The Stovebolt Site Forums The Shop Area Engine Shop Fuel drainback, hard starting...

I've got a 1950's 261 cid 6 cyl. Rochester B carb, if it sits for more than a day or two the sight glass fuel filter in front of the carb is dry (fills in less than 10 seconds of cranking) even with full choke it won't start unless I pour gas down the throat of the carb...it will restart ok for 2-3 hours later, then after that I have to do the priming thing again....Carb has fresh rebuild/needle/seat/float, ?????float level low?????

I am no carb expert, but I would say your fuel bowl is not full. That is one of its purposes. Unless it has a leak and it all drains out while sitting for a while.

On cold days where I go a week with out starting, it takes a few cranks to get things going.

Your fuel pump has two - one way valves in it. It's possible that the one preventing backflow has partially failed and, while still allowing the pump to pump fuel, is allowing the fuel to siphon back out of the carb when the engine is shut off. Just a thought.

Check your accel. pump. Look down the throat of the carb & work the throttle starting from a closed position. You should see a squirt of gas going in each time. The float level may be low also. If the accel. pump is working pump it a few times when starting after setting. That is the same as pouring gas down the throat.

Tiny's probably right. I'm having a similar problem, and I've got a rusty tank.
I think I've some rust in my pump - Maybe you picked up debris from the tank?

your problem is a leaky fuel pump.........ive had the same problem on 3 of my antique autos......i put a fuel pump kit in each one from jim carters and they all hold prime now........and one auto a 1941 ford still has the original fuel pump that has never been touched......im looking for it to happen soon after 67 years.........

Okay. I'm not an expert, but I don't see how the fuel can siphon out of the Rochester Carb normally found on the older 235s and 261s. Where the fuel goes into the carb is on the top of the carb. If the float is up, the seat would be closed, if is open because of low fuel level in the carb, air would enter the fuel line instead of fuel.

Most likely culprit on loosing fuel I would think would be the carb leaking somewhere and emptying out, or the fuel evaporating out of the bowl after it sits a while.

Also, if there is supposed to be a check valve in the carb for the accelator pump it could have been left out on the rebuild and not pumping the fuel into the manifold.

I don't ever remember seeing the glass sediment bowl on my truck completely full, yet the truck runs fine.

Granted it wouldn't syphon out of the bowl but it would the line from the carb to the pump. Add to that heat related percolation & evaporation of the gas in the bowl and you have the symptoms he described.

Fill the carb up and get the truck running, then pull the carb off and set in on the bench and watch it for the three or four hours. If it leaks out, tear it apart and find out why. If there is no leak, then the fuel is evaporating out due to heat, a heat spacer can help this. Check the fuel pump for the check valves, your fuel line should never dry out if the pump is good.

Joe

I'll Give it a try on removing the carb, have to recheck the float level anyway....

Had the same problem when I had a single Roch "B" on my 261. Always had to prime it with gas or use "Nitro" in the rattle can. When I changed to my dual Holley Webers I thought the problem would go away but even with an electric choke, if it sits for a couple of weeks, I need to pump the pedal several times to get it started. Not a real problem but it still give me the impression that the fuel is evaporating in the bowls after sitting a long time.

Found the problem.....Gee I am a Dumb As$...
the spring which wraps around the choke shaft came off....I apply
the choke and the shaft moves, not the plate....
reinstalled and works fine now....Shoulda took off the oilbath aircleaner to check choke operation....DU'oh!