Mazdax605

iTrader: (5)

Hey guys,

I have been fighting an on again off again idling problem with my 79 GS since rebuilding the engine last fall. When I first got it installed it idled great,and then this spring it was dying every time I came to a stop,and then a week or so later it stopped doing that. I immediately thought vacuum leak,but due to no help being around I hadn't had a chance to track it down. About a week or so later I was driving it,and had no idle troubles at all. Well today I took it out,and it is back again.

I started looking at potential vacuum leaks,and found the top bolt on the ACV block off plate was stripped. I thought maybe just put a longer bolt in as it seemed it was stripped only so deep,and maybe I could catch a few good threads. Well that didn't fix it. What can I do to fix this? Could I run a tap into the manifold and hope to fix it,or do I need to remove it,and drill,and tap to a larger size?

Also could this be my source of idle troubles? If so why would it come and go? Anywhere else I should be looking for leaks? If I can't keep it idling,and don't have help how else aside from spraying carb cleaner can I use to find this leak?

Oh yeah it is a stock 79 intake with an 83 Yaw power carb,and it ran great before the engine rebuild,and still does,but the idle is messed up at times where the car just dies instead of idling.

mazdaverx713b

iTrader: (91)

depending on the severity of the damaged threads and any "rounding" depends on if it needs to be tapped to a larger size. in most cases simply tapping it with the exact size thread pitch and diameter with the intake manifold bolted to the engine should suffice. you can also try a heli-a-coil. i would not tap it out too much larger.

if the bolt is not tight there could be the potential for a vacuum leak at the intake manifold and acv block off.

DivinDriver

iTrader: (15)

I'd helicoil it, myself; takes you from aluminum to steel threads, problem will never come back.

Jeff20B

iTrader: (13)

Might I suggest a different course of action? I think I will.

Ok you said the stripped hole is for the ACV? And this is on a 79 manifold? You're in luck. The SA manifolds don't have a connection with the ACV port in your engine's intermediate plate. This means you don't even need an ACV block off plate. All you gotta do is get yourself an NPT 1/8" 27tpi pipe tap, and a brass (or steel) pipe plug; preferebly with an allen key internal hex or slotted screw driver drive and not an external hex. You'll see why (not much room).

Remove ACV block off plate completely. Cut threads in the hole, clean shavings out. Apply teflon tape and install pipe plug. You'll see two small holes going into the runners. I block them with a small screw but you can use a self tapping screw. Whatever, as long as it makes an air-tight seal.



You seem like a smart fella. You can probably handle a fix/mod like this, and learn a new skill (thread cutting) at the same time. Also no need to helicoil if you're worried about it. If anyone asks about the big gaping hole in the manifold, ask them to explain how you can pull off the distributor cap and fire it up. They'll quickly forget all about the ACV hole as they watch the rotor spinning at idle (assuming you've got direct fire on leading). It gets 'em every time.

Mazdax605

iTrader: (5)

Hey guys thanks for the help. Jeff those two holes you mentioned that need small screws to block off,are they threaded,or do I need to thread them? Is that why you mnetioned self taping screws as they are not threaded already?

Would this fix be easier with the manifold off the engine,and do I need to drill out that hole that needs the pipe plug or is it the proper size already?

Chris

So that big round hole is not a soure of a potential leak but rather the smaller one? Wow I never would have guessed that!!

Jeff20B

iTrader: (13)

The big hole might be a source but I can't remember what it goes to. It should be the correct size for the tap. The small holes aren't threaded.

Mazdax605

iTrader: (5)

So I fixed the stripped bolt,and made a gasket for the block off plate. I will try the pipe plug later this week Jeff as I didn't have the right tap today,and had no time to get out to the store to get one. Put it all back together,and still the same no idle problem. I really need some help with revving the engine to keep it running so I can spray it with carb cleaner to find this leak. Anywhere in particular I should check for vacuum leaks?