1978 Yamaha XS400 full tune up

[arm]

Well, you do want the petcock to be able to shut off. My original vacuum petcock also went bad, but to be expected for 40+ year old seals. I tried a rebuild kit on it but it didn't work as there was some pitting in the metal inside thus I changed to a full manual petcock with off/on/reserve switching.
You also need the floats to be able to close off fuel entering the carbs or you could be running rich at the lower rpms and idle as fuel overfills the bowls. I bought new needles and seats and very carefully set the float levels to 26mm measured from the bowl gasket surface to the top most part of the float while holding the carbs upside down. You gently bend the needle tang on the float to adjust height. I also made sure each side of the float was 26mm by twisting them gently. I know it sucks to pull them back off, but dumping that much fuel is no good for the engine as it can wash the oil from the cylinders leading to excess ring wear or make it's way into the oil via the crankcase vent tube in the air filter boot, diluting the oil and then causing main and rod bearing wear.

Yeah i think id opt for the manual petcock just for the peace of mind that I actually shut it off

I watched a few videos on how to set float levels so I have an idea of what you mean by holding them upside down and adjusting the tang.

Do you have a link to where I can get these parts? I'm assuming you have the same BS34 carbs so it should be the same parts

 

[CaptChrome]

Any links to what manual petcock will fit on my bike? Is it a hard swap?

Here is one that should fit https://www.amazon.com/Carbman-Petc...6Y0B2&ref_=ast_sto_dp&tag=namespacebran129-20
Just check the distance between the mounting holes on your old one and make sure that they match the dimensions in the listing (the mounting hole spacing was make larger at some point in the manufacturing run of these bikes, I think 1978 was the first year of the wider spacing). Swapping it is a matter of loosening two JIS screws.

what happens to the vacuum line on my bike then? Do I just leave the vacuum line hanging

Remove the old vacuum hose and put a rubber cap over the nipple on the carb holder that the hose was attached to. If you don't cap the vacuum nipple, you will cause a lean mixture to the engine.

 

[arm]

Hey guys, so i been loking around for parts for the BS34 carb and since I'm in Canada a lot of sites charge around $80 - $100 for a few parts on the carb due to shipping and USD to CAD conversion.
I did find this though (Amazon link). I looked at the mentioned bikes and some have BS32 carbs but what I'm seeing is that the 1982 Yamaha XS400S Heritage has BS34 carbs which is the same as mine

The reviews are pretty solid, and this way, I could replace a good chunk of the carb's internals. What do you all think? Is it good to order?

 

[CaptChrome]

What do you all think? Is it good to order?

It is cheap. But, I would only use the gaskets, o-rings and the float needle/seat for putting the carbs back together and clean and reuse the original pilot, main and needle jets and the original jet needle. I especially don't trust the shape of that jet needle.

 

[arm]

It is cheap. But, I would only use the gaskets, o-rings and the float needle/seat for putting the carbs back together and clean and reuse the original pilot, main and needle jets and the original jet needle. I especially don't trust the shape of that jet needle.

yeah on second look it does look a bit off.

thanks so much for the response guys, really appreciate it, couldn't have gotten this far without the forum

I looked into some trusted sellers and found these options

Option 1:
carb kit
Floats (not sure if its needed though)
Reflector (bikes missing one )

Total: 86 USD (116 CAD)

Option 2:

Total: 103 USD (140 CAD)

Let me know what you guys think, i dont mind picking up new pilot jets considering one of mine is stuck in there but i think somone mentioned earlier that its fine to leave as is

 

[avemachina]

I'd go option 1. Any parts that aren't the same, just don't use. I'd get the new floats too--they sometimes develop pinholes, and that can cause flooding.

Something you can do as well if your jet needle seems to have stuck-on gunk and carb cleaner isn't doing the trick, is using a cleaner/polish like Brasso. I've found it's a great addition to elbow grease Just make sure you rinse thoroughly with soap and water after you use it.

 

[arm]

I'd go option 1. Any parts that aren't the same, just don't use. I'd get the new floats too--they sometimes develop pinholes, and that can cause flooding.

Something you can do as well if your jet needle seems to have stuck-on gunk and carb cleaner isn't doing the trick, is using a cleaner/polish like Brasso. I've found it's a great addition to elbow grease Just make sure you rinse thoroughly with soap and water after you use it.

Awesome will do!

anything else i should be worried about and adjusting in the carbs?

Like @tstidham mentioned the carbs should be able to form a seal and not overflow with gas so I reallyyyy wanna make sure that I get it right this time.

also I think you (@avemachina) mentioned that I should drill out that jet at some point, it looks like this carb kit comes with those jets so do you have any tips on extracting that jet without damaging the rest of the carb?

 

[avemachina]

I do! Pop over to the auto parts store and get yourself a screw extractor set. I got mine at NAPA, but I think they've got these at Princess Auto or Canadian Tire or whatever y'all have up there They look like this:

Sometimes the ends are spiralled, sometimes they're square, sometimes they're kind of a star shape. What you should be looking for is to confirm that you have one that's M3 or 7/64"-sized.

If you've never used these, here's how. The theory behind it is, you widen the stuck jet juuust enough for the extractor bit to get hammered in and create a "new" grab point in the softer brass. The extractor bit is left-handed, so as you twist in the "out" direction, the bit will go deeper into the stuck jet, and the jet itself will come out.

1) Drop a little bit of penetrating oil around the edges of the stuck jet.*
2) Use the little drill included with the kit, or whatever drill bit size is recommended for the extractor bit you'll be using (the packaging usually tells you), drill into the hole to widen it to the correct amount before using the extractor bit. Don't drill too deep! You only need to go maybe 25mm at most.
3) Take the corresponding extractor bit, position it vertically in the newly-widened hole, and hammer it into the stuck jet. It's in the right amount when it can stand up on its own inside the jet.
4) Grab an adjustable wrench or power drill or whatever you've got. Grasp the end of the extractor bit, apply some downward pressure, and start twisting counterclockwise to begin removing the jet. If the bit falls out, hammer it back in. If it's too loose, go up an extractor size. You've already destroyed the jet, so get the whole thing out!
5) When you've got the jet out, clean up the area you removed it from.

That's it!
*Optional, but recommended.

 

[arm]

I do! Pop over to the auto parts store and get yourself a screw extractor set. I got mine at NAPA, but I think they've got these at Princess Auto or Canadian Tire or whatever y'all have up there They look like this:
View attachment 38721

Sometimes the ends are spiralled, sometimes they're square, sometimes they're kind of a star shape. What you should be looking for is to confirm that you have one that's M3 or 7/64"-sized.

If you've never used these, here's how. The theory behind it is, you widen the stuck jet juuust enough for the extractor bit to get hammered in and create a "new" grab point in the softer brass. The extractor bit is left-handed, so as you twist in the "out" direction, the bit will go deeper into the stuck jet, and the jet itself will come out.

1) Drop a little bit of penetrating oil around the edges of the stuck jet.*
2) Use the little drill included with the kit, or whatever drill bit size is recommended for the extractor bit you'll be using (the packaging usually tells you), drill into the hole to widen it to the correct amount before using the extractor bit. Don't drill too deep! You only need to go maybe 25mm at most.
3) Take the corresponding extractor bit, position it vertically in the newly-widened hole, and hammer it into the stuck jet. It's in the right amount when it can stand up on its own inside the jet.
4) Grab an adjustable wrench or power drill or whatever you've got. Grasp the end of the extractor bit, apply some downward pressure, and start twisting counterclockwise to begin removing the jet. If the bit falls out, hammer it back in. If it's too loose, go up an extractor size. You've already destroyed the jet, so get the whole thing out!
5) When you've got the jet out, clean up the area you removed it from.

That's it!
*Optional, but recommended.

I got it running! For the stripped pilot jet, I read up on the forum and saw someone mention banging a T7 screwdriver into the jet and unscrewing it. It worked beautifully! There was no need for a drill or anything.

The bike feels a lot better and there are no overflowing carb bowls with gas leaking out the other end, I think this is cause I adjusted the new floats to be 26mm. I think I'm good to not change out the petcock for now?

One thing I wanted to ask was idle RPM, I read that it's supposed to be 1200RPM and when I have my choke fully out it sits around there but with the choke fully in the bike idles just under 1000RPM (maybe 700-500RPM) for a bit then cuts out, should I adjust the idler? if so which way should I twist it, left or right? Any easy way to access this big screw? I can see it but I cant get my hand to it and I reallyyyy don't want to pull out the carbs again

Another thing is that sometimes the bike exhaust will pop when I'm ripping on it a bit, is this left over gas in the exhaust?

I also noticed that getting the bike to start from cold is a big task, often it requires a bunch of kicking along with an electric start but it mainly starts by kicking it when its cold. The electric start motor spins but I noticed more noises of it clanking if that makes sense?

Sorry for the plethora of questions, I'm super curious as to how I can make this bike hum like the day it rolled out the factory

 

[avemachina]

Hey, great job getting it running!

You might not need to rebuild the petcock if the fuel isn't leaking anymore; the leak was probably due to the floats, which you fixed.

The idle speed is adjusted with the big screw that's in the middle of the two carbs. You won't need to remove the carbs to get to it, just move the kickstart lever out of the way and reach in, or use some pliers if you can't fit your hand down there. Twist it counterclockwise to raise idle speed, clockwise to lower (when viewed from the top of the bike, as if you're sitting on it)

The pops usually indicate a lean condition in the carbs. You remember the idle adjustment screws on each carb body? Those turn inward to make the mix richer, and outward to make it leaner. 2.5 turns out is a good starting point. Here's a useful description on how to adjust these from HoughMade. Try to keep your idle speed around 1000 for this part, so it stays on its idle circuit. I have an 81, so I can't speak to specific carb details, but I found that writeup super helpful. Having a lean mix will make it harder to start, too. The choke pulled out will mask a lean condition by enriching the mix, but once you push it in, you're back in lean mode until you adjust your idle screws.

Another thing to verify is that your battery is charged up--12.1V minimum, I've found. Mine won't electric-start below that voltage for some reason.

 

[arm]

Hey, great job getting it running!

You might not need to rebuild the petcock if the fuel isn't leaking anymore; the leak was probably due to the floats, which you fixed.

The idle speed is adjusted with the big screw that's in the middle of the two carbs. You won't need to remove the carbs to get to it, just move the kickstart lever out of the way and reach in, or use some pliers if you can't fit your hand down there. Twist it counterclockwise to raise idle speed, clockwise to lower (when viewed from the top of the bike, as if you're sitting on it)

The pops usually indicate a lean condition in the carbs. You remember the idle adjustment screws on each carb body? Those turn inward to make the mix richer, and outward to make it leaner. 2.5 turns out is a good starting point. Here's a useful description on how to adjust these from HoughMade. Try to keep your idle speed around 1000 for this part, so it stays on its idle circuit. I have an 81, so I can't speak to specific carb details, but I found that writeup super helpful. Having a lean mix will make it harder to start, too. The choke pulled out will mask a lean condition by enriching the mix, but once you push it in, you're back in lean mode until you adjust your idle screws.

Another thing to verify is that your battery is charged up--12.1V minimum, I've found. Mine won't electric-start below that voltage for some reason.

Thank you! Amazingly explained! i tried reading up on it but kept confusing things, will definitely give this a try when I get around to it. I also saw a video about tunning carbs and how lean conditions can affect the powerband when taking off from 0 which is something I noticed on my bike. I really need to get it up to 3-4k RPM and veryyyy slowly let off the clutch to get a smooth take off otherwise it'll be to slow taking off and the RPM cuts below 1k RPM and welp, it shuts off mid takeoff.

after I get these adjusted, its time to my bike look peeerrtyyy, thanks again!

 

[arm]

Hey, great job getting it running!

You might not need to rebuild the petcock if the fuel isn't leaking anymore; the leak was probably due to the floats, which you fixed.

The idle speed is adjusted with the big screw that's in the middle of the two carbs. You won't need to remove the carbs to get to it, just move the kickstart lever out of the way and reach in, or use some pliers if you can't fit your hand down there. Twist it counterclockwise to raise idle speed, clockwise to lower (when viewed from the top of the bike, as if you're sitting on it)

The pops usually indicate a lean condition in the carbs. You remember the idle adjustment screws on each carb body? Those turn inward to make the mix richer, and outward to make it leaner. 2.5 turns out is a good starting point. Here's a useful description on how to adjust these from HoughMade. Try to keep your idle speed around 1000 for this part, so it stays on its idle circuit. I have an 81, so I can't speak to specific carb details, but I found that writeup super helpful. Having a lean mix will make it harder to start, too. The choke pulled out will mask a lean condition by enriching the mix, but once you push it in, you're back in lean mode until you adjust your idle screws.

Another thing to verify is that your battery is charged up--12.1V minimum, I've found. Mine won't electric-start below that voltage for some reason.

I think this bike is the gift that keeps giving, one of the two ehaust pipes is cold when I ran the bike today
here's a quick video of the bike as it stands

any help would be appreciated!

 

[arm]

New discovery! I pulled the spark plug from the left cylinder of the bike and put it against the engine and no spark, I bought some new plugs and tested it again on the left side of the bike and still no spark. I then tested the new spark on the right side of the bike and sure enough there's spark. So it seems that the spark plugs arent the issue, but what could it be?

I don't really know what goes on past the spark plug so excuse my lack of knowledge, but I know that their is a coil pack and then the cables themselves. I pulled the tank and noticed that the spark plug cable lead into two very different things. The right side (the working plug) leads into a small black piece that connects with this circular connecter. On the left its this bigger sized piece that's skin colour and has no circular connector, instead the cable goes directly into it. Could It be that the previous owner upgraded the right coil and left the left one? any idea of what these two things are?

I

 

[RadlagerMike]

as you wrote, right side has been exchanged in the with something not original

 

[arm]

as you wrote, right side has been exchanged in the with something not original

Ah i see, what is that part called and would you happen to know where I can pickup a new one for the left side since that seems to be the culprit

 

[RadlagerMike]

if it fits the holding screws you can use anything which has between 4 and 5 Ohm

mostly the part where the spark cable is taking to inside, there the spark cable inside is brocken, so only the cable not the complet peace is damaged

you can feel it from outside the spark cable, it feels like the is nothing inside

 

[tstidham]

Those are your coils and the tan one is original, so it's possible it could have gone bad. A quick test you can do to insure the rest of your ignition controls are working correctly is swap the small wires on them and make sure the right coil, now driven by the left control wires is throwing a spark. If so, just replace the left coil. Then remember to swap the control wires back.

 

[cso200]

this is lovely man.

 

[arm]

Those are your coils and the tan one is original, so it's possible it could have gone bad. A quick test you can do to insure the rest of your ignition controls are working correctly is swap the small wires on them and make sure the right coil, now driven by the left control wires is throwing a spark. If so, just replace the left coil. Then remember to swap the control wires back.

The new coil came in but i think there is a bigger issue at hand

So here's how the bike was originally

Highlighted in blue is the old coil pack and it had a orange and red cable, the orange cable connected to another orange cable that is wrapped up in the wiring harness and the red cable from the coil pack feeds into a 2 to 1 splitter that also takes input from the coil pack on the right.

On the left I added the new coil pack (link to where I bought it from). So I wired the yellow cables into the 2 to 1 adapter and connected the black cable to the orange cable. Pretty much just swapped the old coil pack for the new one. But when I tested for spark, no luck. After hooking up the left coil pack to the right coil pack wires (I put the black cable from the left coil pack into the grey wire from the right coil pack). It sparked! when I connected the orange cable to the black cable from the right coil pack, the right plug wouldn't spark. As you can see in the picture above.

what I've narrowed it down to is that the orange cable is the culprit as that's the only thing that causes either coil pack to not spark the plug

The previous owner of the bike has done some work to it so I'm not sure if all the wiring is where it was from the factory, I also found this small 2-prong connector that you can see at the bottom of my picture, no idea what that does.

But yeah I'm really confused as to why that orange cable isn't allowing the coil packs to spark the plugs and I cant figure out if I'm wiring something wrong or what. any ideas?

 

[tstidham]

Then the problem is in either your tci box or the pickup coil on the end of the camshaft. By switching the wires, you proved your original coil was still good and probably didn't need to be replaced.