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Vacuum Testing a Midget 1500

Posted by Thormidget

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Vacuum Testing a Midget 1500 #1
Thormidget Brett Thorsland Watkins Glen, USA	Posted: July 25, 2012 09:10AM Registered: 1 year ago Posts: 128

Where is the best port to use to test the engine using a Vacuum Gauge on a 1977 Midget 1500. The only remaining emissions stuff is the secondary charcoal filter with tubes and the vacuum line running from the Carb to the Distributor. The EGR, Air Rail, Smog Pump, etc. has all been removed. Also, what vacuum value should I get? Everything is running well, I am just looking to get a baseline number.

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Re: Vacuum Testing a Midget 1500 #2
refisk Rick Fisk Frankenmuth, Michigan, USA 1959 Austin-Healey Sprite 1961 Austin-Healey Sprite 1979 MG Midget 1500 "Party Midget"	Posted: July 25, 2012 11:08AM Registered: 1 year ago Posts: 2,243

The best place to connect a vacuum gauge is right on the intake manifold. Some 1500 manifolds have a vacuum port, some don't. You could install a fitting in the hole where the EGR was connected. Reading a vacuum gauge is an art in itself. You should see 15-20 inches of vacuum at idle and ideally the needle should be nice and steady. A needle that bounces around indicates an issue somewhere.

Rick

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Re: Vacuum Testing a Midget 1500 #3
77Midget Y.. Lee western, USA 1977 MG Midget 1500 "Some Friend" 1996 Mercury Cougar "My Antique" 2002 Subaru Forester "Suba One" 2002 Subaru Forester "Suba Too" 2006 Honda Civic "Civic"	Posted: July 25, 2012 12:02PM Registered: 2 years ago Posts: 829

Hi Brent,
I used the vacuum line running from the Carb to the Distributor.

Y.

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Re: Vacuum Testing a Midget 1500 #4
AmishIndy Seth Jones Wheaton, IL, USA 1971 MG Midget MkIII "Guenevire" 2007 Mazda 3 "Porco Rosso"	Posted: July 26, 2012 04:32AM Registered: 2 years ago Posts: 3,074

Heres how the dealers did it

http://www.spridgetguru.com/TA0078.html

Seth Jones

1971 MG Midget

www.SpridgetGuru.com

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Re: Vacuum Testing a Midget 1500 #5
Thormidget Brett Thorsland Watkins Glen, USA	Posted: July 26, 2012 07:57AM Registered: 1 year ago Posts: 128

I tested my 1977 Midget vacuum last night using the port that once held the EGR Valve. My idle usually runs around 1000-1100rpm, any lower than that and it runs noticeably rougher.

At 1000rpm, the vacuum gauge was reading about 16 inofHg and was pretty steady. Dropping the idle down to 850rpm makes the vacuum drop to about 14 inofHg and it jumps around alot.

At 850rpm, the timing is right at 10 BTDC (although I now remember that I did not pull the vacuum advance line off the distributor). I confirmed the 850rpm value using a Tach/Dwell meter.

My valves were just adjusted and I believe that they are set correctly.

Any thoughts on this? Is there any harm in setting the idle at 1000rpm? If I retest the timing with the vacuum advance line pulled off, which way should the timing move, above 10degrees (more retarded) or lower than 10 degrees (more advanced)?

Am I reading into this too much? I mean, the car seems to start and run perfectly, should I just drive and forget it? I think my engineering training is getting the best of me.

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Re: Vacuum Testing a Midget 1500 #6
oldag98 Jeff and Brittany Brackenridge Choctaw, Choctaw, Oklahoma, USA 1965 MG MGB "B" 1976 MG Midget 1500 "Yellow One" 1977 MG Midget 1500 "Dunkirk" 1979 MG Midget 1500 "Parts Car"	Posted: July 27, 2012 10:46PM Registered: 3 years ago Posts: 2,210

We do not know what the initial timing is set at. Always disconnect the advance hose from the distributor, plug the hose to prevent vac leak, set initial timing (or at least check it to see what it is), then reconnect hose and check timing again. This will tell you where the static/initial timing is set and how much it advances/retards at idle with the vacc adv/retard connected. If you tee into the vacc adv line, and connect your timing light, you can manually open the throttle and watch where the advance goes when you open the throttle. This will tell at what rpm and how much total advance you get. You need about four hands and 3 eyes to do this, but it can be done. use some white-out on the line on the crank hub so you can see the mark more easily with the timing light. Some racers even mount a small tach in the engine compartment to do make doing this easier. I'd experiment with initial timing to see at what amount of advance the car responds the best. I can't tell exactly at what settings your car will be the happiest, as all engines are different based on condition, wear, mods, de-mods, etc.

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Re: Vacuum Testing a Midget 1500 #7
mg man 75 maurice sallee Campbellsville, Central Kentucky, USA 1976 MG Midget	Posted: July 28, 2012 04:52PM Registered: 6 years ago Posts: 1,620

Seth Thanks for that link. Maurice

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Re: Vacuum Testing a Midget 1500 #8
Thormidget Brett Thorsland Watkins Glen, USA	Posted: July 31, 2012 11:49AM Registered: 1 year ago Posts: 128

At 850 rpm my timing is set right on 10BTDC as specified. Removing the vacuum advance line does not change the timing one bit. For reference, my EGR was removed so the vacuum advance line just runs between the carb and distributor. Sucking on the carb end of the vacuum advance line causes the engine to die slightly at idle. It requires a pretty hard suction. It that normal?

Again, my car starts and runs very well. I am not looking to change any setting, I am just looking to get a base line or to correct any issue that may give problems in the future.

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Re: Vacuum Testing a Midget 1500 #9
refisk Rick Fisk Frankenmuth, Michigan, USA 1959 Austin-Healey Sprite 1961 Austin-Healey Sprite 1979 MG Midget 1500 "Party Midget"	Posted: July 31, 2012 02:52PM Registered: 1 year ago Posts: 2,243

In reply to # 2134256 by Thormidget At 850 rpm my timing is set right on 10BTDC as specified. Removing the vacuum advance line does not change the timing one bit. For reference, my EGR was removed so the vacuum advance line just runs between the carb and distributor. Sucking on the carb end of the vacuum advance line causes the engine to die slightly at idle. It requires a pretty hard suction. It that normal?

Again, my car starts and runs very well. I am not looking to change any setting, I am just looking to get a base line or to correct any issue that may give problems in the future.

Sounds like the vacuum unit is bad. When you disconnect the vacuum line the engine speed should increase about 500 rpm.

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Re: Vacuum Testing a Midget 1500 #10
Thormidget Brett Thorsland Watkins Glen, USA	Posted: August 01, 2012 08:25AM Registered: 1 year ago Posts: 128

My 1977 1500 has an aftermarket Allison Electronic Ignition. Last night, I pulled the distributor cap off and sucked on the vacuum advance line and the electronic eye inside the distributor cap moved in a counter clockwise direction (as viewed from above). So it seems to work and while running my timing does change as viewed with a timing light. It actually retards more going more than 10 degrees BTDC.

Does having the Allison EI change they way this should work?

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Re: Vacuum Testing a Midget 1500 #11
refisk Rick Fisk Frankenmuth, Michigan, USA 1959 Austin-Healey Sprite 1961 Austin-Healey Sprite 1979 MG Midget 1500 "Party Midget"	Posted: August 01, 2012 09:04AM Registered: 1 year ago Posts: 2,243

In reply to # 2134813 by Thormidget My 1977 1500 has an aftermarket Allison Electronic Ignition. Last night, I pulled the distributor cap off and sucked on the vacuum advance line and the electronic eye inside the distributor cap moved in a counter clockwise direction (as viewed from above). So it seems to work and while running my timing does change as viewed with a timing light. It actually retards more going more than 10 degrees BTDC.

Does having the Allison EI change they way this should work?

The Allison EI works the same way as the original factory ignition, it just provides the spark. The timing is controlled by the vacuum unit and the mechanical advance mechanism. My '79 also has an Allison ignition. I have the timing set to 8 degrees BTDC and the line to the vacuum unit disconnected and plugged at the carb per Jeff Schlemmer.

Rick

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Re: Vacuum Testing a Midget 1500 #12
Thormidget Brett Thorsland Watkins Glen, USA	Posted: August 03, 2012 02:41PM Registered: 1 year ago Posts: 128

My 1977 seems to run the same with or without the vacuum advance line connected or plugged. I guess I will just leave it connected and the timing set to 10 degrees BTDC at idle.

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Re: Vacuum Testing a Midget 1500 #13
oldag98 Jeff and Brittany Brackenridge Choctaw, Choctaw, Oklahoma, USA 1965 MG MGB "B" 1976 MG Midget 1500 "Yellow One" 1977 MG Midget 1500 "Dunkirk" 1979 MG Midget 1500 "Parts Car"	Posted: August 03, 2012 04:51PM Registered: 3 years ago Posts: 2,210

If it runs the same, then more than likely the vac diaphragm has failed, i.e. has a rip, tear, crack, etc. Replace the unit to get it operational again. If you like the way it runs now, then to Heck with it...

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Re: Vacuum Testing a Midget 1500 #14
tmichnay Tim Michnay Wisconsin, USA	Posted: August 04, 2012 09:21AM Registered: 1 year ago Posts: 73

The distributor on the 1500 is actually a vacuum retard unit. It is ported by the throttle plate and will not have any significant efect at idle. To test for this, run the engine at idle and either use a vacuum unit (eze-bleed , etc)or gently suck on ta vacuum line connected to the unit and watch the timing. I have mine disconnected and all of the prots pluggged same as Rick, per advice from Jeff Schlemmer.

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Re: Vacuum Testing a Midget 1500 #15
Thormidget Brett Thorsland Watkins Glen, USA	Posted: August 04, 2012 09:50AM Registered: 1 year ago Posts: 128

By sucking on line, the engine speed slows at idle. So I guess it is working correctly???

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Re: Vacuum Testing a Midget 1500 #16
refisk Rick Fisk Frankenmuth, Michigan, USA 1959 Austin-Healey Sprite 1961 Austin-Healey Sprite 1979 MG Midget 1500 "Party Midget"	Posted: August 04, 2012 11:00AM Registered: 1 year ago Posts: 2,243

Yep.

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Re: Vacuum Testing a Midget 1500 #17
tmichnay Tim Michnay Wisconsin, USA	Posted: August 04, 2012 01:24PM Registered: 1 year ago Posts: 73

Sonds like it is. The best way is to try and watch the timing while you are doing it also.

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Re: Vacuum Testing a Midget 1500 #18
koball Shane Koball New York, USA 1977 MG Midget 1500	Posted: August 08, 2012 12:30PM Registered: 3 years ago Posts: 27

"using the port that once held the EGR Valve"

Is that the threaded hole in the exhaust manifold just above the catalytic converter / exhaust pipe?

I recently got an exhaust leak, then realized it is that threaded hole being a hole...no pipe and no fitting to plug it. I assume the EGR valve we removed and replaced with a fitting that has now fallen out. Anyone have suggestions on where I find a useable plug for that?

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Re: Vacuum Testing a Midget 1500 #19
tmichnay Tim Michnay Wisconsin, USA	Posted: August 08, 2012 07:49PM Registered: 1 year ago Posts: 73

IIRC it is a 3/4" coarse thread on the exhaust manifold. You cold try to find a short bolt and use a copper sealing washer or see if you can find an old EGR valve and put it in. The EGR port that Rick refers to is on top of the intake.

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Re: Vacuum Testing a Midget 1500 #20
koball Shane Koball New York, USA 1977 MG Midget 1500	Posted: August 09, 2012 05:22AM Registered: 3 years ago Posts: 27

Got it - thanks, Tim!

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