Help with 390 After Replacing Head Gaskets

[bweiner32]

New to the forum - looking for advice/guidance on my 76 F-250.

It's a 390 with a 4 barrel carb - 11 year old crate motor with ~30,000 miles on it.

I recently replaced the head gaskets, and while I had the heads off I had them machined and rebuilt, and the intake manifold hot dipped

The carb was rebuilt less than 500 miles ago

I replaced the head gaskets, exhaust manifold gaskets, and intake manifold gasket (I used fel-pro gaskets and the cork "front & back" gaskets on the intake)
Changed the oil and coolant, then once I got the motor back together, I fired it up. It ran really rough for about 20 seconds, and I cut it off. When I attempted to start it again, the starter quit on me. It was late, and I had to head out of town the next day, so I left it for a week. When I came back, I replaced the starter, and now it cranks but won't start. I am getting backfires through the carb ("spitting".) I am also seeing the distributor loose its timing. I will set the motor to TDC, pull the distributor and set it to #1, crank the motor, and after it cranks for a bit (without starting) I will advance to TDC and the distributor will be 180 degrees off. I have replaced the distributor - but the new distributor exhibits the same behavior. Spark is good on on all cylinders, the carb is getting fuel, and I checked compression on #1 and #5 - and it was 92 PSI - which was the same compression I had before I pulled the heads. I have checked the valve train and the valves seem to be functioning fine. I'd appreciate any help or advice to get it running. Thanks much -

 

[Mil1ion]

Was the dizzy pulled before or why did you pull it if the engjne was running before?

There are two TDC'S .
Just before ignition power stroke and Top of exhaust stroke.
Try checking before yanking the dizzy.

Btw...people say rebuilt carb when it was only a basic carb kit.
One big ignored problem is the worn out throttle rod bushings.
Once worn out you have to send the carb to a proper factory type rebuild centre.

Your comments appear as if you never did any troubleshooting.

Is this true?

 

[Mil1ion]

How are you knowing the engine is LOSING timing ?

Isn't this a crate motor...whatever that means today?

Usually it's a brand new engine from the factory.

Timing changes occur in engines with worn out timing chain and gears.

 

[bweiner32]

Was the dizzy pulled before or why did you pull it if the engjne was running before?

I'm not sure I understand this question...I replaced it after noticing the issue with it being 180 off after cranking. The new distributor also does the same though, so it must be something else.

There are two TDC'S .
Just before ignition power stroke and Top of exhaust stroke.
Try checking before yanking the dizzy.

OK - I'm using the timing mark, and have also pulled the #1 plug to validate TDC. I'm working off of what I believe to be the ignition power stroke.

Btw...people say rebuilt carb when it was only a basic carb kit.
One big ignored problem is the worn out throttle rod bushings.
Once worn out you have to send the carb to a proper factory type rebuild centre.

Your comments appear as if you never did any troubleshooting.

Is this true?

I have not done any troubleshooting of the carb - would appreciate any advice or tips on that.

 

[bweiner32]

How are you knowing the engine is LOSING timing ?

Isn't this a crate motor...whatever that means today?

Usually it's a brand new engine from the factory.

Timing changes occur in engines with worn out timing chain and gears.

I will crank to TDC, pull and correctly position the distributor on #1. I will attempt to start it, and it will crank for awhile, sometimes backfire out of the carb. When I re-check the distributor, it will be 180 off.

 

[Fellro]

As stated, the mark on the crank will come to the timing line 2 times per full cycle. One time it will have #1 on compression, next time it will have it on exhaust. The crank makes 2 full revolutions per one turn of the cam, so you must be certain that is is TDC on the COMPRESSION stroke. If not, it will seem half off.

The question about having pulled the distributor refers to if you took the distributor off when changing the head gaskets. Since the distributor does not pass through the intake, it didn't need to be.

With as much that has been done, you really need to get back to a baseline. That means make certain everything is there, fuel, spark, and timing. You can have the timing dead on, but if there is no fuel or spark, there will be no fire. It does seem you are just following the apparent obvious and not verifying much. The ONLY way a distributor can jump time that bad is by a timing chain issue or a pin issue. I find it hard to believe it is doing that. Timing chain would not be likely to bounce back and forth from on time to 1/2 off, and a pin would likely just not turn as the oil pump is driven by the distributor.

 

[bweiner32]

As stated, the mark on the crank will come to the timing line 2 times per full cycle. One time it will have #1 on compression, next time it will have it on exhaust. The crank makes 2 full revolutions per one turn of the cam, so you must be certain that is is TDC on the COMPRESSION stroke. If not, it will seem half off.

This is helpful - and I think explains what I am seeing with the distributor.

The question about having pulled the distributor refers to if you took the distributor off when changing the head gaskets. Since the distributor does not pass through the intake, it didn't need to be.

This is confusing - my distributor absolutely runs through the intake manifold, and it needed to be pulled when I removed the manifold. FWIW - it is an aftermarket Edlebrock aluminum manifold.

With as much that has been done, you really need to get back to a baseline. That means make certain everything is there, fuel, spark, and timing. You can have the timing dead on, but if there is no fuel or spark, there will be no fire. It does seem you are just following the apparent obvious and not verifying much. The ONLY way a distributor can jump time that bad is by a timing chain issue or a pin issue. I find it hard to believe it is doing that. Timing chain would not be likely to bounce back and forth from on time to 1/2 off, and a pin would likely just not turn as the oil pump is driven by the distributor.

If I somehow gave the impression that I had not been troubleshooting this issue - let me correct that. I have spent many hours troubleshooting and trying to get this fixed, but have exhausted my knowledge and understanding (which I admit is not vast - I am a tinkerer and hobbyist, not a mechanic) and was looking for some help and advice because I'm just out of ideas and I don't seem to be making progress. I agree with your back to baseline comment - I'll start there.

 

[cbaker65]

Wow,it sounds like your ready to pull your hair out.It seems that youve
already went over an double check every thing.

Sometimes it can be as simple as getting a couple of plug wires crossed,or
a bad carb base gasket.Bad fuel,or not getting enough fuel.
When you describe sputtering,popping back through carb,Im thinking valve
timing.One of the worst thing that it could be,is a bad cam or lifters.
Just hope its not that!
You must be missing something.Engines will usually start even if the timing
is a little off.
Just go back over an see if you havent miss something.Some times its hard
to figure out other Folks mechanical problems with out actually being there
in person.
Good luck!...

 

[Mil1ion]

I will crank to TDC, pull and correctly position the distributor on #1. I will attempt to start it, and it will crank for awhile, sometimes backfire out of the carb. When I re-check the distributor, it will be 180 off.

You didn't verify TDC on power stroke because you never mentioned it.
You said you checked TDC but you never verified it was TDC power stroke.
It seems like you continue to believe it's 180* since you've mentioned it 2-3 times.

You really need to verify #1 TDC on power stroke. Then check plug position by looking at rotor position.
You can't keep being 180* off when it's so simple to set it correctly.
Also maybe stop using the starter to move the crank.
Use a power bar to finesse it to TDC power stroke.

The next thing is to drop the dizzy so it points to #1 plug.
Number one can be anywhere in the 8 positions as long as they are all in correct order.

Make sure all plug wires are in correct firing order.
Once that is verified you need to crank the engine to see if the rotor is turning.
After that check power to coil +terminal on coil with key in run you should have 7-9v.

Do you need diagrams or other show me's ?

 

[Mil1ion]

 

[Fellro]

This is confusing - my distributor absolutely runs through the intake manifold, and it needed to be pulled when I removed the manifold. FWIW - it is an aftermarket Edlebrock aluminum manifold.

My mistake then, it has been quite a few years since I had an FE apart, so I may have forgotten that it did pass through, and then understand the confusion about why we would ask such a question.

With that, as I mentioned, the oil pump is driven by a hex shaft out the bottom of the distributor (otherwise called a dizzy.. that likes to sometimes stick in the bottom of the distributor when you pull it. When they do this, they pull out of the oil pump, and commonly fall alongside the oil pump drive. So after all the explanation, have you been able to be certain you have oil pressure? That can of course be a big issue.

After re-reading your posts, I would verify first that it is actually at #1 when on the compression stroke, and verify the wires match that, keeping in mind of course the way Ford numbers the cylinders is 1-4 on the passenger side, 5-8 on the driver side starting at the water pump end. The last image of the firing order and distributor cap is the way it needs to be. It is way easy to get the timing 1/2 off when you take out a distributor, or even just 1 tooth off.

 

[1970Custom]

Just to add, for finding your TDC on the compression stroke. Stick your finger in the hole until the pressure forces it out. Then, use a long, skinny screw driver to get it pretty close to TDC. You can adjust on the timing marks from there.

 

[bweiner32]

Solved!

OK - took everything back to baseline - and got it running. I was not setting correct TDC (had been setting it on the exhaust stroke as you all correctly diagnosed.) After I validated TDC using the "blow your thumb off of the spark plug hole" method, I got the timing right. I appreciate all of the comments and advice - stoked to have it running again.

For the bonus round - what is the correct timing advance for this motor - it sounds pretty good at 8 degrees. I don't have any factory indicator or sticker on the hood. Appreciate your help as always.

 

[Fellro]

I want to say factory is 8, but I seem to recall having run mine at 10. Each set up is a little different, so you have to kind of tinker with it a bit.

 

[1970Custom]

8-10 is usually the norm.