bucking pickup

Hello;

I posted a message a while back about my truck. It has a
driveability problem that I can't get a handle on. The truck will
idle roughly and buck and cough on acceleration. Check engine light
does not come on. Makes it a real pain to drive! Then the problem will
clear up mysteriously for a short time and then return.

89 Isuzu Pickup 2WD 5-Speed 2.3L 2bbl. carb 135K miles mech fuel
pump

rebuilt carb, new dist cap, rotor, plugs, wires, have swapped out
the ignition coil with no results, tested compression (low), replaced
timing belt, set ignition timing, checked fuel pressure (little low
) 3.5 normal - 3.0 tested

The truck ran fine when I started it today so I took it for a 12
minute run around the neiborhood. It ran perfectly (good idle and
smooth acceleration with no bucking) until I got home and then started
to idle roughly and stall when I stopped in the driveway.

Does the fact that the truck will run perfectly at times tend
to point to a electrical problem? Something heating up and then
malfunctioning? If so should it not run fine again when this part
cooled off? It does not!

If it were a fuel or vacuum problem would it not run lousy all
the time? (mechanical fuel pump)

Any suggestions on what to look for or how to further test for a
solution to this problem would be greatly appreciated!

Just got mine out of the shop for similar problems.

Water build up in the tank kept gumming up the carb. So, when the float was
floating, it worked fine, but when it had too much water in the bowl, it ran
rough. And it depended on if I got gas at Shell (bad) or Chevron (ok).

A crack around the gas tank sending unit meant when rainy season hit here a
month ago, it got steadilly worse until it died on the road with too much
water in the gas to run.

Most annoying thing is that if you worked on it, it improved....for a few
days.

John

<JW> wrote in message news:3b8c21h4a9foni95bgnvf3b78at8m6i8lg@4ax.com...
> Hello;
>
> I posted a message a while back about my truck. It has a
> driveability problem that I can't get a handle on. The truck will
> idle roughly and buck and cough on acceleration. Check engine light
> does not come on. Makes it a real pain to drive! Then the problem will
> clear up mysteriously for a short time and then return.
>
> 89 Isuzu Pickup 2WD 5-Speed 2.3L 2bbl. carb 135K miles mech fuel
> pump
>
> rebuilt carb, new dist cap, rotor, plugs, wires, have swapped out
> the ignition coil with no results, tested compression (low), replaced
> timing belt, set ignition timing, checked fuel pressure (little low
> ) 3.5 normal - 3.0 tested
>
> The truck ran fine when I started it today so I took it for a 12
> minute run around the neiborhood. It ran perfectly (good idle and
> smooth acceleration with no bucking) until I got home and then started
> to idle roughly and stall when I stopped in the driveway.
>
> Does the fact that the truck will run perfectly at times tend
> to point to a electrical problem? Something heating up and then
> malfunctioning? If so should it not run fine again when this part
> cooled off? It does not!
>
> If it were a fuel or vacuum problem would it not run lousy all
> the time? (mechanical fuel pump)
>
> Any suggestions on what to look for or how to further test for a
> solution to this problem would be greatly appreciated!