Trouble rebuilding petcock (leaking at pinhole)

[coal miner]

Carb Issues (previously Petcock leaking at pinhole)

I receive the petcock disassembled in a box. I have installed new seals, but I dont think I have it back together correctly.

There is a small pinhole that goes into the diaphragm cavity, that has fuel pouring out of it, when in the res or pri position. when in the res position fuel also runs out of the the fuel line as if it were getting vacuum from the carb boot.

I have the metal disc side of the diaphragm sitting in the recessed of the spacer plate. There is a pin hole made into one of the diaphragm rubbers that I have aligned with the same pin hole in the spacer plate and also aligne with the pin hole in the outer petcock housing.

For the record I have read the "how to repair your starving leaking petcock" and anything else I can find. I have even look at all the parts fiche I can find, but they only show the front side of the petcock not the diaphragm side.

Any thoughts or ideas.

 

[lcgtr]

I dont think that pin hole should go all the way through, I think its been made wrong.
I had problems with mine as i screwed it together wrong not alligning the plastic spacer right with the diaphram.

the body may also be warped

 

[xschris]

Looks like this when you assemble it. This is off a 77 xs650 so it will be a little different for a better pic you might want to go to yamaha's website and look up the parts sheet on this.

 

[jmd_forest]

I understand there is a "How To" on rebuilding the petcock on this site somewhere although I haven't seen it. I HAVE used the extremely detailed step by step rebuild "How To" with great pictures on the xjbikes.com site for both my XJ700 and XS400 petcocks

 

[lcgtr]

Looks like this when you assemble it. This is off a 77 xs650 so it will be a little different for a better pic you might want to go to yamaha's website and look up the parts sheet on this.

thats exactly like mine, see no hole and you have to align the plastic spacer and the diaphram

 

[coal miner]

Got it fixed. I reassembled it clocking the diaphragm and spacer a couple different ways, and finally found one that got it working properly. Now on to my next issue... carbs causing rpms to hang up when rpms go over 2500.

 

[xschris]

Time to take them apart and clean them. You will also most likely need new o-rings and seals. Could also be the intake manifolds leaking causing a lean condition.

 

[coal miner]

Time to take them apart and clean them. You will also most likely need new o-rings and seals. Could also be the intake manifolds leaking causing a lean condition.

I sprayed them down with carb cleaner and put them back together when I first got the bike running, but it had this issue. I then completely disassembled them (besides the brass jets? which i was about to booger up trying to get them out, so I left them). Other than that I soaked everything in chem dip for 6hrs then cleaned and reassembled.

I ordered some new intake manifolds/carb boots, cause the old ones were cracked, and got them put on. I checked the float level which needed a little tweeking nothing major. I checked the diaphragms for leaks by covering the oval port and the slides didnt bleed down at all, as soon as i move my thumb they slide down without any issues.

I had KN filters on them, but it didnt want to fire, so I took some red shop rags and folded them in 4ths and clamped them over the intake to try to lower the lean condition I was suspecting was occuring. It then would fire and run smooth, throttle response was decent to good, until you get rpms over 2500.

As long as you keep the rpms under 2500 they will return to idle. If I let them get to 2500, they start to rise uncontrollably until they get to 4000 then hold steady.

THE ONLY WAY TO GET THE RPMS TO RETURN IS TO BLIP THE CHOKE.

Sorry for the long response.

 

[xschris]

If you didn't completely tare them down, there are seals at the ends of the butterfly valves and shafts, the dip would have destroyed them The only way to get them clean is to take every bit apart and clean it and then put compressed air to all the little holes. A proper air filter would be needed to get it to run right.

 

[coal miner]

If you didn't completely tare them down, there are seals at the ends of the butterfly valves and shafts, the dip would have destroyed them The only way to get them clean is to take every bit apart and clean it and then put compressed air to all the little holes. A proper air filter would be needed to get it to run right.

Thanks for the info chris, I did find the butterfly shaft seals, but i didnt pull the brass tube out to find the oring on it. I tried several times to get the jets all out but every one of them was stuck and the heads were trying to strip. At that point I stopped because I wasnt sure of the parts availability for the 360s. From what I have seen, there is a better availability for 400 parts.

Another option I have to work with, is a set of bs34s. I just dont have a set of diaphrams for them. I have read that the carbs on the 360 will give it better bottom end, but from an availability standpoint I am wondering if I would have more success with the 34s.

I say this because I have spent countless hours online just trying to figure out what carbs are on the 360s. All of the repair manuals say they are bs34s, which they clearly are not. Some say they are bs38s which they definitely look like, and the gaskets fit. But some say the look like the 38s but have a 32mm? slides. I have hours of research, and still havent nailed that down.

Just thought from a parts availability standpoint 34s would be easier to find parts for. And i could get a set of the new aircraft rubber diaphragms pretty easily.

Thoughts?

-kc

 

[xschris]

The 360 uses an older style bs34. But a lot of the parts are the same as the bs38 The slides are not like any other bs34 and 38. The only other carb I have found that has the same parts is the 77xs750. ebay has some stuff for them but not a lot. You could also try a local yamaha dealer. Sometimes they will have n.o.s. parts left from years back.

 

[coal miner]

This is the other set I have.

 

[coal miner]

This is what the original set looked like. I wonder if I could get the bike to run on the bs34s.

Sorry about the multi posting. Couldn't get both pics to upload at the same time.

 

[xschris]

They are both bs34's. The first one looks like the 77-79 xs400 bs34's and the last is your stock 76-77 xs360 bs34's.