XJ650L Leaking Petcock: How to Fix?

Last fall when I bought my Turbo Seca, I flooded the crank with gas when I forgot to turn off the gas. I know I need to replace the float seats, that will come closer to spring. In the mean time the bike was mothballed with a half a tank of gas with the petcock on "off". Today I noticed a big puddle of gas/oil dripping from the exhaust pipe. I drained out the oil and sure enough, out poured a mixture of gas & oil. Without tearing the fuel system apart (about 20 degrees in the garage), what went wrong, and how do you fix/rebuild the petcock? What other components need attention?
Thanks to all who read.
Tom

 

Don't no if this is the same as your bike... but it might give you an idea of how it goes...

http://xjbikes.com/Forums/viewtopic/t=2 ... build.html

It's a very nice write up.

 

I rebuilt mine (xj750) and it really was not all tht complicated. It its similar in design, just get a rebuild kit and dive in.

 

The bigger problem IS THE CARBS.

If your floats were working properly, you could leave the petcock on PRI for a week and nothing bad should happen. A leaky petcock only enables the bigger issue, which is indeed the float valves in the carbs.

 

your correct fitz. petcock is easy even for me, however, carbs kick my butt ...... tm, work your carbs over!

 

I ended up getting an aftermarket petcock. It fit perfectly, and no vacuum line to deal with. Simple on and off w/reserve like most older motorcycles

 

OP has a Turbo Seca, which has a simpler ON-OFF-RES petcock, because it has a fuel pump.

You will need to do many things to the fuel system that our naturally aspirated XJ brethren do not:

In addition to an ON-OFF-RES petcock, you also have:
1. Pressurized Carbs
2. Fuel Pump
3. Fuel Check Valve
4. Pressure Regulator

And it is imperative that each of these components work right or you'll overflow the carbs in no time, even while running! (Thanks to the fuel pump, with a 14 psi output).

Your fuel system is designed to run a 2 psi differential from your air box. That way, there is still fuel pressure to fill the carb bowls while on boost. The pressure regulator maintains this differential by operating a diaphragm that actuates a valve allowing fuel to return to the tank if the differential pressure exceeds 2 psi.

If this regulator is stuck, you'll over flow the carbs soon after starting the motorcycle. If you pinch the return line...ditto. Also, if you have the side stand down, run switch on, and hold the start button, the bike won't turn over (safety circuit), but the fuel pump will spin. If either of the above aren't working, you'll over flow the carb.

There is an added safety of a check valve right before the fuel enters the carbs which should prevent the fuel from entering when there is no pressure behind it, if it functioning properly.

Then you have all of the normal issues to deal with for a petcock, if it leaks, rebuild it. Replacement will be harder because you have that return line.

You will need to wet set your float height after the rebuild. I chose to do it with the fuel pump on as I was concerned that the extra pressure would affect the results.

Finally, if it hasn't been done recently consider rebuilding the carbs. You'll want every part of the fuel system in tip-top shape, or you'll be chasing your tail for months. As for parts, BDesignshas put a lot of work into getting parts manufactured for the Turbo Seca. Aftermarket Carb kits and other bits are very affordable there.

 

I see now that my response is almost a repeat of what I posted to your previous thread in Sept.

Have you checked your float height (wet set) method, with the fuel pump running? Have you verified that the pressure regulator works? Rebuilt the carbs?

Have you started it at all since you put it up (even just for a little while)? EDIT: I see you rode it in Dec. You could have pumped the crank case full of gas then. I found out the hard way what happens when excess fuel pressure isn't returned to the tank properly.

With the extra components, fuel could even bypass your whole carb if your pressure regulator is bad and allows fuel to weep into your air box or compressor (where it gets it's pressure signal from).

 

Manbot, No I haven't done anything since my last fall problem. At the time the gas flooded the crank last fall, I drained and re-filled the bike with 20w50, I then put a magic marker dot on the oil level window and I watched faithfully to see if it leaked gas. It did not. This past December when I rode the bike (how could anyone resist?, 65 degrees in Cleveland in December). I still continued to watch the oil level, up until a few days ago there wasn't any problems. But I think this past weeks sub arctic temps must have done in the petcock seals.

So I looked on the Yamaha Site today and the parts are still available to rebuild the petcock. I will do that in combination with the fuel system items recommended by you and Bigfitz. My mistake I guess, I thought the petcock would hold back the gas, I have a couple of old bikes and never had an issue.

Thanks again
TR

 

THE FLOAT VALVES ARE SUPPOSED TO HOLD BACK GAS. The floats, NOT the petcock. And your bike has apparently been relying on the petcock.

The petcock is only ENABLING the issue. If your floats were working correctly you could leave the petcock on PRIME for a week with no ill result. I know, I've done it accidentally and didn't get a crankcase full of gas. Because my floats are working correctly.

If gas gets BEYOND the carbs the float valves didn't do their job. Plain and simple. The fact that they had the gas to misbehave with could be the petcock's fault; but YOUR FLOATS LET YOU DOWN. It's seemingly intermittent because that's how sticky floats (mis) behave. Fix the petcock, by all means; but your underlying problem is a malfunctioning float or floats.

I don't know how much plainer I can make it.

 

http://www.xj4ever.com/setting%20fuel%20levels.pdf

 

OK, the tear down process starts today (too cold and snowy to do anything else). I have the garage heaters going right now, in a few hours it should be a balmy 65 degrees, just right for wrenching.

I really appreciate all the help, If I get stuck somewhere, I know where to get help.

Tom