74 260 Hesitates/runs poorly above 3500rpm in 1st and 2nd after car has heat soaked - runs great for first 30-40 minutes

[Captain Obvious]

Haha!! Yeah, I got all excited when I saw someone working on a 260.  Then I saw the note about the round tops.      

[SteveJ]

35 minutes ago, Captain Obvious said:

Haha!! Yeah, I got all excited when I saw someone working on a 260.  Then I saw the note about the round tops.      

He could have done something really weird like converted the carburetors into throttle bodies.

[Captain Obvious]

That's ridiculous. Nobody in their right mind does that.

[Patcon]

It's good you qualified that statement!

[Captain Obvious]

So now that we've got all this distraction in this thread... I hope the OP has solved his issues!

[Kcusi]

Hahaha I have not. Actually just finished with the timing and new plug wires. Maybe something strange is happening under acceleration once the wires are hot and the way they sag or bounce around is causing an issue like previously stated. I did check the ends like stevej mentioned and couldn't find a culprit or fix my issue. 

 

I also have a can of compressed air and I'll be trying to cool down the ignition module during this next test drive if it persists. 

[siteunseen]

Have you tried to bypass the possibility of a dirty fuel tank and run the fuel hose that comes from the tank to a 2 gallon gas jug? I did this on my '72, put the can between the grill and the radiator and secured it with bungee cords. Drove around the neighborhood, it ran fine off the jug. That's when I found that I a tank full of crud. 

 

[Kcusi]

On 2/11/2023 at 2:44 PM, siteunseen said:

Have you tried to bypass the possibility of a dirty fuel tank and run the fuel hose that comes from the tank to a 2 gallon gas jug? I did this on my '72, put the can between the grill and the radiator and secured it with bungee cords. Drove around the neighborhood, it ran fine off the jug. That's when I found that I a tank full of crud. 

 

Yeah, I've pulled a line and ran about a qt into a clear container, it was clean. It has a relatively new tank (12ish years?) 

[Kcusi]

I have a Gm hei module, I was considering making a pigtail and temporarily converting to the hei ignition module. I found the writeup on this forum, i think it was a stevej  post. I'm not finding fault of anything in the ignition system that I can test. I've got a heatsink and hardware mocked up for it, so it could be worth a shot at this point. 

I dont want to throw parts at it and I've exhausted what I can test as well as swapped in spares of a few components and all have had no effect. If anything it'll give me something to do for a bit and would at least allow me to confirm/deny the ignition module. 

[Zed Head]

Even if it doesn't help, it's always good to have a spare ignition module ready to go.  That original one is going to fail eventually, probably sooner after you get the engine to rev right.  The typical parts failure cascade.

[Kcusi]

Just now, Zed Head said:

Even if it doesn't help, it's always good to have a spare ignition module ready to go.  That original one is going to fail eventually, probably sooner after you get the engine to rev right.  The typical parts failure cascade.

That was part of my thought process. Finding n.o.s. parts are crazy expensive and just going to a known good module that's easy and cheap to replace would be nice. I can just keep a spare in the bag I keep in the car.