Carb Leak Update (VERY LONG!)

[SlowOldGuy]

Here's an update on my carb leak problem that I first reported on back in December.  In summary, I noticed fuel dripping from 2 of the small carb hoses.  I removed the carb assembly from the engine and hooked it up to an aux fuel supply on the bench so I could troubleshoot.  I tried everything to stop the seeping leak.  Different floats, float adjustments, different needle seats, new o-rings, swapping to a different carb body, nothing seemed to work.  I thought it might be bad machining around the needle seat letting fuel seep past the o-ring, but it continued to leak even after I swapped carb bodies. 

To compound this problem, I couldn't get the petcock to stop leaking either.  Installing a new 4mm o-ring worked for a few days, but then it started seeping again. 

So, here's the latest.  I got tired of futzing with the original carbs and decided to install a new set that I had purchased from Randy for just such an occasion.  The original carbs were off of my '85 and thus had a dual 3/8" fuel inlet feed along with the larger diameter needle seats (non-fuel pump model).  The new carb set has the single fuel inlet feed between the #2 and #3 carbs.  I was able to use one of the larger 3/8 fittings from the original carb set in place of the 1/4 fitting that the new carbs come with.  The older fitting is slightly shorter since it fits between two of the end carbs and as we've discussed elsewhere, the spacing on the center carbs is slightly wider.  I was worried about this smaller fitting sliding to one side and possibly leaking even though it is sealed with double o-rings. 

I put a small tie wrap on each end of the fitting and it was the perfect spacer set to keep the old fitting centered in the available space.  After a 4 day soak with them hooked up to the aux fuel tank on the bench, I was convinced that the new carbs would not leak so I installed them on the engine to test.  I get the carbs back on and do an idle adjustment and carb sync while hooked up to the aux tank. 

With this being successful, I start to install the tank.  This is where I realized that the stupid petcock was still leaking.  I decided to go ahead and install the tank and hope that the new floats, needles, and o-rings would not leak.  I'm still trying to put together  an electrical solenoid setup, but the post that suggested a Pingle vacuum shutoff has me reconsidering the electrical approach, at least until I can research the Pingle option a bit more.  There's also not much room to work with since I'm still running the stock airbox. 

I also installed one of those quick disconnect, auto shutoff valves in-line to aid tank removal in the future.  It required me to reroute the fuel line (and in fact, I used new 5/16 hose that is not as flexible as the original stuff) so I was a bit concerned about getting a kink in the line.  I tried to route the line in the original routing, but the stiffer hose really didn't want to cooperate.  I finally get everything tucked up nicely under the tank and am ready for the next run test.  Start the engine up and everything is fine for about 5 minutes.  Then the engine starts acting like it's running low on fuel.  I lift the tank up and notice that the hose has shifted and has quite a bit of vertical loop in it.  I manipulate the hose with the petcock in the Prime position hoping that it's just a bubble in the fuel line.  I also reroute the fuel line to minimize the vertical loop.

This appears to work.  The bubble is burped out of the line and the engine is no longer acting like it's running out of gas.  A quick trip around the neighborhood confirms that the carbs are getting "adequate" fuel.

Unfortunately, this is when I realize that I had forgotten to swap out the needle seats.  This new set of carbs has the smaller diameter seats in them.  I'm fearing that the single inlet combined with the smaller seats will possibly cause a fuel starvation problem.  I'm in no mood to take everything back apart, so I resort to creative Mazzematics (anyone remember that reference?).  I calculate that if I'm running at 80MPH and getting 35MPG, then I'm using slightly less than 5 ounces of fuel per minute (proof is left to the student, show your work for partial credit).  That's only 1 and a quarter ounces per carb per minute.  I figure (hope) that this gravity feed setup is capable of flowing that much fuel. 

An extended test ride last weekend on a gorgeous Saturday that saw temperatures in the 70s and included several high RPM passes experienced no fuel starvation issues.  I even ran the tank past half full (half empty for you pessimists out there) to make sure it would still supply enough fuel. 

So, for now this proves that a new set of carbs will work on the older model FJs, even with a single feed hose and smaller diameter needle seats.  I was able to install a quick disconnect and avoid kinking the fuel line, even with the stock airbox.

I purchased a new set of floats from Randy (thanks again Randy!) and will see if these fix my original carb set.  I'm also going find some way of dealing with the leaking petcock.  Whether it be a solenoid or another form of vacuum shutoff, I'm going to find a solution for this.  The Pingle route is way expensive, I can get 1/4 fuel solenoids for about $30.  The main problem is finding the space to add a solenoid and hoping it doesn't further restrict fuel flow.  Finally, I found a source for stainless quick disconnects at a decent price.  The unit I currently have installed is plastic and came from McMaster Carr. 

I just received a set of the UNI pods (again from Randy) just in case I need to dump the airbox to make this setup work reliably. 

If it continues to stay below freezing here, I might just get ambitious and test install the set of FZ1 carbs I have sitting on the bench.

DavidR.

[andyb]

I calculate that if I'm running at 80MPH and getting 35MPG, then I'm using slightly less than 5 ounces of fuel per minute (proof is left to the student, show your work for partial credit).  That's only 1 and a quarter ounces per carb per minute.  I figure (hope) that this gravity feed setup is capable of flowing that much fuel.  

Probably fine.  Problem is that's not remotely the highest fuel demand you put on that system (unless that's your top speed and your brakes are really, really sticking badly!).

I'd wager that it'd be fine when gravity fed even with the wrong seats in it, though.  You'd notice it wimping out on a top end run (sustained 150mph use), but you also might notice it getting soggy if you're using lots of WOT through an extended set of bends.  Wouldn't worry about it, just pay attention to how it's running, and when you get back in there to fix something else, swap em around.  It might be worth swapping just for peace of mind though--nothing sucks like riding what you fear is a time bomb.

[karl61]

I needed a new petcock as mine was leaking real bad.


I kept searching ebay and non were listed at the time.

I ended up somehow at this site after searching:

http://www.boats.net/parts/search/Yamaha/Motorcycle/1985/FJ1100N/FUEL%20TANK/parts.html

I ordered it online and took about ten days and it was at my front door.

Here is a picture.

http://img715.imageshack.us/i/petcock1.jpg/