XJ700 Petcock Problems

My Petcock used to drip every few seconds. I bought the kit from Chacal and now I made it even worse. Fuel constantly flows in a stream from the nipple that sticks into the fuel hose. It's not leaking anywhere else so it makes me think I have the plastic spacer flipped around or I polished away too much of the valve seat.

I disassembled it and rebuilt again to no luck. Turning the dial to res or pri makes it flow more so I'm thinking it's the seat part. I even added a washer as a spacer but no luck.

 

Moving to PRI or RES = full flow .... ON is vacuum only if it leaks in this position it is a problem without engine running. I would disassemble put face surface on a piece of glass and see if it is flat . you may have it put together backwards swap it around and try it .

 

I thought res was vacuum as well, only it draws from the reserve portion of the tank. Pri is to prime, or fill empty carbs before firing, hence no vacuum. Are I wrongs?

 

On my XJ550, the petcock 'spacer' had to be oriented in a very specific way (with the notch facing a specific direction), even though it looked somewhat not direction specific.

Did you replace it in the proper orientation on your XJ700? (although from the image it looks correct as it would be on my bike).

 

You did it like this?
Rebuilding the Yamaha Vacuum Fuel Valve w/pics

Is the leak from the base of the fule line nipple?
The rebuild kit won't solve that. The Nipple is pressed in, and a leak there can only be fixed by getting a new petcock body, removing the nipple and using fuelproof epoxy to fill the gap when you press the nipple back in (you might get away with a bead around the base), or having an experienced person braze/TIG the nipple to the bare petcock body.

 

You're correct. Both the RES ans ON positions require engine vacuum in order to flow fuel.

 

I used the thread to rebuild it. Fuel flows from the end of the nipple like it's supposed to. Problem is it flows always no matter what the dial is set to

 

I have the same problem. I rebuilt mine as per the process in the thread and it leaks when put on "ON".

 

In both cases that indicates that the diaphram seal isn't sealing. The original seal was cone shaped. The replacements are a normal o-ring. The remedy is to polish the seat again, checking for nicks and that the o-ring can seat without leaking (do this with the petcock disassembled).

 

I had the same problem. Chacal advised me to use a small socket, place the diaphragm in the socket, and very lightly tap it. This slightly bends the metal backing and effectively lengthens the shaft that the o-ring is on enough to seal properly. I did it and have never had a problem since. Use the smallest socket that will easily fit over the shaft and tap it with a small hammer very very lightly. I could hardly see any bend, but it was enough to work.

 

Tabaka, are you saying that you did it after you put a rebuild kit in your petcock?

Smallest socket, like 8 mm or even smaller?

 

You are correct. PRI is the only setting that is NOT vacuum-operated. It is free-flowing. ON and RES are on the vacuum side of things

 

Yes, after a rebuild with all new parts from Chacal. In fact, I had gone through it several times before I contacted Chacal and he told me what to do. I think an 8 mm socket is what I used. He indicated that the original o-rings were a little larger and maybe shaped a little differently which made them seal easier. That's the reason for this procedure which effectively lengthens the shaft that holds the new o-ring. Whatever, the reason, it worked perfectly for me. Just go easy, we are probably talking about 1 mm or less, almost imperceptible.

 

Yes, after a rebuild with all new parts from Chacal. In fact, I had gone through it several times before I contacted Chacal and he told me what to do. I think an 8 mm socket is what I used. He indicated that the original o-rings were a little larger and maybe shaped a little differently which made them seal easier. That's the reason for this procedure which effectively lengthens the shaft that holds the new o-ring. Whatever, the reason, it worked perfectly for me. Just go easy, we are probably talking about 1 mm or less, almost imperceptible.

 

If I remember correctly, I used the washer suggested in the step by step instructions when I rebuilt my XJ550 petcock with Chacal's kit. That, along with polishing the metal surfaces sealed it up nicely. No leaking.

 

The original O-rings were HOLLOW, which made them much more flexible and able to contort to match the (sometimes) slightly off-center machining of the seat in the petcock body (i.e. "factory cheating in order to cover up a recognized defect"). The O-rings that come with the replacement (both OEM and aftermarket) petcock rebuild kits use tranditional SOLID O-rings, which won't/can't "give" enough to make up for the offset seat. The only way around this issue is to slightly "lengthen" the plunger shaft a bit in order to apply more pressure on the (solid) o-ring to make up for the variance. Note that some petcocks, which had their seat drilled quite a bit "off-axis" cannot be "solved" even with the shaft extension technique.....the only solution is to find or re-use the factory hollow o-ring, or to scrap that petcock.........

 

BTW, the "large" petcocks (XJ700, XJ750-X, and XJ900 models) are the only ones where this "off-axis" problem with the seat exists. All of the smaller-body petcocks don't seem to have this issue. That's why the "slightly lengthen the shaft by deforming the metal plate" trick is only (sometimes) needed on the large-body petcocks.

P.S. it's a BS solution to the problem, but it's the only way to make up for a BS situation caused by a BS method of solving a BS problem that should have never made it thru production in the 1st place.......

 

Thanks for sharing.

 

Now, ain't that some BS! I'm glad you provided the explanation--I just knew it worked for me.

 

It worked! Excellent. Thanks again y'all.

My next question:

I cleaned the carbs and wet set the floats. I set them to the spec of 1mm +/- 1mm. Hopefully the picture is what it's supposed to look like.

Well a combo of leaky petcock and 30 year old needle valves caused my crankcase to flood. I replaced the needle valves and seats as a combo and changed the oil. And it flooded again. Are my bowls too high?

 

Could be, but if they measure in spec, then they should not be the cause of the problem. Where did you get the needle valve (seat & needle) units from?

 

Forgot to post it

 

Some random place off eBay. They are slightly longer and look a bit different but that shouldn't matter as long as they're replaced as a set right? I took the bowls off and just held the needles into the seats and they blocked off the gas. And yes I reset the floats after. But I'm thinking they have to be too high.

 

There are some K&L (maybe other mfgs., too) who sell Hitachi float valve sets for these model bikes and they don't work and will leak about 90% of the time............just as you are experiencing. The extra length throws off the geometry with the float tang. So you can "manually" hold them closed (with your finger in place of the float tang) and they will seal against flow, but your finger is pressing "straight" up on the needles, whereas the float tang/needle interface describes an arc as the float moves up and down, and the longer needle disrupts this motion and can/will cause the needle to seize within the seat bore (at least, that's the best that I can figure as to why the longer needles don't work).

Solution: use the correct needle/seat combo. In fact, if you still have your original needle/seats, I'll bet if you put them back in, you'll find that the carbs no longer leak (you'll probably have to re-set the fuel levels, though). Best advice: get a set of the float valves that actually fit properly for these carbs (we have them in stock, in either the OE rubber-tipped or metal-tipped versions.....use the metal-tipped needles if you consistently use E10 or higher fuel in your tank).

 

if your crankcase flooded, the petcock isn't fixed yet

 

Typo?

 

I agree with both comments. If the petcock is sealing--and it is not set to Prime--then no gas would be reaching the carbs in the first place. If the petcock is leaking--or set to prime--and the needles are sealing properly then they will not leak. If you are still getting gas pass the carbs and into the crank--and the petcock is not on Prime, then you have a problem with both the petcock and needles.

When setting my floats I leave the carbs setting for a while just to be sure there isn't a slow leak. I'll even bump them several time before being satisfied that they are sealing well. Also, I bought the correct solid brass needles and seats from Chacal after reading about all the problems with other needles. (He also has the correct rubber tipped needles, but I opted foe the solid tips on his suggestion and they work perfectly.)

 

Even if the petcock leaks, fuel won't get into the crankcase IF the float needles are sealing like they should.
Does your toilet run constantly just because the water valve is always left on?

 

carburetors need a handle to jiggle