Breather Hose Question

[JTG1160]

When I look at pics of the A4 there is a hose running from the block to the air intake backfire filter of the carb. My A4 has never had this hose since myself and the previous owner operated it for the last 15 years or so. Believe it's referred to as the Breather Hose. What's the purpose of this hose and any concern if operating without it? Thx!

John

[Dave Neptune]

The hose is to move the crankcase gases from the engine box-boat instead through the engine and out the exhaust. Cleans things up a bit too.

Dave Neptune

[JTG1160]

Thx Dave, seems like this would dirty up the air-gas mixture going into the carb but obviously not a concern since they all seem to have them, I can see where that would clean up the grime a bit in the as well around the engine

[ronstory]

Or you can just upgrade to the technologies of the 1960's and get PCV kit and ditch the breather. It does make a difference.

[ndutton]

$20.00 vs. $80.00
Unless your engine is worn internally producing excessive blowby, it's pretty easy math.

[thatch]

Slash Tube, the long answer

Hi John, There are definitely two schools of thought regarding the "passive" breather tube, also known as the slash tube and a PCV system. They both attempt to remove crankcase gasses, AKA blow-by, but by different methods. A properly fitting slash tube will remove most of the blow-by from a reasonably sound A4 without the need of an additional vent system. If a PCV system is added, it is normally necessary to add an adjustable main jet valve in order to re-tune the carb's air/fuel ratio. My well worn, accurately timed A4 with a good fitting slash tube, shows virtually no signs of blow-by.
Tom

[sastanley]

I will throw in my $0.02. I bought the PCV kit over 10 years ago, and while it did help remove the crankcase gasses, it made the engine run terribly at low RPM, and won't idle below 1,000 RPM.
I have since removed it, and I am dealing with the blow-by. But I can idle at 700 RPM and that is worth it to deal with a bit of blow-by in my book. The real issue for me is the oil fumes come out of the oil fill. If there was a way to seal that off safely, I would try it.
This is no slight against Indigo that designed the PCV kit. It does what it is designed to do, but at a cost.

[roadnsky]

A properly fitting slash tube will remove most of the blow-by from a reasonably sound A4...
My well worn, accurately timed A4 with a good fitting slash tube, shows virtually no signs of blow-by.

As Tom says, a GOOD FITTING slash tube goes a long way.
To that point, Tom made one of his special "Thatch Mod" slash tubes for me a few years ago.
Since then, my older engine runs much better and with no oily smell in the cabin.
Note in the pic how close fitting the tube is to the flame arrestor.


Shawn-
Before Tom's mod on my engine, I ran a hose up into my blower exhaust hose.
Maybe that would work on your oil fill leak?

[sastanley]

Jerry, I also have the "Thatch slash tube". but I can't get enough 'suction' to pull all the fumes.
In other news, my blower rattles, so I don't run it when the engine is on. If I took all the junk out of the locker and spent an hour checking on the status, I could probably solve that problem too, but it is easier to whine about it.

[Dave Neptune]

On a limb here

I installed a PCV valve as soon as they were available. Upon installation I only needed to open the idle screw less than a quarter turn rich. My idle was still rock solid at 700 RPM.

As far as needing the adj jet I disagree completely. Once I got my carb right by leaning it down and richening the the idle transfer sequence before instalation of the PCV I tossed out the adj jet for two reasons. First and utmost was that it could be a possible leak and it did show me how far off our carbs are from being balanced which I corrected with the help of Zenith.
Once the carb was right I could disconnect the PCV and the only difference was more fumes and loss of a few RPM's as my engine was really tired and very low on compression.

If I got another boat with an A-4 I would make the same changes.

The prime issue with the A-4 is that the carb is just plain ole to large!!!!!

If your engine is any where near correct you should not notice any changes other than a tweak of the idle screw and possibly a reduction in idle speed. You do need the proper PCV valve though!

Dave Neptune

[JOHN COOKSON]

I installed a PCV valve as soon as they were available. Upon installation I only needed to open the idle screw less than a quarter turn rich. My idle was still rock solid at 700 RPM.

As far as needing the adj jet I disagree completely. Once I got my carb right by leaning it down and richening the the idle transfer sequence before instalation of the PCV I tossed out the adj jet for two reasons. First and utmost was that it could be a possible leak and it did show me how far off our carbs are from being balanced which I corrected with the help of Zenith.
Once the carb was right I could disconnect the PCV and the only difference was more fumes and loss of a few RPM's as my engine was really tired and very low on compression.

The prime issue with the A-4 is that the carb is just plain ole to large!!!!!

If your engine is any where near correct you should not notice any changes other than a tweak of the idle screw and possibly a reduction in idle speed. You do need the proper PCV valve though!

Dave Neptune

Absolutely yes to all of the above!
I don't what exactly Dave N. was referring to when he said "engine near correct".
What worked for me was to get my points ignition set up correctly (dwell, timing, advance) then I was able to adjust idle to 575 - 600 RPMs. I could shift into gear at idle and the engine did not die. A side benefit was no fouling of the spark plugs.
If the ignition is not correct the idle speed\mixture will need to be adjusted to compensate.

ex TRUE GRIT