At this time I am not ready to do an LS swap in a Datsun 620. I have a lot of research to do before starting that project. Plus, I need to finish the 89 Mazda B2200. My goal is to get this truck drivable so I can play with it from time to time. Unfortunately, every seal on the carb was leaking. Not fixing or replacing the carb would result in this Datsun going up in flames. I am by no means a carb mechanic and certainly don’t want to learn how to rebuild that stock thing. Only option was a new one. Might as well go bigger.
First thing I did was to search the forums to see what Weber most guys were running on these L20B’s. I settled on a Weber 38/38 Performance conversion kit fits that fits the Datsun 510 610 620 720. Found it on eBay for $338. I went with the larger 38/38 because I want all the power I can get and figure it will get a cam before an engine swap.
After picking a carb, I started looking around at the intake set up on these Datsun’s. What was Nissan thinking?
The exhaust manifold is tied to the intake. Really? The exhaust is actually heating the air going in to the intake thus reducing power. In addition to that there is an insane amount emission junk on this 1977 L20B including an air pump. That has to be robbing some of the valuable power this engine is producing. Besides, I figure it is easier to remove all that and install a header then it is to hook all that junk up to the new carb.
I have changed a fair amount of GM carbs and I promise none of them were this hard to get off. Again, I want to know what Nissan was thinking. It is almost impossible to get the 4 nuts off the carb. I actually had to remove the air injection tubes from the manifold to get a short wrench between the valve cover and the carb. Lots of time was spent looking and thinking. I pretty much took everything off the driver side of the engine to get to those 4 nuts.
Once everything was finally removed I noticed one of the few exhaust bolts was broken off. No, I didn’t break it.
I decided with so few bolts that it needed fixed. I found a drill bit slightly smaller then the bolt and attempted to drill out the center of the broken bolt. I didn’t bother with an easy out. I just drilled the bolt then cut new threads in the aluminum head. I wasn’t dead center, it never is. I was just a little to far to the front and got into some of the head. There was enough slop in the new header to not have any fitment issues. Since the head is aluminum, I simply cut new threads by forcing a bolt into the hole I drilled. Im not that much of a shade tree mechanic. I know that would not hold up for any length of time. I took the bolt out after cutting threads and put a stud in. I filled the hole with JD Weld and forced the stud in then let it dry over night before attempting to put the header on.
See… JB Weld is much better.
Im sure it would have been better to have pulled the head and taken it to a shop to have it done right. That said I bet my JB Weld fix holds just fine. It a $1500 Datsun with an engine I don’t plan to keep.
I installed the header a few days later after cutting the old exhaust off. The old exhaust was in the way and would not let the header bolt on.
Installing the intake was more work then I initially expected. I did not want to keep all the emissions stuff. But… that stuff is kinda made into the factory intake and these days it seems there are no aftermarket intakes. I decided to cap off the EGR valve and the intake heater.
I took the flange off the exhaust manifold and reused the gasket to bolt it to the intake manifold. Had to do something since the bottom of the intake was a giant open hole. A trip to the local hardware store provided me with the new shorter bolts. The bolts are 8mm with 1.25 pitch if your looking for them.
Take note… after taking this picture I took the lower bolts out an flipped them. I preferred the look of the bolt head up but they hit the header. Flipping them gave me more clearance.
As I said I did not want to run the EGR valve anymore. Honestly, I don’t really know what they do and don’t care. Its just one of those things you take off a GM product and trash. I see no reason to treat this any minitruck any different.
I took the gasket off the EGR valve and traced it to a plate of thin steel.
Once it was traced I cut it out with a grinder. Then drilled 3 holes in it. Yes you can see 4 holes in the picture but only 3 were threaded. Using the original gasket I bolted the new cover to the intake.
That pictures shows the EGR block off plate but I got ahead of my self. The intake isn’t on at this point. There was some more work to get it to fit. Do headers ever just fit? They never do for me and this one was no different. The intake hit the header in the center.
I ground the edge of the intake to gain some clearance. Yes, I knew that would not be even close to enough to make it fit. It is still that much less that I would have to dent the header in.
After carefully marking the header with a sharpie I got out the body hammers. No, I did not start out with a 25 lb sledge hammer. This header is very small and doesn’t need beat to hell.
I started trying to dent a nice curve in it with a large bolt. I gave that up after about 5 minutes. I took my time and slowly dented the header more and more trying to keep a nice flow. After a half dozen attempts I got just enough. Should be noted I left the header on while doing this.
It really isn’t as bad as that picture looks. Once the paint dried it blended in pretty well. The dent will have no impact on horse power and it not visible when the intake is on.
Once the intake fit the carb install was very easy.
The kit came with everything needed and instructions telling me where to hook up the vacuum advance. I plugged off the rest of the vacuum lines from the old carb. I left the vacuum port for the brake booster on the intake and hooked that back up. I still need to run the crank case vent and the valve cover vent to the port on the air cleaner. Im not going to tie them to vacuum but I will vent them to the intake so the gasses are pulled back through the engine.
For the choke I was able to use the red lead that powered the choke on the factory carb.
Truck fired right up after the carb filled with gas. I have not adjust anything on the carb. Its straight out of the box. I’m rather impressed with how well it runs at this point.