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  #1   IP: 108.88.37.1
Old 09-05-2019, 05:27 PM
Stiva Stiva is offline
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Scavenger tube loose

Hello!
I've recently purchased a Catalina 27 with an A4 and am attempting to isolate the source of a gasoline odor. While poking around I noticed there appears to be some fluid on the scavenger tube fitting, and I am starting to think this is a source. It may also just be Permatex but the odor says gas.

While reaching in there (it's a tough reach) I found the scavenge tube elbow fitting on the carb is not tight. Given where it is, I'm not actually sure it can be tighetned with the carb on. So the questions are:

Should it be tight?
If so, is it possible to tighten with the carb attached?
Also, it appears that the elbow must be parallel to the engine which may account for it having not being tight. Not sure how to address that.

At this point I'm having trouble even getting in a position to work on it, so up front advice would be appreciated before I contort myself into the lower reaches of the port locker.

Also, fwiw I realize there shouldn't really be much fuel getting picked up by the tube and wouldn't be surprised if I've over used the choke and caused more gas than usual to be getting in there. The engine was somewhat difficult to start when I bought the boat but new plugs, gapped correctly last week has it running smooth and starting with a lot less choke.
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Old 09-05-2019, 07:54 PM
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The A4 uses an updraft carb, and this design is inheritly hard to start. A cold A4 should require full choke and 2-3 tries to start if properly tuned. If your A4 starts without full choke or on the first try, it is probably tuned too rich.
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Old 09-05-2019, 08:00 PM
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Quote:
Originally Posted by edwardc View Post
The A4 uses an updraft carb, and this design is inheritly hard to start. A cold A4 should require full choke and 2-3 tries to start if properly tuned. If your A4 starts without full choke or on the first try, it is probably tuned too rich.
Handy tidbit -- I was wondering since mine almost doesn't like the choke at all. Crank it over on the first try and slap the choke closed as soon as its at idle is my experience. Guess I should read up on carb adjustments.... I'm sure there's a guide around here somewhere.
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Old 09-05-2019, 08:45 PM
Stiva Stiva is offline
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Quote:
Originally Posted by edwardc View Post
The A4 uses an updraft carb, and this design is inheritly hard to start. A cold A4 should require full choke and 2-3 tries to start if properly tuned. If your A4 starts without full choke or on the first try, it is probably tuned too rich.
Thanks for replying. From what I've read here and elsewhere, it starts pretty much as it should. Still won't start without choking, but after changing the plugs it seems pretty much like what you describe. The big difference now is that I can take the choke off as soon as it starts.

I'm really more concerned about the scavenge tube, whether I can get to it and tighten while the carb is attached, or even whether its worth being worried about.

Last edited by Stiva; 09-05-2019 at 08:53 PM.
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Old 09-06-2019, 11:22 AM
Dave Neptune Dave Neptune is offline
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Exclamation Safety

The scavenge tube is a SAFETY devise!!! It takes the raw fuel that drips down the updraft carb and routes it to the manifold. This way the fuel does not accumulate and drip out of the carb~boom.

The tube is just a piece of 1/8 copper tubing usually with compression fittings on both ends. The nuts are 3/8 as I remember and should be snug so they don't leak fuel or air. The extra air is especially bothersome for the carb at low speeds.

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  #6   IP: 207.118.20.35
Old 09-06-2019, 11:39 AM
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important stuff

This is a common source of gasoline odor. If you can smell it without putting your nose on the carb air intake, you have a problem. If you can reach in there far enough to know that it's loose, you can reach it to tighten it. A 4 + 1/2 " long, 3/8" open end wrench should do it. That's the only thing I use that wrench for. The previous owner was seriously remiss in not doing that. If the elbow is not pointing forward, turn it so that it is. If you have to remove the carb, do it. You don't want that to drip into the bilge. Then try to get any gas out of the bilge.
On the subject of using choke to start, you should need full choke to start if engine is cold. After running for a few seconds, the choke can open. With mine, once the engine is warmed up it doesn't need a choke to start. I may have it tuned a little rich, but I like to be able to start quickly by just turning the key and pushing the button. I do a lot of 'motor for bit, sail for a bit', and repeat, because I navigate around small islands in a light wind area.
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Old 09-06-2019, 01:19 PM
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Quote:
Originally Posted by Stiva View Post
I'm really more concerned about the scavenge tube, whether I can get to it and tighten while the carb is attached, or even whether its worth being worried about.
ANY potential gas leak is worth being worried about.

The stiffness of the copper tube can make it difficult to align and start the threads grabbing. I've had success by undoing the manifold end and threading the carb end first. The manifold end is much more accessible and I can then get it aligned and threaded.
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  #8   IP: 207.118.20.35
Old 09-06-2019, 01:53 PM
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I have found that making sure the tube is straight as it nears the fitting helps with getting the threads started. Get it started with your fingers. If you can't do that, don't put the wrench on it.
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Old 09-06-2019, 05:16 PM
Stiva Stiva is offline
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Quote:
Originally Posted by capnward View Post
This is a common source of gasoline odor. If you can smell it without putting your nose on the carb air intake, you have a problem. If you can reach in there far enough to know that it's loose, you can reach it to tighten it. A 4 + 1/2 " long, 3/8" open end wrench should do it. That's the only thing I use that wrench for. The previous owner was seriously remiss in not doing that. If the elbow is not pointing forward, turn it so that it is. If you have to remove the carb, do it. You don't want that to drip into the bilge. Then try to get any gas out of the bilge.
On the subject of using choke to start, you should need full choke to start if engine is cold. After running for a few seconds, the choke can open. With mine, once the engine is warmed up it doesn't need a choke to start. I may have it tuned a little rich, but I like to be able to start quickly by just turning the key and pushing the button. I do a lot of 'motor for bit, sail for a bit', and repeat, because I navigate around small islands in a light wind area.
There is no gas in the bilge, nor is it dripping from the elbow, which points aft toward the shaft end of the motor. I'll be at the boat for another look after dinner, armed with some additional info, thanks to the replies here.
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Old 09-08-2019, 03:52 PM
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Just to muddy the waters...
Most of the scavenge tubes I've seen use flare fittings. The nut is slipped onto the tube and then the end of the tube is enlarged with a special tool to make a small cone. This female cone fits over a male cone on the fitting then the nut tightens it all up.
No reason a compression fitting can't be used, but that requires a compression ring (I wouldn't use plastic), a different nut, and a different fitting.
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Old 09-15-2019, 06:40 PM
Stiva Stiva is offline
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I was able to get one more full turn on the carb side elbow of the scavenger tube. It seems to be ok now, but should i be concerned about the flare fitting. A!so, would the scavenger tube ordinarily be installed dry or with some kind of sealer goop?
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Old 09-15-2019, 06:49 PM
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Quote:
Originally Posted by Stiva View Post
A!so, would the scavenger tube ordinarily be installed dry or with some kind of sealer goop?
Pipe threads take sealant, flares do not.
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  #13   IP: 32.211.28.40
Old 09-15-2019, 07:34 PM
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The male half of the flare is machine made and should be good. The female flare in the tube is made on site by the local mechanic using whatever tool he has - and with whatever skill he has.
So, you might need a little permatex (the brown stuff) - I'd put it on the male flare, keeping it out of the hole.
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Old 09-16-2019, 11:32 PM
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The first time that I addressed it, (out of sight, out of mind) I found that the scavenger tube fitting was quite loose. Tightening it up didnít make any obvious difference. Since itís a vacuum fitting, rather than a pressure fitting, it ought to be self-sealing to some extent.

Earlier this summer, I took the carb off for cleaning and darn if that fitting wasnít loose again! But I have had a vacuum gauge installed for a couple of summers now and it had been reading normal vacuum. Which reinforces my opinion. Still, maybe a little permatex would help the nut stay in place.

BTW, Iíve hardly used the engine this summer, but it has been starting with no choke. However, I changed three variables: Cleaned the carb, installed adjustable main jet, and installed electronic ignition. Guess Iíll have time for adjustments now that the rains are coming in.
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