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What did you do with your MGB today?

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1987FXRP Avatar
1987FXRP Silver Member Jim Graves
Atlanta, GA, USA   USA
1976 MG MGB "Jesse"
Jim and Richard,
Thanks for your replies. I have the vacuum advance correctly hooked up as you advised. Ditto with the PVC valve. I still have a question regarding the lines to the charcoal canister. There are three on top. One vents the fuel tank and one goes to the rocker cover with the restrictor. I don't know what to do with the third, as it went to the float chamber on my ZS carb and my SU's do not have this connection. In the attached diagram it is called "vapor line" and in the Moss diagram it is called "HOSE, canister to carb". Any ideas on what to do with it?

Thanks

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offroad4ever Avatar
offroad4ever Silver Member Chuck W.
Willamette Valley, OR, USA   USA
1979 MG MGB
That does look great Fred!

Worked on the new boot lid, prepping for prime and paint. Almost threw the old one on so I could take it for a drive on the first sunny day for a long time but did some yard work instead.



79 LE w/OD, HS 4 SU's,
D9, Schlemmerized Dist.

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Brazzle99 Avatar
Brazzle99 Brian Aslett
Cape Town, Western Cape, South Africa   ZAF
1970 MG MGB MkIII "Millie"
2010 Honda Accord "Alison"
2014 Toyota Highlander 4WD "Magnus"
In reply to # 3905844 by RichardTS Firstly, the 25D4 will want a vacuum line that gets its vacuum from a tiny port in the rear carb in line with the throttle plate. Since the carbs are HS4’s there should be a small brass tube (~1/8)coming off the rear carb on the firewall side.

What it appears you are also having trouble with is the crankcase ventilation system. Since you are making it like an earlier model it will be best to understand what is supposed to happen. Then you can figure out how to make it happen.

The engine is supposed to run at slightly less than atmospheric pressure in the crankcase. The slight vacuum helps to keep oil and fuel vapors inside the engine. And a PCV enables that to happen. Air should be drawn continuously through the charcoal canister. After it departs the canister it goes to the tube on the rocker cover that has the small orifice (this orifice restricts the flow). Then it passes thru the engine and exits thru the tube on the front tappet cover. At this point it passes thru the PCV and into the inlet manifold so the oil and fuel vapors can be burned.

Your PCV choice is a good one (the one I use with my Mikuni sidedraft) because the $2 ones at the parts store do not have the correct flow for the MG system. Just make site you hook it up the correct way. When you hold it up with the funnel shape on top the bottom of the funnel should go into the inlet manifold. The port coming out the side should go to the tube coming out of the front tappet cover.

Now plug any openings left. As you can see the arrangement allows air to pass completely thru the engine. The orifice in the rocker cover causes the slight vacuum. The air then carries the fuel and oil vapors up thru the PCV and into the engine to be burned. The PCV is designed so that it does not open at idle or with high vacuum but opens at lower vacuum.

The side benefit of all this is the oil and fuel vapors stay inside the engine and you don’t end up with a film of oil all over everything in the engine bay. That is if it is sealed.

I hope this helps.

In reply to # 3905711 by 1987FXRP
The slight negative pressure seems to be important in stopping the rear crankshaft seal from leaking. I put a new one in when I replaced the clutch two years ago and there were no leaks. About a year ago we did a three week trip and at the end of one day's long and tough drive I noticed quite a large pool of oil under the car - 4 inches in diameter, clearly coming from the rear seal. Opened the hood and found that the rear breather pipe had come off its mounting pipe on the carburetor.I refitted it and next day the leak stopped.

I don't know why the pipe came off - but we'd climbed into the mountains with the engine running at full throttle between 3 500rpm and 4 500rpm for about 20 minutes. Perhaps excess blow by pressurising the crankcase and no vacuum from the carbs? It's never happened before or since.

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RichardTS Avatar
RichardTS Richard Smith
Covington, LA, USA   USA
1973 MG MGB "The MG"
The third one goes to the anti-run-on valve as the manual calls it. Your ZS and the later HIF4’s had a connection on the top of the float bowl for the anti-run-on valve. When connected correctly (I can’t remember exactly how -it’s in the Bentley manual) the valve senses oil pressure if the car is running on and applies vacuum to the float bowl(s) thereby starving the engine for fuel. Your SU’s don’t have this so you can plug it.

Others may have more info. I hope this helps.

In reply to # 3906216 by 1987FXRP Jim and Richard,
Thanks for your replies. I have the vacuum advance correctly hooked up as you advised. Ditto with the PVC valve. I still have a question regarding the lines to the charcoal canister. There are three on top. One vents the fuel tank and one goes to the rocker cover with the restrictor. I don't know what to do with the third, as it went to the float chamber on my ZS carb and my SU's do not have this connection. In the attached diagram it is called "vapor line" and in the Moss diagram it is called "HOSE, canister to carb". Any ideas on what to do with it?

Thanks

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ianscrawford Avatar
ianscrawford Ian Crawford
Lousiville, KY, USA   USA
Out with the old:



Clean-up, rebuild, replace:







In with the new!
















Increased negative camber wishbones

Heavy duty, MGBGT V8 a-arm bushings

New kingpin kits

Polyurethane cross member pads

NOS Import (World Wide Automotive) shocks

500 lb lowering springs

New sway bar end links

Polyurethane sway bar bushings

Steering boots

New outer tie-rods

New front wheel bearings

... I think that's about it.

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MG Logic Phil Pierce
Newtown, CT, USA   USA
In reply to # 3905711 by 1987FXRP I have a 1976 MGB and I am doing a carb conversion from the ZS to dual SU's. I have searched the MGE for help in routing various lines and have come up with the following: I am installing HS-4 carbs. They are AUD135's, rebuilt by Joe Curto and they do not have ports for the oil separator line like the later ones, so I am planning on installing a PVC valve as per the 1964-1967 diagram on page 20 of Moss' catalog. From my research, my intake manifold is from an 18GK engine that I think is from 1969-70. I am adding a port where one of the plugs went for the ARV. I am using a 25D4 distributor, Lucas #41043, which I think came from a Talbot/Chrysler/Minx 1967-1970. It was on the car when I bought it and has performed pretty well. I understand that the vacuum advance line should go to a port on the rear carb. The car has been de-smoged and still has the carbon canister with a line to the valve cover (restricted). There is another line that went to the ZS carb and there is not a port for it on the SU's. What should I do with this line? I have read that some route the carb overflow lines to it. What happens in this case if there is an overflow? It looks like originally the overflows were routed to atmosphere below the engine. In this case, what should I do with the extra canister line? Should I just plug it?


Any advice would be greatly appreciated. I have learned a lot about my car from this forum.


Jim Graves

Yes, just plug it. Remember you are dealing with flammable fuel vapors!

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1987FXRP Avatar
1987FXRP Silver Member Jim Graves
Atlanta, GA, USA   USA
1976 MG MGB "Jesse"
"Yes, just plug it. Remember you are dealing with flammable fuel vapors!"


Thanks, Phil.

That is what I thought. I assume that the fuel vapors from the tank will continue to be drawn through canister and the engine via the rocker cover and oil separator. Will the anti run on system still work?

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MG Logic Phil Pierce
Newtown, CT, USA   USA
Jim - no the anti run-on won't work because it relied on vacuum being applied to the float bowls to stop fuel from flowing into the carb. If your carbs don't have the attachment to the canister then that function is lost.

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RichardTS Avatar
RichardTS Richard Smith
Covington, LA, USA   USA
1973 MG MGB "The MG"
The anti-run on system can only work with a connection to the top of the float bowls.

In reply to # 3906968 by 1987FXRP "Yes, just plug it. Remember you are dealing with flammable fuel vapors!"


Thanks, Phil.

That is what I thought. I assume that the fuel vapors from the tank will continue to be drawn through canister and the engine via the rocker cover and oil separator. Will the anti run on system still work?

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J Baz Avatar
J Baz Silver Member Jerard Basmagy
Middletown, NJ, USA   USA
The rains washed the salt away so I dropped the car to the ground and took here for her maiden voyage for 2019.
While driving today she turned the clock and was reborn returned with 54 miles on the clock. Nice when the prep for the big sleep
allows for instant gratification upon awakening.



jb

Too soon we get old, too late we get smart!

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2003JAG Avatar
2003JAG Gold Member Chuck Hassler
Monument, CO, USA   USA
1968 MG MGC "Blue Boy"
1980 MG MGB Limited Edition (LE)
Removed the factory hardtop from the B and installed the canvas soft top. All this in anticipation (optimistic) of Spring. A drive up Colorado 105 today through some ranch country is in order. Tomorrow, we are looking at a foot of wet snow and 50-70 mph winds. Back to the normal 50's by the weekend. Looking forward to top down driving.

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dohc281 Avatar
dohc281 Silver Member Ira Eckstein
Laurel Springs, NJ, USA   USA
Busy day for the B. Adjusted idle speed after getting carbs back from Joe Curto, replaced copper washer for the bolt holding the inverted oil filter on and then changed the oil and filter. Tightened the valve cover as it was leaking oil. Took the car out for a short ride. I’m done for the day.



If you hit your pony over the nose at the outset of your acquaintance, he may not love you, but he will take a deep interest in your movements ever afterwards.



Rudyard Kipling

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Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
Renewed my early USA double brake MC today. See the unit on my workbench with the rear banjo coupling still loose. If the clutch slave and pedal box are not removed, taking it out and putting a new one in is only possible with this banjo part removed and put back afterwards. Putting back was tricky: this tiny valve and spring kept falling out before I finally managed to get the hollow bolt straight in. thumbs up

Bleeding with the Ezibleed and a modified cap from an earlier unit was possible with tire pressure on 10psi only, without the cap lifting and blowing fluid all over the place smiling bouncing smiley
Still there is some air left inside, there is just a small distance on the pedal where it feels a bit elastic. Rebleed after driving over a few weeks (it rains cats and dogs now) will get it out I'm sure....

PS I found out it is the fourth unit now going in: 1972 build year/0 miles, at 1979?/36.000miles, 1988?/90.500 miles now 2019/ 135-140.000 miles (had a speedo failure for 5000miles once)
So the first one excepted they seem to last about 50.000 miles or 80.000kms before they start to leak at the front. Refurbisihing them with new seals is a PITA, but in some cases doable eye rolling smiley



Edited 2 time(s). Last edit at 2019-03-15 11:43 AM by Donthuis.


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RichardTS Avatar
RichardTS Richard Smith
Covington, LA, USA   USA
1973 MG MGB "The MG"
I did the same MC in my ‘73 about 20 years ago. Can’t remember how I did it but I suspect I did the banjo without the MC being mounted. Did not remove the pedal box but I do remember having to put the bolts in backwards from the way they were.

Just thought about this job the other day and said a prayer that my MC would stay together. It is a bear to change.

If I were you, get plenty of beer on hand and do a gravity bleed. Takes a pretty good while but it works. I get a rock hard pedal when I do it. Bleeding any other way results in a spongy pedal.

In reply to # 3909196 by Donthuis Renewed my early USA double brake MC today. See the unit on my workbench with the rear banjo coupling still loose. If the clutch slave and pedal box are not removed, taking it out and putting a new one in is only possible with this banjo part removed and put back afterwards. Putting back was tricky: this tiny valve and spring kept falling out before I finally managed to get the hollow bolt straight in. thumbs up

Bleeding with the Ezibleed and a modified cap from an earlier unit was possible with tire pressure on 10psi only, without the cap lifting and blowing fluid all over the place smiling bouncing smiley
Still there is some air left inside, there is just a small distance on the pedal where it feels a bit elastic. Rebleed after driving over a few weeks (it rains cats and dogs now) will get it out I'm sure....

PS I found out it is the fourth unit now going in: 1972 build year/0 miles, at 1979?/36.000miles, 1988?/90.500 miles now 2019/ 135-140.000 miles (had a speedo failure for 5000miles once)
So the first one excepted they seem to last about 50.000 miles or 80.000kms before they start to leak at the front. Refurbisihing them with new seals is a PITA, but in some cases doable eye rolling smiley

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1987FXRP Avatar
1987FXRP Silver Member Jim Graves
Atlanta, GA, USA   USA
1976 MG MGB "Jesse"
After getting the engine back in my 1976 MGB I hooked up the exhaust. Getting the headpipe connected to the exhaust manifold was a real PITA. I was getting ready to install my rebuilt HS-4's and was looking at how the K&N air filters attached. There is a screw on the back of the backing plates (see photo) that will not let it sit flat to the carb inlets, It hits the carb body where the green tape is in the photo. I searched the forum and the only thing I found was one post where someone made a 1/4" aluminum spacer matching the gasket. Does anyone know if these spacers are available somewhere? I don't have machining capabilities to make them.
Thanks.


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