Fuel Starvation issues

[Mitchell]

Hi All

I have a 2000 Bigfoot with 18 HP Vanguard Engine (260 hrs). I just changed the fuel filter, but I don't know if previous owner ever serviced the carb. I have it out two times now with the same problem occurring. It won't start cold without first priming through the carb (a real pain). The choke does not seem to have any affect. After running for about an hour (idling most of the time), the gas gives out. The engine won't accelerate even in neutral. It will still idle but barely, and then just quits. I was out in the snow a mile from the trailer, and the only way I could get back was to prime through the carb all the way. It seems however if I wait a while (30 minutes) it will start and run OK. I did crack the gas cap open and heard a whoosh of air (in or out not sure) when I got home. Is this my problem or should I be looking at something else? Thanks for all your replies. Desperate

[jtb51b]

I bet you have a cap with a stopped up vent. Try starting it with the fuel cap off or loose. I would also check for rotting fuel and vacuum lines, ages gets those..

Jason

[ARGOJIM]

Sounds like the cap, another member mentioned a problem with the rear vent line collapsing, sound as if you may have both. the whoosh is a vacuum lock so the fuel pmp can not pull anymore gas.

[Mitchell]

Thanks for the advice. Do you know where is the rear vent line is located?

[dzg]

The fuel cap sound like it. But just for S's and G's you didn't put the fuel filter on backwards did ya?

[Mitchell]

Hi All

I am still having the same problem, even with the fuel cap loose or off. I double cheched the fuel filter and the arrow points to the carb. The engine runs for the first 30 minutes or so, but then suddenly dies and the only way to keep it running is with a prime to the carb. I have noticed an excessive amount of oil coming from the black vent tube and leaking into the carb. It dibbles from this tube all the time especially when you gun the engine. I have to wipe the top of the carb every few minutes. The exhaust is generally smoky. Does anyone know why I should see so much oil in the cab? It actually spilling onto the top of the engine.

[ARGOJIM]

Did you check your oil level? There are some known issues with overfull engines affecting the vacuum for the pulse of the fuel pump.

[msafi65]

I've also had the pulse line to fuel pump freeze over with condensate in the valve cover at temps below 32f. To check it out you need to check fuel flow from pump to carb or put a vacume gauge to pulse line when engine is dead. The cure is raising the air temp the engine runs in by restricting air intake slightly. An a MAX I close off almost all the engine cover and malt it run I warm air from inside the tub. Argo is a bit more touchy as the engine is enclosed more and needs some air to cool. Carb ice is similar and can be seen in the throat of carb with aircleaner removed. Look straight down in carb after engine dies and see if there is ice in the Venturi. Same cure, raise air temp to carb. This can happen in high humidity areas at anything below 40 F. Air cools engines in cold weather are tough to keep running good. Aircraft people know how to do it well. We walk home they fall out of the sky.

[Mitchell]

The oil level was high. I removed the oil (thinking gas contamination), added 5W-30, and changed the fuel pump. It started for about a 5 minute idle, and a 5 minute run in gear, then sputered out and died. Kept it going only with a prime to the carb. What are the issues to look which affect the pulsating vacuum develo[ped in the crank case?

[ARGOJIM]

Try an electric fuel pump and see if the problem cures or not. There is a thread on this down this forum a little.
If you can get the thing up to temperature do a compression test. Also may want to check the valve adjustment. If it has no compression it may have no intake suction.