Poor engine performance (no power rough idle) Help!

[kc jones]

Ok here's the deal. I have an 86 cj7 with the 258 4.2 L. The motor is basically stock with a few minor mods that include 4 barrel intake and holley 600 cfm 4bbl carb. To my knowledge no internal work has been done. Now, my problem engine idles rough missing and popping slightly. When I accelerate it misses like there is a plug wire off. When I get up to about 60 mph it pops and bogs and struggles to hold that speed. This problem has gotten more noticable in the past month. Put new plugs, rotor and cap on today ,wires on order. Did not help. Insulator on old plugs was burnt on one side as if timing was too far advanced. I set it at 5 degrees. I have owned this jeep for about 6 mos and I have been fighting this problem ever since. Any suggestions? I am stumped. I have a ping now I am guessing I am now for sure advanced to far. Oh also the missing gets worse when engine heats up.

 

[Saddle Tramp]

I know the frustration. Your problem could be a bunch of things like compression etc but often, in my experience this kind of performance comes down to vacuum leaks and/or the carburetor itself. The carb could be a little to much for the stock motor too.

 

[kc jones]

Yeah I was thinking that carb was a bit much myself. I think I'm going to take the carb off today and take it apart to clean it real good. I might as well go back with new gaskets and vacume lines. It just seems it wasn't near this bad 6 mos ago.
Thanks.

 

[Saddle Tramp]

My concern is that the carb is dumping more gas than the motor can digest. Maybe others who have more experience can help here because I am not an expert on carbs but The Holley Universal carb listed on 4WD states it is for the AMC V8s and the Truck Avenger 470 cfm states that the AMC 304 will require a larger cam to work properly. Other than potential vacuum leaks logic tells me your probably drowning your motor.

 

[kc jones]

I found my problem today. Started out this morning takeing carb off for cleaning and Inspection in doing this I discovered the vacume secondary butterflies were stuck and apeared to have been that way for some time. So after some cleaning, lubeing and a set of plug wires I was ready for a test run.I was pretty confident that my problem was history. Started up fine and pured like a kitten. A mile down the road I realized nothing had changed. By the time I got home it was running horrible. It was like it was running on 4 cylinders. I left it running and started pulling plug wires one by one. #5 and 6 Cylinders had no effect on the engine. I pulled the plugs and they were fireing good. I pulled the valve cover and 5 and 6 intake valve rocker arms are really loose. So I'm guessing lifter failure ,flat cam or both either way it sucks. Gona pull the head tomorow And find out.