My jeep has recently developed this obnoxious problem and I am completely stumped. When driving it will be completely fine then occasionally when idling (at a traffic light, rpm drop when downshifting, rpm drop when taking a slow turn) it will sputter and stall. I have a weber carb on top of my 4.2. The weber is freshly rebuilt (within the last three months) and it's tuned to idle around 800 rpm and when it runs it runs pretty smoothly for a carberated engine. My first thought was that it may be a fuel problem so I dropped the gas tank, cleaned it out, ran new lines, new fuel pump, and new filters. The problem still occurs. It seems to happen randomly but once it happens once it will happen every time it idles until the vehicle sits for a long period of time (such as overnight). I was told that it could be a timing issue or an exhaust blockage (not from a reputable spurce), would either of those cause that? The exhaust on it is a flowmaster muffler welded into the stock exhaust. Any help or suggestions would be greatly appreciated!
Usually the long period of time is me geting frustrated and walking away and not messing with it for a day or so. The battery (optima red top) is clean as well as the connections. The only thing I can think of would be maybe an exhaust blockage maybe that gets jarred when driving causing it to block the out flow? IS that plausible? How do you even check for that
Make sure fuel lines are routed away from hot exhaust. I would check the carb float setting to make sure the fuel level in the bowl is not set too low (just shut it off in a level spot and pop the top plate off the carb to see where the fuel level is) and also the fuel pump output (you can disconnect the fuel line where it goes into the carb and put it into a glass bottle/jar then turn the engine over and observe the output). Make sure you are getting something over 13 volts at the battery when the engine is running at idle and accessories are turned on. Also, check all of your vacuum lines to make sure there are no leaks. Another thing to check for would be the advance spring and weights in the distributor. If the springs are stretched/loose or the weights or vacuum advance unit are sticking this could cause sudden changes in timing as the plate shifts and could account for the problem you are having. Here is a link to a good article to look at: http://www.4wdmechanix.com/Rebuildin...arburetor.html of course the stock carb is different but there is good info on disty and vacuum system troubleshooting.
I will look into the vaccum advance/lines, replacing hte distributer cap, and possibly re-routing or insulating my fuel lines. I have the stock configuration with the line coming from the left side, under the engine then to the pump on the right then over top of the engine to the carb. In line I have a holly fuel regulator which I believe is set at 3.5 psi (had it set up and dialed in at a shop). I will also look into checking the timing.