Weber 32/36 Carb spitting on 1975 Datsun 620

[H3nleY]

Hey y'all!

 

I've been working on getting a 1975 Datsun 620 running that has been sitting in the yard of the car museum I work at for at least three years now. Thanks to his forum and much research, I was finally able to get it to start.

 

The issue now is keeping it running. Keep in mind I'm still pretty green when it comes to fixing cars but I learn quickly.

 

The truck is equipped with a Weber 32/36 carb and an automatic choke in place of the stock one. I have an external, electric fuel pump hooked up to a gas can to feed the carb as the mechanical fuel pump doesn't seem to work. 

 

Whenever it starts and the choke is open any amount, it will spit through the carb and die (sometimes in an exciting and fiery fashion). When it does this, the RPM ramps up alarmingly and pulls the choke plates open before putting on the fireworks show. If I keep the choke plates closed by hand, it will run but also alarmingly ramp up the RPM until I have to kill it in fear of blowing something up.

 

I've cleaned the carburetor so I know it is gunk-free. I've tried adjusting the idle mixture and idle speed screws but to seemingly no avail. The carb is tightened down but the vacuum advance is not hooked up anywhere. It's just plugged.

 

Is it possible that the pump I am using isn't giving it gas fast enough to keep it idling thus creating a lean condition when the choke plates are open? Could the lack of distributor-provided advance play a hand in this? Or, alternatively, do I have a vacuum leak somewhere? I'm open to suggestions.

 

Thanks!

[datzenmike]

Make sure the secondary is closed.

 

When cold, the mixture does not vaporize efficiently and the engine will act lean. When lean there is a tendency to 'lean backfire' through the carburetor. Choke should still be on, to some extent, after start up. If backfiring, try turning the choke adjustment towards richer.

 

Engine should rev up slightly when the choke is on. The choke linkage sets it to 'fast idle' Fast idle should be around 2,000 RPMs. Fast idle when cold it the fastest way to warm the engine.

[victhewhimpykid]

I agree with everything Mike said but have you set the fast idle speed screw and mixture screw to factory settings??? I would disconnect the wire for the automatic choke for now till the engine is warmed up then set the choke setting you like. You can actually set where you want the engine to fast idle at when you first start it. I had it originally set at 2k but then lowered it to 1500. I would also hook up a 1/4 inch vaccum hose from the carb to the vacuum advace on the distributor just to rule out that isnt causing the problem.