Leaking petcock?

Hey all,

I'm wondering if I need to rebuild/replace my petcock. Wondering if y'all can tell if this is the case...

Here are the symptoms:

1) If the bike sits overnight (or any long period) with the petcock in PRI, fuel may leak from the airbox but the bike will not start right away. Instead, it will make a loud "bang" and the start will cut off. Scared the crap out of me the first time it happened. I thought I had broken something inside, but I've been told it might be a backfire in the engine (the noise is coming from the manifolds instead of the muffler) which causes the engine or something to rotate backwards, cutting off the starter. In any case, it will make that loud bang two or three times before it starts chugging and trying to start. It will eventually catch and start.

2) Now, I no longer leave it in PRI when I walk away from the bike. I turn the petcock off, but whenever the bike has been sitting for more than a couple of hours, the bike does not want to start. It cranks and cranks, and I can hear the "blub-blub" that sounds like it is almost going to catch and fire up. Sometimes, it will finally catch after many minutes of trying, then I need to keep a hand on the throttle until it will keep running on choke. After that, it runs fine. Sometimes, as it did this am, it won't start and the battery just wears down and I have to take my VW to work. I have tried draining fuel from the lower fuel ports, but I'm not sure if I drained enough. Once, it seemed to help a bit. This am, it didn't.

3) I'm getting really rotten mileage. I suppose this could be something else alltogether, but it really ticks me off. I get maybe 65 miles before my fuel light comes on. My commute is 7 miles each way. I don't race it and I only stop for maybe 3 or 4 lights each time. I understand I should be getting somewhere closer to 90 or 100 miles on a tank of gas. Carbs seem to be in good shape. Engine sounds good when it gets running. No backfires and idle is smooth. If I can get back to easy starts, I can put up with bad fuel economy until I can chase down that problem if it isn't related.

Here's my theory:

I think the petcock is leaking, causing fuel to flow into the cylinders and the airbox when in PRI or just flooding the carbs when it is off.

I've thought of putting a cutoff valve in the fuel line, but I'd rather fix the petcock. Or, alternatively, I could replace it with Chakal's replacement fuel valve. I'd rather have a working petcock, though.

Any thoughts?

 

I might get a reputation for saying.."chuck the petcock in the bin.."and get a replacement fuel valve, ..ya get off it ya turn it OFF.. ya get on it ya turn it ON, simple.....Prime is ONLY for filling the carbs if for some reason they're empty, it works ALL the time its turned to prime (on mine it actually feeds from reserve Edit ..did..) ..... If fuel is in the airbox its in your crankcase, drain the oil and put new oil in, you WILL wreck the engine with fuel in the oil.!!!
Low mpg...you need to clean the carbs and adjust float levels, synch' and adjust pilot jets at least.

 

Here's my twisted logic on leaking Petcocks.
Replace it with a NEW one.
You save money and get a new Petcock.
Save money???
Yep.

You save what you do not spend.
If you took the Bike in for a Petcock rebuild:
$39.95 in Parts ... plus 1.5 Hrs Labor at $80 @ Hr = $159.95

A new Petcock Costs $75.00 ÷ 25-Years Service = $0.25 @ Month

 

OK. So, do y'all think this sounds like a leaky petcock then? That's my theory, but I've never had a motorcycle other than this one, so I'm not certain. Just seems logical. But, before I buy a new one (or a fuel valve, which is tempting...) I'm hoping to hear someone say "Yup, sounds like a leaky petcock to me. All the symptoms fit."

Thanks for the suggestion, Bushy. I just got another oil filter and some oil to go with it. I'll get on a change right away.

 

It sounds like you have a couple of problems.

Even with the petcock in "PRI" the float valves should keep fuel flow shut off, so if you're getting gas in the cylinders then you've got a float or float valve issue also.

You may have a VACUUM leak between the petcock and the motor which would account for difficult starting unless the petcock is in "PRI." Try this: Right before you get ready to fire up the bike, put the petcock in PRI and wait a couple of minutes. Once it's running, put it back on "ON" and see if it stays running, or if it instead acts like it's running our of gas.

 

Dang, I was really hoping to avoid getting into my carbs again so soon after disassembling them and cleaning everything out (and setting and confirming float height). That, there, might just wreck my week, and it hasn't even started yet.

So, what would happen if the fuel continued to drain into the carbs with the float valves closed (assuming they work properly)? Where would the fuel go? Or would it just stay in the hose, not able to go anywhere?

As far as using the petcock in PRI, that is where I move it to try and start. It was in PRI for a good 10 - 15 minutes this am, and no joy.

When I shut the bike off, I turn the petcock down, between PRI and RES. I thought that was OFF, but I could be mistaken. Is that "ON"? Maybe I'm just a bonehead and I don't know how it all works. That would make more sense, if it is "ON" because I've accidentally left it in that position and driven the bike for many miles.

 

On the OEM petcock, straight down is "ON." There is no "OFF" just ON, PRI and RES. ON and RES are vacuum operated; PRI is fuel on all the time.

When everything is working properly, you should be able to leave the petcock in PRI with the bike off and have the float valves hold the fuel in the hose and bowls. I say "should" because even a perfectly functioning and properly adjusted float can hang once in a great while. Hence the whole reason for turning the fuel off to begin with.

Did you use gas to verify the float heights, using the "clear tube" method?

 

Ah! So that's the thing! Shoot, nobody ever explained that to me. OK. So, I should normally be riding with the petcock in the down position. Now that starts to make sense.

OK. I'll check the fuel level again using the clear tube. Hopefully that will reveal something. I'll also try letting it sit in PRI for a couple of minutes prior to trying to start it up.

Just out of curiosity, if the diaphragm is leaking, or something, would I be able to see fuel dripping out of the hose if I put the petcock in ON and disconnect the hose from the inline fuel filter?

 

Yes. (You might get a drip or two after the initial disconnect.) With the petcock in ON, you should get no drippage. Apply a little gentle vacuum to the vacuum port (suck on a hose attached to it) and fuel should flow, and stop when there's no vacuum.

(You should also get no taste of fuel "applying vacuum" as above; if you do then the diaphragm is leaking between the "fuel" side and the "vacuum" side.)

A stuck float will immediately reveal itself during a float level check using the clear tube method-- the fuel will never stop at ANY level.

 

A fix don't get no cheaper than this!

Briggs and Stratton Plastic Fuel Valve.

Leave ON: When you are riding.
Leave OFF: For peace of mind.

Less than 8-Bucks for everything.
The Hose Clamps are made by a starving orphan chained to his metal press in a sweatshop, fire-trap in a bad neighborhood.
3 for $1.49
The Briggs valve is solid and works like a charm.
Made down the street.

 

the last time mine leaked i took it off the tank and took it apart and found a nice green grass clipping in there
don't know how it could have got there but was pretty sure it didn't belong in there
haven't had a problem since

 

Thanks for the suggestions, all. I'll nail it down this week. Bigfitz, thanks for the description of the vacuum check. I haven't looked into the CDs yet, but that was going to be my next stop...

 

Read the Oracle :wink:

http://www.maxim-x.com/petcock.html

 

Just rebuilt my Petcock Bought all new orings and diaphram for about $30 OEM parts. Also new gasket in my Fuel sender. Works great.

 

I see you folks mentioning "OEM" parts, but I can't seem to find an OEM diaphram, or outlet gasket, just o-rings on the outside of the petcock.

Where are you folks sourcing OEM parts?

 

Hey Skippy, same deal here.

I can't find any OEM "original equipment manufacturer" diaphragm, etc... Lucky for me I live in the city where they make the rebuild kits (Kitchener, Ontario), hopefully I can pick one up this week, i get a very fine gas spray out the side of the diaphragm when running (and almost unnoticeable leak when stopped)...