Cheapo Petcock

[Rio Wil]

Out of necessity I bought one of those $20 made in china petcocks from ebay to get my beast running for a while. It is a perfect fit for the original except the pipe height to draw from main fuel level is about a quarter inch shorter which will ever so slightly leave less reserve fuel.....no big deal.

In testing the valve, it only took 2-3 inches of vacuum to open to max flow. Installed it and it works, but, I got to wondering about the vacuum that is applied from carb 6. I have a fast reacting vacuum gauge. Plugged it to port six and started the bike and let it run with just the fuel in the carbs.

I was amazed at how hard that poor diaphragm got hammered by the vacuum pulses. At idle it would pulse wildly from 2' to 6', at a couple of grand it was pulsing about 22"......way more than needed. I wonder why Honda didn't put in a vacuum smoothing  valve of some sort.....pounding the petcock diaphragm this way seems hell bent on destruction.  Can't believe they last as long as they do....

At WOT it is probably only 2-4 inches,,,,but at highway cruising speed its way over 20", wonder it doesn't pull the diaphragm plumb through the petcock.

I didn't pull the diaphragm side apart to verify this, but I suspect it has only one diaphragm inside, so if that tears, then fuel would be drawn straight into the vacuum port of intake 6.......not good.. Am I thinking clearly about this possibility?

 

[hueco]

At the risk of being banned. I replaced my petcock with ,God Forbid. A harley davidson petcock.

[Rio Wil]

Really......tell us more......

[hubcapsc]

Everyone who wants a non-vacuum petcock ought to read JimC's "alternate petcock"
thread... he thinks it works and it is from another Honda and it fits right onto the
regular Valkyrie petcock knob and everything...

-Mike

[MarkT]

This has me thinking about the vacuum-driven cruise control.  IIRC it uses several vacuum sources into a common tank to buffer the pulses.  Some report - like Daniel - that it lasts a long time.  (He posted he was waiting for it to fail so he could check out the Rostra electronic version - made by the same folks I understand.  Incidentally I installed a Rostra on Jade.)

[Bagger John - #3785]

Everyone who wants a non-vacuum petcock ought to read JimC's "alternate petcock"
thread... he thinks it works and it is from another Honda and it fits right onto the
regular Valkyrie petcock knob and everything...

-Mike

Except it (apparently) has no Reserve functionality.

See that thread. A Main/Off/Res function might be an easy addition, with commonly available tubing.

[Daniel Meyer]

I was amazed at how hard that poor diaphragm got hammered by the vacuum pulses.

Yes, the valk has a fairly severe cam profile and thus, a wicked intake pulse (the reason for that bizarre airbox...honda does scavenging on intake AND exhaust better than just about anybody)...

Anyway, the OEM petcock has a dampener in the coverset to help protect the diaphragm (the reason you get the new cover along with the diaphragm kit). The cheap/alternate petcocks don't...and it will disintegrate in short order.

Can't comment on the one or two diaphragm issue in yours as I've not seen it...I've seen 'em both ways. Also the one I bought (hey, $20, worth a look, eh?) when I took it apart, had a fair amount of casting sand or metal debris inside it...

I don't recommend any of the cheap petcocks. If you simply MUST change away from the OEM, go with a pingel, but do be aware of their shortcomings as well.