Am I sporting a vac leak?

[AK260]

That's not controversial to me at all. I completely agree 100%!!

I'll check on those round air cleaner filter gizmos for you... Tagging [mention=27892]GGRIII[/mention] . That's his car and he bought the air cleaners. I don't know where he got them, but I remember something about "cheap clones of the expensive ones". Hopefully he come in and shed some light. And hopefully they might be cheaper on your end of the pond as well.

 

That is very kind of you sir but please don’t go out of your way to do it.

 

And thanks for tagging George Gregory Regina the third! [emoji106][emoji12]

 

Look what I found In the plumbing toolbox ...

 

 

And they are the EXACT dimension too for the job! I bought these as a mixed pack in 2002 when I was fitting a bath!! Amazing how things come back to usefulness! ;)

 

 

 

[Captain Obvious]

No trouble on the air cleaner info. Regina the 3rd will see it eventually and speak up. He's a lurker. Says he's "busy" or some crap like that.  I'll bug him again @GGRIII .

3 hours ago, AK260 said:

Look what I found In the plumbing toolbox ...

Nice. They won't like getting crushed, but still probably thinner than the foam. The real trick would be to chuck up the dome or body in a lathe and cut an O-ring groove.

[siteunseen]

I think the body would be easiest for that trick.  

[AK260]

Yes true!! Although the base already has a little indentation in it for something to go there I think! I will take a photo when I get round to doing it. Started the bearing job on the rear left yesterday. I’m using a stop watch for elapsed time as every 20 mins one of my kids comes out needing something and the half day job becomes a two to three day job! No one tells you this stuff before you have kids.

 

 

 

I’m also experimenting with different rear silencers. The Z story classic straight through produces the best top end power - the engine positively sprints between 5-7k rpm. The turbo muffler on in the photo above does a great job but MASSIVELY quieter for long journeys although it robs the fun power at the top, given it’s more restricted.

 

[AK260]

What think yea wise ones, is this idle vacuum behaviour normal for a lumpy cam or should I be looking for another air leak?

 

Interesting the same test before my homemade gaskets didn’t go over 50KPA but now hits about 75. So I was loosing vacuum before. But it’s the idle thing that has me thinking.

 

 https://youtu.be/n2dLeRsJxT4

 

 

Edit - part of the reason I ask is that going from a turbo muffler back to the straight through made the AFR lean everywhere expect for WOT and the reversion points where it became even richer on the latter. I am wondering if with less back pressure, the engine is able to suck harder and finding another leak I haven’t yet found? Or is this wobbly vacuum at idle a feature of higher duration / lift cams?

 

 

[AK260]

Alright gang, the hunt for air leaks continues ....

 

I could tell that despite the car feeling better, there was still something amiss with the rear carb.

 

Using self penetrating oil (as it froths up nicely and is runny), I sprayed around the typical areas and found that that outer end of the throttle shaft on the rear carb was showing a perfect line in the froth between the end cap and the carb body. Using a razor blade, I gently encouraged it out (which was frankly quite easy).

 

I discovered a putty type material in there which I assume is there to seal the cap. Not much of it left though.

 

 

Looking at the fingers in the cap, you can see where it was leaking has the dark residue.

 

 

So I cleaned both the cap and carb big up and using a gasket making paste, I covered the cap, pushed it home and wiped off the residue. I’m sure someone will tell me that I have used the wrong paste ;). Incidentally, I used the same thing on the intake manifold and carb insulators gaskets to ensure a good seal.

 

 

I then did the other side to play it safe.

 

Having given it a good hour to set, I fired up the engine and did the same test, froth everywhere!

 

So if your ZT carbs start to leak, at least the fix is very quick and simple. Mine have been on for 7 years at an average of 2k miles a year. So I guess it’s fair to expect a little maintenance being required.

 

 

 

 

 

 

 

[Captain Obvious]

You used the wrong paste.

[Captain Obvious]

I used to use that silicone RTV style for pretty much everything, but a couple years ago I switched over to Pertmatex MotoSeal for gasoline intensive applications. I don't know if you've got something similar on your part of the globe, but I assume you could find something.

I ran some tests on both in gasoline, and the MotoSeal came out to be the clear winner. I think I've got some pics around here somewhere if I could only find them...

 

[siteunseen]

7 hours ago, AK260 said:

I’m sure someone will tell me that I have used the wrong paste ;). 

 

34 minutes ago, Captain Obvious said:

You used the wrong paste.

You got me Captain, I thought you were kidding. It is Saturday night so...

[Captain Obvious]

Well honestly, I was mostly kidding since @AK260 left me little choice with my first comment. 

But some more detail? I'm no sealant expert, but I think that in the application where AK used RTV silicone, it'll be "fine". It's not bathed in gasoline, and it's what I would consider a "low stress" application. I wouldn't use it to seal the fuel bowl gaskets or the carb to intake manifold, but at the end of that throttle shaft, I think it will be good enough.

So after posting last night, I was able to poke around on the computer a little and found some detail about my testing and my pics. I don't remember what type of carb I was messing with that spurred me into the experiments, but I did the following...

I put a dab of both Permatex Ultra-Gray silicone (my go-to) and MotoSeal on an index card and let them both cure for a couple days. Looked like this:

Then I cut the little dabs out of the index card and gave them a couple day immersion bath in gasoline:

Then I took them out and gave them and compared the results. Here's the ultra-scientific "poke test":

MotoSeal after poking:

Silicone poke:

Silicone after poke:

And here's the summary result:

And then after the soaking, I let them sit on the bench and dry out for a couple more days, and here's the results of that:

So after that testing, I've stopped using the Ultra-Gray and have switched over to MotoSeal in gasoline intensive applications,. I still use the Ultra-Gray for most everything else that doesn't involve potential direct exposure to gasoline.

 

[AK260]

You got me Captain, I thought you were kidding. It is Saturday night so...

What you didn’t realise is that the trap was set and he completely went for it ;)


However. He does have a penchant for the geeky details and I salute his experiment! Nice work CO; I will take up your recommendation on sealants! [emoji106]

[siteunseen]

50 minutes ago, AK260 said:

What you didn’t realise is that the trap was set and he completely went for it ;

 

 

I do it all the time!