As I quickly found out when I purchased my 1980 Yamaha XS850SG, the petcocks on these old bikes have quite a few issues. It seems that they all leak and end up flooding the carbs, cascading fuel into the pistons. That fuel works its way into the engine oil where it spells trouble for the engine. My bike was no exception. And as luck would have it, replacement petcocks are on extended backorder at every place I found that carries the part.
With this parts shortage in mind, not wanting to screw with a rebuild kit, and wanting to ride the XS850 without risk to the engine, I decided to cut out the source of the leak and refashion the petcocks into fuel taps. Yes my friends, I decided to hack apart the existing petcocks and install some brass ball valves instead.
Step 1: Remove petcocks and find hacksaw.
Step 2: Hack off the part of the petcock that hangs out of the fuel tank.
Step 3: Acquire brass barb fittings and put them into the hacked off petcocks. JBWeld them in place.
Step 6: Get some gasket maker that is rated for fuel (NAPA had it) and apply as per instructions.
The gasket goop I used is supposed to go on both mating surfaces.
Step 7: mount the hacked-apart, JBWelded petcocks on the tank and attach your desired fittings. I found the brass fittings at a local, family-run hardware store.
Step 8: Leak check the assembly overnight. No leaks!
Look at those beautiful new ball valves! The whole project cost me about $35. That’s the same cost as one new petcock or just a little more than a rebuilt kit. I think I go the better deal.
Note that doing this, you will need to put in in-line fuel filters. I picked up a couple inexpensive filters from a local autoparts store that are working great. As soon as the air filter comes for the bike, I will be out on the highway.
how about the other tits on the petcock which suppose to suck a little petrol to fire her up, wazzup up wid dat??
Hi Ashley,
Sorry it took me so long to respond.
I believe you are referring to the “prime” position on the factory petcocks? That position is no longer needed with my modified XS850 petcocks. Before, the petcocks when set to the “prime” position would suck gas from the very bottom of the tank. This is useful when you run low on fuel or when priming the carbs after having drained the fuel system. The modification that I performed leaves the petcocks in a permanent “prime” state meaning that they are drawing fuel from the very bottom of the tank. This also bypasses the original internal fuel filters. That is why I had to add in-line fuel filters further downstream. I also capped off the vacuum ports on the carb bodies as my petcock modifications no longer rely upon vacuum to open and operate the petcocks. The downside to this is that you have to remember to turn off the manual in-line valves (and turn them on). Otherwise, the fuel can overflow the float bowls in the carbs, end up pooling in the cylinders, and work its way into the oil where it will do lots of damage to your engine.
Does that answer your question?
Cheers!
Douglas
I rebuilt one of my petcocks about a month ago and its leaking again.Trying your solution today so far its going pretty well,only difference I just put a shutoff on the fuel line itself,thinking I’m doing the same with the other.I am having truble starting the bike after it gets hot,wondering if it was getting gas into the cylinders after I shut it off hot would it vapor lock,would you have any ideas?
I redid the spark plug wires,gas cap gasket,now this pecock thing,I want to do all the cheap stuff before I decide to pay 150.00 per coil.
Will appreciate any input.
I don’t think putting a shutoff valve inline would cause vapor lock if you shut it off when the engine is hot. Mine have been in place for about a year and are still working just fine. Mine were bad enough that they were leaking gas from the petcock housing. There was no way around having to replace the whole unit because the screws holding the petcocks together were all mangled and the petcock body threads were even worse.
Cheers!
Douglas
Outstanding! I have hacksaw, gasket goop, JB Weld, and the desire to cure the automatic petcock issues. Thanks for sharing your successful modification!
Good luck! It is sure a bunch cheaper than buying replacement petcocks.
Cheers!
Douglas
Just got my 1980 LG home. All fine. Turned petcock to prime?? Next day middle carb was leaking fuel. Why dont they hace an off position on these damned things?
It has been a while since I had my XS850 but as I recall, there was an off position on mine. My XS1100 is now having the fuel leak problem even after I rebuilt the petcocks. My solution for winter storage was to drain the fuel out of the tank. I’ll deal with any rust spots next spring.
Cheers!
Douglas
Gas problem on my 850 seems to be leaking into the air cleaner box, not out of the petcocks yet…would that be related to petcocks also ?
Why give rust a chance to take hold in the tank ? Isn’t that just creating more problems to deal with re clogged carb jets & filters assuming filters are stopping everything ?
That might be a stuck or sticky float valve in your carbs. My XS1100 has a very similar problem right now that I haven’t been able to fix. I moved to Colorado and had to leave the XS1100 in a garage in Oregon right when the problem started. I couldn’t leave that bike leaking gas into a garage when I am 1500 miles away. Hopefully next summer when I’m back in Oregon, the tank won’t be too bad and I’ll be able to fix the leak. My intent is to ride the XS1100 back to Colorado.