MGExp

MG Midget Forum

'77 Midget Air Pump System

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

sbarner Stephen Barner
Bolton, VT, USA   USA
I live in a state that requires the original emissions systems to be intact. I bought my '77 Midget without noticing that the entire air pump system had been removed. The cat is still in place and from what I've read, it's not a good idea to run these with a cat but no air pump, as the cat can overheat and it's right underneath the carb.

I believe at this point I've located all the missing parts, with the exception of the hoses. I have three questions. First, there doesn't seem to be any provision for an air filter, as in earlier systems, such as the one for the 1275cc engine. Am I correct in that the filter was eliminated when they replaced the gulp valve with a diverter valve?

Second, the hose from the diverter to the rail looks to have a 90 degree bend. Since replacements are no longer available, does anyone know of a suitable replacement that might be? I'm betting there are lots of other vehicles that had a similar hose somewhere under the hood.

Finally, the diverter valve has a 3/16" hose fitting that I assume went to a manifold vacuum signal. Can anyone tell me specifically where it connected?

Please don't reply just to complain about emissions controls. There's enough of that in other threads, so you won't be writing anything useful.

Thanks,
Stephen Barner
Bolton, Vermont
'77 Midget
'60 MGA

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
76lucas Avatar
76lucas Gold Member Josh L
Floyd, VA, USA   USA
1978 MG Midget 1500
1979 MG Midget 1500 "Parts Car"
Is it Federal or California emmissions? The setups are different. I have the workshop manual and there doesn't appear to be a filter in the system. I not sure if mine system is still all there. I could look later today. It would be awhile since I'm heading out shortly to West Virgina.



If you never try to do it You will never be able to do it

76lucas Avatar
76lucas Gold Member Josh L
Floyd, VA, USA   USA
1978 MG Midget 1500
1979 MG Midget 1500 "Parts Car"
I took a look at mine. It does not have a diverter valve or a gulp valve So not much help there sorry.



If you never try to do it You will never be able to do it

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
sbarner Stephen Barner
Bolton, VT, USA   USA
It's got the remnants of a California emissions decal. From what I've seen of engine compartment photos, I think the diverter signal comes from a T-fitting that also connects to the EGR valve and the carb. If my car was supposed to also have an anti-run-on valve, that's missing as well. I haven't driven it enough yet to tell if that's going to be a problem, but the plan is to get it on the road this season, even if it looks like a poor high school kid's car.

76lucas Avatar
76lucas Gold Member Josh L
Floyd, VA, USA   USA
1978 MG Midget 1500
1979 MG Midget 1500 "Parts Car"
To make sure it is a California emissions car look for the flat place on the block just behind the distributor.There will be a series of letters and numbers stamped there. They should start FP then some numbers. What your concerned with is the last set of letters. If it ends in UE it's a federal engine UCE is California. Has long has the engine has not been changed that should tell you which set-up to use. Are the photos you using of that car are just ones you have found? I ask because my manual does not show any diverter valve after 76. But it does show a gulp valve for the California emissions cars for 78-79. The anti run-on valve for 77 is given has if fitted which I take to mean that it may or may not have had one. But nothing given to help figure out of it did. My manual does not give much help in figuring out the vacuum lines. Not sure if I can be of much more help but hopefully someone with a complete emissions set-up will jump in and get you going the right way.



If you never try to do it You will never be able to do it

sbarner Stephen Barner
Bolton, VT, USA   USA
I think I'm wrong about it being a CA car. The end of the motor number is UESS and the emissions decal is yellow. According to what I found on SpridgetGuru, the CA decal is red and the federal decal is yellow. It has non-electronic ignition and the carbon canister is back by the firewall.

I'm thinking I got the wrong air rail. My EGR valve is on the top of the exhaust manifold and it looks like the long runners on the air rail I picked up will interfere with it. From what I can see of the leftover fittings, I believe the air pump mounted on the left side of the engine, under the alternator, with the air rail wrapping around the back, but I could be wrong. I can't see anywhere that a gulp valve would connect to the intake manifold, which is what lead me to believe that it used a diverter valve, instead. From what I understand of these systems, a gulp valve is supposed to lean out the mixture during deceleration, while a diverter dumps the pressure from the air pump to the atmosphere, with both systems designed to reduce backfire.

I only spot two small hose connections to the carb and none to the intake manifold. One is connected to the carbon canister, and the other goes to the vacuum advance on the distributor. The EGR valve is disconnected, but it's there. Perhaps there were Ts in the spark advance hose for the hoses to the EGR and diverter valve?

I just took another look and I spotted a capped-off fitting on the firewall side of the exhaust manifold that I hadn't noticed before. The head has holes for the air rail that have bolts plugging them, which is what led me to think that it had originally had the older style of air rail with separate runners to each exhaust port, but now I think it had the single tube to the manifold style. Perhaps the head has been replaced at some time, or it may have come from the factory as a transitional setup.



Edited 1 time(s). Last edit at 2018-04-15 05:21 PM by sbarner.

sbarner Stephen Barner
Bolton, VT, USA   USA
I've since found a few photos of other '77s that I believe were similar to mine, all with the EGR valve on top of the manifold. I believe Josh L is correct in that this version does not use a diverter valve. Instead, the air pump, which is mounted below the alternator, connects via a hose directly to the backfire arrestor valve, which is screwed onto a fitting at the end of a steel tube that wraps around the back of the engine and connects via a single compression fitting to the exhaust manifold. It's starting to look like I'll need to fabricate the pipe--which shouldn't be a problem. Apparently, this particular configuration was short-lived, bridging the earlier versions that used air rails, and the later ones that added the front carbon canister. Perhaps the version with the separate, long runners on the air rail is the California one? I believe the attached photo shows the correct air rail.

The photos I found also appear to show the vacuum hose splitting to supply both the EGR and distributor advance. A couple of the photos show an inline, metal object near the T. I have no idea what this is, but I suspect it's designed to avoid sudden fluctuations in the vacuum signal.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

Attachments:
s-l1600.jpg    19.5 KB
s-l1600.jpg

76lucas Avatar
76lucas Gold Member Josh L
Floyd, VA, USA   USA
1978 MG Midget 1500
1979 MG Midget 1500 "Parts Car"
This may help. It's useful for knowing what parts should be there. Not much for vacuum lines. I included the carb since it does have some of the lines on it. I will warn you of one thing. It shows on the carb diagram the distributor vacuum coming off the bottom of the carb by a metal threaded pipe. I and quite a few other 1500 owners have noticed that this pipe is not only not on our cars but that there is no place for it. And by that I mean that the carb itself not only doesn't have it but that there is not even a place made in the carb body to have ever attached it (i.e.,no threads or plugged areas)



If you never try to do it You will never be able to do it


Attachments:
20180416_221844.jpg    29.3 KB
20180416_221844.jpg

20180416_222026.jpg    26.3 KB
Sign In or Register to view this photo
kking96 Kevin King
Bend, OR, USA   USA
This 78 emissions manual should be pretty close to what you have.

http://www.spridgetguru.com/TchIndx06a_files/BLDlrTrng_S1044.pdf

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
sbarner Stephen Barner
Bolton, VT, USA   USA
The '78 air pump system is indeed the same as what it looks like my '77 had. The vacuum system was a bit different, as the '78 drawings show the front carbon canister, which is not part of my system (or of the diagram for '77). I see that the item I couldn't identify in the vacuum line is called a flame arrestor or petrol trap, in different places. There shouldn't be any exhaust gasses getting into that line, but the EGR valve can get mighty hot, and I suspect they wanted to keep as much gasoline vapor away from that area as possible.

Thanks,
--SB

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster