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MG MGB Technical - Venting the Gas tank

What is the best way to vent the gas tank and vented valve cover after removing the SMOG equipment canisters from my 1980 B.


Cec
Cec

Vented petrol cap and any sort of filter on the cover, just to stop crap getting in there, ie bit of spong rubber.
By the way the charcol canister doesn't really de-power your motor in any way. Essentially it's just an air filter to allow the tank (and crankcase to a lesser extent))to breath cleanly. If you are concerned that the vacuum line off the intake maniifiold to the cannister is detracting from the performance of the car (I doubt it's got much effect though), then block it off, but leave the other lines attached. Others (probably Paul, who seems to be some sort of MG work shop manual with legs) can tell you all about crank case vacuum lines and what they do.
Peter

The tank will vent fine through the line that used to go to the canister. The rocker vent should have a filtered air supply since air is sucked through the engine to the carbs. A small engine air filter, like for a chain saw or weed eater can be fitted to the pipe.
All that said, why take off the EVAP system? If working, it does absolutely nothing bad, and keeps the air clean.The only likely source of trouble is wiring or the small vacuum connection to the manifold, both easy to deal with. Removing these things for no gain is not good, and WILL BRING THE AUTHORITIES DOWN ON US, sooner or later. There is a large contingent who would like to take our cars away from us, and it will get worse. So far, we get by under the radar, or with exemptions. We can argue no parts and the like to a point, but irresponsible and unjustifiable mods which gain little to nothing do not help the cause.
FRM
http://usachoice.net/gofanu
FR Millmore

Hi,
Forgot to mention that I changed the Zenith Stromberg for a Weber and there are no accomodations for the SMOG however I shelved every part just in case


Cec
Cec

OK, the carb change makes it different. The stock system had several advantages: 1) the engine was no longer open to the atmosphere, and didn't suck in crap from the road. One of the reasons modern engines don't need oil changes so often. There is a certain amount of in-out pumping going on, and under high vacuum conditions like going down a hill with closed throttle a significant amount of inflow through the vents. 2)The manifold vacuum applied through the PCV/smog system put negative pressure inside the whole engine, improving oil control through guides and rings, and helped stop general seepage through gaskets and seals.

Stock had a controlled leak through the canister by way of the restrictor in the rocker cover pipe, through the engine, out the vents, to the carb.The oil filler cap is sealed.
Earlier cars had a vented but restricted filler cap....to the carb. The later plastic versions of vented cap have a filter to keep dirt out.On your present setup, instead of fitting the filter to the rocker pipe as suggested earlier, block the rocker pipe and fit the earlier vented and filtered plastic oil cap.
Very early cars have a metal cap and ran the rocker vent to the air filter. These pulled air from the side vent, with dirt, through the engine, but not a lot since there was no real vacuum at the air filter. Later versions of this had a separator/filter in the side cover vent pipe.

In order of efficiency, there are a number of ways to improve things.
You could connect the rocker pipe to the side vent pipe, or plug the rocker pipe, and run whatever is left to a can with a filter of some sort, like pieces of lawnmower foam air filter, then to atmosphere. That would keep dirt out.
Instead of venting this to atmosphere, you could make a fitting and feed the vent into the air filter inboard of the element. This doesn't need the homemade vent filter but should have a flame trap, which can be a metal pot scrubber stuffed in the vent pipe, or there are flame trap/filters that came on some cars in the PCV lines. This duplicates the earliest system.
You could put a filter on the side vent, and connect the restricted rocker pipe to the manifold, which is a bit better, and similar to early PCV systems. The effect is to lean the mixture at idle, decreasing as the throttle is opened and vacuum drops. Might have to richen up the idle a bit, above idle the generic Weber is probably already too rich.
With the rocker pipe plugged and the vented/filtered oil cap, run the side vent to the manifold. This puts vacuum back in the engine and keeps it all clean. It will probably need the same carb fiddling as the last method. This should also have the flame trap to keep backfires from lighting the crankcase up. If the engine is in good shape this should work fine, but too much blowby will cause trouble.
FRM
http://www.usachoice.net/gofanu
FR Millmore

FRM,

I have since reinstalled one of my canisters and connected the original hose back to the Vented Valve cover and the line to vent the Gas tank. Now all I have left to consider is the Vent pipe from the front side cover. My Weber Carb kit has a plastic elbow which connects to the new filter housing and can be used to vent the base however Brit-Tek recommends I put a tube from the vent line to the road like to old 60 era road breather system.
It seems you understand this system better than me but I know the old Chevy's ,maybe the new ones also, had a hose going to the Air Filter housing but there was a filter at the end of this line inside the housing. I was thinking of the new carb gumming up if the base vent is not filtered if I vent it to the carb.

Cec
Cec

Cec,
As I said, the vent to filter keeps dirt out of the engine and burns the vapors = good. If the engine is not blowing a lot of oil you will have no problem. If the elbow exits inside the filter element, the thing has to be really worn out, in which case it could foul a plug once in a while. The Chev and similar had the vent entering outside the filter element and the rudimentary filter scrap was to prevent oil vapors from gumming up the paper air filter, ie it was more of an oil separator. On foam or K&N type filters this would not be a problem, but with the vent outboard of the main element, you can still get dirt into the engine. It is far better than sucking it up off the road though! If the car has the original oil separator on the tappet cover (rectangular box with pipe coming out the top) it has a flame trap/filter built in. Doesn't hurt to remove and wash it in solvent every 15 years or so!
After long use, there could be some deposits formed on the carb bore, but the gasoline will wash most away, and it will be largely cosmetic anyhow, it won't block jets etc.. Spray carb cleaner will remove it. Modern FI cars have some problems if they are using oil, but that is because there is no gas in the air manifold.
You get points for cleaning it up a bit.
FRM
http://www.usachoice.net/gofanu
FR Millmore

Thanks for the information it was most helpful. The engine does'nt burn or blow any oil because it has less than 50,000 miles. It has the rectanlgular box for the side cover I cleaned it, painted it with heat resistant paint and installed new gaskets, didn't know it was an oil seperator though! I am trying to make this Weber conversion as neat as I can and doing some detailing in the engine compartment.

Once again thanks to you and the fine people on this BBS

Cec
Cec

This thread was discussed between 14/05/2004 and 17/05/2004

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