pcv valve for 1500 midget?

[recordsj]

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?

 

[Guest]

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.

 

[recordsj]

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

 

[Guest]

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.

 

[recordsj]

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]

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

 

[Guest]

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]

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]

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.

 

[recordsj]

some info on ported vacuum and manifold vacuum
https://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf

https://www.corvetteactioncenter.com/foru...um-advance.html

 

[Guest]

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]

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

Kurt.

 

[Guest]

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

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

 

[MGGuy]

Glad I came here. I have a 77 Midget 1500. California Smog shop says I need one, but they never came with one, and of course they wont tell me how to fabricate a PCV system. Can anyone advise me (with pics if possible) as to where and how to install it, what parts, and where it should end up? I remember on my older cars now long gone that they came from the top of the valve cover and had a grommet to keep them secure, PCV valve sat in there, then a hose just ran to...cant recall, and I think there was a filter in whatever it attached to where the hose came in. Any advice?

 

[Boink]

I tried fitting one on my Bugeye (to the oil separator - I have no vent from the valve cover)... and ended up sucking oil in a big way (lots of smoke). Garrard says that the trick is to neck the intake down just enough to get the right amount of suction. I never found that point... and mine, like many, is vented to the ground.

 

[SNClocks]

It turns out there is an outfit that makes adjustable PCV valves - M/E Wagner. OK - they ain't cheap. > M/E Wagner Performance Products – High Performance Crankcase Ventilation Systems <

But. Ain't there always a but? NTL, they work. Background. We have several cars with V8's. One, a Roush 427, had a nasty habit of popping the dipstick out at odd moments - because of pressure buildup in the crankcase. And venting out of the rocker cover vent, even though there was a "correct" PCV installed. Oh, and of course, a few more oil leaks than I wanted. I installed one of Wagner's adjustable PCV's, went through the pretty easy set-up, and wow. All better. As in wowser.

So, as I finished up the restomod on our '60 bugeye I figured it needed a good PCV as well. I installed the Wagner just above the oil separator, with the discharge of the PCV going to the inlet manifold.

I also installed a filter on the doohickey that MiniMania installed on the side of the crankcase on the 1380 they built for us. The doohickey is a round oil/air separator installed where the fuel pump would otherwise mount. Looked like a good place to draw fresh air into the crankcase for the PCV...

I asked MiniMania what the doohickey was for, but they didn't respond.

NTL - there you have it. I just got this little bugger running and now am waiting for good weather to test everything out. I hope this helps at least a little.

 

[dave99]

I put a 1/2” T in the hose from the valve cover. Run a new section of 1/2” hose off the T to the charcoal canister. Drill and tap a 1/8npt just below the carb in the intake manifold. This will ensure equal mixture goes to all cylinders. Add a 90 degree 1/8npt to 1/8npt at the manifold, then attach a 1/8npt to 1/2” barb fitting. Now cut an inch or so of 1/2” aluminum rod and drill a 5/64” hole through the center. Push that into the 1/2” hose that will connect to the new barb nearest the intake manifold. This will ensure both the crankcase and canister is properly vented into the intake. If you have the fuel bowl vent fitting add a fitting to the Weber and run a hose to the canister. After this mod you’ll address all your oil leaks and fuel smell. If you have oil leaks after this, then replace the gaskets or seals. I‘ve been running this setup for about 1800 miles and works perfectly on my 1500 with a Weber 38.

edit: apparently I can not post photos. Sorry.

 

[mrodtn]

I put a 1/2” T in the hose from the valve cover. Run a new section of 1/2” hose off the T to the charcoal canister. Drill and tap a 1/8npt just below the carb in the intake manifold. This will ensure equal mixture goes to all cylinders. Add a 90 degree 1/8npt to 1/8npt at the manifold, then attach a 1/8npt to 1/2” barb fitting. Now cut an inch or so of 1/2” aluminum rod and drill a 5/64” hole through the center. Push that into the 1/2” hose that will connect to the new barb nearest the intake manifold. This will ensure both the crankcase and canister is properly vented into the intake. If you have the fuel bowl vent fitting add a fitting to the Weber and run a hose to the canister. After this mod you’ll address all your oil leaks and fuel smell. If you have oil leaks after this, then replace the gaskets or seals. I‘ve been running this setup for about 1800 miles and works perfectly on my 1500 with a Weber 38.

edit: apparently I can not post photos. Sorry.

This sounds promising. Considering doing this to my 1979 MG Midget 1500. I am running a Weber dgv 36/38 venting the valve cover port to the underside of the carb via the supplied elbow from the Weber carb kit. The alloy valve cover has a vented cap.
I currently have the mini mania mechanical fuel pump baffle vented to a catch can then to the charcoal canister. At idle if I disconnect the line coming from the catch can there is pressure and small amount of smoke coming out of that line.
I saw in the John Twist video where he had plumbed the valve cover vent to the side of the Weber air filter. I wonder what adapter he used for this.

 

[dave99]

Ahh, I can upload photos. Here you go…. Just a tip, if you go larger than 5/64” in the aluminum rod you risk drawing to much air from the crankcase and this will affect your mixture and rpm response. Driving 40mph and taking your foot off the pedal takes the rpm forever to drop down If the hole is too large. So keep the hole as small as possible. I had a 3 foot section of aluminum rod and tried different hole sizes. The 5/64” worked best for the Weber 38. Have fun.