Datsun Roadster Forum-311s.org

I have a '70 1600 and I've changed something with my carburetor connections that causes the engine to flood.

I removed my carburetor, cleaned it (chem dip + wire brush, new seals, some new lines), and reinstalled it back into the Datsun. My Before pictures weren't good enough because I don't seem to have connected the lines correctly. I can start the engine and it'll run, but after I turn it off, it smells strongly of gasoline, the starter turns, but the engine won't start. I think it's flooded because it'll start if I wait an hour or two.

Two views of the carbs in their current condition: Couple of questions:

• I've marked the fuel line in red. It goes from the fuel filter at the front-right of the car (not shown), feeds both carbs, and then goes into a tube leading into the firewall.

• What is the line in green? It currently goes from the bottom of the left carb to a t-junction in between the carbs, and then to the bottom of the right carb. Is that correct?

• What is the component in yellow? The t-junction leads into this.

I've looked at the Sheeler books, an SU carb book, and some online diagrams, but I can't find a diagram that includes the hoses. Any ideas on what I did to cause the engine to flood?

Thanks,

BC

I’m not familiar with SUs, just Solexes, and the connections there are unfamiliar to a ‘68/‘69 U20 owner, but this could easily be sunk floats or needle valves jammed open.

Ah, so maybe the lines are in the right place. I'll see if the floats or needles are stuck.

Device in yellow is emission control bypass valve. Green and red Hoses look correct

See this diagram: https://www.carpartsmanual.com/datsun/s ... l-device#2

Thanks, Joe. Looks like the problem is in side the carbs then. Needles or float. Maybe something is sticking...

You can check the float bowl level by removing the overflow tubes and eyeballing into the top of float chamber.
They should not be full but the float should be able to be seen and poked at to check if is still indeed a float.
Mind you it doesn't take much debris to jam the float valve open, been there seen that

bchen wrote: Mon Nov 27, 2023 11:56 pm Thanks, Joe. Looks like the problem is in side the carbs then. Needles or float. Maybe something is sticking...

Doesn't have to be ,with a choke. It may have fuel fowled a spark plug , and isn't going to fire
I'd pull the plugs to crank it over to see how much fuel is in the cyl & intake ....let it air out then just put the s plugs back to see if it floods again with 6 -10 cranks , best to go with new plugs after

Alright let’s see if I can give you some clarity about float levels and why it’s so important. In carburetors the fuel level is very critical as fuel has weight and it’s on these principles that carburetors function. Think of it this way, as an air enters the engine it crosses over what ever method a given type of carburetors uses to draw fuel from the float bowl. In the case of the SU, it the nozzle that the needle enters and controls the volume to be delivered. As the needle rises it slowed more fuel to flow and conversely as the needle fills the nozzle bore it reduces flow. Now the reason the level and weight of the fuel is so important has to do with how easily it can be siphoned out of the nozzle. Low fuel takes greater velocity to siphon than higher fuel levels which can take little to no effort to siphon. Additionally if the needle valve assembly fails to seal you automatically have rich condition.

So always with carbureted engines you need to verify that every is in proper working order. Fuel level and delivery along with proper pressure are maintained. If you are smelling fuel after the engine is run and turned off, I would be suspicious of a flooding condition related to failed a needle valve or improper fuel level. Now you need to investigate if the problem is 1 float related, 2 needle valve assembly or 3 fuel pressure related. Good luck, and remember to do one check and verification of each item at a time so you can come to a definitive conclusion.
Dave

What I see are new fuel lines from the float chambers to the jets. They look too thick and stiff. It could be holding the jets from going back up after the choke has been used. The original lines are small and very flexible for that reason. Also in the first photo it looks like the choke is fully engaged but I don't know at what time in the process the photo was taken. You really need to run the float vent hoses longer so they are down below your frame rails. Really don't want to see a post about gas hitting the hot headers.

Thought I'd close the loop on this thread.

Turns out that RBMann can see a lot in a picture.

• My choke cables were too short. They were too ratty to thread through the tiny hole, so I cut some off not thinking that shorter cables would cause a problem. I ended up buying some bicycle brake cable and re-running them. Very satisfying fix.

• The replacement, non-standard fuel line caused one of the jets to get stuck in the lowered position. I ended up swapping fuel lines from a "practice carb" (a sacrificial carb that I've been assembling/disassembling for my own education).

The float vent hoses attach to the air box (where the air filter is). I'm assuming it's ok if fuel ends up in there.

Thanks for everyone's help!

Thanks for closing out this thread with your solution!