New to XS member, project bike excited to wrench

I looked deep into my EBay purchase history and dug this up..

https://www.ebay.com/itm/Yamaha-Pet...h=item2f053b2664:g:lKQAAOSwYxBZ7elR:rk:1:pf:0

Thats the petcock I use. It eliminates the need for a vacuum line. Now you can just cap off the bungs on the intake boots, which need to have a good seal. You must use an inline filter too.

The drain screws are on the bottom of the fuel bowls at the carbs, pretty sure they are 8 or 10mm.

The neutral light will be illuminated any time the key is on and the bike is in neutral. The oil light should be illuminated as well until oil pressure is detected after a kick or two. The bike will start regardless of the oil light. Theres a neutral safety switch that prevents the bike from being started while in gear.
 
Forgive my ignorance, but where is this filtered air hose running to? It comes off the air intake h pipe going towards the crankcase?

Didn't see it in the parts catalogue or find anything specific on it in manual...
IMG_20190305_164038__01.jpg
 
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thought I had figured out the vacuum pet cock as it seems to only be flowing freely upon crank. Came into the garage today and found it puddle of gas. Seems to be coming through the right air filter. Yuck
 
I agree that you should keep it too, as long as you keep the factory setup. I capped off the H-pipe for and ran a breather filter off of the crankcase vent for a while. No performance came of it, but every time Id come to a stop, all I could smell was oil and fumes and I hated it.

I had a thought a while back, that the oil mist being pushed back into the intake tract may be beneficial for an old engine that was designed when leaded gas was the norm... This is purely my own speculation though. I do know that Japan started using hardened valve seats early.

That much gas inside your engine isnt good. It will soak down in to the crankcase. Dump the vacuum petcock. If the gas was coming out of your filters, that means that it was still flowing by the float valves in the carbs. So now you gotta rebuild the carbs lol

Always go for the maintenance and engine first. Thats what Ive learned and it keeps me from wasting money. Get the engine running first, and then worry about brakes lol. My situation was a bit different, since I bought my bike with a seized engine and was headed for the dumpster. I rebuilt the engine and the rest of it from the frame up.
 
Carbs have been removed and will be operated on in coming days. Particles definitely already visible from dumping bowls. Did hear a couple signs of life as I cranked with some starter fluid. Second time I did it was a loud backfire, presumably not surprising since I did with carbs removed and dash of starter fluid straight in. Was relieving to hear it fire tho!

And i have a working electronic start! New button with in tact plastic flange arrived today :)
 
Thanks Mike . Won't I be able to potentially reuse the parts on it after clean? I could see gaskets being good idea, possibly float needle. But if they're in decent shape I didn't think I'd be replacing.

I didn't even see the diaphragm as part of the kits, would've thought the likely wear parts are gasket, float needle and seat, and rubber y diaphragm...
 
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buztabuzt said:
thought I had figured out the vacuum pet cock as it seems to only be flowing freely upon crank. Came into the garage today and found it puddle of gas. Seems to be coming through the right air filter. Yuck
Click to expand...
If you pull the petcock off and measure it's width you can definitely find one that's non-vacuum online. I did that with mine and couldn't be happier. I'm trying to remember where I got it from, I wanna say I bought the xs650 petcock from mikesxs after having to return one that didn't fit from ebay, but I don't wanna say for sure and I think the site is sold out right now. I would definitely recommend not putting any gas in the tank and through the system until you get that sorted. I ended up with gas everywhere you don't want it (inside the oil etc.) because it was leaking so much. If I can say for sure where I found mine I'll add that in. Seems like you're doing some good work!
 
Thanks for all the continued input A-Team! I found the petcock for $13 shipped on fleabay (UPDATE - DIDN'T FIT!). So cheap it must be used as a smuggling device:shrug:

Separately:
xschris said:
I would clean everything and ride the bike for a while. Then you can see where all the leaks are.

For what you will need to take apart to get to the tach seal it's a good time to replace the cam seal also.
Click to expand...

I thought the cam seal was much more involved than tach seal: tach is outside access removing one screw on top of engine. Cam seal looks inside the block?
CamSeal.JPG OilSeal.JPG
 
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Needles, pilot jet plugs, o-ring for float valve, bowl gaskets and o-ring for pilot mix screws. 80-82 sohc xs400 carbs. The 80-84 xs650 carbs use the same. Butterfly shaft seals are good to do but not easy to replace. If you need jets use mikuni jets only. They are made far better than aftermarket ones. They will have a square within a square marked on them. Those are oem.
 
Hello everyone, new to the forum, just purchased a 1982 XS400 Seca. I'm also looking to replace/rebuild my petcock, although it appears to function fine on prime and on position, I would rather have a fresh one mainly because the PO described it as leaky previously. Unfortunately, I bought the petcock that xschris posted, but it doesn't fit the Seca as the switch would impact the tank in the on position, and looks completely different to boot. Does anyone know of a good source for a complete petcock for an 82 seca or should I just buy a rebuild kit for it? I could just dremel off part of the handle of the non-fitting petcock I already have and make it fit....what do you guys think?
 
pcream said:
Does anyone know of a good source for a complete petcock for an 82 seca or should I just buy a rebuild kit for it?
Click to expand...

I would buy a new one or try to remedy your old one. I find the rebuild kit to cost 75% of a new petcock with the chance it might not fix it, so why not just buy new. I thought this video was helpful for easy fix / trying to kick the can down the road, but mine is beyond repair and I probably wasn't gentle enough anyway

If buying, Confirm your bike exact model, then go to Bike bandit and partzilla to get part numbers for your specific model and part. Then google the part #. Then buy :thumbsup:
 
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buztabuzt said:
Thanks Mike . Won't I be able to potentially reuse the parts on it after clean? I could see gaskets being good idea, possibly float needle. But if they're in decent shape I didn't think I'd be replacing.
I didn't even see the diaphragm as part of the kits, would've thought the likely wear parts are gasket, float needle and seat, and rubber y diaphragm...
Click to expand...

The brass inside the carb also wears down and becomes out of round, especially float needles and needle jets. If you can see a ring on the float needle, it needs to be replaced. Getting the right needle jet is probably impossible, but that part is made of aluminum. The emulsion tube is brass. Those should be matched together. Id only be worried about the float needle for now. Might as well check the floats for leaks too.

Be gentle with the diaphragms, that part can be expensive if they get ruined or are already no good.

Ideally, youd want to completely gut the carbs and soak the bodies. I use an ultrasonic cleaner. Cleaning the carbs is very very important. Dont soak any rubber either.
 
Posted in a new carb thread, but found some major year model differences.

In mine ( 400G 1980) it is needle, plastic ring, washer, spring, screw plate (as pictured). Stumped me at first today because Will's video has needle, spring, washer, plastic ring, c clip. Almost opposite!
IMG_20190310_172212.jpg
 
77-79 sohc xs400 and 80-82 carbs are not the same. Order parts for those years.
 

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