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pcv valve for 1500 midget?

recordsj

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I have a 1500 miget with a weber dgv carb.
How can I find the correct PCV (if going to Autozone, Napa and etc) for the car?
 
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I don't use one. I just hook the hose from the valve cover to the nipple on the underside of the air cleaner. I did buy one once. I want to say it was for a 91 Corrolla but don't hold me to it.
 
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recordsj

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anyone else with response about using a PCV (positive crankcase valve).

Also on mine I have a hose from the valve cover to PCV, which after the PCV it tees to the vacuum port on the weber carb and to the carbon canister (which the carbon canistor has a restrictor on the hose going into it
 
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recordsj said:
anyone else with response about using a PCV (positive crankcase valve).

Nobody uses them. If you get a lot of blowby into the filter, time to rering.

That's ported vacuum there and you want straight mainfold vacuum.

If you're serious, drill the side of the plenum and tap it, run a hose from that to the PCV valve mounted in a HEI style 90 degree plug wire boot pluged onto the valve cover nipple. Valve faces up.
 
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recordsj

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kellysguy said:
recordsj said:
anyone else with response about using a PCV (positive crankcase valve).

That's ported vacuum there and you want straight mainfold vacuum.

If you're serious, drill the side of the plenum and tap it, run a hose from that to the PCV valve mounted in a HEI style 90 degree plug wire boot pluged onto the valve cover nipple. Valve faces up.

what is the issue between ported vacuum and straight manifold vacuum?
 

nomad

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OK I've been messing with PCV valves as well. Opened up an old pancake BMC PCV valve just to refresh my memory on how they worked.
The diaphram adjust's the opening from the crankcase according to what the vacuum is at the intake manifold. When the carb is closed mostly, such as at idle or cruise, the manifold vacuum is high but when you put your foot in it and the butterfly opens and the manifold vacuum drops.
The BMC PCV try's to keep the suction on the crankcase constant.
The common PCV valve doesn't do this so you would be getting a variation in what is coming out of the crankcase to be burned by your engine. At times it will tend to lean the mixture more than others.
The ones I have looked at are just check valves and to make them work well you are either going to have to restrict the air that is being sucked into the crankcase thru a vent or the amount that is being sucked into the manifold from the crankcase.
Maybe someone will come up with one that has maybe a spring load to the valve and therefore a restriction.
Anyone??

Kurt
 
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nomad said:
Maybe someone will come up with one that has maybe a spring load to the valve and therefore a restriction.
Anyone??

Kurt

No need for that as they have worked on MILLIONS of vehicles as-is and it doesn't make a difference where it's from. Vacuum is vacuum and it'll temporarily drop when the throttle is opened regardless. Best thing is use one off the same size engine as not to induce too large a vacuum leak. It doesn't surprise me BMC did it that way as we all know they over complicate EVERYTHING. I'm surprised they didn't come out with a digital brick.

Recy, manifold vacuum is constant, ported vacuum only comes on as the throttle is opened in that location. In other words, it'll only work when you're off idle and how much depends on how far the throttle is opened.
 

nomad

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Kellys guy: I'm currently trying to get one to work on a 1500 Datsun. Had it hooked up to a port on one end of the manifold. Engine didn't sound right or run well till I mostly blocked the vent tube on the valve cover. Plugs on that end of the engine appeared lean.
I have to dig up the original air cleaner to be sure but I believe there is some kind of control to the intake for that vent tube. Maybe wrong but I will take a look.
It would appear that manifold vacuum has to change when the carb butterfly is opened. Perhaps it is insignificant but I remember the days of vacuum wipers. You stomped on the gas and the wipers stopped. Let off and they went crazy!

Kurt.
 

nomad

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Kellys guy: I finally decided to read the "struction" manual. Said under most conditions the PCV allows gases from the crankcase to be sucked into the manifold and burned but under hard acceleration the excess are forced back thru the valve cover vent pipe to the air cleaner.
So it appears you are correct in that I need to just select one that matches the engine requiremants. I'm also rerouting the line to the manifold to a point just at the carb so that all cylinders take in a equal amount from the PCV.

Kurt.
 
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nomad said:
Had it hooked up to a port on one end of the manifold. Engine didn't sound right or run well till I mostly blocked the vent tube on the valve cover. Plugs on that end of the engine appeared lean.

Right, gotta catch it @ the plenum.
 

nomad

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Thanks for the input guys! Especially interesting vacuum info!! Saved to favorites.

Kurt.
 
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Yeah, but don't let it fool ya, vacuum SUCKS !

( Well, technically it blows; pressure differential.) :wink:
 
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