Vacuum and pressure pipes and wading system.

davem201m38 · Post by **davem201m38** » Fri Mar 31, 2017 7:19 am

Hi all,
I've just gotten round to fitting a YS50 to the M38. I've gone through my TM's but can't find the answer to this question.

On the Carter carb there is a air tube that comes out of the carb just above the petrol delivery pipe and goes into the metal air cross-over pipe.
What does this pipe do? Putting the wading system pipes back on will take a while (have to make new ones first) So can I blank off the carb too cross-over pipe air/vacuum line at the carb or is it essential to have it open to atmosphere?

Cheers,
Dave.

4x4M38 · Post by **4x4M38** » Fri Mar 31, 2017 8:09 am

Hello Dave,
Assuming you have an M38?

Here is everything to know (at present) about the M38 fording system.
Note that there were two systems, an early and a late, but to your
specific question that one line is common to both.

http://www.cj3a.info/sibling/m38vent/vent.htm

Cheers,

Post by **wesk** » Fri Mar 31, 2017 8:11 am

I hope you put a YS637S on your L134 powered M38. The YS950S is for the F134 powered M38A1 and is bigger than the M38 manifold.

That vent tube is to vent the bowl. This is necessary as the carb bowl feeds fuel through the main jet to the intake manifold and the fuel level needs to drop in the bowl. For the fuel level to drop and feed down we must allow air in to occupy the space above the fuel or the lack of air in will slow down and finally stop the flow of fuel. Same issue arises with the fuel tank if it's vents get plugged.

4x4M38 · Post by **4x4M38** » Sat Apr 01, 2017 6:55 am

Wes,
Can he use one of those axle/rear end vents until he gets
the proper vent line made or bought?

Post by **wesk** » Sat Apr 01, 2017 9:23 am

I wouldn't. The air that is allowed in there needs to be filtered. Just fabricate the 8" tube and hook her to the crossover pipe.

davem201m38 · Post by **davem201m38** » Sun Apr 02, 2017 2:15 pm

Thank you all for your responses, hugely appreciated. I acquired the jeep with a 'odd' wading system from the Greek army (ex MAP). I'd set it up some years ago (see photos here someplace) but the original MC engine nipped up over a couple of winters. So until the MC engine is rebuilt there's a French M201in there with the YS.

Out of interest, what is the difference between a M38 carburettor and a M38/A1 carburettor.
All the best,
Dave.

4x4M38 · Post by **4x4M38** » Sun Apr 02, 2017 3:55 pm

Several differences Dave but the big one is the base
flange mount is 90 degrees different between the two.

Without a lot of work you can't just bolt a YS637 onto
an M38A1, nor a 950 to an M38.

Take care,

Post by **wesk** » Sun Apr 02, 2017 10:38 pm

The biggest issue is they are two different SAE bore (throat) diameters. You can address indexing but you will need a bore adapter and I know of no makers of such an animal.

davem201m38 · Post by **davem201m38** » Mon Apr 03, 2017 1:45 am

Oh well, it's good to know that the carb that's been sitting on the shelf for 25 years is a M38 one!