Petcock doesnt work in "On" position

I recently rebuilt my petcock and it isnt working in the "On" position. Fuel flows freely on Prime and flows with vacuum on Reserve. But it wont flow with vacuum at the On position. What could be causing this?

 

Got enough gas in the tank for the "ON" position? If so open the gas cap while it's running. Does gas flow?

Gary H.

 

Did you make sure that the rubber valving under the petcock handle was installed in the correct orientation?
http://www.xjbikes.com/forums/bookmarks/8/view-item

 

Well i feel pretty dumb now... I thought that a gallon would be enough. I went and got another gallon and put it in and sure enough, it works.

 

Don't...there's nothing dumb about it. Now you can help other members in the future with the same issue. I assure you we'll see it again.

Gary H.

 

Yep, you aren't the first--or last.

 

Ahh, fuel flow problems...

Initially, the petcock on my XJ700 was leaky so I bought the rebuild parts from Len @ XJ Forever. After clean and rebuild (all replaceable parts are new), it was still leaking. Len suggested that I put a slight "bend" in the metal diaphragm plate (make it concave or convex depending on how you look at it so it seats better) using the inside of an appropriately sized deep socket and a slight tap from a hammer and a slight stretch of the new spring.

This solved the leaking problem, but then I found that the vacuum from cyl #2 was not enough to open the darn thing to allow fuel to flow on ON position. It was giving me intermittent fuel flow. Sometimes to the point of starving the carbs.

I'm also noticing that the new inline fuel filter (gold cone looking thing) seems to be creating some problems with fuel flow as there is always an air bubble in the fuel line (it is clear fuel line so I can see it!). Fuel is fully in the fuel line from tank to filter, then there is an air gap after the filter between it and the carbs, though i can see that the line always maintains fuel just as it enters the "T" fitting of the carbs... so I know the fuel is getting around the gap.

My filter might be faulty or perhaps the fuel line should be shorter to create an even greater downward angle from tank to carbs. Fixing these potential problems may also alleviate my PRI/ON position problem. RES doesn't seem to change things. Does RES require the presence of vacuum? Or is it just a fuel dump like PRI, but from a lower level in the tank... Not sure about that.

Till I get it figured, out my short runs in PRI position seems to work. I don't think my solution is a difficult one to find, once I get to it.

 

Both ON and RES require vacuum.

Your fuel filter isn't faulty, it just needs to be moved so the air bubble can get out.

Make sure that you vacuum line isn't collapsing, and make sure that it is real vacuum ilne and not a thin-walled vent line.

Also tend to the vent in the gas cap. If the cap isn't venting properly ait inflow wont' match fuel outflow, and you will have a reduced amount of (or even no) fuel getting to the carbs.

 

With the current set-up open the gas cap while it's running.
Switch the vac line to #3 and plug #2.
With pc on prime open and close each drain plug to bleed air out.
Did you rebuild the gas cap?
Is the sintered filter cone oriented correctly?
The reserve position operates the same as the on position. Fuel level in tank is the only difference.
Len sells a washer that can be installed behind the diaphragm spring to make the o-ring seat better. Make certain you turn the pc back to the on position when you're not riding to prevent any mis-haps until you get this sorted.

Gary H.

 

at least it was a quick and cheap fix and you did not have to remove the petcock to check your work.

 

this sounds like a problem, unless you had a sharp bend in vac line or clogged nipple

check your clamps i had this problem I had to adjust the fuel line at the petcock and move the clamp a little turning petcock to prime will bleed out the bubble

move filter as far away from petcock as possible, trying to get filter body below petcock nipple

better to run on reserve than prime

 

I had a a bubble between the filter and the carbs also. My filter allows a 90% hook up so I attached the filter to the fuel line coming out of the "T" so that it is in the upright position and low enough so that there is a definite downward slope from the petcock to the filer. It is a little harder to get the filter in place but it seems to solve the bubble problem.

Here's the filter I used.

http://www.ebay.com/itm/Visu-In-Lin...uad-/150917138477?hash=item23235cc82d&vxp=mtr

Chacal gave me the same advice about the petcock and I think the key is to dent it so slightly that you almost can't see the change.

Also, I went to a thick rubber fuel line for my vacuum line just to insure it can't collapse.

So far everything is working well.

 

Hello all...

I have disassembled the gas cap, lubed where needed as per directions here in the forum (I believe it was a .pdf?) and replaced the gasket. Petcock rebuild included the little washer behind the new spring. New clear fuel line, inline filter (installed with the arrowing pointing towards the carbs [FLOW==>]) and vacuum line (holy thickness on this one!) from Len. I'm sure we'll all agree if that is where the parts came from, the parts are spot on!

Need to get that confounded bubble out of the fuel line. It's tough to lift the tank high enough to diddle with things under there when the fuel line itself is so short... I'm preaching to the choir though... I know... Going to shorten the fuel line a bit more if I can. Will take length from the span between the inline filter and carbs. Right now, the filter is positioned somewhat level with the ground. Less fuel line will enable a more downward position.

p.s. Just an FYI... took a ride tonight. This was the first time I really filled her up to the top. Perhaps the level of fuel in the tank as "rocs" suggested above, is part of the problem and will help me to resolve my bubble issue. With no air gap, I'm hoping my flow issues disappear.

 

Turn the petcock to the prime position.
Run a length of clear tubing from carb #1 bowl nipple to a empty container (i use a empty plastic coffee jug).
Open carb #1 drain screw until a steady stream of fuel flows. Close it tight.
Do the same in sequence for #2-#4.
Turn the petcock back to the on position.
Use a coffee filter in a funnel to strain the removed fuel and put it back in the tank.
The air bubble should be gone.

Gary H.

 

I ran my bike with a bubble in the line for 6-8 months with no problems. I decided to relocate the filter and get a positive slope to the fuel line after having the bike shut down with a tank almost full, and then starting and running on prime. Assuming a petcock problem I checked it and finding no problem there decided to get rid of the bubble. It would seem to me that the bubble would only be a problem if it was in and upward bend (mine did) of the fuel line where the bubble couldn't flow up the line and got big enough to cause an air block. At least that's my justification for doing what I did. It would also seem to me that if there is a positive upward slant to the fuel line the bubble would work itself out if you simple set the petcock to prime.

 

setting to prime bike not running allows bubble to go into the tank. a bubble can cause vapor lock when it is hot out.

I hope that bubble stays in the tank where it belongs

edited

 

DOes it make sense for anybody or is it just because I'm not actually bilingual?

 

Hey, give XJ550H a break. It was almost mid-night when he crafted that interesting sentence crafted that interesting sentence.

 

late night key board skills
allows the bubble removed from post.

of course your bilingual you speak English and Canadian

 

I'm a French Canadian living in Quebec, so English language is not in my genes, and I'm far from being bilingual. Writing it properly is something, but my biggest challenge would be a conversation with 5 or 6 English speaking XJ bikers around a table full of empty beer bottles, lol

 

This would be a challenge for most of us as well. Our English is considered Broken English. I watch shows from across the pond on television and have no clue as to some of things they're saying.

Gary H.

 

Fuel released from each of the bowls one at a time while bike off (of course) and in PRI position. Got a bunch of air from #1 drain as this was the first one I bled. It was deceiving at first because at first a TON of bubbles were coming out. I realized it was probably because I had the drain screw loosened too much and air was more than likely sneaking around the threads, getting in and then coming back out the nipple. The bubble in the line either traveled towards the carbs, or backfilled with fuel. Either way, at that point, bubble gone!

It did help to open the cap and blow into the filler hole (don't laugh) to move it along. Started the bike and ran it a few minutes in ON position and the bubble came back, though it definitely was not as large as before. A few more fuel purge attempts might just do the trick.

Thank you all for the help on this.

 

UPDATE:

I was able to shorten the fuel line by another 2 inches (about an inch from both sides of the inline filter) The filter is at a good downward 45 degree angle now. Looks like my bubble and fuel supply issues are resolved. I've also run in it in ON position without incident so far... which I was not able to do previously.

Again, thanks all...

 

This thread reminded me that the guy I bought my second Seca900 from had a hard time making the bike idle properly, now I suspect it was partly due to his poor fuel line setup

 

I'd say so.

Gary H.

 

Haha! I'm the same way with French... but Tabernac! All the good words seem to come out when the beer bottles are empty! Your english is much better than my French, though.
Might that fuel filter be too restrictive to get enough gas to the carbs? 4 thirsty mouths to feed! I don't have a filter, but I hear that most recommend the brass filter material.

 

The paper filters don't allow the fuel to flow fast enough for the four hungry mouths.

Gary H.

 

Those four mouths are not that hungry at idle but I understand that it could become a problem at higher revs.

 

I have a question? What is the on position? Could somebody post a pic of the different positions? I really don't like this petcock setup but maybe if I knew what was what I wouldn't feel this way. Thanks guys.

 

Look at the lever. The end of it should have an arrow that points to the position it is set to.

 

Well that might explain it. I gotta put my glasses on and go look at it. Thank you

 

Rebuilding the Yamaha Vacuum Fuel Valve w/pics
photo from above thread set to ON position see the little arrow?