I brought this up a few pages back.

 

I ran a 10ga wire straight off the battery to the coil. It didn't make a difference, so it ain't the switch.

On a separate note, the advance curve on my distributor seems like it might be off. My total timing is about 30-32 degrees, but it comes in at about 2k. Which seems ok with how it runs. But I think it could use more by the time it gets up above 3k range.

 

Here is my take on this truck:

I was not going to say it was I who tried to help but after this post it would be quite obvious. I would still like to help him figure this out for once and for all.

It just got a lot more involved than I had hoped and thought.
I dropped everything I was doing including cancelling a doctor visit.

He was spot on time and arrived at my place @ 7:00 am sharp

For his age he is a pretty sharp young man.

First thing I did was give a good listen to what engine was doing. Major major misfire on 4 & 7 cylinders, almost to the point it did not want to idle.

Recently I had a couple similar engines doing same with carbs needing work, another with a bad coil.

First thing I did was verify the firing order and plug wire routing as it was also acting like plug wires were actually crossed. He could do the proper wire routing in his sleep.

We then tried a new 4412 Holley 500 CFM carb from my '66 F100. This carb makes everything run like a swiss watch and always my go to carb when need be.

As he said it ran no better and maybe slightly worse.

Balancer seemed to not have slipped

We then let it cool a touch and did a compression test and also a leakdown test. By that time we had about a hour into it.

This is what we found:

1) 140 lbs comp and 26% leakdown

2) 145 22% leakdown

3) 141 14%

4) 143 21%


5) 146 22%

6) 149 16%

7) 148 15%

8) 151 13%

At this point the thought was valves hanging open when running,
Had to chase all over town to try and find a shim kit for then non adj rockers.
If we backed off a rocker the leakdown would change and as soon as we tried to tighten up the rocker the leakdown would go over 90% then stay there for a minute or so. So it appeared the valve adj was a tad tight.

It also appeared that there is a issue with losing comp past rings but with numbers in the teens to low 20's it should run great.

By looking at the #4 & 7 cyl at idle making little to no diff when pulling plug wires off they share the same intake runner.

We also checked cam to make sure firing order was correct, not unheard of to find a error there. It was fine.

This along with calling, searching and going to fetch parts took up a lot of time. Most places did not know what we were talking about looking for rocker shims . . We ended up driving half way across town to pick some up from a friend.

We did also set up a dial indicator to see how much the lifter plunger was moving at TDC on the Comp stroke. Never did check with plunger fully compressed but did see valve travel over .100 by just backing off rocker bolt a bit and tightening it up again. We then did more leakdown tests after shimming and things did improve a bit. Did not recheck comp on all.

Ford Spec calls for .100-.150 clearance at valve when lifter plunger is all the way down.

So in all we did gain a fair amount with what we did including swapping plug wires and tweaking here and there but the misfire never went away. Seems around 2700 rpm or so on cruise it would get better. Still had that roughness to it though.

I wanted to try another dist as not a big fan of that type. I had a bunch but found they had all been taken apart.

My thought at this time is intake manifold or gasket issue on 4 or 7 as intake runners also shared. Still not sure on the distributor either and would actually try another before pulling intake manifold to have a look see.

Tried to do all I could in the limited time without having him spend money without knowing for sure. Tried to eliminate everything else first.

How it ran in end was much improved but still a glitch~ Vacuum leak of sorts or a Distributor (HEI) issue. I am just not that familiar with that one.

 

You don't know how much I appreciated your help boss! I'm sorry I took up your whole day.

I just checked again after a short drive to warm the engine, and yes cylinders 4&7 are still dead. All others are firing great.

 

No Problem! LOL Thats what FTE is all about right?

I thought I would give you an hour or so of my time but I was as curious as everyone else what was up with it!

Just stop by to help with the '70 a bit, could use a bit of your talent!

I think even though you are 99% on the dist to try one I or you could pick up and if it does not help pull the intake.

I was a bit concerned seeing the color of the plugs with a bit of reddish on them being unleaded fuel.

Another possible is a bit of coolant getting where it does not belong.

Its so weird that it seemed cleared up around what 2700 rpm or so?

Remember too there is a lot more power to be had with tuning once we get the misfire taken care of . . . .

Were the heads magnafluxed? Cracks in chambers . . . The mystery continues another day. LOL

#4 intake leak of sorts or coolant getting in chamber although I did not see white smoke.

 

The heads were cleaned and inspected closely for any cracks/ irregularities. They were fine.

It's not coolant, the truck never smokes at all. And I'm not getting bubbles in the radiator. The Cleveland uses a dry intake manifold. So it's not coming in the intake.

Although it smooths at higher rpm I can still feel a misfire now after driving it some more.

My only thought now is that there is somehow an internal vacuum leak in the intake manifold. So I ordered the edelbrock that I've been wanting. And dug out my 1405 edelbrock carb. to get it cleaned up and ready to go.

 

One would think when we sprayed carb cleaner around a vacuum leak would have showed . . . You wanted that 4v intake anyway.

 

You would think so. But I'm thinking it may be an internal leak. Like between the exhaust crossover and an intake runner.

We've all pretty much ruled out normal problems, time to start getting creative. (Ya, I wanted a 4bbl anyway! Lol)

 

A compromised intake gasket will give you fits. Compression, spark and a fuel/air charge are all that is necessary for successful combustion. This is what I meant by lean condition. Same intake runner for the affected cylinders.

 

I mentioned the common intake runner earlier. Got to be there somewhere!

It acted like bad vacuum leak, crossed plug wires, wrong firing order etc

Interesting thing is if it had that bad of a intake gasket leak internally one would think it would show in engine as we did a carb cleaner spray and also washed engine with the pressure washer. With vacuum in crankcase one would think it would show but we saw the complete opposite effect.

 

Indeed it can, however since I've had this intake off and on several times already, replacing the gaskets each time, I can't believe it's a gasket problem.

Because they are on the same runner that is cause to believe its intake/ air / fuel related.

 

For sure. I wouldn't be able to sleep until I had the intake off if it were mine.

 

I'll have my new edelbrock 2750 intake soon. And I'm working on my 1405 carb as I type this.

 

I TIP MY HAT TO YOU RANDY!

 

Seems like you have checked everything. There are things that only show up after things get a little warm. Did you Magnaflux block and heads? Sometimes a crack in cylinder wall, head, or intake will only show up after a little heat. Not by just spinning things over and checking compression. And could be valve seat, or valve guide might be a little off, or valve slightly bent. I only say this because it seems you have done a pretty through check of things.