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1
Upkeep and Performance Hints / John Twist on Detoxing the MGB (1975-1980)
« Last post by JohnTwist on May 06, 2018, 06:30:15 PM »
One of the most frequently encountered questions once asked by owners of late model MGBs (1975-1980) was how to remove the smog equipment.  Today most of these vehicles have been “de-toxed.”  Detoxing involves removing the array of emissions equipment with which these cars were burdened by the engineers attempting to meet government regulations.  The equipment was added during a time when the this technology was in its primitive stages and could only do its job by impeding performance and drivability.
   Why detox? It often seems difficult, if not impossible, to adjust the various components of the emission control system to allow for good acceleration, good deceleration, yet avoid a red-hot converter or the popping common during deceleration. The belt-driven air pump draws a bit of horsepower from an already detuned engine. The major improvements gained by detoxing are better acceleration, faster deceleration, and a smooth idle. 
   The instructions are divided into four steps, the first two of which must be performed at the same time. The third step, removal of the  EGR valve, is helpful to smooth the idle. The fourth step, soldering the overrun valve, requires the removal of the carburetor.
   (1) Air pump – air manifold – gulp valve: Remove the two air hoses to the air pump, then remove the adjuster bracket bolt and fixing bolt and nut with a ½” wrench and socket. Twist the smog pump back and forth and remove it from the thermostat housing.
   Remove the ½” head bolt at the rear of the air manifold securing the pipe to the right rear head nut. Then unscrew each of the four injectors with a 7/16” wrench. It may be helpful to remove the spark plug wires for easier access. Then, plug the four injector holes with 7/16-20 x ¾ Allen set screws.  Bolts can be used, but do not provide the clean look afforded by the Allen set screws.
   Hold the tall thermostat nut with a ½” wrench and remove the two 7/16” headed bolts. Pull the small vacuum line off the unit. Either remove the hose from the 90 manifold fitting, or sometimes the 90   fitting lifts away from the manifold without any restriction. Use a 1” socket and remove the bolt from the manifold that secures the gulp valve bracket. Leave both copper washers on the bolt and retighten the bolt, having removed the bracket.
   If the 90 fitting did not easily lift away from the manifold, then grasp it with pliers and twist it back and forth until it lifts free. Then tap the manifold ¼” NPT. Use a good sharp tap and coat the flutes with grease to keep the shavings and swarf from dropping into the manifold. Screw the tap into the manifold about ⅔ of its length. Then, fit a ¼” NPT allen screw or brass plug into the manifold.
   Finally, remove the extra pulley and bracket associated with the air pump. On the 1977 to 1980 models this is an easy task as the two items are exposed. On the 1975 and 1976 models, however, it is easier to remove the radiator first to gain access. The reason the pulley is removed is simply for appearance.  The adjuster bracket should be removed so that it can never loosen and fall into the alternator fan!
    This completes the first step – removal of the air pump, air manifold and gulp valve.
   (2) Vacuum Advance: Reroute the vacuum advance tubing directly from the distributor to the intake manifold. On 1977-1980 models the vacuum advance line is run through the TCSA switch on the master cylinder box. This switch can be removed for a better appearance, and the wires taped and hidden.
   If the MGB does not have overdrive, then the gearbox power wire MUST be disconnected. If the MGB does have overdrive, it is advisable to install an in-line fuse (10 amp) to this unfused circuit. The single wire involved is white with brown and either runs to the gearbox by itself or is incorporated into the gearbox wiring loom. It is disconnected at the junction of the main, rear, and gearbox looms at the rear of the right inner fender. The main loom has about a hundred wires, the rear loom twelve, and the gearbox loom three.
   Check the ignition timing. With the vacuum disconnected, set the timing at 32° BTDC at full mechanical advance (about 3-4000 rpm).  This timing specification is true for all MGs (except Twin Cams) from 1946-1980.
   This completes the second step, rerouting the vacuum advance and setting the timing.
   (3) EGR Valve: The EGR valve is located on the top of the intake manifold, just to the rear of the carburetor (as seen from the left fender). Remove the two bolts (½” wrench or socket) securing it to the manifold and remove the valve. Make two gaskets with only the holes for the bolts. Sandwich the old asbestos gasket with these two new gaskets, using a liberal amount of Permatex “The Right Stuff” gasket compound to hold the sandwich together. Fill the cavities on the underside of the EGR valve with the gasket compound and replace the unit.
   This stops a fresh air leak that is always present and makes adjustment of the carb easier. If the EGR valve has failed, then the air leak can be quite massive. Reconnect the tube to the carb even though it serves no purpose – it looks better than stuffing a small screw in the end of the hose.
   (4) Carburetor: The last step involves the overrun valve and carb adjustment. Remove the carb from the manifold by (1) removing the air cleaner with a ½” wrench and disconnect the throttle return spring(s); (2) removing the heat mass and water lines out of the way with a piece of wire around the unit pulling it to the front valve cover stud; (3) removing the fuel line and overflow line by first twisting the hoses on their brass fittings – this loosens them and makes removal much easier; (4) removing the throttle cable using two 7/16” wrenches; (5) and finally removing the four nuts holding the carb to the manifold with a ½” wrench.
   Turn the carb upside down and allow all the gasoline to escape from the vent tube. Place the carb into a vise (carefully) and hold the throttle disc open with a screwdriver wedged into the external linkage or cam. The overrun valve should be positioned with the spring upwards.  Using a small propane torch to heat the underside of the throttle disc, flow some soldering flux onto the topside of the disc, and finally flow a generous amount of solder into the base of the valve (under the spring). Allow this to cool before removing from the vise. Ensure that there is no solder on the edge of the throttle disc – if some has crept there, scrape it away with the edge of a screwdriver.
   Close down the idle CO adjuster screw – the air bleed -- by unscrewing the brass screw, tightening the white plastic nut, and then retightening the brass screw.
   The carb can now be replaced.  Use new 5/16” fine nuts to make installation easier. If a new gasket is required, use Moss part 366-235. Use GREASE on the gasket to ensure there are no air leaks. Leave the throttle cable loose until the final adjustments have been made to avoid getting it positioned incorrectly.
   (5) Adjusting the carb: Start up the engine and allow it to reach operating temperature. Check the mixture by using the SU technique of lifting the piston. As the piston is lifted a very small amount (⅛” or so) judge the change in rpm. If the rpm climb as the piston is lifted then the mixture is too rich; if the rpm drops off immediately then the mixture is too lean. The optimum setting allows an increase of 50-100 rpm then a steadying or dropping off. Use a Stromberg adjusting tool to make the adjustments (clockwise richens, anticlockwise leans). Refit the throttle cable and air cleaner and take the car out for a test run.
2
Engine Related Items / John Twist on Detoxing the MGB (1975-1980)
« Last post by JohnTwist on May 06, 2018, 06:30:15 PM »
One of the most frequently encountered questions once asked by owners of late model MGBs (1975-1980) was how to remove the smog equipment.  Today most of these vehicles have been “de-toxed.”  Detoxing involves removing the array of emissions equipment with which these cars were burdened by the engineers attempting to meet government regulations.  The equipment was added during a time when the this technology was in its primitive stages and could only do its job by impeding performance and drivability.
   Why detox? It often seems difficult, if not impossible, to adjust the various components of the emission control system to allow for good acceleration, good deceleration, yet avoid a red-hot converter or the popping common during deceleration. The belt-driven air pump draws a bit of horsepower from an already detuned engine. The major improvements gained by detoxing are better acceleration, faster deceleration, and a smooth idle. 
   The instructions are divided into four steps, the first two of which must be performed at the same time. The third step, removal of the  EGR valve, is helpful to smooth the idle. The fourth step, soldering the overrun valve, requires the removal of the carburetor.
   (1) Air pump – air manifold – gulp valve: Remove the two air hoses to the air pump, then remove the adjuster bracket bolt and fixing bolt and nut with a ½” wrench and socket. Twist the smog pump back and forth and remove it from the thermostat housing.
   Remove the ½” head bolt at the rear of the air manifold securing the pipe to the right rear head nut. Then unscrew each of the four injectors with a 7/16” wrench. It may be helpful to remove the spark plug wires for easier access. Then, plug the four injector holes with 7/16-20 x ¾ Allen set screws.  Bolts can be used, but do not provide the clean look afforded by the Allen set screws.
   Hold the tall thermostat nut with a ½” wrench and remove the two 7/16” headed bolts. Pull the small vacuum line off the unit. Either remove the hose from the 90 manifold fitting, or sometimes the 90   fitting lifts away from the manifold without any restriction. Use a 1” socket and remove the bolt from the manifold that secures the gulp valve bracket. Leave both copper washers on the bolt and retighten the bolt, having removed the bracket.
   If the 90 fitting did not easily lift away from the manifold, then grasp it with pliers and twist it back and forth until it lifts free. Then tap the manifold ¼” NPT. Use a good sharp tap and coat the flutes with grease to keep the shavings and swarf from dropping into the manifold. Screw the tap into the manifold about ⅔ of its length. Then, fit a ¼” NPT allen screw or brass plug into the manifold.
   Finally, remove the extra pulley and bracket associated with the air pump. On the 1977 to 1980 models this is an easy task as the two items are exposed. On the 1975 and 1976 models, however, it is easier to remove the radiator first to gain access. The reason the pulley is removed is simply for appearance.  The adjuster bracket should be removed so that it can never loosen and fall into the alternator fan!
    This completes the first step – removal of the air pump, air manifold and gulp valve.
   (2) Vacuum Advance: Reroute the vacuum advance tubing directly from the distributor to the intake manifold. On 1977-1980 models the vacuum advance line is run through the TCSA switch on the master cylinder box. This switch can be removed for a better appearance, and the wires taped and hidden.
   If the MGB does not have overdrive, then the gearbox power wire MUST be disconnected. If the MGB does have overdrive, it is advisable to install an in-line fuse (10 amp) to this unfused circuit. The single wire involved is white with brown and either runs to the gearbox by itself or is incorporated into the gearbox wiring loom. It is disconnected at the junction of the main, rear, and gearbox looms at the rear of the right inner fender. The main loom has about a hundred wires, the rear loom twelve, and the gearbox loom three.
   Check the ignition timing. With the vacuum disconnected, set the timing at 32° BTDC at full mechanical advance (about 3-4000 rpm).  This timing specification is true for all MGs (except Twin Cams) from 1946-1980.
   This completes the second step, rerouting the vacuum advance and setting the timing.
   (3) EGR Valve: The EGR valve is located on the top of the intake manifold, just to the rear of the carburetor (as seen from the left fender). Remove the two bolts (½” wrench or socket) securing it to the manifold and remove the valve. Make two gaskets with only the holes for the bolts. Sandwich the old asbestos gasket with these two new gaskets, using a liberal amount of Permatex “The Right Stuff” gasket compound to hold the sandwich together. Fill the cavities on the underside of the EGR valve with the gasket compound and replace the unit.
   This stops a fresh air leak that is always present and makes adjustment of the carb easier. If the EGR valve has failed, then the air leak can be quite massive. Reconnect the tube to the carb even though it serves no purpose – it looks better than stuffing a small screw in the end of the hose.
   (4) Carburetor: The last step involves the overrun valve and carb adjustment. Remove the carb from the manifold by (1) removing the air cleaner with a ½” wrench and disconnect the throttle return spring(s); (2) removing the heat mass and water lines out of the way with a piece of wire around the unit pulling it to the front valve cover stud; (3) removing the fuel line and overflow line by first twisting the hoses on their brass fittings – this loosens them and makes removal much easier; (4) removing the throttle cable using two 7/16” wrenches; (5) and finally removing the four nuts holding the carb to the manifold with a ½” wrench.
   Turn the carb upside down and allow all the gasoline to escape from the vent tube. Place the carb into a vise (carefully) and hold the throttle disc open with a screwdriver wedged into the external linkage or cam. The overrun valve should be positioned with the spring upwards.  Using a small propane torch to heat the underside of the throttle disc, flow some soldering flux onto the topside of the disc, and finally flow a generous amount of solder into the base of the valve (under the spring). Allow this to cool before removing from the vise. Ensure that there is no solder on the edge of the throttle disc – if some has crept there, scrape it away with the edge of a screwdriver.
   Close down the idle CO adjuster screw – the air bleed -- by unscrewing the brass screw, tightening the white plastic nut, and then retightening the brass screw.
   The carb can now be replaced.  Use new 5/16” fine nuts to make installation easier. If a new gasket is required, use Moss part 366-235. Use GREASE on the gasket to ensure there are no air leaks. Leave the throttle cable loose until the final adjustments have been made to avoid getting it positioned incorrectly.
   (5) Adjusting the carb: Start up the engine and allow it to reach operating temperature. Check the mixture by using the SU technique of lifting the piston. As the piston is lifted a very small amount (⅛” or so) judge the change in rpm. If the rpm climb as the piston is lifted then the mixture is too rich; if the rpm drops off immediately then the mixture is too lean. The optimum setting allows an increase of 50-100 rpm then a steadying or dropping off. Use a Stromberg adjusting tool to make the adjustments (clockwise richens, anticlockwise leans). Refit the throttle cable and air cleaner and take the car out for a test run.
3
Engine Related Items / Re: AC Unit Causing Engine To Stall
« Last post by JohnTwist on May 06, 2018, 06:44:01 PM »
I have little experience with air conditioners, that’s a fact.  It must be that the idle is the correct speed unless the compressor kicks on – otherwise you would simply increase the idle.  That extra load on the engine is causing the stall, but it shouldn’t.  Take a look at your timing.  First of all, the vacuum advance should be connected from MANIFOLD vacuum (highest at idle and deceleration) directly (and not through the TCSA switch on the master cylinder box).  If you cannot get manifold vacuum (about 18 inches at idle) from the carb, then drill each leg of the inlet manifold, install a hose connection, then “tee” those two fittings to the vacuum advance.  (Using only one leg will pulse the vacuum advance diaphragm to death.)  Check the timing to assure that you have 32 degrees BTDC at full mechanical advance, vacuum disconnected.  This occurs around 3-4000 rpm.  You need a dial back timing light to set this correctly.

Hope this little bit helps.  Please feel free to call with more questions or for clarification.

SAFETY FAST!
John H Twist
4
Engine Related Items / AC Unit Causing Engine To Stall
« Last post by amgba on May 06, 2018, 06:32:46 PM »
I have a 1977 MGB which I have added a AC unit from Nostalgic A/C out of Ocala, Florida. The unit works fine but I have an issue with engine stopping at intersections because of the extra load from compressor.

I have a Weber (32/36 DGV DGEV DGAV) down draft carb on this unit. I am wondering if this could be my problem. Other than this the engine runs great.

I have been reading your posted info for years and want to thank you for service to us MGB owner.

Richard Ehrlich
South Padre Island, Texas
5
Suspension Related Items / Re: Wire Wheel Hubs
« Last post by JohnTwist on May 06, 2018, 06:44:59 PM »
Those hubs are most certainly on the wrong sides!   It’s a good thing the engine didn’t run or you would have taken it out and had one nasty surprise.

“Back in the day” when these cars were used for regular transport, we’d get a call every summer from one of the local tow truck companies looking for a spinner.  The wheel is often easy to find – the spinner all but impossible!  I’d say, “Towing it from the back end, were you?” 

We had a customer who couldn’t keep the spinners on his rear axle (he’d accidentally switched sides) so he drilled a hole through one of the ears and safety wired the spinner to a spoke.  Necessity is the mother of invention.

Good luck with the engine – and get those hubs swapped around!

SAFETY FAST!
John H Twist
6
Suspension Related Items / Wire Wheel Hubs
« Last post by amgba on May 06, 2018, 06:34:02 PM »
You have given me some real important information aiding me with the original equipment information that I could not find.
Attached are some pics of my project on my '69 B roadster..

M.Vanetten
7
Restoration Discussion / Re: MGB Stored for More Than 20 Years
« Last post by JohnTwist on May 06, 2018, 06:46:18 PM »
After such a sleep, you’ll want to attend to a great number of mechanical items on your MGB.  As an aside, the true 1974 ½ models have the full rubber bumpers.  The MGBs with the Sabrinas (or Dolly Parton overriders as I usually call them) are the mid-production style.  http://www.goon.org/usgoons/sabrina/

Find the “Complete Lubrication” on my website and follow it thoroughly.  Change ALL the rubber lines, fuel, cooling, and brake.  Change the tank only if you detect rust (just peer into the tank once the filler neck is moved out of the way.  The steel brake lines are usually OK, but you can literally stand on the brakes to try to find weak (leak) points.  Better in your shop than on the road!  Leave the charcoal canister in place – that’s a passive system that takes no energy and allows the anti run-on circuit to operate.

SAFETY FAST!
John H Twist.
8
Restoration Discussion / MGB Stored for More Than 20 Years
« Last post by amgba on May 06, 2018, 06:37:19 PM »
I have in my garage, a 1974 Sabrina MGB that was parked in 1994, and there it has sat. All that gasoline, oil, fluids and such, just sitting there for the past 23 years. I believe there may be some issues

What do you think about the gas tank and the metal brake lines, not to mention everything else. Oh, one more thing. I am going to de-smog most of the engine, I’ll have the heads machined, match the ignition and re-jet the carbs to match. Should I stay with the HIF’s or move to HS4’s, in other words, would that be money well spent or fuelish.

The MG straddles a 1907 era service pit that is part of our garage.

Enjoy your website very much. I’m sure a jolly time awaits.

Ron Nugent
Pasadena, California
9
Engine Related Items / Re: Air Manifold Holes
« Last post by JohnTwist on May 06, 2018, 06:47:03 PM »
Those holes are 7/16-20 SAE American Fine Thread.  We usually use ¾” socket set screws as those disappear nicely beneath the surface. 

SAFETY FAST!
John H Twist
10
Engine Related Items / Air Manifold Holes
« Last post by amgba on May 06, 2018, 06:36:13 PM »
If I remove the Air manifold from the exhaust, which screws can plug the holes in the cylinder head? Are the screws tapered?
I read you can plug them with brake bleeder nipples. Do you know which size?
Fred Lombard
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