pcv or evacuation system for a weber set up

[Karl Bebout]

Wolf, thanks for the pictures. Nice set up.

[paul cass]

Some follow up to some of the posts. You can run lines from breathers to the headers for an evacuation system. Did this when I ran on the track in the 90's. Had blow by and it solved that problem. Later found out I had a broken piston causing the blow by. Check valves are to prevent any combustion in headers from being sucked back into engine and possibly causing an explosion. I'm trying to run a crude form of evacuation system for the engine. If it does build up some pressure, if any oil does leak out then the catch can should collect it. And I don't have to deal with a blow by with open breathers. At 71 I'm past the age of racing everything in site. A little lead foot here and there should be enough. Basically I'm looking to have an engine that can breathe with out making a mess. And I'm not looking to drill and tap. Once I get my system installed I'll report what happens. Mainly I want to have an effective system before I cruise the hill country during our Texas Cobra Club Spring Meet in April. Tried to download a video but with my limited skills it didn't work.

[wolf k]

^ I agree with Gaz here. Also, no need to use a PCV valve if you are not returning the vapors to engine intake manifold. This appears what you are doing, just venting to atmosphere, correct?
I am also running IDF's with just stack filters, however, I am very leery of unfiltered air entering the air bleeds and also the bowl vents. I need to come up with some type of filtration for the vents and bleeds.

[paul cass]

Hi Gary and Wolf. Don't mind the suggestions. The breather cap has an internal pcv valve. So both sides have the same pressure. I know that some guys run their weber's without filters. Living on the coast with constant high winds and sand and anything else you can think off I need to run filters. I haven't seen any difference in the operation of the engine with or without these filters. I spent all day today fine tuning the weber's with the assistance of a good friend. Bill was a very successful race car driver and has much more knowledge on engine tuning than me. Found that three of the stacks were not sucking air like the other 5. And when the engine was shut down fuel bled into one of the stacks, and leaked into all the others a little. Took all of the tops off and found that the float level was set too high on all of them. Adjusted the float and fixed the problem. I played around with the idle speed, per your suggestion Gary, and eventually Bill, by ear mostly, was able to adjust all the idle mix screws to get a smooth idle and no skip or stutter. I didn't get to do a test run as we had rain in the area. Later tomorrow the weather is supposed to clear and I'll do a test drive. Still somewhat disappointed in Top End and Red Line. Absolutely no info on the weber's and why wouldn't the floats be set correctly. Noticed that three of the needles were round and the 4th had shoulders. All were set at 5 mm or less.

[Gaz64]

Hi Paul,

Both of your valve cover fittings should be freeflowing without any PCV valve.

Make the hoses as large as the smallest fitting, at least 1/2 inch ID.

Keep an eye out for any dust etc that gets near the top of the carb lids.

Gary

[paul cass]

A question Gary. I've gotten feedback both ways with the pcv system. Some say to leave them in while you and a couple of others say leave them out. What is your reasoning for leaving them out. Some guys use only breather caps but then you deal with oil contamination in the engine compartment. With the catch can I keep the vapors etc. away from the engine and engine bay.

[Gaz64]

Hello Paul,

Your PCV valve fitted to the passenger valve cover is a restriction to blowby gas when the engine produces more blowby under load.

Pull the valve out, and blow through it from the valve cover end, then compare that to a hose of the same diameter.

Your system appears to vent the engine to a catch can, which is vented to the atmosphere with a K&N filter, which is a very common way of allowing the crankcase to be vented.
Because it is vented to atmosphere, it is not classed as a PCV system, since the engine is not consuming the crankcase gases.

So, in a nutshell, there should be free flowing hoses without PCV valves fitted in your system.

Hope this helps.

Gary