H8tnBS

Okay, so I bought a new HEI vacuum advance distributor. I didn't hook the vacuum up first since that's optional..it's an adjustable one. I have a digital timing light... set the timing perfectly. Brand new spark plugs and wires. My timing jumps when you give it gas. It doesn't retard at all, it only advances. My biggest issue is when I take it on the interstate and hit 3500 rpms, the timing advances way off the mark by 20 or so. I tried switching it to vacuum and it's worse. I have been wracking my brain tryin to figure out why I set it to the mark and the timing is perfect driving around town but get on the interstate and it's out of control...

InfernalVortex

iTrader: (4)

Are you saying it doesnt fall back to base timing?

If it gets stuck in an advanced position you probably just need to try to lubricate or loosen up the mechanical advance mechanism somehow. Just make sure it moves easily when you try to manipulate it by hand.

Seven_MPG

Are you running a carb?

ex-x-fire

Is there a one way vacuum valve where you hooked up the advance?

Damon

So even if you are only running on the centrifugal advance (vacuum advance is disconnected) it advances when the RPMs come up but doesn't fall back to the original setting when you drop back down to idle speed? Do I have that right?

sofakingdom

iTrader: (1)

It's SUPPOSED TO advance as RPMs increase.

With it sitting in the driveway and the vac disconnected from it, it should be at the "base" timing at low RPMs. Then if you slowly open the throttle and bring up the RPMs, as it passes some certain threshold (1200 RPM is usually a good starting point for a street setup) the timing should begin to advance. As the RPMs continue to climb, so should the timing. When the RPMs reach the "full power" range (2700 - 3000 RPM or so) it should reach its maximum value. As you open the throttle further, it should stay at that spot. THen as you bring the revs back down, it should go back to the "base" setting.

Typical timing values for a good hot street motor might be something like 36° of "total" timing at full advance, 15 - 18° at idle, therefore around 18 - 20° of centrifugal advance from idle to full speed. Virtually EVERY engine will want something close to 36° of "total" advance, because this is a property of THE FUEL, not THE ENGINE; engine design can tweeek it a few degrees, but it won't be much. VERY few engines will make best power at less than 33° or more than 38° of "total" timing.

Then, when vacuum is applied, it should advance about 12° or so beyond that. This makes up for the slower fuel burn of leaner mixtures when cruising. It often adds 5 mpg or more to highway gas mileage so you DO NOT want to do without it. Makes no differene to "full power" because it's only active at high vacuum, i.e. low load, i.e. low power.

It's entirely possible, LIKELY even, that you should see around 50° of advance while cruising.

H8tnBS

So here's a better description of what the main issue is. The drivers side exhaust manafold gets cherry red after 10 mins of interstate driving, and only when the cars at high rpms. I can drive the care around all day and its fine as long as I keep the rpms low. Did an engine swap, the only thing that changed was the engine block, heads and intake. Its got the same quadajet carb that ran fine before swap. Swaped the distributer because I thought that was the issue, turns out its not. And yes the timing goes down fine, the issue im having is the amount of advance it does. Timing mark is set to +2 on the angled mark. At 3500 rpms the timing mark is to the left of strait up. Again i understand the timing should move but isnt that a bit much.

TreeFiddy

First - is your 0 timing mark actually at tdc? Should confirm that.

If so, then idle timing at 2 degrees is actually way retarded, should be 12-20 degrees to allow advance to 35 ish degrees > 3000 rpm. This would probably explain your red-hot manifold. Got a bad idle and poor acceleration?

Low load cruising (with vac advance connected and operating) should result in advance approaching 40-50 degrees depending on the amount of vac advance. Assuming your timing marks are correct (with balancer mark zero at 45 degrees to the right of 'straight up', or in-line with no 1 rod at tdc), this amount of advance would put the balancer mark somewhere around straight up.

IOW, sounds like the initial timing is too retarded and needs advancing 10-15 degrees (whatever the motor wants), and there's a bit too much vac advance on top of that. Disconnect and plug the vac advance, and get the mechanical timing right first as Sofa outlined above. Then add the vac advance that back into the equation, might need to get an adjustable can to dial it down a bit.

H8tnBS

I did confirm when I put new timing chain in the 0 is tdc. What I did first was set my timing gun to +10 and adjusted timing till balancer was lined up with the zero on the marker. At this point the car starts and cuts off perfectly. It also runs quite well, but the drivers side manafold gets cherry red. Now that was with vacuum blocked first. And it was set with the vacuum blocked of. It sounds and runs like a champ with the original set up but just cant get the right manafold to remain cool. I saw in some forums that the carb could be runing to lean or rich but I didnt adjust it from when I took it off and it ran great then. Im going to try some more this week end and see how much I can advance it while keeping it starting and cutting off right. So one last thing to help since I dont have video of it, picture the front of my engine being a clock. 230 is the 0 and tdc. When rezzed to 3000 the mark goes to 11, no vacuum hooked up. Is that normal. My truck with a 350 doesnt more that much at all. Thanks for all your help, i must be missing something.

TreeFiddy

Never mind the o'clock of the balancer mark for now - if you are sure about the zero tdc mark to take meaning measurements (note 2:30 doesn't sound quite right to me, should be 1:30 unless balancer has slipped or been re-marked) - what do you have initial mech and final mech adv set to at the moment (vac disconnected and assume your dial-back can go at least to 40?)

H8tnBS

Yeah im sure of the tdc mark, I can dial back beyond 40. with no vac hooked up I set it at +10 which gave me the best power, best start up and cut off. I havent tried to set the timing any higher then +15. I can this week end when I work on it again.

H8tnBS

So I went ahead and took your advice, set the gun to 40 and set it on 0 and it helped a good amount. I don't understand why the mark would be there but it helped. I had to back it down some since it was idleing to high and I had the carb idel screw nearly all the way out. The manifold still gets red but now it takes about a hour of interstate driving at 70. I'm going to have to tweak the timing more I guess. Thanks for you help.