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Mazda Engine General \  87 B2000 idleing wierd....

87 B2000 idleing wierd....

Mazda Engine General Mazda Engine Mazda Tech
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replies 2
following 3
 
twisted   +1y
This is my truck we're working on but I'm gonna copy and paste the post a friend made elsewhere since he's helping me try to fix it.

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Im working on a buddies B2000.

It has this bizzare problem lately (it started after another friend "rebuilt" the carb for him). It will run fine, idle at about 800 rpm, and then it will slowly rev up until it hits about 2000 rpm, where it kinda bounces around. It runs fine and such, its just revving high, until you hit the brakes, where it slowly loses rpm's till it dies.
the motor was rebuilt about 3 or 4 years ago, and has had no real problems since. its stock except for a pace setter header and an aftermarket muffler of some flavor.

heres what ive tried to solve the problem.
-I swapped on another carb that i know to be functioning correctly (it was off a running truck)
-I swapped back to the original carb and eliminated all the smog silliness(capped all the vaccuum lines and double checked that I didnt miss any)
-swapped back on the known to be good carb (this time with all vaccuum stuff off and capped)
-I replaced the inake manifold gasket.
-I unhooked and capped the vaccuum assist for the brakes.
- I took off the valve cover today and ran it, everything appeared to be fine. I confirmed that the head was torqued.

Im at a loss now. none of the things I tried above made any difference at all. It continued to behave wierd fashion thru it all. Experience has taught me that when theres a problem, undo the last thing you did, and swapping on a good carb should have fixed whatever was "rebuilt" on the original carb.

Does anyone have any ideas?

Dave

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In addition we put a clear fuel filter on it so we can see the fuel and it seems to be getting a constant flow of fuel. Definatly not starving it. Should also mention it has less than 20k miles on the rebuild as it doesn't get driven much.
hocbj23   +1y
Number 1 cause of erratic RPM's is vacuum leak(s).Did u torque intake properly when u replaced gasket? Is truck timed correctly?Look at sight glass on side of carb and see if fuel is at correct level. Float may be out of adjustment.Is throttle cable installed properly and working properly?There is a small spring that returns throttle to stop position. Sometimes they break or are not installed properly.Just a few suggestions. Hope this helps. BJ
never2low   +1y
My truck's carb has gone through so much, i got vaccum lines in incorrect places, some arent even connected, and it revvs all weird. Sometimes at 800, sometimes at 2000, mostly at 200 though, it seems to like that spot too. So its probably some vaccum leak in your case.
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