I can't believe it...sledgehammering petcock ***SOLVED***

Ok,first of all i wish everybody a nice weekend, then here's what happened:

Some days ago i rebuilt the petcock, then i drove 50 miles and no problem at all.

Today i took the bike for a ride and i start to hear a sort of "clackclackclackclackclackclack" noise.

My first tought went to the cam chain or the valvles, then i noticed that over 3000 RPM the noise went away or at least went down a lot.

Searching for a place to stop, i had to put on the reserve...and suddently the noise went down a lot (???)

Then, i pulled over in a gas station trying to locate the source of the noise and i noticed that i heard it from ABOVE the engine...i put my ear over the gas tank and THERE HE IS! Opened the cap and it really looking like there was a smurf in my tank with a mini sledgehammer!

So, i put my fingers over the vacuum line and i felt it pulsing, like a heartbeat. By chocking the line , the noise went away, so yes, it is definitely the petcock that opens and closes at extreme ratio.

I searched for a leak in the vacuum line with the good old system (one end in my mouth and the other closed with the tip of my fingers) but apparently is not leaking. By safety i cut away 1/2 cm (0,2 in) from every end but the problem i still the same, at the moment the line is hooked to my 3rd carburetor, the bike is running nice and smoothly.

So, is normal that the vacuum line pulses? Or is more probable that i made some mistake in the rebuilding of the petcock?

 

Re: I can't believe it...sledgehammering petcock & vacuum line..

The Vacuum Line Pulses.
The Vacuum follows the Firing Order.
That's why ists difficult to get a Vacuum Reading without a Restriction Piece to
buffer the Fluctuations.

Pretty unusual "Hearing" the Vacuum Operated Petcock being Opened and Closed by manifold Vacuum, though.

 

Re: I can't believe it...sledgehammering petcock & vacuum line..

As Rick says it does pulse - I would suspect your petcock rebuild. I'd start there.

 

Re: I can't believe it...sledgehammering petcock & vacuum line..

wild.

 

Re: I can't believe it...sledgehammering petcock & vacuum line..

Yeah nuts man. Maybe thats where my "sound" is coming from too

 

Re: I can't believe it...sledgehammering petcock & vacuum line..

Holy crap! Your carburetor Smurf has escaped and made his way into the petcock and is trying to signal for help.

Seriously, methinks your little rubber donut is missing off the diapharagm valve in the petcock.

My recent unexplained intermittent metallic rattle turned out to be a broken rubber strap for the safety relay. The relay was hanging against the top of the cam cover and just barely touching.

 

Re: I can't believe it...sledgehammering petcock & vacuum li

Thanks for the answers, i did another scientific test by screaming in the tank "is anybody in there?".

As i haven't got "I HATE this tank!" as answer i can exclude the presence of the Grouchy Smurf :lol: :lol: :lol: :lol:

Next step, will be a re-rebuild of the petcock.

 

Re: I can't believe it...sledgehammering petcock & vacuum li

fitz,
I had more or less the same metallic rattle. It turned out to be my horn touching my cam cover. I was wondering too, if it is my chain being lose. It sure sounded like it. And it too was just barely touching the cam cover.

 

Re: I can't believe it...sledgehammering petcock & vacuum line..

By any chance did the diaphragm spring not get put back in when the petcock was reassembled?

 

Re: I can't believe it...sledgehammering petcock & vacuum line..

No, the spring was set again in place...i did not forget any parts

 

Re: I can't believe it...sledgehammering petcock ***SOLVED**

EPILOGUE:

Opened the petcock, everything's in place, no visible problems.

Then, at the moment of setting again in place the handle, i saw that the o-ring dilatated so much it was impossible to put the handle inside without damaging the ring.

So, i re-used the old o-ring, put back everything togheter but the noise was still there.

Again, open petcock and take a look at the diaphragm. Didn't looked that good. Replace it with the old diaphragm. Problem solved.

In 3 words: CRAPPY REBUILD KIT.

does somebody know where i can get a petcock with RES, ON and the good old and safe OFF?

 

Wow glad you solved it. Chacal on this site carried vacuum and non vacuum versions of petcocks.