OK, here's the deal. 1983 Nissan 720 truck. Z-24 engine. Power brakes. 5 speed, manual trans. I think it's either got a bad carburator or it's running real lean. so I'm hoping it's got a vacuum leak but I can't find it. I've replaced all the vac lines, checked the EGR, VAV, etc. Vac pressure 20 lbs @idle but 10 lbs on the freeway. Seems a little low to me. Timing is right. Timing chain is right. Compression is goog (170 lbs each cyl.) Plugs, cap, rtr. and wires new; Coils (dual coils) firing well; Rebuilt carb; New fuel pump and filter; blah, blah, blah. I've shot carb cleaner all over trying to find a leak but nothing so far. note: it's impossible to squirt the bottom side of the intake manifold so that's still a possibility I guess.

Why do I thik it's got a bad carb or running lean? Bad Carb: To be honest, I can't tell if it's the right carb or not. It's been rebuilt/acid cleaned so the numbers are all gone. It bolts on OK but the throttle cable doesn't fit right. I had to bore holes in the bracket and lower it. I got another bracket from the wrecking yard but had same problem. Brackets all seem to be generic anyway. Could be the wrong throttle cable I guess. Still, even if it was the wrong carb, would it run that bad? Vacuum Leak: Well, it runs great when it's cold and the chokes on. (lots of power) However, when it warms up it gets real doggy. Kinda like it's not getting enough gas. Also backfires out the exhaust pipe in between shifts and when decelerating. Spark plugs are black like it's too rich though. This puzzles me. Maybe I'm wrong, it's not too lean? I dunno anymore. Frustration...

Problem: the truck was given to me. Didn't run when I got it. Person that worked on it before me obviously had no idea what they were doing. Unfortunately, I can't contact old owner to question. All vac lines hooked up wrong, wiring not right, etc. It's possible there are parts off of another truck on it, not sure. Maybe even different engine. VIN code says it came with Z-20, it has a Z-24 engine in it. Doesn't match the vac diagrams in book exactly. Even went to dealer but they had same diagrams. Did the best I could. At least it runs fairly decent now.

So as you can see, this is a big mess. I'm convinced it has a vac leak but like I said, I can't find it. Does anybody have a better way to check for one? Any suggestions? Do you think the problem's a bad carb? Do you think it's something else? Do you think I outta just shoot it!?!

HELP!