Gas mileage tanked... fuel leak?

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Re: Gas mileage tanked... fuel leak?

Postby elizilla » Thu Jul 12, 2012 2:57 pm

Take the dipstick out and sniff it. If the dipstick smells like gas you know there is gas in the oil.
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Re: Gas mileage tanked... fuel leak?

Postby Darkblood » Thu Jul 12, 2012 3:05 pm

The Yamaha manual petcock swap is well worth it in my opinion. I did it and now can sleep through the night without worrying about it leaking into the cylinder. I also found that it runs at WOT better than it did with the vacuum petcock.

It really is an easy swap out. most of the time required is in draining the tank, but it sounds like yours is doing that already for you.
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Re: Gas mileage tanked... fuel leak?

Postby Dachary » Thu Jul 12, 2012 4:08 pm

Darkblood wrote:The Yamaha manual petcock swap is well worth it in my opinion. I did it and now can sleep through the night without worrying about it leaking into the cylinder. I also found that it runs at WOT better than it did with the vacuum petcock.

It really is an easy swap out. most of the time required is in draining the tank, but it sounds like yours is doing that already for you.


Yeah, I'm really leaning toward doing the petcock swap - especially after the conversation the SO had with the dealer this afternoon.

My only real quibble with this is how long it may take to get the Yamaha petcock in my hands. I'm short on time with our trip coming around next week and I don't wanna be doing something like this last minute. I'll make a call in the AM when I get the rig in my hands and do what I shoulda done in the first place - disconnect the fuel hose from the petcock and see if gas comes spewing out.

I spent some time this morning reading up on vacuum petcock failures and one I saw said something about turning the petcock into prime position and then back to the regular position, and how that stopped the petcock from spewing gas - at least temporarily. Would seem to point to crud in the petcock, I'm guessing. But it sounds like that's what happened today - I think a guy at the sailmaking shop turned the petcock to "prime" for a while and then turned it back, and it hasn't leaked any more since then. (They put something under it to catch the fuel this morning and it's still empty, but when they came in this AM, there was probably a 12 inch puddle of gas, he said.) So it may be that when I get there in the morning, it won't leak when I pull the hose off. If it's an intermittent failure, that would also explain why I had that "missing" gas on the 23rd last month but nothing again until this AM.

Oh well. I guess I'll just wait and see what's waiting for me in the morning.
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Re: Gas mileage tanked... fuel leak?

Postby Darkblood » Thu Jul 12, 2012 4:16 pm

Worst case do what both gobium and I did while waiting for the Yamaha swap. Go to a hardware store and get a 1/4 inch fuel line shut off valve for like a Briggs and Stratton Lawnmower and put inline just after the petcock but before the T. That way when you shut down you shut off the fuel at that location. this effectively gives you the off position while you wait for the replacement part.
Heck I think Gobium is still running that setup.
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Gas mileage tanked... fuel leak?

Postby Dachary » Fri Jul 13, 2012 12:25 pm

Well that was a fun morning!

Gas definitely in the cylinder heads - pulled the spark plugs and slowly kicked it over a few times. I heard splooshing and smelled gas so I gave it a more vigorous kick (key off, kill switch off) and a big whoosh of gas spurted out the right cylinder all over the sidecar. Kicked it some more and some dribbled out the left, and more out the right. Plenty of gas in there! (Also the left spark plug had some gas on it, too.)

After getting as much of the gas out of the cylinder heads as I could, we put the plugs back in and checked the oil.

WAY too much fluid in there! A sniff revealed a hint of gasoline, but it wasn't as strong as it was in the cylinder heads - but given the volume of fluid and the fact that I checked it before driving it down there, there was no question it was gas in the oil. Thankfully I took y'all's advice and brought the oil change stuff, so we did an emergency oil change. Didn't take too long and it was only 100-200km early.

Oil changed, plugs back in, we kicked it over... It kicked just fine so I assume we'd cleared enough of the gas from the cylinder heads. Turned on the key, hit the starter... Some rumbling but no starting. Waited a bit. Tried again. Still no starting. Waited a bit. Tried kick-starting it - nada.

Finally we considered that maybe enough gas had leaked that it didn't have gas, so we switched the petcock to reserve and tried again. Eureka! It took a little finagling but it finally started that time. Ran a little rough for a minute or two, but we let it idle and cough back to life. Rode it a couple miles down the road and put some gas in - only 2.7 gallons. So at least not *all* the gas came out.

Haven't checked the petcock yet - wanted to get more gas in first so it's roughly under the same conditions/strain where it started leaking. I'll go out and check it in a few minutes.

But thank you all very much for the advice re:changing the oil! That was invaluable. I got a lot of info re: hydrostatic lock and fuel leaking into the engine via the Search function here - I'm very grateful y'all have shared your collective knowledge because I have no doubt that without it, I woulda had a VERY unhappy rig this AM!

Pictures later after I get them off the camera. And also pictures of my convertible top for the sidecar, too! :)
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Re: Gas mileage tanked... fuel leak?

Postby MartyL » Fri Jul 13, 2012 12:46 pm

You should check your carb floats as if they are stuck it will pass the fuel . The petcock is upstream and only a part of the equation.
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Re: Gas mileage tanked... fuel leak?

Postby Sailing Rider » Fri Jul 13, 2012 12:50 pm

One thing I dont understand is how gas got to the floor of the shop. Were did it leak out of?
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Re: Gas mileage tanked... fuel leak?

Postby Dachary » Fri Jul 13, 2012 1:49 pm

MartyL wrote:You should check your carb floats as if they are stuck it will pass the fuel . The petcock is upstream and only a part of the equation.


Yeah, Marty - one of my savvy MC-riding friends on Facebook already pointed this out ;) I do intend to check the carb floats as it's been suggested to me that even if the petcock failed, the carb floats should have kept the gas out of the engine. I'm just trying to figure out exactly how :P

Sailing Rider wrote:One thing I dont understand is how gas got to the floor of the shop. Were did it leak out of?


The guy at the shop told us it was leaking off the left carb somewhere. When we got there, the big hose on the carb had come loose and was just hanging there. No idea how that happened. The hose clamp was still on it and still tightened down. I can only imagine it got knocked while they were working on installing the snaps on our sidecar (or, let's be honest, I'm sure in a week in a public shop with lots of people interested some folks must have sat on it, potentially screwed with it, etc). But in spite of that, it wasn't clear if the leak was coming from inside that hose or where - he couldn't quite tell us. Might have even been the nipple on the bottom of the carb for all I know. We're working now to see if we can replicate it.

We just went out about 45 minutes ago and removed the hose from the petcock. Nothing came out at first, but after we also disconnected the hose that runs from the bottom of the petcock to the left carb, we got a little splurt of gasoline from the right-side of the petcock - basically at the prime position. We didn't mess with the petcock settings though. After that little splurt, we didn't see any more gasoline building.

We've now taped a clear ziplock baggie to the petcock so hopefully we can go check it in a couple of hours to see if there's anything in it.
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Re: Gas mileage tanked... fuel leak?

Postby Dachary » Sun Jul 15, 2012 3:02 pm

Just following up with this for the sake of fully documenting the results...

After 2 days of screwing around with the petcock - i.e. disconnecting it from the carbs to see if we can replicate a leak situation - no dice. I can't figure out if it's failing intermittently or if it got knocked while it was in the shop. On the heels of the earlier "really bad mileage" day when basically a gallon of gas went missing, I thought it had to be a fuel leak... but I can't seem to replicate it. So I guess we'll just keep riding and see if we have any more problems with it.

I did pull the carbs yesterday and completely disassemble them. The floats *seemed* to be fine, but we sprayed some carb cleaner around - there was a bit of gunk in there but it didn't seem to be interfering with the action of the floats - and I guess we'll have to wait and see what happens.

While I was in there, I did swap the pilot jet from 40 to 42, and when I put the carbs back on the bike, I synched them with our new Twinmax. I don't know whether it was the bigger jet or the sync (we'd previously synched them with a Harmonizer and they were theoretically "in balance" before we pulled the carbs) but this *did* fix our wanting to die when idling problem in high ambient temps. We took her out for a long test ride this morning - about 150 miles - in temps up to 92 degrees and she idled just fine at stop lights, when she was wanting to die before. Tweaked the clutch this AM and now we can sit at a stoplight with the clutch in (if we're having trouble getting into Neutral) and it doesn't die, either. So we've got a net gain of improved performance, even though we weren't able to identify a clear reason for this issue.
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Re: Gas mileage tanked... fuel leak?

Postby cdscoot » Sun Jul 15, 2012 3:15 pm

Have you ever disassembled the vacuum petcock and cleaned out the tank connection? If not you may want to do that and get rid of the crud before it causes you a problem. If you have already done that then good!
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