Pressure test fail help

[Vintage Engine Repairs]

Hi guys.


I tried pressure testing, but the seal between the carb and rubber manifold won’t seal with a thick piece of pliable rubber and is leaking. If I take the carb off and force my finger into the manifold it stops and holds pressure. Why is this the case? Is it a problem for the engine? Seals and gaskits are holding perfectly well.


I’m so close and so frustrated at the same time


Thanks in advance

 

[drf255]

If it holds pressure perfectly with your finger in there you’re probably fine Tom. Especially if you can have another rotate the crank for ya (or try yourself).

Try some grease on the rubber and don’t snug the carb nuts up too much.

I personally don’t pressure/vac test any saw I build from the bottom up unless there are issues with idle after I run it. If it’s a used saw, it’s my first step.

 

[Vintage Engine Repairs]

Thanks mate, now it sounds like it’s comig from the exhaust but I can’t see ANY bubbles coming to my wits end with it!

 

[Vintage Engine Repairs]

All I hear is a little whistling. I want to stick it in a bucket of water, but I don’t think that will do the saw any good!!

 

[drf255]

Run the saw. See where the L screw is at idle.

Forget the test for now.

 

[mkinslow]

Just keep spraying soapy water all over the saw, are you sure it's not the mityvac making the sound. I'm also with @drf255 I want pressure test a new build unless something is going on at initial start up stages

Sent from my SM-G892A using Tapatalk

 

[Vintage Engine Repairs]

Just keep spraying soapy water all over the saw, are you sure it's not the mityvac making the sound. I'm also with @drf255 I want pressure test a new build unless something is going on at initial start up stages

Sent from my SM-G892A using Tapatalk

Hey,

Na Mityvac isn’t leaking I tested it.

No matter how much I spray soap water and where I can’t see bubbles. It’s tricky because the handle and side of the case half is in the way of the cylinder gaskit.

Thanks for your reply.

 

[Vintage Engine Repairs]

Run the saw. See where the L screw is at idle.

Forget the test for now.

Ookk, can you explain, so I understand for future, why it wouldn’t bother you?

 

[mkinslow]

Ookk, can you explain, so I understand for future, why it wouldn’t bother you?

Set you carb adjustments at 1 turn out as a starting point, fuel the saw and start it ,let it idle ,tip saw forward,side to side all over and if nothing changes with idle speed in each position you should be good. If idle races in any position an airleak may be present, just get it running. By the way, if you do have an airleak it's not gonna burn up the saw in an instant, just don't keep running it

Sent from my SM-G892A using Tapatalk

 

[drf255]

Ookk, can you explain, so I understand for future, why it wouldn’t bother you?

Cause its a new assembly and u followed the rules. Chance of leak under 1%.

And if it acts normal, shouldnt be an issue.

 

[trains]

Tom, if its holding pressure when you use your finger to seal the inlet side, then you have found your leak, its the rubber you use for the pressure test when you have it snugged up using the carb, there is something wrong with that blanking seal, not the rest of the saw.
if thats correct, and its only leaking from something that will be removed anyway for the saw to run, I would confidently move forward and set the needles as per spec, and go from there.

Re tilting the saw all over the place, I find it usually just moves pooled fuel around and that causes changes in idle more than an air leak.
specially on a new saw that holds pressure and vac

 

[Vintage Engine Repairs]

Damn I’m glad I have you guys here...

Okk, it is 100% without question, a leak between the carb and the manifold. If I plug the manifold it holds pressure and vacuum at 6psi whilst spinning the crank. It may drop a fraction over a couple mins...

So this space here, when assembled, if it still leaks, shouldn’t be an issue?

 

[drf255]

You have inner and outer ring on boot?

 

[Vintage Engine Repairs]

You have inner and outer ring on boot?

I tried with and without during the testing made no difference. Actually bent both by accident so straightened them out as best as I could

 

[Mad Professor]

What are you using for a seal from carb to manifold?

A tractor tire tube cutout should work. Bicycle use two.

 

[homemade]

I say run it. If it’s leaking at the muff, it shouldn’t affect performance. You can always spray some carb cleaner on the gaskets as the saw is running at idle to see if it revs up.

 

[HarleyT]

A little KY Jelly on the finger always helps a bit.....
Tell the saw that you love her...
That helps too.

Spraying all over with soapy water...... well.......

 

[Sepia]

A little KY Jelly on the finger always helps a bit.....
Tell the saw that you love her...
That helps too.

Spraying all over with soapy water...... well.......

You are truly the Don Juan of chainsaws.

 

[Vintage Engine Repairs]

What are you using for a seal from carb to manifold?

A tractor tire tube cutout should work. Bicycle use two.

Both a thick rubber sheeting and then tried a very soft playable sheeting neither worked.

 

[Vintage Engine Repairs]

I say run it. If it’s leaking at the muff, it shouldn’t affect performance. You can always spray some carb cleaner on the gaskets as the saw is running at idle to see if it revs up.

That’s a really interesting idea!!