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I have a 1980 xs400 special-II, it's in great condition. I bought it in the spring and it's my first bike. I've had some stalling/bogging down problems over the summer. For example wide open freeway and starts to bog down, or just got off freeway and idleing problems.

Classic vacuum tank symtoms, right? Unfortunatly it does this with the tank lid open (don't ask) and no vacuum sound when you open the lid.

I know it's not a carb problem because I can resolve the issue by flipping the petcock to prime. When I did this, I noticed the fuel line filled up with gas. It was almost empty previous to this, which tells my my carb bowls were running out.

The next suspect is a weak or no vacuum for the vacuum operated petcock. Unfortuantly the vacuum is quite strong.

Which leads me to my next symptom, when I went to drain the carb bowls for winter, the gas didn't stop flowing. I double checked that the petcock wasn't in prime, and there was no vacuum to make the petcock open, but it kept comming.

And finally when I removed the tank to try and get the petcock off, I hear what sounds like a tiny ball bearing rolling around inside my tank. Which I can't simply pour our because of a lip at the top of the tank.

Sorry for the long post but I figured better tell you everything I can think of from the start.
Now for the questions:
1. Will a petcock rebuild kit do anything for me?
2. How do you get a 27 year old petcock off a bike that has striped philips screws?(thanks previous owner)
3. Where did the ball bearing come from?
4. Is this the reason PO sold the bike?

its probably the in tank fuel filter partially blocked. does it do the same with a full tank of fuel?
PJ

the amount of fuel doesn't seem to matter.
I hope it's something simple like a dirty filter.
Now to go see what I can do to get that petcock off.

Thanks for the idea, keep em comming

edit:
I got the petcock assembally off the tank. By the looks of everything the problem is from a bad seal inside the petcock causing the petcock not to open. Now to sit and wait for parts, yey.

. Got my Bike Feb3.
A1999 500GS with 8200 miles, the dealer said they did the carbs rebuild, and Tank Kit,new plugs,Break lines & back pads. Mine will not Run over 5500-6000RPM.. Then it Bogs down, thats in any gear?? It runs great up to 5500RPM! After that it's Bogs?? The fuel is full or not no change..
Help anyone?
p51]

P51mustang wrote: . Got my Bike Feb3.
A1999 500GS with 8200 miles, the dealer said they did the carbs rebuild, and Tank Kit,new plugs,Break lines & back pads. Mine will not Run over 5500-6000RPM.. Then it Bogs down, thats in any gear?? It runs great up to 5500RPM! After that it's Bogs?? The fuel is full or not no change..
Help anyone?
p51]

You should start your own topic, you will get more/better help


Back ON TOPIC. techyguru, MikesXS.com carries a standard petcock that should work on your bike. You can eliminate the vaccum part and have a more reliable petcock with the typical on/off/res settings. If I remember right, its not expensive.

I guess I should do an update. I installed the new seal and put the petcock back on the bike. The bike started up and ran well but due to snow and ice everywhere on the roads I will be unable to test it on the highways for a few months.

Yeah- I bet your diaphragm went bad. Hopefully the rebuild kit fixes it!