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Just bought a 521


mainer311

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There is significantly less flow with those holes than when the t-stat is open. At some point it will reach steady-state and open up.

 

It will be interesting to see what this one does. If the engine never gets warm, I’ll just replace it.

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As I said guys, if you look how big the bypass hose is on the L20b lower thermostat housings, his multiple holes might work out close to the same bypass volume.

That is why I asked him to tell us how long it takes for the temp needle to get up to normal operating temp, I suspect 4 of them holes out of the 6 equals one bypass hose. 

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What overflow bottle did you go With?

Curious how it mounted and fit....

It's one of the things on my list of things to buy...

The first one I bought on Amazon for $10 and it was way too big. I bought a smaller one at Pepboys tonight and it’s an exact fit on the passenger side of the radiator. I’m making a L-shaped bracket that bolts to the front inner sheetmetal in which the reservoir will hang from.

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I need some help understanding the Hitachi carb. I’m coming from twin SU’s, so the principles are the same, but everything is just...different.

 

To my understanding (I think), there are two adjustment screws: throttle stop (idle) and idle mixture adjustment, which only affects the mixture at idle and just off idle.

 

Is the high speed mixture determined by jetting and fuel bowl level? What is the “proper” fuel bowl level?

 

I just started digging into the tuning of this truck tonight, after I guessed that it was running super rich. I pulled the plugs and I was right. Very sooty black. So I took the air cleaner off, and found that the fuel level in the bowl is what I would estimate to be 80% from the bottom of the glass. So in other words, near the top of the glass. If these carbs act like SU’s, that would result in an overly rich condition. Is that a correct statement? Are the floats in the hitachis known for sinking or getting stuck with the valve open?

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I need some help understanding the Hitachi carb. I’m coming from twin SU’s, so the principles are the same, but everything is just...different.

 

To my understanding (I think), there are two adjustment screws: throttle stop (idle) and idle mixture adjustment, which only affects the mixture at idle and just off idle.

 

Is the high speed mixture determined by jetting and fuel bowl level? What is the “proper” fuel bowl level?

 

I just started digging into the tuning of this truck tonight, after I guessed that it was running super rich. I pulled the plugs and I was right. Very sooty black. So I took the air cleaner off, and found that the fuel level in the bowl is what I would estimate to be 80% from the bottom of the glass. So in other words, near the top of the glass. If these carbs act like SU’s, that would result in an overly rich condition. Is that a correct statement? Are the floats in the hitachis known for sinking or getting stuck with the valve open?

 

So your going from SUs to a down draft, I have SUs on all my daily drivers, they are so easy to adjust with a flow meter and instructions(the first time).

I hate down drafts, I cannot figure out how to adjust them.

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I’m not switching from SU’s to a downdraft, I’m just used to adjusting SU’s with their needles and nozzles, and don’t know my way around these truck carbs yet.

 

I’m actually running MG needles (ADQ) in my roadster since they have a leaner idle. You can play little tricks with SU’s like different oil weights in the dashpots and moving the needles out of the dashpots by a few thou to adjust idle mixture, etc. I’m probably preaching to the choir.

 

I messed around with the truck idle adjustments today and got it pretty good, but didn’t want to muck with the bowl until I know that is what’s causing my richness.

 

Was also poking around and found that the throttle return spring is about to break free from its little hole on the bottom. Yikes. I’ll have to drill a new hole.

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So you know how to adjust your Roadster carbs as you have done it before.

I found if I can close the adjustment on the bottom of the SU and disable the other carb and the engine doesn't die then the carb is not serviceable and needs rebuilt.

I myself just get mine close as I can, then I drive it for a while and then pull the plugs, if they are black I lean that carb more, if they are white I richen it, if they are tan I leave well enough alone.

All you need is one hole, if you can get the jiggle valve out just drill that hole to an eighth inch and call it good.

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I an restoring a 1970 Datsun 521 in Arizona, I am restirund original other than front disc brakes, AC, and a 5-speed. I'm finished with everything but the inside of the bed. No rust just dents. Had it sandbasted, now just fixing dents. I would post a picture but can't seem to figure that out.

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Also: 6 holes in the t-stat was way too many like you guys predicted. I bought a new one and will remove the jiggle valve and drill one extra hole.

 

Actually the jiggle valve should be enough. That's what it's for. Some think for letting air burp out after re filling the cooling system but it can't help getting out as soon as the thermostat opens for the first time.

 

As I said guys, if you look how big the bypass hose is on the L20b lower thermostat housings, his multiple holes might work out close to the same bypass volume.

That is why I asked him to tell us how long it takes for the temp needle to get up to normal operating temp, I suspect 4 of them holes out of the 6 equals one bypass hose. 

 

The by-pass does not go to the rad but directly back into the engine uncooled. Flow into the rad displaces cold rad water back into the engine delaying warm up. Bypass is always better, jiggle valve not as good.

 

 

 

dUpN0SO.jpg

 

My '710 sedan heat would never rise above the bottom of the run range on the gauge when I first got it. I removed probably the original thermostat (22K miles original, with L18 and jiggle valve) to find the rubber seal corrugated and showing gaps. Replaced with one from a scraped engine and viola, engine now heats up in minutes to about half way on the gauge.

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I an restoring a 1970 Datsun 521 in Arizona, I am restirund original other than front disc brakes, AC, and a 5-speed. I'm finished with everything but the inside of the bed. No rust just dents. Had it sandbasted, now just fixing dents. I would post a picture but can't seem to figure that out.

 

You need a picture hosting site like  https://imgur.com/  . There are others but don't use Photobucket. Join free and folloe directions to stop photos there. You then copy the picture information and bring here. Look under the yellow smiley face at the green framed picture. Click it follow the prompts.

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I an restoring a 1970 Datsun 521 in Arizona, I am restirund original other than front disc brakes, AC, and a 5-speed. I'm finished with everything but the inside of the bed. No rust just dents. Had it sandbasted, now just fixing dents. I would post a picture but can't seem to figure that out.

 

Welcome :)

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Alright, so I replaced the t-stat today...again. Cut the jiggle valve and drilled the hole to a #21 (0.159”) since that’s what I had in my drill.

 

Dismantled the front float chamber and flipped the glass around so the etch is on the outside. Cleaned the bowl and needle valve. Pulled the screen out of the banjo and cleaned in there. Cleaned the linkages and all over the carb housing. Fuel is now a hair below the line. Should be a lot better. Even idles better when cold w/o the choke pulled.

 

Also installed an MkI VW duckbill. Think it looks pretty good. It hides the tension rods well.

 

0ZqdrXP.jpg

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