yup, turns out i attached the bracket that goes ontop of the carb backwards so the sheath was facing the air filters rather than the engine, no biggie, just swapped it around. New development, the bike wont start, here's a video of what I'm seeing. sounds ok, battery is ok, starter is ok, not sure where the issue lies
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1978 Yamaha XS400 full tune up
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Turn the petcock to pri for prime. This bypasses the vacuum valve to fill the carbs. Also I'll say check the kill switch is on. On my third rebuild of my carbs, being a little flustered and tired I was also getting a no start. Thankfully my neighbor walked over after hearing me struggle for about 20 minutes. We chit chatted about the bike not starting suddenly and he goes, "oh, try it now" and flicked the kill switch on. Fired right up! DOH!
I tried it on prime and no luck, the starters sounding weak because of how much I've been using the battery so I got it on charge at the moment
Haha the kill switch is definitely on, on my bike and i did double check this morning
maybe im not understanding the choke, when its pulled all the way out that means the choke is open right?
so when I start the bike I should have
kill switch on
fuel on
choke pulled outwards
then warm up the bike the push in the choke?
avemachina
XSasperated but XScited!
Yes, but you don't necessarily need to pull the choke out all the way--if it's warm where you are, you might only need it half-way, or pushed all the way in.
It's about 26 degrees Celsius here so not to warm at the moment, I'm trying a combination of pulling the choke all the way out which if I'm not mistaken, closes the air intake and makes a more richer fuel mixture.
Also do I leave the petcock on prime or do I set it to prime momentarily?
I came back home to a fully charged battery and still no luck. Maybe the idle screw or the air/fuel mixture screw ontop of each carb Is wrong? Can fiddling with those fix my issue?
new development, so i pulled off the air intakes since I felt gas on the frame and in the left rubber boot that connect the carb and the left air intake there was a small puddle of gass, but none in the right one. I inspect the right side and find that I'm really dumb and haven't reattached the right spark plugs cable. I don't know when I took it off but I guess I did, I cleaned up as much of the gas as I could and reattached the cable but still no luck, maybe the engines flooded? no idea how go about that
got it running! just needed to kick it a few times and then it started. The bike does feel better, more throttle response, I might even say it sounds better, taking off from first is a lot smoother but the bike still seems a bit underpowered? when I started it up I got a decent bit of white smoke which eventually went away. 0-60km/h is very slow, I really Gotta push the bike to keep up with cars on the road, I remember driving 125cc bikes in Asia that were still a bit more snappy then this. any suggestions?
avemachina
XSasperated but XScited!
Great work getting it back together and running! If you keep seeing fuel dump out of one of your air filters, that's a symptom of stuck floats in one of your carbs.
As far as performance... it is a pretty old machine. The common wisdom around here is that the engines really don't come alive until you're at 3000-4000 RPM.
If the acceleration bothers you too much, you can start experimenting with different sprocket sizes. A lot of folks change up their gearing (you might not have the stock sprockets to begin with). Tons of threads here with tips on which way to go, but here's a good place to start from XSChris:
The search function is your friend here, because there's plenty of examples of gearing setups and what experiences people had with them. I can't speak with any authority about that since I kept my stock gearing, but that's an avenue you can explore now that your carbs are in order.
As far as performance... it is a pretty old machine. The common wisdom around here is that the engines really don't come alive until you're at 3000-4000 RPM.
If the acceleration bothers you too much, you can start experimenting with different sprocket sizes. A lot of folks change up their gearing (you might not have the stock sprockets to begin with). Tons of threads here with tips on which way to go, but here's a good place to start from XSChris:
The search function is your friend here, because there's plenty of examples of gearing setups and what experiences people had with them. I can't speak with any authority about that since I kept my stock gearing, but that's an avenue you can explore now that your carbs are in order.
Wow thanks for the tip I didn't think about messing with that. And yes I'll keep a eye on the boots to make sure no liquids are wandering around.
I also saw some mentions on reddit that this *could* be the clutch slipping? I think I'm gonna give it a cable adjustment from the posted manuals
The fuel leak could also be from bad needle and seats in the carbs. I had this issue as well, especially when on the side stand with fuel leaking out the left side carburetor. Also make sure your float heights are correct, i set mine to 26mm as detailed in several posts, others prefer the clear fuel line method to visually see the assembled carb fuel level. That white smoke was probably flooded fuel that made it into the exhaust unburnt.
yep so this happened
Drove the bike around last night, came home parked it in the garage and smelt a ton of fumes, and found this under my bike
So there was gas leaking from the boot connecting the left air filter and the carb, and gas was also dripping out of the exhaust. It's not a ton of gas, but I did refill the tank last night, and it's still full, so that's at least good.
looking into the left boot there was a decent bit of gas puddled up, a bit in the right boot to but not to much, whats weird is that the bike was on its center stand so it wasn't leaning in any particular direction. Im kinda scratching my head as to what it could be since its only the carbs I touched. Maybe the fuel/air mixture screw on each carb is allowing more gas in then it should? the bike ran fine so there isn't anything catastrophically wrong but these leaks are certainly a big issue.
Any suggestions?
Float levels or needles and seats are leaking. Check your oil level too, if it increased, then the fuel also leaked into the crankcase either via the rings or the crankcase breather tube in the intake boot.
I saw some ppl mention that a float could be stuck and tapping on the carb could help.
I rlly don't wanna pull everything apart atm
and if I do I'm making sure my floats are level and needles are functional?I think i found the cause, i went to go pull of the carbs and found more fuel in the boots, confused as to why there's more gas in the boots considering I haven't started or rode the bike since last night. So I go to pull of the tank cause it makes it easier to work on the bike, and the petcock is just dumping fuel everywhere. it didn't help that I topped up the bike last night so I frantically bottled an ENTIRE tank of gas.
Sitting there I thought that this is most likely the cause? fuel keeps flowing into the carbs, overfilling the bowls and leaking into the boots.
So I think I won't have to pull the carbs, but now I don't know how to fix the petcock since the lever for RES, ON, and PRI (prime) didn't help. i did have the vacuum line connected so I'm confused as to how or why petcock is doing this
Unfortunately no. The floats and seats should hold enough of a seal to not flood even with the petcock open. I ditched my vacuum petcock for manual one and have left it on a few times after a ride and no fuel has leaked out the carbs.
Oh wow, what do you suggest? Replace the petcock with a manual one or go ahead and look at the floats?
The needles seemed fine to me when I pulled apart the carb the first time and I was able to easily pull of the tank with minimal gas leaking the first time around
Probably need to either rebuild the vacuum operated petcock or replace it with a manual petcock AND replace the float bowl valves and seats in both carbs as they seem to be leaking. Not addressing this has the potential to really F-up your engine, eventually, due to washing out oil to the bearings.
Any links to what manual petcock will fit on my bike? Is it a hard swap?
what happens to the vacuum line on my bike then? Do I just leave the vacuum line hanging
Also could you please post a picture for those parts in the float?
Should I try fiddling with the floats first or just replace those parts you mentioned
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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.
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.
