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My 1971 521


d.p

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Btw. D.p. did u check ur adapter plate, maybe its warp.

 

He has an adapter, it's just not a plate, it's like the one in the photo below.

DSCN7342.jpg

If you look close at mine you can see it is slightly bent, maybe his is bent also and he didn't check it before installing it, he is new to classic vehicles and the stuff we automatically do and don't even think about telling him to do isn't getting done, to use this adapter above I will have to seal it real good.

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I know this from experience if its not flat, it can cause a vacuum leak. What's worse is the 2 adapter plates. And u can't overtigthen them, it can get warped. One way to tell is spray some carb cleaner around the carb base, if rpm goes up, there's a leak and if you tighten it and still leaks, then strong possibility its warped. I would also spray carb cleaner around intake area. I'm just saying a lot of problems we faced w these Datsuns is simple. Good to do a diagnosis first before replacing parts.

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Why don't you just mill it flat?

Right now it is loose and I am not using it, I do plan to use it on my L320 when I get back to that build, the Weber carb with adapters sits too low to modify and use the stock air filter on it, I believe that using that tall adapter will get it high enough to use a modified 320 air filter or something similar.

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Fucked with it a little more today. Pulled vacuum advance and it didn’t make a difference. Plugged PCV with my finger didn’t mane any difference. So I pulled the plugs and they were fouled (dry black). Put new plugs in (didn’t gap them) and turned in the mixture screw and it idled much better drove it around and it didn’t die on decel. Felt like it had good power too.... fingers crossed it stays that way.

Not sure how or why I keep fouling plugs but just going to buy a bunch of them. Any ideas?

 

37621534985_12846f8cc2.jpg

 

 

-Jb weld dizzy mount seems to be holding so no plans to replace timing cover.

-Weber sent me a new carb but not sure I need to.

-Got an el dizzy with the proper mount but no plans to install that.

-Also got a tachometer that crash gave me which I will most likely install soon.

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You know that short drives do not give you a good sample of how the engine is mixture wise, it's always going to be rich, what counts is when you take it on the freeway for a while, I check my plugs every 6 months or so and adjust accordingly, but I have dual SUs.

I adjusted the Weber on my 320 by turning the screw way out till it was obviously to rich, then I turned it in till it started to not idle so good, then I kept going back and forth till I found the best idle in the middle of the two extremes.

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What I do and seems to work is when I adjust my mixture screw, not more than 1.5 turns out, I take the car for a test drive, not just the streets but freeway also and pull over and check my plugs. You don't need AF gauges! Back in the days, the would b mechanic would smell the exhaust, check spark plugs and pay attention to how many turns w screw driver. Plugs should be like tan color, not too white, lean, and not sooty black, rich...u want in between. Been doing adjusting on old carb cars, American and Japanese. If u r not sure how to go on line or you tube how to adjust 32.36 weber, very easy to do.

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So drive it around, check plugs and adjust  mixture screw as necessary to get white/tan plugs?  Question though when I adjust the mixture do you need to adjust the idle speed screw as well?  In my experience when I adjust the mixture screw it either raises or lowers the idle so then I have to adjust the idle speed screw.

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Everything works in conjunction with everything else. Valve adjustment will affect carb tuning, and so will ignition timing.

When the rpm goes up, that will add ignition advance. If the throttle is open above idle, that will add vacuum advance.

Adding ignition advance will increase idle speed.

 

Because a even a very small vacuum leak is a lot of air in relation to the amount of air that goes through a carb at idle,

you must get rid of all vacuum leaks. I cannot stress the importance of getting rid of vacuum leaks enough.

 

Adjust the valves. Check them again when the engine is hot, not warm, hot. Check the compression, it must be good to get

a good carb tune.

 

Set the ignition timing. 10 degrees BTDC is a factory setting. There cannot be any mechanical advance, or vacuum advance

when setting the timing. If the engine is running, it must be below 750 rpm. On old engines, you must also check the

mechanical advance below the timing points plate in the distributor. Make sure the springs that retract the centrifugal

advance are not broken, disconnected, or in other ways malfunctioning. Clean the old grease off the timing parts, make

sure the weights move freely.

 

If your exhaust is quiet enough, and you know what spark knock sounds like, you can set the initial timing a little more

than 10 degrees BTDC. Spark knock destroys engines. If you are not sure of what detonation sounds like, I do not recommend

using that to set the timing. if you can recognize spark knock, advance the timing until it barely knocks, and retard it

about 2 degrees.

 

After checking all that, then you can tune the carb. I strongly suggest you get a vacuum gauge to adjust the carb. It

will show you changes in engine tune you cannot hear. You also need a low RPM tachometer, you must keep the engine RPM

below about 750 RPM, or mechanical advance will start coming in on the distributor. As you tune the mixture screw in the

throttle body of the carb, you need to adjust the throttle stop screw to keep the engine RPM below 750. If the throttle

stop screw loses contact with the throttle, and you cannot lower the idle speed, check the throttle cable for slack.

Check also that the secondary of the carb closes all the way. Check for vacuum leaks.

 

Your engine should idle around 20 inches of vacuum, if it is a pretty normal stock engine, at sea level. If the vacuum

is significantly less than that, you have a problem you need to find the root cause of. In my mind, you are fighting a

vacuum leak.

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I cannot get a decent idle that low Daniel, when I try to adjust my dual SUs with the idle that low it dies when I disable either of the carbs to adjust the other one, not every ones engine is going to idle that low even with a new carb.

I prefer between 800 and 900rpms myself, it doesn't die all the time.

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