The Stovebolt Site Forums The Shop Area Engine Shop fuel pump flow and pressure during cranking

I have a hard starting problem, it appears to be not enough fuel flow while cranking. Choke is no help. A little ether and starts fine and runs fine. What should the fuel pressure and flow be during cranking for a 1952 GMC 6 cyl one ton? It has a manual fuel pump. I put a clear fuel filter in-line and it does not fill up while cranking and only 1/2 full while running. The filter is just in front and level with the carburetor. Would you suggest a 6v electric pump?

Sounds more like the carburetor bowl draining down. I'm no expert but there should always be a full carburetor bowl when starting, unless you've let it set so long that the fuel has evaporated. An electric pump would be a band-aid. It would be better to track down the cause of the issue.

If you are having issue with starting after setting for extended periods, then it's just the modern gasoline causing issues. Todays fuels evaporate much quicker and leave behind more stuff when they do. In this case, a small electric booster pump would be a good thing. Only use it to prime the system, have a push button switch that only works if you have your finger on it. They can be placed inline with the OEM pump, fuel can be pulled through them with the stock pump.
If this starting issue is everyday or so, you may have a weak pump. I wouldn't expect to see the glass filter full, they never are. Lawn mower filters are the same way, they are never full. Stock pumps would be in the 3-5 psi range.

Over the past 20-something years, I have posted the correct fuel pump testing procedure at least 50 times. To the best of my knowledge, nobody has EVER followed it correctly. It takes less than 10 minutes. Good luck!
Jerry

I looked for your previous posts about fuel pump testing procedure and could not find them. Would you please repost it. Thank You

One more time- - - - -might as well add to the "won't do it" list! Obtain a pressure/vacuum gauge from a local parts store, Ebay, Amazon, or a dozen other sources. They're less than 20 bucks no matter where you find one. "deadhead" the fuel line at the carburetor into the gauge line and run the engine at idle on the fuel in the float bowl. The pressure should be somewhere in the 2-4 PSI range, and (this is important)- - - -it will stay there for at least several seconds after the engine is shut down. This tests the outlet check valve of the pump. Now, switch the gauge to the inlet fitting of the fuel pump. Idle the engine. The vacuum should be around 10 inches of mercury or more. The vacuum should also stay there for a while after shutdown, checking the inlet check valve. Final test- - - -run the engine at idle for 30 seconds with the carburetor line plumbed to a catch container- - - - -it should flow at least a pint of gasoline (2 cups). It sounds like your hard start problem is one or both check valves are failed, allowing the fuel to drain back and empty the carb inlet line. A pinhole leak in the flex line from the fuel pump to the frame will also allow the fuel line to develop an air lock, usually without making a puddle of gas in the floor.


www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html


I learned the above procedure in the early 1960's and I've done it a minimum of several hundred times since then.
Jerry

Jerry, ask Woogeroo or Phak1 to add the fuel pump test to the Engine Tech Tips. You would need to provide a clear procedure and narrative for them to post.

I would be happy to make it a tech tip. Please clean out your PM’s. Tried to send you a PM but your over your limit.

You can either edit your previous post to look more like a procedure or send it to me!

I just spent 30 minutes writing a tech tip and the forum ate it when I tried to do an edit. I'll try again later!
Jerry

It’s done! You will find it under the “Engine” forum at the very top as a Sticky Note Here is a[LINK].

Thank you on behalf of all the ‘bolters including myself, that will use it in the future!