M20J “sniffle” check valve leaking

[sleeper-319]

Hey all, I have an 87 M20J 201. The check valve between the intake plenum and muffler is not closing when running, so it’s creating a small induction leak via that drain tube. I’ve read a bunch of threads, and I think this is what everyone calls the “sniffle valve.” But there seems to be some variability over the years, and I am not entirely clear what’s on the J. I have a PowerFlow exhaust if that changes anything.

Does cleaning the valve generally work, or does it often need replacing? Is the one that LASAR sells the proper replacement? Any wisdom or advice y’all have to offer is appreciated. :-) 

 

[PT20J]

The sniffle valve on the M20J is a custom Mooney part in order to clear the stock muffler. I don't know if the Powerflow will allow a different sniffle. The Mooney part is made by inserting a plastic ball in a right angle AN fitting held in with a small pin. None of them seem to seal perfectly but the leak is so small that it doesn't cause a problem at any power setting above idle. If you have a small induction leak, it usually affects the idle. If it is causing a problem, you can remove it and clean it in solvent. I might try setting the mixture rich and the throttle open and running the boost pump with the engine shut down which will cause gasoline to drain through it (which is it's purpose) and that might be enough to unstick it. Gasoline is a pretty good solvent.

[sleeper-319]

Interesting idea. I’ll give it a try.  

The one I have is a 90 degree valve that looks like the one on the LASAR website. There isn’t any extra room between the muffler and intake plenum for a different type. It’s a tight squeeze there. 

Edit: I’ll also say… I don’t know that this is my only problem, but it is a problem; I know it’s leaking air back into the intake. I installed a SureFly several months ago, and for the first 2 weeks, the cold starting was improved, and the hot starting was about the same. But then about 2 weeks after the install, both hot and cold starting began getting progressively worse, and it was accompanied by needing a richer mixture to idle properly (without popping & stumbling). Hot starts went from pretty easy to being an absolute bitch. I don’t know if any of this has anything to do with the surefly (it doesn’t seem like it, and surefly doesn’t think so). In any case, I’ll take care of this and see where it goes. The plane flies and runs fine apart from starting and idle.  

 

 

 

Edited May 19, 2024 by sleeper-319

[Shadrach]

37 minutes ago, sleeper-319 said:

Hey all, I have an 87 M20J 201. The check valve between the intake plenum and muffler is not closing when running, so it’s creating a small induction leak via that drain tube. I’ve read a bunch of threads, and I think this is what everyone calls the “sniffle valve.” But there seems to be some variability over the years, and I am not entirely clear what’s on the J. I have a PowerFlow exhaust if that changes anything.

Does cleaning the valve generally work, or does it often need replacing? Is the one that LASAR sells the proper replacement? Any wisdom or advice y’all have to offer is appreciated. :-) 

 

Clean it before replacing it. It’s fairly easy to access.  

[PT20J]

The LASAR one is the Mooney part number and it is out of stock. Are you sure it is source of the leak? You can check by plugging the hose temporarily. It's possible for the seals on the intake tubes to leak, also.

[jetdriven]

Airflow performance sells a sniffle valve that you can thread into a 90° brass adapter

[201Steve]

Also pointed out by Doc (RIP!), Lycoming makes a sniffle valve at 1/10th the cost of a “Mooney” sniffle valve. Don’t recall the part#. 

[LANCECASPER]

46 minutes ago, 201Steve said:

Also pointed out by Doc (RIP!), Lycoming makes a sniffle valve at 1/10th the cost of a “Mooney” sniffle valve. Don’t recall the part#. 

The part number is mentioned in this thread:

 

In stock: https://www.airpowerinc.com/75444

[sleeper-319]

Yes, I did confirm it was leaking before I started the thread. I took it out to clean it. The ball moves freely, and sucks back to the seat when vacuum is applied, but it just doesn’t seal very well. And to reiterate, I know that part isn’t working right, but I have no idea how much that one thing is contributing to the overall problem.

Thanks for the heads up re the LASAR vs Lycoming part. 

[PT20J]

10 hours ago, sleeper-319 said:

Yes, I did confirm it was leaking before I started the thread. I took it out to clean it. The ball moves freely, and sucks back to the seat when vacuum is applied, but it just doesn’t seal very well. And to reiterate, I know that part isn’t working right, but I have no idea how much that one thing is contributing to the overall problem.

Thanks for the heads up re the LASAR vs Lycoming part. 

I did the same with mine when I replaced the engine. I don’t think they seal perfectly - mine didn’t — and mine idles fine. 

I’d cap the sniffle drain tube and see if that makes a difference. If not, the leak is elsewhere. You could pressurize the intake system with a clean shop vac and spray soapy water around all the joints and look for bubbles.

[sleeper-319]

I did, and it seemed to make a difference. I didn’t fly it and get it hot for a hot start check though. I have a suspicion that’s something else, but one thing at a time I guess.   

[Shadrach]

7 hours ago, sleeper-319 said:

I did, and it seemed to make a difference. I didn’t fly it and get it hot for a hot start check though. I have a suspicion that’s something else, but one thing at a time I guess.   

I find that a lot of IO360s surge a bit at idle when warm. I think this is common and caused by a sticky sniffle valve. 

[A64Pilot]

I bet intake gasket leaks, they are just paper and seem to squish out over time. Tightening them often makes it worse as it makes them squish out more.

I’ve heard the Superior gasket is better but don't have experience with them myself.

Poorly made gasket in my opinion, be easy to make a better one, but at least they are cheap and not too hard to change. Pretty common I just did a set on an O-320 on a Super Cub on straight floats last week. At least on Carb motors they get bad enough so that the engine begins to pop through the exhaust at idle, has very little effect at high power of course because there is very little vacuum to leak there.

I do not use glue or sealant myself on them, others of course will say different, but I don’t think Lycoming does either. Sometimes sealant is more of a pain to clean off the next time than it’s worth.

Oh, and a sniffle valve that leaks a little the idle richness adjustment ought to make the engine run fine with that small leak, I bet they all leak some.