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Midget emissions system

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Midget emissions system
#1
  This topic is about my 1974 MG Midget MkIII
tripp2loo Avatar
tripp2loo Paul Bateman
Noblesville, Indiana, USA   USA
I'm resurrecting my 1974 Midget that has been sitting somewhere for over 12 years.
What I've done so far;

Rebuilt the carbs with master rebuild kit, setting the initial mixture at 2 turns out.
Went through fuel system, clean and replace all fuel lines.
Removed fuel pump and tested.
Replaced plugs, rotor, dizzy cap and leads.
Checked gap on the points and cleaned them.
Replaced all connectors for ignition wiring.

The air pump is off right now and I'm not sure if this system is that critical. When I start the car it will idle fine, but as soon as I throttle up the engine dies.
I've read a few forum posts where they suggest this could be caused by points/condenser/ignition coil so I've ordered new ones for all those.

My question is, how much does the air pump system affect the engine performance, can it be removed without issue and could it be causing my current problem?

Cheers..

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refisk Avatar
refisk Rick Fisk
Frankenmuth, Michigan, USA   USA
1972 MG Midget MkIII "For Sale $4000"
Hi Paul,

The air pump doesn't really affect performance, except for the fact that it takes several HP to turn the pump. The air injection system injects clean air in the exhaust port to promote burning of hydrocarbons that weren't burned in the normal combustion cycle. In other words it just cleans up the exhaust. But it also doesn't cause your throttle up problem. Something else is causing that problem.

Get the new ignition bits installed and let us know how it runs.

Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
"new ignition bits" - make sure you only buy them from Jeff at Advanced Distributors. There have been far too many cases of sh*t poor quality ignition parts sold by all of the normal LBC parts suppliers for me to trust getting them from anywhere else.

Engine idles ok but dies when opening the throttle - sounds like a vacuum leak somewhere in the intake tract. Make sure all holes are plugged and while it is idling, spray some aerosol all around every seam, joint and plugged hole from the carburetors to the head (there are a lot of them). Any change in idle speed while doing so points to a leak.

Once it is confirmed there is no leak, anywhere in the intake tract, then try applying the choke to see if it helps (sign of too lean). If it makes it worse, that's a sign of too rich.


By the way, if you removed the air pump, did you plug the manifold holes in the exhaust? They should be closed to avoid causing running issues. Also, the gulp valve and the other parts of the air pump which are connected to the intake side should also be removed and plugged.


Hope this helps. Post some photos of what you are working with so we can help you further (carb x throttle linkage, images around your intake manifold, details like that).

N

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tripp2loo Avatar
tripp2loo Paul Bateman
Noblesville, Indiana, USA   USA
Thanks, I started to worry about the gulp valve and all those other parts.
I read this http://www.mossmotors.com/graphics/products/PDF/366-010.pdf and realized open tubes on this is going to cause an issue.
I'll be removing the gulp valve and associated parts and making sure there are no air leaks.
Does anyone have detailed information on what can be removed from this system?

I ordered the following from Moss.
153-830 CONNECTOR, plastic pipe to carb.
143-201 SPORTS COIL, Intermotor
143-256 Universal Coil Mounting Bracket - Zinc Plated
153-840 CONNECTOR, to vacuum unit
152-221 CONDENSER & POINT SET, Intermotor brand

These parts are all kind of temporary just to get he car running so I can gauge the engine and transmission's condition. I have a spare dizzy that I'm going to send into Advanced Distributers for the finished car.

khallam Kurtis Hallam
Lincoln, California, USA   USA
I have only heard of the electrical system causing the engine to die after it warms up as it looses conductivity with heat. If it dies when you throttle up the engine it sounds more like an air/fuel issue. Are you able to start the car up again right after it dies and resume a "good" idle? If that is the case you are getting too much air through the intake compared to fuel. Have you re-callibrated your choke if you have an auto choke on it? My bet is too much air or not enough fuel i.e. leaning it out too much. I would also check to see what happens when covering the air intake side of the car while running and see what happens, both while idling and while trying to throttle up.

Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
"Does anyone have detailed information on what can be removed from this system?"

The easiest way to approach it is the way that you are doing: remove the air pump, then remove everything directly related to it and securely plug all of the holes.

The vapor recovery system is completely separate from that, and is all outside of the intake flow so it doesn't harm anything, performance wise, and doesn't weigh anything, and keeps the car (and the garage) from smelling like gas, and cuts down the hydrocarbon emissions of the car to a small % of what it would be otherwise. So, I vote to leave that alone (simply confirm the lines are all leak free and you can replace the activated charcoal in the canister with aquarium charcoal (same stuff).

The only other "emissions" stuff there is are these things:

The "pop off valves" on the throttle plates - get rid of them and replace with solid plates. They didn't work well when new and they work even more poorly when old. No one makes them anymore, only solid is available because of those things.

The distributor advance - have Jeff rebuild it for you and that will be as good as it gets.

Other than those things, if the engine is healthy, and the carbs are mechanically in good shape, then you should be all set to drive and enjoy (as long as your front suspension doesn't need rebuilding - a common weak point in these cars, so it is very typically needed).


N

tripp2loo Avatar
tripp2loo Paul Bateman
Noblesville, Indiana, USA   USA
I'll go through all the suggestions tomorrow night and let you know the results. Thanks for all the info.

Norm, I bought the rebuild kit not the Master rebuild. This is turning out to be a mistake.
The rebuild kit comes with needles and all other general carb items, the Master comes with Throttle shafts, bushes and disks. Turns out to add the last 3 items it's almost $100 bucks, where as adding the needles to the Master kit is around $30. Live and learn I guess. Probably end up buying a master kit as well.
Do you know how much it normally cost for a 25D rebuild at Advanced Dizzy's?

Cheers

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tripp2loo Avatar
tripp2loo Paul Bateman
Noblesville, Indiana, USA   USA
So far not so good.
I blocked off all the air intake vents from the emission control system.
Still when I try to accelerate it bogs down, although it doesn't die. If I remove the distributer vacuum connection it seems to perform better.
It's acting like a total like of air flow when you throttle up. I don't see the discs move at all. Could I of made a mistake in reassembly of the carbs?

Once the motor was hot, it really won't run at all.
Still waiting on my "ignition bits" to arrive.

I also did a compression test on all cylinders with the motor idling.
Note this is with a 35 year old tester, but I got 1=70, 2=70, 3=60 & 4=60.
I'm guessing by these numbers the motor is pretty worn the hell out.

Cheers

Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
a compression test should be done with the spark plugs out, throttle wide open and only spin the engine with the starter



Regarding your running issues, it is highly likely that you've got something in the carb linkage on backwards. Post photos.

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tripp2loo Avatar
tripp2loo Paul Bateman
Noblesville, Indiana, USA   USA
OK, After I wrote the previous I read I was doing the compression test incorrectly. I did it again and I'm getting around 120. Livable.

New "ignition bits" have helped, but now still can't throttle up. My thought now is I am really rich.

I videoed it. Thoughts?

1974MGMidget Avatar
1974MGMidget Silver Member Jack Orkin
Grayson, Georgia, USA   USA
It may be my end, but I cannot view the video. It says it is private.

tripp2loo Avatar
tripp2loo Paul Bateman
Noblesville, Indiana, USA   USA
Sorry, try again please

Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
is it fully warmed up and with the choke off?

From the video is sort of seems like a cold engine, just started, with the choke turned off too soon, before the engine was warmed up.


N

Robert H Gold Member Robert Harvey
Wichita, Kansas, USA   USA
1951 MG TD "Millicent Grace (Millie)"
The way that it is spitting back thru the carbs, it could be timing. Maybe way too advanced? I would check that.

tripp2loo Avatar
tripp2loo Paul Bateman
Noblesville, Indiana, USA   USA
It was warmed up and I had taken the choke off. The idle seemed OK.
As for timing. I statically timed at 5 degrees.
Could shitty gas have this kind of affect also?

I'll check the static timing again tomorrow.

Thanks all the help...

Cheers.

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