1983 Ranger - Sputtering under load

Hi,

I'm a newbie and need some direction. The girlfriend is vehicle illiterate so I'm the lucky garage mechanic that gets to do the trouble shooting. Unfortunately my experience is limited to trouble shooting general maintenance and working on older Honda's (1989 to be exact). Her Ranger is carburated, which I'm somewhat familiar with, but not versed enough.

Basically, when it's under a load it spits and sputters and hesitates. It seems to get worse when the truck is warmer. This is a relatively new development and the carb was replaced nearly 18 months ago. So, I'm assuming the carb is not the issue. It's been checked by a mechanic and it is working fine, although with any reman carb there is a millimeter type gap between the carb and manifold. Mechanic said not a big deal it'll just idle rough when the seasons change. Seems to be the case as time has gone by. Then issue developed probably a month or so ago and she drove the truck the way it was since it wasn't consistent. Recently (4 days ago) she took it to a mechanic i've gone to for years and the Plugs, Wires, Distro, and Rotor were all replaced at this reputable mechanic in the area. I know reputable doesn't necessarily mean much, but they're pretty straight forward and honest. They've always been straight with me. They tested the engine and said it was fine, it ran strong. They assumed the issue was a tune up since carbed trucks can sometimes foul plugs more frequently then fuel injected based on driving behavior and conditions. Anyway, the problem is not resolved. I imagine she will take it back down for another look, but I like research for unbiased qualified second opinion

A couple of things I noticed, it doesn't miss-fire or backfire when the clutch is engaged, only under load. She does have a hole in her muffler, which I'm guessing this is the problem or a contributing factor. Also, it doesn't backfire under load either. I thought maybe the catalytic converter needs to be replaced, but there is no smell. It really feels like there's a restriction an the exhaust is not burning off like it should. Seems like it's getting back in the combustion and causing it to sputter. A low RMP and low speed it'll drive relatively fine but you can feel it slightly missing - not a transmission miss, a miss-fire miss or like the combustion is being smothered. I didn't notice any strong smell of gas.............. That's pretty much all I can think of right now, but please ask questions if you have them and I'll answer as best I can. I have driven it and experienced it myself.

 

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I should clarify when I say backfire I mean it doesn't sound like a gun shot. Sounds like air forced through a small/medium hole - hence why i'm venturing a guess that the issue might relate to the muffler/exhaust or the cat.