I finally found the port in the RH manifold for the clean air tube after a short search tonight for part numbers (the manifold is a 902, hurray...). Of course, the car is lacking the clean air tube and rubber hose. Any opinions on whether it makes a difference to the car's functioning? I will probably get one (looks like Doc Rebuild's got the setup) just to be closer to being correct, but what was the purpose of said tube? The archives didn't shed much light. Thanks!
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Re: Clean Air tube- nice to have, or necessary?-62
The clean air tube draws air from the filtered side of your air cleaner. The air goes through the exhaust mainfold where it is heated and into the choke and then the carb. If the air is not filtered particles can be sucked into the carburator. -
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Purpose is to speed engine warm-up and opening of the choke. With air warmed by the exhaust manifold, the choke's bi-metal responds more quickly vs. waiting for under-hood air to naturally convect and stimulate the choke mechanism. Gives improved cold start drivability, but ultimately the choke WILL heat and open naturally without the fresh air system installed.Comment
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Thanks, Bob- that raises the obvious question
If I remove the choke tube, it looks like the hole in the manifold opens right into the main body of the manifold itself. Unless the clean air tube and the choke tube holes are contiguous and isolated from the exhaust flow in the manifold itself, what's the point if all of the exhaust is free to blow up the choke tube? Or am I missing something obvious here? Thanks for the reply!Comment
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Re: Thanks, Bob- that raises the obvious question
There is a tube that goes thru the manifold to manage the air from the bottom to the top, heating it without exposig
g it to exhaust gas contamination. If the tube is not intact, you will hear the escaping exhaust if you pull out the tube to the choke.Bill Clupper #618Comment
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Re: Thanks, Bob- that raises the obvious question
You're missing the understanding of the bits/pieces of the system.... The fresh air system has TWO tubes. One is press fit into the exhaust manifold. It simply forms a path from the lower forward side of the mani to the upper rear side of the mani. This tube sits in the middle of the exhaust flow and is SEALED because it's a continuous pipe.
Then, a second pipe is tapped into the upper end of the lower pipe which serves to route warm air from the mainfold to the carb's choke. The 'warning' that was mentioned in the thread above is sometimes folks PRESUME the lower pipe (totally contained inside/across the exhaust manifold) is OK....
Truth is these lower pipes can deteriorate with age and spring holes. That's where red hot exhuast gas can enter the fresh air system and become a threat....
So, savvy restorers take no chances. With the exhaust manifold off the engine during restoration, they take the opportunity to cut out/remove the LOWER fresh air tube inside the manifold and replace it with a fresh/new one. Getting the old tube out is ususally the biggest job because it's typically siezed itself pretty well in the step-bored upper hole of the exhaust manifold from years of use. Sometimes, you have to come up the lower manifold exhaust port, cut the old tube and remove it in two pieces to get it out....Comment
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