Truck has been running great, today driving to work on the interstate it began losing power going up hills, could not maintain speed. When I was coming home it could not go more than 50 up hills. It starts fine and idles fine. But when under full load it bucks, makes a buzzing sound, and loses speed. I changed fuel filter and put in gas treatment to no avail.

 

I forgot, it's manual, and has a carburetor.

 

It sounds like you are losing fuel pressure to me, this is a classic symptom. At idle, it does not need as much fuel supply. It bucks and backfires because it is running lean.

 

Try replaceing your fuel filter.

 

He said he did that already. ^^

 

Would you suggest changing out the fuel pump?

 

I would suggest checking the pressure.

Here is the specs:
Electric pump 2.8-3.6 psi
Mechanical pump 3.7-4.7 psi

 

Replaced the fuel pump, it was only 20 bucks. Same problem, no improvement.

 

hmm iam having the same issue with a 91 b2200 2.2bbl as well.
cant get it over 80klm at all. when i rev the motor it starts to lose power at about 5000rpm and blows out blue smoke. its also eating up gas like a crack ***** and buring oil at a 1L per day.

its also got 185k on it so wtf.
if you got yours fixed please tell me what u did.

 

sounds like you need a new carb. that is what happen in my 89 b2200