Need help with an ignition issue.... Please!

[ORB1TAL]

Good day Ratsun Community! This is my first post on this forum and I look forward to chatting with all of you fellow enthusiasts. I have been  along time admirer of 520's and 620's and I'm happy to say I've have finally picked up a 1973 620 as of two days ago. With that being said, 95% of my experience working on cars has been my 370z and helping friends out with their cars (which have all been 2010+ model years) and therefore I have little knowledge on what it takes to maintain carbureted engines. The 620 I bought is in decent shape, runs and drives but has some small issues. PO said that the OEM engine (came with the 1.6) was swapped with the 1.8 Liter (which I'm assuming is the L18?). It has a weber Carb on it with an electric choke. In the mornings I have to sit there for upward of 15 minutes trying to get it started. A few hours later, when its time for my lunch break from work, starting it maybe takes 2-3 minutes, and when I go home it takes usually 2-3 cranks before it's running. Via the research I've done online I'm led to believe that the electric choke may be out of adjustment, but I'm not 100% sure. Does anyone know of some good reading material or YouTube videos that may be able to point me in the right direction of what's going on? I also haven't seen any kind of stamping or plate on the engine designating what it is, although I don't really know where to look  Any help would be greatly appreciated! Pictures added for reference.

 

 

TL;DR: This is my first carbureted vehicle(bought two days ago). 1973 Datsun 620 with 18L (as for as I believe) takes an unusually long time to start in the mornings, slowly gets better throughout the day. Looking for reading material or media of some kind that may help me figure out what's wrong.

 

[datzenmike]

When starting your cold engine do you step on the gas first? Unlike all EFI engines a carburetor needs to be told that you intend to start the engine. Stepping on the gas sets the choke. Now you may be doing this I don't know.

 

Next time the engine is cold take the top off the air filter and look down inside. Have someone step on the gas and the choke plate should snap closed.

[ORB1TAL]

3 minutes ago, datzenmike said:

When starting your cold engine do you step on the gas first? Unlike all EFI engines a carburetor needs to be told that you intend to start the engine. Stepping on the gas sets the choke. Now you may be doing this I don't know.

 

Next time the engine is cold take the top off the air filter and look down inside. Have someone step on the gas and the choke plate should snap closed.

Thank you for the tip I did not know this, am I holding the pedal as I'm cranking or is it pedal in and release, then crank?

[datzenmike]

I would release it. As the weather gets a lot colder you can try 2 or 3 pumps.

[ORB1TAL]

4 minutes ago, datzenmike said:

I would release it. As the weather gets a lot colder you can try 2 or 3 pumps.

Thank you very much!

[banzai510(hainz)]

As Mike mentioned the choke plate will be closed when cold.

I always pumps the pedal a few times before start up.

when it warms up the choke plate on the side of the carb will heat up like a coil stove element and then it bends and opens the choke plate.

I will assume you have a wire that was 12volts on there with the key ON.. If the plate moves when it warms up then yes you have it. I CANT SEE IF THERE IS A WIRE on the choke. take close up photos.

 

I have 2 questions

1) where is that red and blk wires coming from and where they go?  is this a Pertronix and they routed it up and over to the coil or where does this go? If it is the Pertronix wire why didnt you just jumper over to the coil. its shorter. just blk tape it and still looks stock.

 

2) the coke Bottle in the back by firewall with the hose going in. It cant be th radiator cause I see that hose. what is this?

 

Your truck is the simplest of the early L motors as no emissions. No reason why this cant last ez any 5 years

 

 

your truck onced warmed up does it idle ok? is so then the mixture screw is pretty much set right. I would get a timing light and time the truck also. say around 10-12 before top dead center would be fine

Edited November 10, 2023 by banzai510(hainz)

[ORB1TAL]

On 11/9/2023 at 7:06 PM, banzai510(hainz) said:

As Mike mentioned the choke plate will be closed when cold.

I always pumps the pedal a few times before start up.

when it warms up the choke plate on the side of the carb will heat up like a coil stove element and then it bends and opens the choke plate.

I will assume you have a wire that was 12volts on there with the key ON.. If the plate moves when it warms up then yes you have it. I CANT SEE IF THERE IS A WIRE on the choke. take close up photos.

 

I have 2 questions

1) where is that red and blk wires coming from and where they go?  is this a Pertronix and they routed it up and over to the coil or where does this go? If it is the Pertronix wire why didnt you just jumper over to the coil. its shorter. just blk tape it and still looks stock.

 

2) the coke Bottle in the back by firewall with the hose going in. It cant be th radiator cause I see that hose. what is this?

 

Your truck is the simplest of the early L motors as no emissions. No reason why this cant last ez any 5 years

 

 

your truck onced warmed up does it idle ok? is so then the mixture screw is pretty much set right. I would get a timing light and time the truck also. say around 10-12 before top dead center would be fine

Sorry for the late reply, gets busy around the holidays. I have gotten a more consistent start after learning about the need to pump the pedal so thank you for that, as for your questions I can answer both of them. The red and black wires going up and around go to the ignition coil. It seems that the PO had wired them up that way, if there is a better/cleaner way to wire them please let me know. There is a wire on the choke, it follows the ignition coil wires and goes up and around the engine bay. As for your second question, it is a washer fluid reservoir. Both that and the coolant reservoir are coke bottles, I haven't yet had the time to look for actual reservoirs haha. I will post better photos below.

 

 

I seem to be having a few new issues now, as you can see from the last picture there is a lot more carbon buildup on the left barrel of the carb. Secondly, upon tapping the gas pedal before starting, occasionally the butterfly will get stuck closed and I have to take the filter off, push the plate open, start it and then put the filter back on. Lastly, upon starting, after letting the high idle run for about 10 seconds, I tap the gas to bring the idle down, and after doing that the idle will slow down and eventually the engine will die. I can start it up again after it dies and it runs fine. I'm not sure if these problems are related but after researching it seems to be as simple as a carb cleaning/adjustment? any information would be greatly appreciated as I'm going to do a ton of research/video watching in preparation for this carb maintenance. Thank you!

[datzenmike]

I wouldn't worry too much about the black stains on the inside of the carburetor.

 

There is no need to tap the throttle to bring the idle down. 10 seconds is a long way from being warmed up and ready to idle by itself. If you have a couple of minutes let it warm up, if ready to go, start driving.

[ORB1TAL]

8 hours ago, datzenmike said:

I wouldn't worry too much about the black stains on the inside of the carburetor.

 

There is no need to tap the throttle to bring the idle down. 10 seconds is a long way from being warmed up and ready to idle by itself. If you have a couple of minutes let it warm up, if ready to go, start driving.

Ahh I see, so just like a modern car has open loop/closed loop fuel injection the idle should go down on its own as it gets warmer?

 

Thank you for your help!