Carb swap?

[Randog]

Hello,

I'm considering my buying a '80 720 thats in better shape than my 620. According to Weber's website, the carburetor for a 620 is the same one they sell for the 720. So I was wondering if I would be able to swap carburetors before I got rid of my '73 620 that has an almost new Weber on it. Do they share the same intake manifold and adapter plate? Will the 620 run okay with a 1980 carburetor on it? Because If I can do it okay, I really rather keep my almost new Weber and sell the carburetor thats on the 720 with the 620. Thanks in advance.

[Zeusimo]

They Won't Swap

You Could Add The Weber To The 720

But I'm Sure You're Going To Need A New Adapter, And Linkage.

Unless There Both L Motors

[jefe de jefes]

1980 720

 

Should be a L engine so it should work. I think that was the last year for the L series. At least in Cali anyways. :cool:

[datzenmike]

You don't say what size motor is in the '73... could be L16 or L18, then again it could have been swapped. The '80 720 only has an L20B motor and that '73 carb won't be jetted for an '80 motor. It can be jetted for one, but isn't as it is.

[Randog]

Sorry, I didn't realize that Datsun offered more than one engine on these trucks. The engine in the 620 is an L16, the engine in the 720 is an L20.

 

It can be jetted for one...so it needs new jets, or the jets need adjusting? What will happen if I don't, it'll starve on fuel?

[Zeusimo]

Assuming It's Jetted For A L16, Then Adding It To A L20b Without Rejetting... It Would Run Lean?

[Randog]

Now also, my L16 620 has twice the power of the L20 720. I don't want to buy the 720 if I don't think I can get up hill doing better than 40. The 720 is pathetic! My '64 beetle had more power than it with a bad carburetor and a vacuum leak! A tune-up should fix that, right? Timing, air cleaner, spark plugs, things like that? I like the way my 620 drives. Just hums along down the road...like the cars in heaven, if there are any. If the 720 won't run that good, I don't know if I want it.

[ggzilla]

I didn't realize that Datsun offered more than one engine on these trucks

Datsun didn't. But it is common for owners to have swapped them.

 

When new there was no choice:

1973 was L16

1974 was L18

1975-1979 was L20B

[ggzilla]

my L16 620 has twice the power of the L20 720

 

It only feels that way because:

* 620 is much lighter than 720

* 620 is lower-geared tha most 720

* Possibly, your 720 issn't tune right, carburetor may be worn or inducation system has vacuum leak

 

But I suspect the 1973 carburetors are more richer jetted than 1980 carburetors. L20B and L16 both take require the same air fuel ratio, but for 1973 it wasn't so critical to run on the edge of lean.

[Randog]

So maybe it will never seem as light and touchy as the 620, but I'm still thinking maybe it ain't tuned right. I don't think thats all of it, the 620 will climb the hill by my house at 60 miles the hour, with a little work, the 720 is flat ground, petal on the floor, 60 the hour. But it climbs the same hill at 40. If the hill was any longer, the 720 would be in 3rd gear. The 720 should probably even do better than 60 on flat ground if its geared higher, right? One thing my grandfather, the proud owner of 3 Datsuns (that I know of) says is that if the timing is off even a little bit, that can and probably will cause it to lack power. Sparks to late, then the full power of the explosion won't be felt by the engine as it should be, therefor causing it to lack power. Who knows how long its been since the 720 has been maintenanced. Obviously I don't want to put any money into it until I know I want it, so the very first thing I was gonna do was time it. And if I can get away with swapping carburators, that will make a worn or out-of-adjustment carburator the problem of whoever buys my 620.

 

What do you mean "but for 1973 it wasn't so critical to run on the edge of lean."? If an L20 is rich, is that somehow worse than if an L16 is running rich? Or is it some sort of emissions deal? And then therefore, wouldn't I be able to just take off on the lean rich a little bit?

 

But, the basic answer to my original question is yes. Since they're both L engines, the carburetors will bolt up to fit, but I may need to adjust the Weber or even re-jet it in order for it to run like it should. Thats good to know. Thank you!

[ggzilla]

720 2WD was jetted lean. 4x4 720s are jetted for performance. None of them were jetted "rich". You can't adjust that away with the idle mixture screw, because it is the main jets & air bleeds, the power valve, and accelerator pump specs.

 

Yes, go ahead and time it. Takes about 15 minutes. You need an RPM meter, a timing light, and a 10mm wrench.

[Randog]

I went to time it and not only does my lousy manual not have ignition timing in it, but you also can't seem to find that information on the internet. What is a 1980 L20B supposed to be timed at?

[ggzilla]

Put it at 10 degrees BTDC. It'll work fine at that setting.

[Randog]

Alright, thank you.