65 Riv - PCV vacuum leak, helped with electrical tape?

[moran75]

Hi all

 

I appear to have a vacuum leak at the PCV valve /grommet...

 

I say that because RPMs drop (not increase) when I spray with carb cleaner...car in Park , not Drive.

 

Both valve and grommet have been replaced - but rpms still drop with the spray...

Is there a way making a better vacuum seal? I see wrapping valve with electrical tape has been suggested on the forum ...anyone tried that ? 
 

any opinions /experience welcome

 

kev

[60FlatTop]

Sounds like you are running right on the money to me. That carb cleaner would be less dense and more volatile than air. If you are running the right mixture the spray will richen the mixture a bit and bog her down. I have done that when checking out my tune ups in the past, just a shot down the carb.

With the light load of being in drive your vacuum may be slightly lower and, combined with the action of the power valve other conditions might negate it. Try the test while watching a vacuum gauge. Maybe retard it a degree or two and see if it goes away. Working on a car with MAFS, MAPS, LAMBDA sensors it might affect your LTFT, but with a good old AFB, 4GC, or MV4 the acronyms are on your side. You're good.

Bernie

[moran75]

Hi Bernie

 

thanks for response.

 

can I check one thing - if I’m spraying carb cleaner directly onto PCV valve and it’s grommet and RPMs change (reduce in this case ), then carb cleaner is getting past the grommet/seal - which shouldnt be possible if grommet/valve make a good seal?

 

Thanks in advance

 

kevin

 

 

[Bloo]

The end of the PCV hose must seal absolutely to the PCV valve (and the hose nipple at the other end of the PCV hose!). Tape wont do the trick, nor will clamps usually. The hose must be pliable. It must stretch over the nipple and seal on it. Clamps are sometimes used for longevity, but wont help if the hose doesn't seal in the first place.

 

The connection to the crankcase vapors (via a grommet) is less critical. If it leaks, the engine won't know the difference, although it will probably ooze oil vapor.

 

 

Edited January 18, 2020 by Bloo (see edit history)

[moran75]

24 minutes ago, Bloo said:

The end of the PCV hose must seal absolutely to the PCV valve (and the hose nipple at the other end of the PCV hose!). Tape wont do the trick, nor will clamps usually. The hose must be pliable. It must stretch over the nipple and seal on it. Clamps are sometimes used for longevity, but wont help if the hose doesn't seal in the first place.

 

The connection to the crankcase vapors (via a grommet) is less critical. If it leaks, the engine won't know the difference, although it will probably ooze oil vapor.

 

 

Aha...see what you mean re grommet ...I was thinking it had to be 100% air tight...

 

So maybe carb cleaner is getting in through the clamp and each end of my pcv hose - nipple at one end and valve at other 

 

but I was thinking that revs would go up, rather than down when source of leak sprayed?

 

kevin

 

[Bloo]

It depends....

 

Back in the day I used to leak check with carb cleaner or brake cleaner a lot. Today, some of it is not flammable. Results can be sketchy at best.

 

If we assume the carb cleaner is still able to be used as fuel, then a tiny leak should cause the engine to speed up, and a bigger leak should cause it to slow down.

 

That also assumes that we are idling, and the carb was set with either the old "lean roll" method, or a gas analyzer, and is running at about a 14.7:1 fuel mixture. A little more fuel will speed the engine up (just like backing out the idle screws would), and a lot more will cause a rich loading/miss and slow the engine down.

 

If the engine was tuned to max RPM with the idle screws (not advisable IMHO, but many people do it), then any extra fuel you add will slow the engine down.

 

One exception: If the vacuum leak is causing a lean miss somewhere, and adding fuel at the point of the leak brings a misfiring cylinder or two back to life, then the engine will probably speed up regardless of the overall mixture.

 

That last thing is less likely to occur with PCV because PCV systems are a constant vacuum bleed, and 98% of the time are arranged to mix with the fuel/air coming out of the idle jets. They don't usually kill just one or two cylinders when they leak.

[moran75]

1 hour ago, Bloo said:

It depends....

 

Back in the day I used to leak check with carb cleaner or brake cleaner a lot. Today, some of it is not flammable. Results can be sketchy at best.

 

If we assume the carb cleaner is still able to be used as fuel, then a tiny leak should cause the engine to speed up, and a bigger leak should cause it to slow down.

 

That also assumes that we are idling, and the carb was set with either the old "lean roll" method, or a gas analyzer, and is running at about a 14.7:1 fuel mixture. A little more fuel will speed the engine up (just like backing out the idle screws would), and a lot more will cause a rich loading/miss and slow the engine down.

 

If the engine was tuned to max RPM with the idle screws (not advisable IMHO, but many people do it), then any extra fuel you add will slow the engine down.

 

One exception: If the vacuum leak is causing a lean miss somewhere, and adding fuel at the point of the leak brings a misfiring cylinder or two back to life, then the engine will probably speed up regardless of the overall mixture.

 

That last thing is less likely to occur with PCV because PCV systems are a constant vacuum bleed, and 98% of the time are arranged to mix with the fuel/air coming out of the idle jets. They don't usually kill just one or two cylinders when they leak.

interesting stuff...many thanks

[RivNut]

What happens if you pull the PCV valve from the valve cover and hold your thumb over it?  Some cars have PCV valves that screw into the valley cover and use the openings in the valve covers for two breathers.  Early nailheads didn't have a PCV valve, they solid valve covers, an oil filler tube (with a breather cap) coming from the front of the valley cover, and a draft tube coming out of the back of the valley cover.  

[moran75]

12 hours ago, RivNut said:

What happens if you pull the PCV valve from the valve cover and hold your thumb over it?  Some cars have PCV valves that screw into the valley cover and use the openings in the valve covers for two breathers.  Early nailheads didn't have a PCV valve, they solid valve covers, an oil filler tube (with a breather cap) coming from the front of the valley cover, and a draft tube coming out of the back of the valley cover.  

I’ll let you know how I get on when back at the car....

Duty calls ...family trip today 😀

[60FlatTop]

If it was mine I would drive it for a few weeks without spraying any volatile chemicals around the breather and see how it goes. If you get my drift.

Bernie

[moran75]

On 1/19/2020 at 2:07 AM, RivNut said:

What happens if you pull the PCV valve from the valve cover and hold your thumb over it?  Some cars have PCV valves that screw into the valley cover and use the openings in the valve covers for two breathers.  Early nailheads didn't have a PCV valve, they solid valve covers, an oil filler tube (with a breather cap) coming from the front of the valley cover, and a draft tube coming out of the back of the valley cover.  

...all sorted...a bit of a convoluted story...reason for all this hoo-ha was that idle screws were having little effect - so was searching for obvious places for vacuum leaks...I put two and two together and got 5 and blamed pcv grommet but as result of advice here I  got a feeling I was barking up wrong tree..and I was ...indeed the real culprit was a leaky inlet manifold gasket ..all good now...thanks all

 

kev