240 dies under load idles rough

Scuzzy_1250

Active member
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
 

Shorty

Well-known member
I had a nearly plugged exhaust in one of my trucks and it would barely run and backfire thru the carb.......
 

Daubee 1978

New member
I would do a comp. check. If it sat for a while you may have an intake valve not seating with could cause a intake back fire.
 

Stonebreaker

New member
The thing to do is to be systematic in your troubleshooting. You've been working on the spark, finish going through the entire electrical system until you're getting a reliable spark at the plugs - check for frayed wiring, check your coil, check your alternator, etc. Then start on your air. Is your air filter clean? Do you have cats? Try disconnecting the exhaust and see how it runs. If it runs ok without the exhaust, you have a plugged cat. Then start on your fuel. Check your fuel filter, then the fuel pump (torn diaphram maybe, or a bent cam rod?) and then go through your carb. After you've eliminated all of that, either the engine will be running fine or you know you have major engine work ahead of you.
 

bubba22349

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X 2 first thing you need to do is a compression test the vacuum readings jumping around indicate valves that are not sealing or cylinders with low compression. X2 that carb could also use a good cleaning and rebuild. Good luck (y) :nod:
 

Scuzzy_1250

Active member
Sorry y'all i have not had time to get to the truck to continue trouble shooting. My in-laws are in town and i have to entertain them. But tomorrow, I'll be picking up a compression Gage and will move forward with trouble shooting.

Do any of y'all know where i can find literature on the truck for cheap or free?
 

GPGoverMPG

Well-known member
Local library, my local one has lots of maintenance manuals people have donated after selling there rides. (I know, print is dead)
 

Scuzzy_1250

Active member
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
 

bubba22349

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Scuzzy_1250":d8eemnb4 said:
Is it possible for the dizzy to jump teeth with out braking,?

No! Your compression test seems a bit low too. Are the plug wires, cap and rotor in good condistion? :nod:
 

Scuzzy_1250

Active member
So I reset the points to .017 and it runs so much better. I have to dial it in but holy gezz it's such leap.

The compression test I did cold due it not running at the beginning of the day. A dry and cold test.
 

pmuller9

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Nice!
When you get a chance, take the distributor cap off and see how tight the shaft is by trying to move the rotor side to side in several directions. If the shaft bearing is worn and the shaft can float back and forth there will be some spark scatter.
 

worken2much

Famous Member
Point gap, (dwell) effects timing. After adjusting your point gap, then set your timing. After fully warmed up, adjust your idle mixture & idle speed.

Bet it purrs like a Tomcat in a dairy...
 

Scuzzy_1250

Active member
So I'm back at it yall. It ran fine for a day. Then it went right back to missing again. -_-


https://youtu.be/I3ObWVPwNqk


I really checked my points and it's missing and stumbling again. Dies under load....

Rebuild the carb again??? But actually chem dip it this time? Hmmmmm

Any input?
 

Shorty

Well-known member
If the point adjustment made a big difference in how it ran (as suggested by a previous post) then you are barking up the right tree I think. Have you considered an electronic ignition conversion (pertronix or something similar) to eliminate the points?
 

Scuzzy_1250

Active member
It's something I started to read on. Is it all just plug and play I wad also reading that dome dude prefer duraspark over electric ig. What do y'all thing?
 

Shorty

Well-known member
If you have a truck to pull the parts (wiring harness, control box, distributor) then duraspark II is great but the pertronix just screws into the distributor where the points would have been. I have an old farmall tractor that was very hard to start and I couldn't seem to set the points but when I installed the pertronix (two wires, two screws) it has started instantly every time.
 

worken2much

Famous Member
Very possible it's a bad condensor. Have seen only a couple times. Missing, stumbling would come & go with no rhyme or reason. Idle fine, any load would buck & jerk. Sometimes hard to start.

Good luck,
Worken2much
 
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