The Stovebolt Site Forums The Shop Area Engine Shop Fuel pump output

Generic question. Mechanical fuel pump rotating at a normal 6 volt cranking speed. How much should it pump in a 10 second cranking session? The one I’m checking pumps about 1/4 cup in rather erratic spurts. 🛠

Cranking speed is not a good way to check a fuel pump. At curb idle with a warmed-up engine, a disconnected fuel line at the carburetor should pump a minimum of a pint in 30 seconds -. Use a piece of rubber fuel line and a catch can held away from the engine compartment to minimize the fire hazard. If the engine won't idle for 30 seconds on the fuel in the float bowl, you've got carburetor problems.

The volume test is one third of a fuel pump check. Now check the pressure and vacuum of the pump. Since I've been recommending this for 20-something years and I can't ever recall anybody doing the full test, I might as well go look for a chicken with lips!
Jerry

Jerry, I agree that the other 2 tests are needed and I have the equipment to do them. Just posed the question, during a break, to see if it was necessary to continue on with the testing or if 1/4 cup in 10 seconds was good enough. FWIW the engine starts then immediately dies so I can’t do a curb idle test right now.

Rig a gravity feed fuel source and find out why the engine won't keep running. Then do things the right way. Model T's and Model A's ran millions of miles without a fuel pump.
Jerry

But sometimes, Model T's had to back up a hill with a low fuel level and the tank mounted under the seat. Model A's, with a cowl mounted tank didn't have that problem.

I can't seem to find the fuel pump on my Harley EVO, and it's got nearly 90K miles on it! Gasoline, like a plumber's favorite moneymaker, "flows downhill!"
Jerry

"It may be $%!* to you, but it's bread and butter to me"

1/4 cup in 10 full, timed with a clock, seconds, sounds low. 6V system or 12V system, makes no difference. Your test is good, it is real life condition. Simulating trying to start a motor that may have no gas in the carb bowl. Starts immediately? Then dies. Does it die immediately? Like real fast? That there is electrics. The ignition switch or foot switch or if you had a ballast system, it would be that. After it dies, check the throat of carb for squirt. Run a gravity gas feed into carb inlet without blowing yourself up. Seems odd there would be just enough gas in bowl for one squirt start and nothing left to run a minute. I'm going with electrics until you try some stuff. Check the linkage too.....and choke.
Erratic spurts is one thing.....it will pulse but be a evenly spaced steady pulse, and strong if battery is good. After lines are full, maybe one pulse per second. Try 15 clock seconds and see how much gas you get. The cam shaft is only running at half speed of the crank, so 10 seconds is short. On the other hand 1/4 cup will fill a carb bowl. So OK, I talked myself back to electrics/spark.

BOTTOM LINE: Your truck won't stay running, right? We should start there with normal trouble shooting. Gas/spark/air/compression.
I don't know what motor or ignition system we are talking about. Would be nice to know that. What key switch? solenoid or foot start? Must be 6V???? Must be 39 or 47?????? You have no right to remain silent, nothing you say will be held against you.

bartamos, the project must for obvious reasons remain undercover. Foot start, good spark (tested), electronic ignition, fresh pro rebuild on Stromberg BXV-3, fresh real gas. Right now I’m leaning toward a mess up by the carb rebuilder but I’m going to complete the fuel system tests before I exercise my 6 month warranty option. All ideas are welcome.

6V ? Pertronix? Rigging carb with a gravity feed bottle, no fuel pump, will sure help to eliminate or identify carb. Eliminate or identify any up stream problem. Pump, lines, debris, venting lock..... Rig it up and you will know today.

Any lawn mower or boat tank hung high will do. Temp. Tank must be vented or open top. Did you observe squirt after is dies?

“Did you observe squirt after it dies”, yes a fine mist. From what I’ve read the Stromberg has a circuit that comes into play as the engine starts to keep the gas flowing. May have gotten accidentally plugged during the rebuild. BTW the engine ran, although with a bit of hesitation, and the vehicle had several miles on it prior to the carb being removed for rebuild. I will rig a temporary tank tomorrow and complete Jerry’s other pump tests. Thanks for the helpful suggestions.

A pro rebuilder should be able to rebuild that carb easily. But Jerry knows that is wishful thinking. I just now see he said to rig a tank already. Sorry about the repeat but I feel good in that crowd.

Didn’t have time today to complete the testing. I pulled the spark plugs and all 6 were fuel fouled. I rounded up an old plastic lawnmower tank to rig up. I’ll pick up the new plugs and some fuel hose at the flaps tomorrow. Grandkids the rest of the day.

Just to catch everyone up. Fuel pump tested fine. Engine would not stay running even with an auxiliary tank. Carburetor was okay. Started chasing the wiring and found a broken ignition switch wire inside of a heat shrink sleeve. Sometimes it would make circuit and sometimes it wouldn’t. That bugger was a real treat to find. All is well and the suggestions were a big help.

Those are the most rewarding to find. Very wonderful result.