct. if all good then ill have to live with it. thx again dave for your input it's been very helpful..I ordered new charcol can. i know it dosent effect idle but im getting no advance vacuum at any rpm to the dizzy..
for fun I did the following test.
vacuum gauge to large hose on canister from intake manifold, engine idles, normal vacuum about 17in Hg
vacuum gauge to small hose on cansiter (ported vacuum) no vacuum some vacuum while blipping throttle, momentary and less that intake vacuum.
vacuum hose on bottom of canister (I am using a non stock canister from a later model Nissan, rather that being open on the bottom it is sealed with a LARGE port that allows atmosphere into the bottom. function is the same, just a smaller hole vs a large opening.
no vacuum at all until I blip the throttle. then a small steady vacuum, blip it again, still more, I presume I was pulling a vacuum and it was slowly creating a vacuum inside the canister and I presume the fuel tank. I did not try removing the tank filler cap, that should have relieved the vacuum, it was not much, prob not enough to trigger the tank cap vent, maybe if I had kept at it but really I just wanted to see the system working (and it clearly does). Pretty neat system to capture gas fumes store in charcoal, then retrieve and burn when the engine is running and the throttle is applied. all mechanical with no computer to go bad.
vacuum gauge to large hose on canister from intake manifold, engine idles, normal vacuum about 17in Hg
vacuum gauge to small hose on cansiter (ported vacuum) no vacuum some vacuum while blipping throttle, momentary and less that intake vacuum.
vacuum hose on bottom of canister (I am using a non stock canister from a later model Nissan, rather that being open on the bottom it is sealed with a LARGE port that allows atmosphere into the bottom. function is the same, just a smaller hole vs a large opening.
no vacuum at all until I blip the throttle. then a small steady vacuum, blip it again, still more, I presume I was pulling a vacuum and it was slowly creating a vacuum inside the canister and I presume the fuel tank. I did not try removing the tank filler cap, that should have relieved the vacuum, it was not much, prob not enough to trigger the tank cap vent, maybe if I had kept at it but really I just wanted to see the system working (and it clearly does). Pretty neat system to capture gas fumes store in charcoal, then retrieve and burn when the engine is running and the throttle is applied. all mechanical with no computer to go bad.
it sounds like the advanced vacuum is created by a venturi effect created in the charcol canister pulling fumes from the gas tank, doesn't seem like it would create enough vacuum to advance vacuum mechanism in the distributor..
here a photo of the distributer key location at top dead center. it looks like it might be ok.
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The vacuum source is always from the intake manifold, not from the charcoal cannister. The small dizzy hose is supposed to hook up to secondary vacuum which it sounds like your cannister hose is set up the correct way. The larger hose to the canister is hooked to primary vacuum. Secondary vacuum is once the throttle valve has started to open. If your crank pulley is accurate and it's set at TDC then your dizzy driveshaft is off 1 tooth. The center of the shaft in your pic looks to be about 12:30 and it should be at 11:30 for TDC. Double check your crank pulley in relation to your piston travel on #1 like someone mentioned earlier and go from there. If your crank pulley has slipped then it needs to be rebuilt. One of my vendors rebuilds just about any kind of crank pulley and does a perfect job every time. I've been using them for about 15 years. I try to carry most of the crank pulleys in stock as much as I can. If you need a crank pulley contact me directly at 360-668-2979 or [email protected] and be sure to let me know that you use this specific forum for a discount. Z man of Washington
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