1987 b2000 bucking or or power loss at cruising speeds

[campsite428]

new forum member...just got a 1987 mazda b2000 (carb) 260K miles...have done all the normal tuneup stuff, replaced lots, cleaned carb (made a huge difference), etc....runs pretty darn good except that as i am coming up to the cruising speed for each gear it starts to buck, or stall sort of, feeling like either its timing isnt staying advanced, suddenly dropping or like its all of a sudden getting starved for gas...mostly only happens when warm, not when cold...will do its acceleration curve fine if i step into the throttle, but if i just lightly cruise up to speed it jerks and stumbles at medium to higher rpms (say 2200-3000, not sure no tach)...but if i really hit the gas, it just powers through it (sometimes...it will also feel like its just lightly losing power, and the accelreration curve just flattens, smooth running, but not raising in RPMs the same)...was thinking it was the fuel air control solenoid inside the carb...cleaned it real good, no diff....even replaced the vacuum advance module...just confused now...please help.....BTW the spark plugs are white at the tips...should i be thinking timing advance or carb mixture?



I HAVE SOLVED THE PROBLEM.......TURNED OUT TO BE THE CARBURETORS SECONDARY VACUUM DIAPHRAGM...was slightly cracked, creating a vacuum leak, and not opening the secondary properly, and allowing it to close when at higher rpms, starving the engine of gas and air...created rather odd symptoms while driving, but makes sense now that its fixed....i hope that this post helps someone else with similar problems...just go rebuild the carb throughly

[chickenandpickles]

sounds a bit like a vacuum problem in combination with carb setting...make sure your hoses are all connected right...make sure your not sucking air from around the carb gasket...

[campsite428]

im pretty sure the hoses are all correct, and plugged in, checked when doing the carb rebuild..but ill look again...and i had to clean off the carb gasket area, so it should be good, but ill get out my propane and check it....if these are good though, then what?.....is this even a symptom of the fuel mixture solenoid being sticky, or does that do something completely different?