1969 f100 240 stumbles and dies under load

[Scuzzy_1250]

So I'm the 4th owner of this 69 and it's been a pain in the but since it got it. The wiring was trash and i got it enough to get by. Now my issues is it's running like death. It drove fine for a little while. Then it got progressively worse. I rebuilt the carb Holley 1940 and at first it would flood out all the time. Turned out to be junk in the needle and seat. Then would idle fine and die once i put it in drive. I tweaked the timing a bit and that went away. After that issue was solved it drove around fine for a few days. I fouled out plugs which blew my mind cause a size under stock. Which would be 68, i jumped down to a 65, and i had a lean pops through the carb. I went back up to 68, the lean pops went away. But still junking out plugs. I had another back fire through the carb. At that point the truck won't hardly drive at all. It idles rough, it misses and it dies under load. I took it up the road to a shop to throw a timing light on it. And he had problems finding the timing marks and it didn't go anywhere. Today i put new wires cap coil plugs and still runs terrible. I located the 0 on the pully and marked it clear for the timing gun. After timing I'm stuck on what else i should check any ideas? Any help is much appreciated. Also I'm new here so if this belongs in a better post please move.

I have some YouTube links of videos i took of the tuck running.

https://youtu.be/JRtJUjlnfOE

https://youtu.be/dZGmwBgl7FI

https://youtu.be/Er8bwZKQXko

[idaho_cowboy]

Hope I can help..

What's your compression in each hole?
Have you found the little mark for timing on these, and figured out where it needs to be for sure?
If so then what's your initial timing set at now? Also, what's your total at wide open throttle, or around 2800-3200rpm?

Based on vacuum gauge readings I'm guessing we've got some valve related issues. Worn exhaust seats very likely.

We need to answer these questions..

Any backfire through the carb is a timing related issue. At the very least a valve that's sticking a bit. And it makes me nervous that there's such confusion.

Might just be an old low compression motor that's way past due for a rebuild. Could also be something very simple. But we need some more info!

- Joseph

[colnago]

First, welcome to the group!

Second, adjust timing to 10 degrees BTDC.

Third, start with the idle. Turn the idle screws out 1-1/ turns, set your idle speed to 550RPM. Do you have a vacuum gauge? If so, hook it up to manifold vacuum. Adjust the idle screws to get max vacuum, adjusting idle to keep it at 550RPM. Once you have a decent idle, go from there.

I'm not a Holley guy. How many CFM is it rated for? Is it too big for your engine? I have an Edelbrock on my 352. It's rated for 600CFM, and I'm playing around with sizing it down to 500CFM. The basic equation is this:

Displacement x RPM / 3456 --> CFM

Just my two cents. Hopefully, someone with more experience will join in the conversation.

Joseph

[Scuzzy_1250]

Ok just a heads up I'm not gonna be able to get back to the truck but i will address the question asked. I appreciate the responses guys I'll keep you posted. I've also been scoping out motor there is another 240 for sale for about 500 ok price? Supposed to have been rebuild "recently" comes with carb and all.

[colnago]

That's hard to answer. If it's been rebuilt recently, that's a great price. Are there receipts? Is it just partially rebuilt (just the heads, or new main bearings, or ...)? How many miles? New carb, or rebuilt, or just cleaned?

In comparison, I bought a disassembled 352 for $200. I had it bored and honed, and the heads rebuilt for $400-ish (Too long ago; I'd have to dig out receipts). I spent $600 on a "kit" with new piston, rings, bearings, etc. I reused my starter, alternator, and carb. I probably spent another couple hundred. Call it $2K total. In comparison, $500 is a steal, if he did it right, and a potential PITA if he didn't. Be careful you don't buy someone else's headache.

Joseph

[Scuzzy_1250]

Ok so here is where I am with compression

1. 2. 3. 4. 5. 6.
130 125 120 120 130 110



So I got it at zero as best I could, but my timing marks is jumping around so I cant be sure. I can't get my base line.

I do have 12v at coil. Here is the video of the timing mark jumping

https://youtu.be/zV7uJOfRE4o


As far as the carb cfm Im not sure. It's the service replacement for the single barrel autolite from the 70s. At this point I'm thinking the carb is junk...???

[colnago]

My thinking is that the timing light has more to do with your distributor, and when #1 gets the spark signal. That's not to say that your carb doesn't need rebuilding, but hook up a vacuum gauge and see what the engine is doing. My timing light "dithers" about one degree (0, 0, 0, 1, 0, 0, 0 ...), which lets me dink around with the carb. Either that, or your timing light is bad.

Joseph

[Scuzzy_1250]

This is about where I'm at now. It runs so much better. I can actually drive it. I reset the points to .017 and the timing is 10* out.

https://youtu.be/u9GRYQgfIu4

[WarEagle]

The motor sounds ok from the link you posted. Get a vacuum gauge from Harbor Freight and hook it up. You can learn a lot from it. It also makes it easier to fine tune your motor. Compression looks a little low, especially #6.