Can someone explain how to set timing to maximum vacuum?

I just put a new intake and 1406 on a stock 400. It starts perfectly with one turn of the key, it warms up, idles, and revs up with no problems, it turns off as soon as they key is turned off, no deisling. Problem is, when I put it in reverse while running, with my foot on the brake, it dies. I havent tried any forward gears yet, just trying to back it out of the driveway. It will stay running if I keep my foot on the gas while putting it in reverse.

My first step is to check for vacuum leaks, which Im pretty sure there are none, but I'll check anyways. I sealed the intake and valley pan very well. Then I'll time it. It has a new replacement oem style vacuum advance distributor (something from autozone) that I put a pertronix 3 in. It has matching flamethrower coil.

I read on a mopar forum to unplug the vacuum advance and set base timing to 16 deg, then set my idle mix screws until I get max vacuum, then have someone rev to 3000 and set my total timing to 34 degrees, then plug vacuum back in and adjust +/- about 5 degress to find optimum.

Im a little confused by this can someone enlighten me?

cap the vac adv & set the initial to 16-18. connect vac can line to front pass side carb (ported) nipple. Have the idle mix screws out maybe ~2&1/2 turns from lightly seated. That'll get us started. you will need a strip kit for the 1406 or I could send you a pair of richer jets if you want to swap them in. then we can set initial to (max vac minus 1 in hg) but we gotta get it runable first. EDIT & the floats are at 7/16". MORE EDIT did not mean to imply that we need to richen the rods/jets before we can solve the problem. it has enough power to idle/free rev in neutral but not enough power to pull the car. I'm thinkng vac leak or carb issue (lean/lean), not a healthy enough (A/F) mixture to develop power

Idle speed could be too low as well.

Just remember that as you play with timing, idle mixture adjustment and idle speed the manifold vacuum will change, it's a balancing act between all three.

To do it right you will need, at a minimum, a vacuum gauge, a timing light, a tachometer and a flat tip screwdriver.

Sorry I abandoned the post. Didnt have the right equipment at the time then forgot about it all together. Im right back where I left now. I've bumped up the idle so it will run and not die when it goes into gear. It's weird some days it runs fine with just a high idle, other days it will still want to die if put in gear.

I have a vacuum gauge hooked up to manifold vacuum. warmed up, choke off, the vacuum gauge surges from values of 16" to 19". It's always moving back and forth, but not always to the same values, for example it will go from 16 to 18 to 16 to 19 to 17 to 18 to 16 etc but always between a minimum 16 and maximum 19.

Now, from the limited sources I've read this indicates sticking valves or retarded ignition, possibly misfire?

When I set base timing, with my plain jane timing light, the balancer mark would bounce a bit. At first I thought also there was a misfire or worn chain, but then I read that if I have a multi spark ignition, then a basic timing light wont work at idle. I have a pertronix III and I think this may be the cause of the bouncing timing mark, but I wont know for sure until my new timing light gets here (innova 5568, summit racing claims it works with multi spark ignitions.) I needed a new light anyways.

So I got my base timing what I suspect is 16-18 degrees, and turning of the mixture screws doesnt have any effect really on the vacuum readings.

What should my next step be?

If the P ain't making the marks dance & if you are sure the chain is tight then turn the rotor slightly back & forth & see how much circumferential play (rotating distance) you have as 2 deg there (intergear slot/dist lower tang interface play) can make the marks vary in a 4 deg range on the dampener which is the "spark scatter" that you see with the light. Stock 400/stock intake/eddy 1406. what cam? stock also? with 16-18 initial what is your idle speed and are you on ported or manifold? Still sounds like a vac leak & you do need a strip kit but that is unrelated to the jumping. A stock 400 with the only swap from OE being the eddy 1406 should idle dead smooth at 500-600 RPM. holler back with more info as I may have missed something

It's all stock 1977 400 other than eddy performer intake, 1406 carb, vacuum advance distributor (whatever autozone sells for a 1972 400), pertronix 3 ignition. All lean burn stuff gone and rewired.

The cam is stock.

The distributor is hooked to passenger side ported vacuum.

The timing mark bounces about 2 degrees variance rapidly while timing light is on.

It will not idle without foot on gas, so I had to bump idle to about 1200 or 1300 from the sound of it.

Not sure it's a vacuum leak, wouldnt that cause a more defined steady drop in vacuum? When I put the intake on, I sandwiched the valley pan with felpro gaskets and used hylomar on every surface.

Funny thing is, it started working fine a few days ago, I was able to reduce the idle speed and it ran smooth. Then, a day later leaving a stop I punched the gas and it instantly went back to this state.

Also, I noticed it feels very rough like a misfire, but all my wires are firing I checked with the timing light, Im almost thinking I have a bad valve stem leaking oil constantly and fouling a plug somewhere. I dont think I have a head gasket leak, not seeing oil in coolant or any white smoke, or bubbles in coolant.

I'd bet my (next to) last dollar on a vac leak. it ran OK (for a stocker) with the OE intake/carb & the problems started after the intake/carb swap? & no other changes ex carb/intake? Oh I forgot about the P but I cant see it jacking up the idle speed but you might toss the point dist in for a quick test before you get after the valley pan again

No it didnt run too well before the swap. When I bought it, it had the lean burn distributor and a non stock quadrajet carb, I dont know what was working and what wasnt working. I just drove it home. There was an obvious misfire though and the radiator was leaking. It came close to overheating.

As soon as I got it back home I took off the intake, removed the distributor, removed the lean burn wiring. Installed the new components. It turned on with the first turn of the key and ran very well in park. As soon as I put it in gear it would die.

This got progressively worse to where it would not idle in park unless I had my foot on the gas, and it felt like there was a misfire.

Then, for 2 days it just randomly starting running fine and smooth again like it did when I first started it up after the new parts were installed. I was able to reduce the idle speed, probably to only 1000rpm, but it didnt die at all when put into gear and it didnt shake. So Im driving home from a restaurant and decide to see if it will do a burnout. I put the gas to the floor then let go of my brake. The car eeks out a tiny wheel spin but then instantly the engine starts running like crap again and I have to keep my foot on the gas at all times so it wont die. It has run like this ever since.

Symptoms:

Vacuum gauge shows a constant slow movement between various readings ranging between 17" and 20" (it was 16-19 earlier today but I tweaked the base timing after I posted that and got it better.)

In neutral or park, engine stalls if idle speed isnt kept above 1200rpm.

Even with the idle bumped up, engine rpm constantly surges slowly between various ranges of about 1100 to 1300 rpm.

When put into gear, I must keep foot on gas to keep RPM's high or engine dies

engine vibrates at slower rpms



I sprayed some starting fluid around the base of the intake ports to see if it was leaking, but the results are inconclusive because it is hard to hear a difference in rpm when the rpm is already constantly searching.

Just throwing this out there, power brakes? I had a booster go stupid on me and create the same kind of erratic issues.

When pressing on the brakepedal, if the idle-rpm rises, then you have a leaky brakebooster. But with such a leakage, it should be fairly audible imo.


Somewhat unrelated to your engine issue, but just after a (cold) engine start, it's not really 'advised' to put the transmission straight into Reverse from Park or Neutral.
Put it in Drive first, then go to Reverse.

Adam do you have a spare ECU and coil that you can sub in or take em off of one of your other running vehicles. since you have the P you'd also need a regular electronic dist or another point one/ballast for a quick test. I missed the obvious, that a vac leak would not be part time unless something is loose in the booster check valve if PB or possibly the PCV (clamp it (hose) shut will elim that). & the P install inside the cap is correct right (nothing loose/moving that ain't supposed to be)?

Do you have access to another distributor that you could throw the pertronix into? Not to send you on a wild goose chase, but when I installed a P2 system on my 360, I put it in a fresh store bought rebuilt distributor and couldnt get it to work correctly. The exact troubles escape me now but I tried/checked it several different ways. When I stuck the P2 in my scuzzy original distributor, it worked great. And has for the last three years. HTH, Karlin.

The 400s are famous for losing teeth on the nylon timing gear. Are you certain this didn't jump a tooth on the last owner? I would verify the mechanicals on this as it shoudl idle just fine. You can also check the timing chain slop by setting the timing mark at "0" and rotating the crank by hand back and forth. Take note of the number of degrees it moves by watching how far it goes before the rotor moves.

Robert, I'll go through my distributer again and make sure everything set up right. Im getting current through every wire. EDIT but it really feels like I have a misfire... unknown if it's being cause by wrong volt/amp through wires, wrong gap in plugs, fouled plugs or a valve issue.

fshd4it, the original distributor was the funky lean burn electronic distributor, and the pertronix III unit I have doesnt fit it. Plus it was haggard and I threw it away. I bought new distributor for a 1972 year model of 400, because it was the only year that had points (cheap and easy to install pertronix). I almost want to buy another points distributor (I foolishly threw away the guts of mine) and throw it in and see if my problems go away, I think they are only $35.

moper, I didnt know 400's had nylon teeth, I have only seen those on engines that dont run a chain, like my 1990 s10 4cyl, with the purpose of reducing vibrations and noise. Wouldnt a steel chain wear nylon teeth out quickly?

Ill check the brake booster line too. But there's no change I can see in rpm or operation when I press on the brake in park or N

I should probably take a video too.

With the idle up at 1200rpm. The throttle blades may be open too far uncovering the transfer slots.

This is probably why the idle mixture screws have no effect on idle quality.

Have you pulled the plugs to check them? How old are the plugs? What plugs are installed?

One time I replaced some NGK with brand new Champions. Drove about 25 miles and the right side rear plug fouled out. Thought I lost a lifter, or developed a valve train problem. Pulled the plugs and found carbon bridged the plug gap, and killing that cylinder. Put the old plugs back in and ran a few more years. Never had another problem.

Check your plugs.
Ron

You misunderstand... The factory cam gear has nylon covering the teeth where the chain engages. It's to keep things quieter. 440s and 400s had them I think after '72. As they age the nylon gets brittle and the nylon covering breaks off the tooth and falls into the pan. If it happens enough the chain can slip. Chains can also slip just from chain stretch. The symptoms you describe IMO are an engine that isn't makig much power on each power stroke. Not necessarilly like one that is really lean from a vacuum leak.

Ok, so when I started it up today it's decided to run smooth. I turned the idle down to about 700 or 800, adjusted the base timing 18, and adjusted the idle mixture screws until I got a steady 19" vacuum reading. I can put it in gear without my foot on the gas and it runs great.

So, this should narrow down the possible problems. Every problem I've listed in this post went away all together at the same time.

I think issue that causes all those symptoms is misfire, caused by either my ignition, plug or valves. Because now that the engine is running fine, it doesn't vibrate and run smooth. I've reved it a couple times, but Im afraid to punch it from a stop, or brake hard, for fear it will bring the problem back. There's more I want to learn while it's running well.

I'll pull plugs next and see if I have fouling.

FYI the mixture screws had an obvious effect on the vacuum once I was able to bring the idle down to normal

That is a strange one. We will stay with it till we get it. I remembered (basis for my last post) that 30 yrs ago I had a Sears white replacement ECU that did the same thing (actually 5 of them in a row) part time acting up. MP dist with an accell super coil and the above HEI modules. went to a black OE '75 chebby HEI (used) module & ran flawless

The petronix kit is very sensitive to voltage. Be double sure you have a solid connection feeding it HOT. That is critical to know when setting one up.

I second the call to check the chain. The nylon might be causing some weird timing events on occasion.

I also agree a funky set if plugs could be derailing you. Ngk is good and ive had good luck with densos as well.