78' 620 carburator to 71' 521

[Gerbear2017]

Will the carburetor from my 78' 620 KC fit the l18 in my 71' 521. 

Put a new fuel pump on the 71', it idols okay. When I drive at low speeds it does fine, but at higher speeds it bogs when I push gas and dies at times. Next step is carburetor I think. Any advice?

[BrothersGarage]

Depends on the part, but there are carbs that work on all of the trucks such as this: https://www.amazon.com/DATSUN-CARBURETOR-CONVERSION-NISSAN-CARB/dp/B00TZ9E4B8

[datzenmike]

Easier to fix the carburetor. You say high speeds it falls on it's face? Probably not getting enough fuel.

 

1/Look at the glass front of the carburetor while idling. Is the fuel level at the horizontal line? Or close to it?

 

2/ This could simply be a dirty, part plugged fuel filter. At high speeds more gas is used by the engine than can get through the blocked filter. If you have never changed the fuel filter do so now. They are cheap and no harm done if this does not help you.

 

3/A partly blocked primary or secondary jet can also produce the same symptoms.

 

Remove the carburetor and look under the float chamber for two 12mm metal plugs that cover the primary and secondary jets. This carburetor is upside down so the brass jet shown up inside is the secondary. You'll need a flat blade screw driver that will fit the jet but also narrow enough to reach up inside. I had to grind one down for this.

 

They look like this with a small easily plugged hole in the center and small number stamped on them. Check that they are clean. Do NOT mix them up they will interchange. Primary jets are 'around' 99 and secondary around 150 so the larger hole goes in the secondary position.

 

 

 

[Gerbear2017]

I will do this. It has a Holly carb on it. Probably just rebuild it

[datzenmike]

Now you tell me. This is info that should have been included. I have no idea what Holly you have but I know that the 521 carburetor was like.

 

A Holly 5200? Built under license from Weber? Or a 2 bbl for a 5 liter engine which is too large and probably the real problem?

[Gerbear2017]

So it came on the truck when I bought it. It's a 2BBL 4421-5 model 2300. It's a mess

[datzenmike]

Yeah that's a 500 CFM carb when you only need just over 200. Too big and both barrels open at the same time so it's bound to bog badly. Jets are probably for a 6 or small V8.

 

 That '78 would be closer to what you want.

[Gerbear2017]

Ok. So it will swap over? Haven't tried it yet. Planning tomorrow for it.

[datzenmike]

Check the bolt pattern but I think the  L18 used a 340 style carburetor. 

[banzai510(hainz)]

Holly hads a 5200 which is a Pinto/Capri carb I think.

 

you check the timming?