Really Bad Gas Mileage???

I have a question for all the pros out there. I inherited a 88 b2200 truck over a year ago. I have had several mechanical problems with the truck over that time.
From the start... the head gasket failed so i got the head totally rebuilt and when i was doing that job I replaced the distributer cap, wires, sparkplugs, and timing belt. The truck seemed to run great after all that was done. But about 3 months ago it started running really rough at idle (runs fine when you are 10kms and faster) as well as it started puffing black smoke. My gas mileage really dropped off aswell, i used to get about 425 km to a tank and now im lucky to get 290km/tank thats only 180 miles per tank.
So i decided to replace the stock carb with a brand new carb. And it still really hasnt fixed the probllem. Still has a really rough popping idle (like it vibrates the whole truck) and when you are driving say 60mph and you back of the throdle it seems to surge and buck a little.
But the wierd thing is every now and again it will idle fine and seems to run great... just often enogh to give me hope that it is possible for it to run properly.
Oh i have also had a new exhaust installed aswell.
so if any of these problems seem like something you have experienced in the past please let me knopw what i could try
thanks for your time.
Eric

You check your 02 sensor?

forgot to say that ... brand new o2 sensor aswell

vacuum advance line to the dirtibutor has a hole in it, or the vacuum advance diaprham has failed.

Take the line off the distributor when running and see if the idle changes. It should.

Or, take the line off the manifold that runs to the diaprham, and suck on it. You should not be able to pull air through, it should pull vacuum and hold it.

By the way, you need vaccum to have that line work, so dont automatically assume its the diaphram. A big enough vacuum leak in the vacuum system will prevent the diaphram from working just the same as haveing a hole in it. Use a can of starter fluid or an unlit propane torch waved around the vacuum lines to find the source of the leak. Usually its something dumb, a line you knocked off while messing with something else.

ill definatley give that a try... thanks for the help... ill keep you posted with the results

no doubt vacuum lines could have came loose

have you changed the fuel filter if not might wont to try that mine would buck and lose power as well turned out the filter was cloged im gone drop the tank this weekend maybe and clean it out

thats one thing i have not yet changed.....but i asumed because it was drinking gas like crazy that there wasnt an issue with blockage....but ill have to replace that too.

Thanks for the tips

Is it normal to be getting around 425km to a full tank? That's about what I get with mine,and that's with doing all highway miles,a tonneau cover,everything in top notch shape and an Accel air filter.

I assume 425km sounds about right,because it's a fairly small fuel tank. I travel about 175km and use a little more than a 1/4 tank.

Just kinda seems strange to me,how a little 2.2L in a light little truck only gets about 425km when my '95 Contour 2.5 V6 with a 57L tank would see me over 600km. When I got my truck though,it was running rich,failed the emission test 7 times over the limit and had 4 vacuum leaks,one of which the line was not even connected to the EGR. Wonder why it failed eh?

yeah let us know webpage if you have solved the prob or not