Desmogged 74 struggles on cold starts (1 Viewer)

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Portland, OR
I'm wondering why fuel is not getting to the cylinders on cold starts. There is initially some firing for a second or two but that's all. Takes too long to get it going. Fuel in the carb glass window. Ignition is all good. Tank is vented.
Stumped!
 
Will do on the next cold start. The engine and carb and everything is brand new. Did these engines ever just fire up?
 
I just go full choke and leave the pedal alone when cranking. Works like a charm on my 71 F. The carb is a made in Japan Aisan.
 
Nope. Full choke makes no difference. Cranking for 2 minutes. The trick seems to be cranking it a bunch and then letting it sit awhile and then cranking it again. Too much battery being used. Somethings still not right.
 
I'm wondering why fuel is not getting to the cylinders on cold starts. There is initially some firing for a second or two but that's all. Takes too long to get it going. Fuel in the carb glass window. Ignition is all good. Tank is vented.
Stumped!

This sounds like there is fuel in the bowl initially, but the fuel pump is not pumping fuel after the “initially firing”.

Do you have an oem mechanical fuel pump or an electric fuel pump?

If mechanical, are you sure it’s actually pumping properly? Have you tested your fuel pressure at start-up? Have you sniffed your dipstick to see if it smells like gas?

If electric, is the electric pump lower than the fuel level in the fuel tank? Electric pumps push fuel, rather than suck fuel. But, they will generally self-prime if they are “downhill” from the fuel tank. Unless it’s an old or defective electric pump and is having a problem self-priming.

Are you using a clean fuel filter?

If your soft fuel line is old and brittle, the pump could be sucking air.

Your hard lines, along passenger frame rail, are the low point in the fuel system. They could need to be cleaned out.
 
All the fuel lines, components and pump are brand new. Everything is mechanical. It would seem the fuel pump is initially slow at getting fuel to the carb. Or the lines empty out somewhere. Probably because the tank is vented, the fuel just drains back. I imagine the fuel is supposed to remain under pressure but that was causing me the opposite problem of preventing fuel from getting to the carb.
 
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So, it’s a new mechanical pump... and you’ve had this problem for the life of the pump?

Test the fuel volume (<— Edited: thanks @thebigredrocker !!) ... use @Pin_Head’s method:

“Remove the coil center wire and the fuel inlet pipe at the carb. Stick the pipe into a bottle and crank the engine for 15 seconds. You should get at least a half a cup of fuel.”
 
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So, it’s a new mechanical pump... and you’ve had this problem for the life of the pump?

Test the fuel pressure... use @Pin_Head’s method:

“Remove the coil center wire and the fuel inlet pipe at the carb. Stick the pipe into a bottle and crank the engine for 15 seconds. You should get at least a half a cup of fuel.”

volume does not equal pressure.
 
will it start if you give it a squirt of ether or dump some fuel down the carb?
 
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On my 74 if I have not driven it in a day or two I pump the pedal 10 times and have the choke out - not fully but pretty far. Even then it might take a couple turns of the ignition to get it started. Then I usually adjust down the choke as it is too high (need to fix that at some point). Then I'm good to go. Let it warm up for about 5 minutes, still sputters a bit at low RPMs. Not until the engine is nice and hot does that go away. Usually another 5+ minutes of driving.

I recall reading modern gasoline drains from the carb due to its composition vs. the good ol' stuff...

And @pngunme there is an edit function on the iphone, it is small however - three faint lines.
 
If vacuum is low overall, it will be even harder to start when cold and vacuum is extra low. How does it run when it's all warmed up?
 

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