If the vacsucker has an orifice and a one way valve to keep the suck in, how does it know to release when the engine stops?

Durn thing jest keeps picking up more & more internal complexity levels (and some additional failure modes) the more we know about it, doesn't it?

I am perfectly aware that engine vacuum comes in pulses. The vacuum is caused by airflow past a restriction, either the throttle butterfly or the throttle slide depending on which is in control at the moment. Airflow through the filter and intake system also has an effect. When the intake valve is closed the airflow stops and the vacuum goes away. The venturi vacuum also goes away with the cessation of airflow, so the throttle slide can also dance to the vacuum pulses unless it is damped in some way.

I am also tired of arguing with the converted (vacuum petcock BAD; manual petcock Solution to All Problems) and so am dropping out of this discussion.

 
Lou,

Cost is the first reason we wouldn't go buy a new Suzuki petcock, they want nearly $90 at the dealerships for a new one.

The second reason we wouldn't go for the new Suzuki petcock is functionality, we would get more of the same sorts of "error actions" we got before, given enough years to develop it by hardening the diaphragm, etc.  

Remember WE ARE MOSTLY DOING THIS PETCOCK THING TO OURSELVES by removing our stock restrictive air filters and going after the 10 additional horsepower which requires more gas to flow.

How much more gas does a full performance modded bike need?   I can answer that pretty cleanly, 20% more gas.   I used to get 100 miles per tankful, now I get 80 miles per tankful.   And I can say clearly that a stock Suzuki petcock won't give it to you after you mod your bike, you will "run out of gas" during higher speed runs with fair regularity.


=============================


Lou, have you ever tried to modify a stock vac petcock to overcome these difficulties that we are having?    I know Verslagen has, he has the most tuned and modified vac petcocks on the face of the earth.   And he won't talk about petcocks very much (although he will straighten me out a little when I get off kilter on the internals, which is fine -- somebody needs to).

One other tidbit I will leave to you, what makes you think your vac petcock really cuts the gas off completely when the engine stops?

You trust that it does, but I had one that sure didn't.   For all the bullshite that it put me through when it was on the bike it didn't even reliably do the one thing that it was intended to do, which was cut the gas off completely when the engine wasn't running.   Mine would drip gas continously at a very slow pace (which my float valve then stopped when the bowl got full).

Charon, thank you for participating and bringing up all the very  good points that you made.   I especially liked the service bulletins and recall notices -- I'd have never gone looking for them otherwise.

Lou, you come from a different Suzuki Savage culture and I value the perspectives you bring (and the fact the Japanese did a much better job of translating into German than they did into English).  

Actually, you and Verslagen both believe the vac petcock can be fixed, the only difference he has spent years fixing on them at this point.   He also knows the vac petcock symptoms well as he has had them for years (multiple multiple times).

I take the relatively crude position of "tear the bitchy thing off of there, it don't work right" and replace it with the Raptor manual petcock.   For justification,  I only hold up the success factor, it does fix all of the multitude of false symptoms completely and immediately.    

And so far, the Raptor downsides haven't arrived yet, although there are LOTS and LOTS of us now all looking each and every day for them to arrive.  

And we do ask when we think we see a Raptor downside -- witness the young man who wrecked his bike or his petcock or something who owes us all an answer as to what exactly he did to get a Raptor to have a leak.

 
Ok, back to my dumb question -- how does it know when to quit doing that?

.... preserving the vacuum, keeping the fuel valve open, allowing the gas to flow

                           you knew what I meant ......      

changed mine to the raptor before i had issues. loved the raptor

Oldfeller and verslagen1, let me thank you for your modest and very informative answer.

I must say, I disassembled several petcocks and did not find any faults except worn O-rings, that funnel formed rubber gasket on the pin of the diaphragm and in one case a diaphragm which would leak soon.
I also reassembled a petcock because his owner did not know how to.

I was just out in the garage to find that one way valve.
Oh, it is there, and it is quite good hidden.
And I found the rubber plug to be a good bit smeary, no more like rubber uses to be, it was a bit like chewing gum. I apologize for my claim that there is no valve!

But, in my opinion, it should produce a tiny leak itself. And it can't do it, if the rubber plug gets that smeary and sticky, that's right. But before I disassembled it, it worked well and there was no effect that it would clog completely. Far from it, I could hear the release of the diaphragm very clear when I stopped sucking.

I think, gassy portions of fuel can reach that little rubber plug and destroy it after many years until it then does, what you found out. Holding the petcock open in an unplanned and unwanted way.

This may be a matter, what stuff fuel contains. Seems we got the same petcocks at all, maybe the fuel on your side has a different composition. (Something I think, fuel composition is one cheap way for the producers to get rid of stuff which would produce high costs on deposit. We got up to 5% of methanol in the fuel for many many years and nobody bothered about. But that's another story)
I never heard about petcock failure in that way in europe or to be more detailing in germany and I easily could have had in over 30 years of 'business', if there was something about it.

BTT... That little valve, albeit not in a perfect state, did not block the reflux of air to release the diaphragm. It leaves me a bit at a loss and I will sure give in you encountering bigger problems with it than me.
But.. whats the purpose of it. Considering it should not clog completely the airflow, it must have to do with avoiding the diaphragm to flutter! Just like a very small jet in the line outside the carburetor would do. Sampling up vac but not coming through pulses.
And soft releasing if the engine stops. I aditionally give in, if it clogs and holds the petcock open, that's really an issue.

I own a 87 Savage with K&N cone filter, with a modified camshaft but for more 'steam' on lower revs, not at high rpm, and did some work on the exhaust porting and better gas flow in the muffler (Jets are 155 and 52,5 or a bit more). But, may be my fault, I don't like to go faster than 75mph or at least 80 mph. I like to come up there quite quickly, but that way I could not experience fuel starvation. My '89 sidecar savage has a lot more full throttle experience but it is all stock equipment except minor changes like handlebar. It runs about 85 mph or a bit more. But I like to go about 60-65 mph with it.
So I can agree with a different culture  

Oldfeller,

some do like you do, yes. In cases for performance enhancement.

But, right, still we are limited to our two-year inspections by tech surveillance orgs who give you a stamp on the license plate.
Special assemblations and modifications have to pass there a non-regular presentation with approvement but with a remark in your bike papers. And those modifications are restrictive in cases of safety, noise pollution and so on. One can't do anything he wants to.
Papers, approvals, permissions, papers again.

I could refer later if anyone has an interest in how it works down here in Germany.

Well done, Dave and fine pictures!

But, what if the small bleeding hole seems to be failing and vacuum still holds the petcock open after shutting down the engine?

I can only guess, I think, then something might have clogged the small bleeder hole, maybe parts of the decomposing rubber plug right beneath or a tiny bit of the diaphragm came off and goes astray there.