Engine sputters on acceleration then smoothes out at higher RPM

[csd1982]

I have a 1975 Fj40. The engine is stock. Recently it has been getting harder and harder to start it up. I really would have to hold the key in the start position forever and pump the gas pedal to get it started. More just hold the the key in start position to get it to fire up.

Also sometimes when I shut it down it sounds like it wants to fire back up right before the engine finally dies. It does not backfire.

However today I went on a long drive and I could hear the exhaust sputtering every now and then on acceleration. After about 1 hour it got really bad. When in 1st or 2nd it sputters so bad it's like the engine might die. If I run in 3rd gear at high RPM's as in right before to move it in 4th the engine runs fine. Once I put it into 4th it starts sputtering really bad again and can't accelerate. After maybe 8-12 minutes of flooring the gas peddle in 4th gear and having in sputter not gaining any speed it seems to finally pick up acceleration and eventually I'm running at about 65-70 mph (34' tires, 4.11) and sounds are runs great.

Any ideas whats going on or where to look. Ignition issue or carb issue?

 

[tymayo34]

Since you have at least two separate issues you'll want to start slow and simple in diagnosing the problems. Plug a voltmeter and check the numbers before you turn the key. If it's below 12.6-12.7 or is wavering, check the battery cables and connections. Clean them up and replace anything that looks rusted or tired and see how it affects the voltage. Sometimes if the electrics aren't right it can make for a rough drive.

 

[FJ40Jim]

Hard to start and laggy acceleration are both symptoms of carb accel pump failure/

Not wanting to make power, then gradually getting power is indicative of a fuel supply problem. Look for a plugged filter, weak pump, plugged carb inlet screen, etc.

This stuff could all be related to dirt in fuel system: plugging the filter and plugging the tiny AP discharge nozzle.