petcock question, 81 GS450T

[mhardig]

I've used the search feature to read other petcock questions, and it seems the consensus is to just replace the whole petcock.

Is there a specific reason to replace rather than rebuild? (beside the fact that rebuild kits are nearly impossible to find). It is clear that the diaphragm is leaky so it doesn't open the valve enough. The bike runs fine in "prime" mode but if I forget it fills the crank with fuel.

My local dealer tried to get me to put a "generic" petcock on it, but it seems what he's trying to get me to do is no different than just running in the "prime" position, which I can already do.

So:
1: what is the advantage to replacing the petcock? Mine is in perfect condition except for the diaphragm, and
2: If this is going to be a recurrent problem Am i better off changing to a "normal" style petcock instead of the vacuum actuated type?

Thanks in advance!

[chuckycheese]

Choice!

It's a matter of personal choice. I think the ones that are the worst are the ones from the 1980 model. They are very small, since space was limited, and they have no handle..and worse, no reserve.

The Pingel petcocks are very nice but also relatively expensive. I'm sure some of the cheaper ones as well as some of the OEM petcocks are just fine. As far as the vacuum operated feature is concerned, I think it's great..just as long as it works properly. If you get one that isn't vacuum operated, you have to remember to shut it off but, after a short time, you get where you do that without even thinking about it. (I have an '80 model and switched to a Pingel a long time ago.)

[SAN]

petcock

www.oldbikebarn.com rebuild kit about 19.00

[Killer2600]

A new petcock has the benefit of being new so it shouldn't have any problems after putting it in. Everyone here pushes for it but unless it can't be fixed with a rebuild kit I prefer to save some money and rebuild it.

[kurifu]

Considering the amount of trouble I hear from petcocks and some people complaining about rebuilds not working so well I just today replaced my petcock with an aftermarket one I found on ebay.

A couple of points to watch out for if you go new:

1) The vaccuum and fuel barbs are on the right side (mine were not, not a big deal though)

2) The new fuel tap has a good rubber seal with it, the one I bought only sealed around the outer edge and didn't seal between the tap and the bolts, so I had to buy O rings to seal it properly.

Considering the price and how long a new fuel tap will last I figure it is best to go that route, I only paid $29.99 for mine.

[chuckycheese]

Good!

[quote=kurifu;653019

Considering the price and how long a new fuel tap will last I figure it is best to go that route, I only paid $29.99 for mine.[/quote]

If it works well, I'd say you got a very good price!\\/

[mf70]

If you go the rebuild route, be sure old (probably corroded) mating surfaces will seal agains the nice new rubber.

[mhardig]

Update:

Got a rebuild kit from Sirius Consolidated in Canada, payed with paypal, got the kit in four days.

As part of the learning experience, I discovered the rubber o-ring seal that closes off the gas is supposed to be attached to the diaphragm; mine was glued into the housing. I also discovered the housing was very slightly warped, a piece of sandpaper glued to a piece of windowpane fixed that fast. So it's back together, and on the desk. Goes back on the bike this afternoon. I'll see how it works. With the seals in the right place it ought to be a LOT better.

[mhardig]

Rebuilt

OK, the petcock kit is in, no leaks, seems to work fine.

Needed a new battery, but as soon as I got one in it, it started right up. Now I've got "new" problems. Well, not so much problems as opportunities, as they say.

THe bike is coldblooded. It hasn't run much for years, but it should warm faster than it does. Takes maybe five minutes before I can crack the throttle, if I do before then it dies right off.

The engine races a bit at first, I can control this with the choke.

Once it does warm, it seems to run OK, but the petcock is always opening/closing with the vacuum. No leaks, but it seems as if the vacuum is pulsing and not constant, even at higher RPMS. It seems to be allowing adequate fuel flow now that it's fresh, but you can hear that tick-tick-ticking in the tank all the time. I have new boots and o-rings, and the clamps are tight.

I do not have a gauge to measure the vacuum nor to tune the carbs, but I suppose I should. Any advice in the interim? Something I should be looking for?

[Nessism]

A quick and dirty sync job can be performed on a twin by pulling off one plug wire at a time and seeing how the bike idles. Adjust the balance until the idle is the same...or the engine chugs to a stop in roughly the same amount of time. BMW specifies this technique on their airhead engines, honest, so I'm not on drugs here.

Good luck.