Intermittent Loss of Power

[Winooski]

My 72 Series 3 with 2.25L Pertol has been giving me fits lately. She will occasionally lose power in various situations (both hills and relatively flat roads). When this happens, she backfires when I hit the gas and nearly stalls when I slowly push the accelerator to the floor. If I get her moving, she randomly backfires (softly, not a cannon shot). I usually have to limp along with the choke engaged and feathering the clutch to get her to move. The crazy part is that it stops after a while (variable time spent swearing and asking why), and the truck runs great again.

I have recently gone through the valve/timing/carb tune-up route after changing the spark plugs, all seemed to be in proper order. Have been running a Petronix ignition for some time now without issue, and the sediment bowl on the fuel pump seems clear (will be checking that again tonight). There is an line filter in the fuel line just before the carb. I am also going to give the carb a good looking at tonight to make sure its clean/clear (Weber 34ICH). I also tightened the bolts on the exhaust and carb to see if a slight air leak might be the cause. No obvious holes along the exhaust either.

The return to normal function after these episodes is confusing. Any thoughts about potential causes? Vapor lock (truck has not been running too hot lately)? Other timing issues I should be looking at (timing chain)? Are there parts I should uniformly replace to eliminate potential problems while troubleshooting?

Thanks,

Patrick

[Rineheitzgabot]

You need to drain the diesel fuel that you accidentally put in when you grabbed the black pump nozzle instead of the green one, the other night while at the gas station.

Seriously, how good is the fuel? Someone put water in it? I would check the fuel, literally, and the fuel, generally speaking (i.e., tank, filter, pump, lines). Do you smell any gas outside the vehicle?

When it recovers and runs well, how long 'til it takes a dump again? Overall, does it run better more often, or worse, more often (looking for a percentage here).

-Gary

[Winooski]

I would say I get about 70% running OK and 30% running crap-tastic. There is an occasional smell of gas outside the vehicle, but not overpowering or ever-present. I have used the same gas station for a while, but maybe some fuel cleaner is in order as well.

Patrick

[NickDawson]

Two thoughts based on similar experience (with a 2.5L petrol and slightly different weber carb):

edited:
after typing a nice post about my experience with a bad condenser and points I re-read you post...never mind. :D

Mr. Mohan had similar issues that he finally solved with an electric fuel pump

[thixon]

Air leaks are a possibility, but Nick gave you good advice on the fuel pump. Try an electric clicker from NAPA. Also, replace that fuel filter.

[73series88]

my weber has to cleaned out about every 6 months

just sedement in the jets
i have 3 filters including the pump bowl
just collects in the bowl