Help! Intake carburetor plug missing.

[Ralph E.]

What happens when the plug used for blocking off the exhaust crossover to keep heat off the carburetor falls into the intake manifold. Discovered one of the plugs is missing today. Was removing the intake manifold today to fix an oil leak behind the distributor and made this discovery. Engine is in my 1967 Corvette with 327/300hp

[Stuart F.]

Re: Help! Intake carburetor plug missing.

Ralph;

Was this a threaded plug or just one that may have been pressed in? Which side is missing, driver's side or passenger side?

IMO, but I have no experience to back this up, if it is the driver's side it might have been sucked into the exhaust system and resides now in your driver's side muffler (hear any rattles back there?). If it is the passenger side it might also be able to pass the heat riser valve and again be residing in your passenger side muffler. I believe the chances of it fouling an exhaust valve are rather slim as the pressure of exhaust flow is to the downstream of the valves.

Is it possible someone intended to only use one plug to just limit the flow of heat to the base of the carb rather than block it entirely? Some people accomplish this by using a block off plate at the manifold port on one side only (the side being determined on whether a heat riser valve is in place or not.

Stu Fox

[Ralph E.]

Re: Help! Intake carburetor plug missing.

Stu, the plugs was located on the drivers side. It was a pressed in plug. I installed it years ago. But I know it was there last spring because I needed to remove the intake to repair a bent push rod at the #4 cylinder. I do not think these two issues are related.
I hope you are correct that it could have just shot out the exhaust.

[Edward J.]

Re: Help! Intake carburetor plug missing.

Ralph, I believe that the plug likely is in the exhaust system somewhere maybe lodged in the muffler? or out the tail pipe it went, that crossover I am pretty sure it there not much obstruction for a object of that size. if you don.t find it in the intake look into the exhaust ports in the head.

[Jim T.]

Re: Help! Intake carburetor plug missing.

I do not know where this plug could of ended up. I only think the size of plug big enough to tightly fit in the intake would not be able to pass a valve opening into the engine. If you cannot find it with the intake removed where is it?
When I installed plugs for the crossover heat path in my 68's intake, I used plugs (leftover carburetor parts) that had a center screw that I wired together from each installed plug's vertical screw to prevent a displaced plug. Think of it as my safety wire although the plugs fit securely.

[Ralph E.]

Re: Help! Intake carburetor plug missing.

Guys, I checked the heads, I even vacuumed out all of the ports. Found nothing. Please tell me there is no way it could have got to the oil valley and screwed up up lifter or something else.

[Edward J.]

Re: Help! Intake carburetor plug missing.

Ralph, there no way it will find its way into the internals of the engine. this is a exhaust port, so like I say its in the exhaust system somewhere if you don't see it anywhere.

[Ralph E.]

Re: Help! Intake carburetor plug missing.

Thanks Ed, sounds like I dodged a bullet. I will need to replace it, not sure if I should press in another plug. Any thoughts/suggestions?

[Stuart F.]

Re: Help! Intake carburetor plug missing.

Ralph;

What was the plug made from? Perhaps it just burned up or melted. At any rate, like I said in my first post, it no doubt was blown through the exhaust system. On that side there is little to impede its' movement through the system (unlike the passenger side which has the heat riser valve).
However, if you have stock mufflers with baffles it no doubt did not get through the muffler. That's why I asked if you heard any rattle back there.
At any rate, I wouldn't worry about it.

My 63 L-76 engine has a chrome plated air filter assembly. Right now, most all the chrome on the inside of the housing has peeled off. Granted, a lot of it I peeled off myself over the years when I found a loose edge, but the rest no doubt was ingested into the engine and its' still running well. Who knows, maybe it stuck to my valves or piston tops, but it has not hurt it a bit. The engine is still original and has never been apart, nor do I see a reason to take it apart for now. It only has 47,000 miles on it and runs like a top.

Stu Fox

[Ralph E.]

Re: Help! Intake carburetor plug missing.

Stu,
i have a side pipe car so I hope the plugs is gone.
The plug was just cheap zinc plated plug.
I am thinking about replacing with a brass plug.

[Timothy B.]

Re: Help! Intake carburetor plug missing.

Tap the slot holes for 1/4" pipe threads and use allen head flush plugs. Put some blue loctite, the pipe threads are tapered so tap deep enough to where the plugs get tight and fully engage the threads, look at the pics of my 300hp manifold. Try to find that plug or be certain it's gone. What could have caused the push rod to bend on the engine, if it's a exhaust valve I would be suspect of the plug.

Also, get a magnet and probe around the exhaust valves in the head looking for the plug and probe through that manifold good to be certain it's not lodged inside somewhere. It's also a good idea to remove the oil splash shield on the bottom and clean all the baked oil off the plenum bottom then re-install the shield.

[Stuart F.]

Re: Help! Intake carburetor plug missing.

There you go Ralph, you've heard from the plug expert. Thanks Tim. I still find it hard to believe that plug could foul an exhaust valve, but stranger things have happened. The bent pushrod would be suspect had not Ralph said that the plug was still in place when he replaced the pushrod.

Stu Fox

[Timothy B.]

Re: Help! Intake carburetor plug missing.

Hi Stu,

This same thing happened on my 67 on that manifold pictured. After driving myself crazy trying to find the plug I decided to remove the manifold and there it was sitting on top of #3 or 5 exhaust valve. Would it have gone through into the exhaust or just wedged itself side ways in the open valve, I don't know but I am glad I found it. That led to the shot peen, taping of holes, 1/4" plugs etc.

Ralph, all I am saying is just be certain that plug is no where around the related exhaust valves and while the manifold is off be certain it's not in there.

[Ralph E.]

Re: Help! Intake carburetor plug missing.

Hi Stu,

This same thing happened on my 67 on that manifold pictured. After driving myself crazy trying to find the plug I decided to remove the manifold and there it was sitting on top of #3 or 5 exhaust valve. Would it have gone through into the exhaust or just wedged itself side ways in the open valve, I don't know but I am glad I found it. That led to the shot peen, taping of holes, 1/4" plugs etc.

Ralph, all I am saying is just be certain that plug is no where around the related exhaust valves and while the manifold is off be certain it's not in there.

Guys, thanks again. Believe me I am still looking for it.

Tim, how did you find it sitting on top of an exhaust valve. Did you find it when you removed the valve covers?
My plan is to remove the remaining plug and installed threaded allen plugs.

[Stuart F.]

Re: Help! Intake carburetor plug missing.

Ralph;

I believe Tim found it by removing the driver's side exhaust manifold. That is the only possible way you could actually see an exhaust valve, I.e. Not by removing a valve cover, but possibly through the crossover port in the head with the intake off as you have now done. If that was where he saw it, then for sure it would be by either the #5 or #7 exhaust valve as those two very close to each other in the middle of the hear (not siamesed, but close). That is a small port, but it's worth a look. When Tim relates to 1/4" NPT he means "pipe thread", not a physical measureable 1/4" in diameter of the hole. That, as you said, measures 7/16" diameter.

Stu Fox