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Help finding source of vacuum leak in 1974 Midget

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phoffman Peter Hoffman
Miller Place, NY, USA   USA
I replaced the engine in a 1974 midget with another engine. Original engine had a oil cooler hose break and the engine seized.
I went to drive it and it had very little power so I went looking for possible reasons.

The vacuum gauge connected to the port on the front carb that goes to the vacuum advance unit shows about 1 psi at idle.
When I rev it up it does increase.

I have tried the unlit propane torch method around the intake manifold without seeing an increase in idle speed.
The carbs have been adjusted and synced. I have checked the advance and have tried it at both 10 and 20 degrees without a change in vacuum level.
I have used a indirect temp gauge and the front of the exhaust manifold shows around 280 and the back shows around 400.
I have pulled each plug while running and speed drops.

Any ideas?

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phoffman Peter Hoffman
Miller Place, NY, USA   USA
Got back to working on this car and found that there is too much air entering the carbs from the timing chain breather pipe. On this year car it splits at a y and enters both carbs.
I called and asked Joe Curto and he lead me onto this potential source of vacuum leak.
I am looking at using a PVC valve as there is not one on this car.
What do other members do for this?

Thanks.



Edited 1 time(s). Last edit at 2019-03-15 04:37 PM by phoffman.

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Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
The stock setup was that Y pipe went to the front cover, and then there was a metered hole in the end of a nipple on the top of the valve cover.

Is your nipple missing?

The hole is pretty small, like 1/16". It prevents that very clever PCV system from drawing too much air (with no moving parts).

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refisk Avatar
refisk Rick Fisk
Frankenmuth, MI, USA   USA
That type of crankcase ventilation system only works if all components are in place. The oil fill cap has to be the sealed type - not vented. The rocker arm cover has to be the kind with a restricted tube. Even the dipstick should have a seal on it where it meets the crankcase tube. The carbon adsorbtion canister can be missing, but the rocker arm tube has to be restricted. My last '72 Midget used this system and it worked great.


In reply to # 3909368 by phoffman Got back to working on this car and found that there is too much air entering the carbs from the timing chain breather pipe. On this year car it splits at a y and enters both carbs.
I called and asked Joe Curto and he lead me onto this potential source of vacuum leak.
I am looking at using a PVC valve as there is not one on this car.
What do other members do for this?

Thanks.


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150725EA-B44A-4E33-8B84-3258ABF9E593.jpeg

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phoffman Peter Hoffman
Miller Place, NY, USA   USA
Norm, Rick,

The oil fill cap has a small hole in it, that can be plugged. The restricted tube is going to the canister, not sure if it has any leaks,ditto for dipstick tube I will check it tomorrow.
Thanks for the help.

Peter

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1974MGMidget Avatar
1974MGMidget Silver Member Jack Orkin
Grayson, GA, USA   USA
If I read your first post correctly, you said the vacuum advance went to the front carb. On my '74, the vacuum advance comes off the intake manifold. Is that what you meant? Not sure if that would cause your problem, but it may not provide proper advance.

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phoffman Peter Hoffman
Miller Place, NY, USA   USA
Yes, the vacuum advance is hooked up to the front carb, not the intake manifold. I have a 1970 midget with similar setup.

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refisk Avatar
refisk Rick Fisk
Frankenmuth, MI, USA   USA
My '72 had the vacuum advance connected to the front carb as well.

In reply to # 3909487 by phoffman Yes, the vacuum advance is hooked up to the front carb, not the intake manifold. I have a 1970 midget with similar setup.

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ice Avatar
ice Gold Member Larry Ice
Lawrenceville, GA, USA   USA
Peter, your car will run fine with the vacuum hose from the frt cover venting just to the outside, no other connection needed. If you try to use parts of the emission system and discard others you may find the engine runs roughly.



Iceman

Atlanta GA

60 AH MK1
62 AH MKII
67 Midget
71 Midget

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phoffman Peter Hoffman
Miller Place, NY, USA   USA
Larry, then I assume I have to block off the y connection into the carbs?

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ice Avatar
ice Gold Member Larry Ice
Lawrenceville, GA, USA   USA
I did mine. Open venting is fine for your engine. Just run a hose from the cam cover to underneath the engine. Some will say you have to make a vacuum from the cam cover to the carbs. Piping vacuum to the carbs is not necessary to keep your engine from weeping oil. If your car leaks then it has oil to run! Just try it, if you don't agree switch it back. I know some will object to venting to the outside as not environmentally correct but then our cars aren't miracle environmental machines are they?
Now let the comments begin!



Iceman

Atlanta GA

60 AH MK1
62 AH MKII
67 Midget
71 Midget

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ken472 Avatar
ken472 Ken Petersen
Luverne, MN, USA   USA
I'm with you Larry. The Original Owner did mine this way when he removed the smog gear. Works great. Only very minor rear seal leak.

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