You are correct. Your symptoms indicate a fuel delivery issue over ignition. You have a blockage or restriction somewhere, whether it's in the carb or line/pump/tank getting to the carb. Even something as simple as a plugged vent will do that. You might even start with removing the fuel filler cap and take for a drive just to see.

 

Ross,
Yeah, it's got that pull off too...though I guess I didn't catch that was a pull off too. Behind the air horn there is a diaphram with a cylinder that rides on top of it and operates another pull off.

I found a better pic of one online...


Dave,
I rebuilt the carb while it was off. Soaked it in Chem-Dip and sprayed everything out...but I'm about to the point of tearing it apart to see if something's wrong there.

It did sit after the rebuild for 2-3 weeks before it got fuel in it.

Anybody know a good way to test the fuel pump? I just replaced it, but knowing it was doing its job would also remove the eccentric from the list of possibilities.

Jim

Edit: Several others chimed in while I was typing that response. We've got another line of thunderstorms rolling through, but it looks like we'll get a break after that so maybe I can go out and test a few things again.

 

Okay...the rain moved off so I took some time out in the garage to test some things. Here's a little vid for your enjoyment...


After taking the vid I had the wife come out and help me run a few tests. The truck runs best and has the highest vacuum (19") at about 24 degrees BTC. It will run all the way down to 14-18degrees but with far less vacuum...around 12".

With the timing set at 24 degrees, we ran some rev tests. The truck craps out around 1600rpm, which is also when the timing has advanced past the marks on the balancer...I believe 35 degrees? I can't remember for sure.

We also revved the truck with the carb open and I watched the steady flow of fuel. At low rpm there's a little bubbling. As the rpm increase the bubbling increases, but the fuel level stays steady. So the carb/fuel system doesn't seem to be the problem.

I didn't try running the timing back down to 14 and trying a rev test there to see what the rpm would do. But I seem to think as I type...I go run some tests, then type a response or question here, and in the process think of something else to try.

Thanks guys for all the suggestions and helps!

Jim

 

Jim, I've been following this thread and am not completely sure what is going on but.... Is 24 degrees your initial timing with the vacuum disconnected? Ford 302 is usually 8-12 degrees and I have never heard of a mild street engine above 16 initial. Lets say you have 14 initial plus 22 centrifugal for a total of 36, this is about right for a iron head motor (I would not exceed 40). If you are starting at 24 you would be exceeding 46 max, way too much. Also it sounds like you are getting 15 or so degrees of centrifugal advance at 1500 RPM this is very aggressive, usually the 22 or so degrees of mechanical advance is in by 3000-4000 rpm. To all of these vacuum advance can add another 10-15 degrees.

As an example my iron head 312 with a mild street cam has 16 initial with 21 centrifugal and another 10 vacuum. A fairly conservative setup.

 

I've been through so many back and forth changes with the machine shop's goofs that I can't remember at what point the truck was doing what...so I ran a compression test. Came back good, 138-140psi in every cylinder. Set timing down to 12 degrees BTC where it used to be pre-build. Got a smooth idle at 625-650. Truck fell down at 1750rpm. So that gained me some space...still way off, but this was a step in the right direction.

Made a call to my uncle the mechanic. He's been wrenching for 50+yrs and has forgotten more than I'll ever know. He's also the kind of guy that makes Grouch from Sesame Street seem warm and friendly. His first question was about fuel supply. But then when that was out of the way, it became timing. He's suggesting 8degrees, and that the advance is too agressive...that by 1700rpm the spark is so far advanced that it's counteracting itself. I haven't heard any spark knock, but at that rpm I might not.

So the game plan for tomorrow after services is to drop the timing even further and see what that gets me. It seems counter-intuitive that I would need to retard the timing with the new cam vs the old, but perhaps.

Wisdom? Sage Knowledge? Derisive laughter?

Jim

Plans fail for lack of counsel, but with many advisors they succeed.- Proverbs 15:22

 

What is the vacuum reading with ignition at 12 deg., after adjusting needle valves?

I agree, you have way too much advance. Do you have the vacuum tubing disconnected and plugged while you are adjusting the timing?

 

Jim, I can definitely feel your pain. I am going thru somewhat similar conditions with another earlier car. My symptoms are hard starting and lack of power ( I also have good compression readings and no leakdown issues based on testing). I also thought fuel delivery/carb might be the problem. I did a number of things in the fuel delivery/carb area initially based on symptoms. I did not have a manifold vacuum port for diagnostics so I created one. Manifold vacuum monitoring will help with diagnosis. In my case vacuum is in the 15" range at idle and drops as rpm increases to as low as 4-8 at wot, all too low. I have not been able to find the cause but knowing that the engine is not breathing correctly provides focus. In my case, I am confident that I do not have a vacuum leak. I am going to eliminate exhaust as the problem next by taking the muffler off. Despite the fact that I carefully degreed the camshaft, I remain suspicious of cam timing. Are you confident that your cam timing is correct?

 

Bill, 15" at idle and 4 - 5 WOT isn't unusual. Here's the diagnostic chart

 

In your case, I would suggest that 15 may be a bit low at idle but at WOT, expect extremely low or no reading. Not to the thread, just for information .

 

Ross,
The vacuum line is disconnected at the distributor and plugged.

================================================== =

Went out this afternoon and dropped the timing back to 8 degrees. Still had a steady smooth idle. Still pulling 17" vacuum as it was at 12 degrees. Can't go lower than eight or it starts to stumble. Idles right at 600 (digital tach reads 585-615ish...mocked up an analogue tach so I could read it from the engine compartment and it reads sub 500).

Had the wife get in and rev the engine steadily to 1800. It never made it. The timing light begins to show advance around 1000 rpm (that's mechanical...the vacuum line's disconnected and plugged). By 1500 rpm the light's showing 18 degrees advance and it's beginning to stumble.

From about 1600-1650 the rpms stumble down to 950, but the advance stays right around 16-18 degrees. IF she keeps her foot in it the rpms slowly rise to about 1200 rpm and advance climbs up to 26 degrees. But it sounds like it's turning a heck of a lot faster than 1200 rpm.

I'm starting to wonder if maybe the icm has crapped out. It's a 1980 Ranger distributor with the stock control box. It's been several years since I swapped it out and I'm wondering if it or the coil aren't crapping out on me. I don't know. This one's really got me puzzled.



Jim

 

Jim, you might try hooking the timing light to each of the cylinders one at a time. Have your wife accelerate till engine starts to stumble while you watch the light. Any misfiring on a cylinder will show as missed flashes on the light. I have also put chalk marks , 1 line 2 lines etc. around the damper. This way I can watch each cylinder and see if the timing is varying.

 

I'm wondering if a mechanical advance spring might have broken.

 

At this point, you can prove or disprove a fuel problem. Run the engine to where it falls off and spray some starting fluid, WD40 or any nice combustible fluid into the carb throat and see what happens.

 

Bingo! No other way I can think of that you could get that much advance by 1500. Hell, it may be missing.

 

Okay...so here we are this far into this and I'm a bit embarrassed at what I found.

First, the vacuum advance pot on the distributor is shot. You can just suck air through it...or blow through it. I even hooked it to the vacuum line and revved the engine with no motion of the arm.

I pulled the reluctor and breaker plate and the weights and springs appear to be in good shape. Well, I thought, guess that eliminates another possibility. So I put it all back together save the vacuum pot and slid the rotor down into place...and it twisted.

That's odd, I thought. And pushed more. It turned more. I can't get the rotor to lock down on the notch. It just turns. I have run this truck with this rotor for at least eight years (I remember what house I was living in when I swapped in the newer distributor). Looking the rotor over I can see where plastic has been displaced on the inside. Did it just fit so tight that I didn't have a problem, and now it's worked itself loose? Maybe that was the problem...or part of the problem...before I tore the engine down? (The heads were in BAD shape, so it wouldn't have been all of the problem)

It seems feasible now that the rotor was slipping inside the cap and causing the problem, but I won't know for sure until I get a new one. Now I have to figure out what that is, because what I remember getting years ago does not bring up the same part online today!

At this point I don't even know what to say...

Unbelievable.