Can anyone tell me if the vacuum petcocks on XS650's will fit on an XS400? I see Mike's XS has a kit that will retrofit a standard petcock in place of the vacuum disaster that was fitted as stock to the XS650's. I want to retrofit the vacuum petcock on my 81 XS400H with a standard on-off-reserve unit like what he's offering, but don't know if they'll interchange.

Can anyone research the two Yamaha part numbers and see if they're one and the same?

parts lists here

select bike year and model

Can anyone tell me if the vacuum petcocks on XS650's will fit on an XS400? I see Mike's XS has a kit that will retrofit a standard petcock in place of the vacuum disaster that was fitted as stock to the XS650's. I want to retrofit the vacuum petcock on my 81 XS400H with a standard on-off-reserve unit like what he's offering, but don't know if they'll interchange.

Can anyone research the two Yamaha part numbers and see if they're one and the same?

From what I have been able to discover they are NOT the same. That said I'm not sure that one of the kits from Mikes XS won't work. Also some other things that will work are carb kits, vacumm slide kits (the BS34 ones) and the handlebar control pods (which are also the same). I got the carb kits and they worked well and had most of the parts I needed (I'm going to replace the idle screws as well but the're a seperate kit).

what do you mean vacuum disaster?

as long as your float bowl needles and floats are good, your fuel "shuts" off.

what do you mean vacuum disaster?

as long as your float bowl needles and floats are good, your fuel "shuts" off.

what do you mean vacuum disaster?

as long as your float bowl needles and floats are good, your fuel "shuts" off.

I have to agree. I have never had a problem with my petcock at all. When the engine runs fuel gets to the carbs, when the engine stops, the fuel does. That said, if I could find a conversion kit that didn't cost nearly as much as the bike is worth, I would probably change over.

what do you mean vacuum disaster?

as long as your float bowl needles and floats are good, your fuel "shuts" off.

In all fairness, your experience isn't the same for all persons everywhere. My petcock, after rebuild, flows just slightly less fuel on 'ON' as it does on 'PRIME'. That's a problem for which I have found no solution.

When the bike sits on it's sidestand, it leaks from the right side carb onto the engine then onto the floor. On the centerstand it leaks from both carbs, just not as badly as the one carb when on its sidestand.

I've rebuilt the carbs three times now. If I move the float bowls any lower, it starves the engine and it won't rev over 4k. If I move them any higher, it leaks all over the place.

My best bet (based on vehicle value and my tolerance for rebuilding this bike every weekend) is to replace the petcock with an 'ON-OFF-RES' version. I'd rather have a petcock that works and an engine that revs where I need it to so I can ride it, than have the gas spill all over the place.

Anyway:

The '81 XS400H petcock part number is 3X8-24500-00-00.

The '81 XS650H petcock part number is 3G1-24500-03-00.

Can anyone decode these numbers? Are the first three the model and the next 5 the part? I hope? The '24500' part looks promising.

there is a computer program called yamx which cross references all USA spec yamha's.

I have the progrm but don't have the code to use it

get it here

In all fairness, your experience isn't the same for all persons everywhere. My petcock, after rebuild, flows just slightly less fuel on 'ON' as it does on 'PRIME'. That's a problem for which I have found no solution.

When the bike sits on it's sidestand, it leaks from the right side carb onto the engine then onto the floor. On the centerstand it leaks from both carbs, just not as badly as the one carb when on its sidestand.

I've rebuilt the carbs three times now. If I move the float bowls any lower, it starves the engine and it won't rev over 4k. If I move them any higher, it leaks all over the place.

My best bet (based on vehicle value and my tolerance for rebuilding this bike every weekend) is to replace the petcock with an 'ON-OFF-RES' version. I'd rather have a petcock that works and an engine that revs where I need it to so I can ride it, than have the gas spill all over the place.

Anyway:

The '81 XS400H petcock part number is 3X8-24500-00-00.

The '81 XS650H petcock part number is 3G1-24500-03-00.

Can anyone decode these numbers? Are the first three the model and the next 5 the part? I hope? The '24500' part looks promising.

Have you replaced the needle valve seats? On mine I found that the seats thenselves were actually ok, but that the o-rings were shot, and I couldn't find ones that fit, so I got replacements as part of a rebuilt kit from mikes-xs and even if I leave it on prime there's no leakage. Now that said, I don't leave it on prime normally anyways. If you rebuilt the petcock and it still leaks there is either sometihng wrong with the assembly or something wrong with the kit you got to rebuild it. Properly rebuild and assembled the petcock should work well for years to come. The primary problem I have read about with them is that under heavy load (going up a steep grade two up) fuel flow can shut off.

While posting this I took a quick look, maybe this will work. Try this alternate site that carries XS400 stuff https://www.partsnmore.com/cat_index.php?mo...p;category=carb

They have a universal and an adapter plate, I'm going to measure my spare tank mounting holes to see if this will fit, if it does I just may order it.

if you are feeling flush, use a pingel fuel tap

Have you replaced the needle valve seats? On mine I found that the seats thenselves were actually ok, but that the o-rings were shot, and I couldn't find ones that fit, so I got replacements as part of a rebuilt kit from mikes-xs and even if I leave it on prime there's no leakage. Now that said, I don't leave it on prime normally anyways. If you rebuilt the petcock and it still leaks there is either sometihng wrong with the assembly or something wrong with the kit you got to rebuild it. Properly rebuild and assembled the petcock should work well for years to come. The primary problem I have read about with them is that under heavy load (going up a steep grade two up) fuel flow can shut off.

While posting this I took a quick look, maybe this will work. Try this alternate site that carries XS400 stuff https://www.partsnmore.com/cat_index.php?mo...p;category=carb

They have a universal and an adapter plate, I'm going to measure my spare tank mounting holes to see if this will fit, if it does I just may order it.

No, I have not replaced the needle valves or the seats. That's the last thing, I guess. I hadn't figured they would have been a problem (they passed visual inspection), but since I've cleaned and replaced every other component of the fuel system from the petcock filter to the air/idle screws, it must be the jet needles/needle jet.

That site you posted is awesome, it's got some great stuff. Between that and Mike's XS, I should have a complete resto done on this thing in the next few weeks.

I did get it running yesterday pretty good. I test rode it for about 6 miles around the neighborhood in 58 degree weather and it ran fine, didn't even leak. Well, I opened up the garage door this morning (39 degrees) and I could smell it before I saw it. Gas was leaking again. I dried it off, started it up and it ran like crap! All the way to work it ran progressively worse. 12.5 miles, mostly neighborhood streets, stop & go, between 30 and 55 MPH, and cold this morning. But at lunch it had warmed up to around 55 degrees and it ran better but not perfect. On the way home tonight in 63 degree weather it ran flawless. I can't figure it out, other than it likes warm weather.

The biggest problem this morning was it wouldn't hold an idle (had to run on 1/2 choke the whole time) and it had no throttle response. It would rev up to 6K and go no further. It wouldn't pull hills unless a lot of down shifting was involved, and it would occasionally buck & surge at level throttle.

No, I have not replaced the needle valves or the seats. That's the last thing, I guess. I hadn't figured they would have been a problem (they passed visual inspection), but since I've cleaned and replaced every other component of the fuel system from the petcock filter to the air/idle screws, it must be the jet needles/needle jet.

That site you posted is awesome, it's got some great stuff. Between that and Mike's XS, I should have a complete resto done on this thing in the next few weeks.

I did get it running yesterday pretty good. I test rode it for about 6 miles around the neighborhood in 58 degree weather and it ran fine, didn't even leak. Well, I opened up the garage door this morning (39 degrees) and I could smell it before I saw it. Gas was leaking again. I dried it off, started it up and it ran like crap! All the way to work it ran progressively worse. 12.5 miles, mostly neighborhood streets, stop & go, between 30 and 55 MPH, and cold this morning. But at lunch it had warmed up to around 55 degrees and it ran better but not perfect. On the way home tonight in 63 degree weather it ran flawless. I can't figure it out, other than it likes warm weather.

The biggest problem this morning was it wouldn't hold an idle (had to run on 1/2 choke the whole time) and it had no throttle response. It would rev up to 6K and go no further. It wouldn't pull hills unless a lot of down shifting was involved, and it would occasionally buck & surge at level throttle.

check your condensor, by viewing the contacts (if you have them that is) if they are sparking, condensor gone.(happened to my friend who thought it carbs and it was 6k revs problem.

sounds also like your pilot drillings are blocked as they operate the bike up to 4k. get a couple of carb kits from sirius online, they are in canada but excelent service. THey are also on ebay.

try bikebandit.com for xs as they have tons of OEM stock

check your condensor, by viewing the contacts (if you have them that is) if they are sparking, condensor gone.(happened to my friend who thought it carbs and it was 6k revs problem.

sounds also like your pilot drillings are blocked as they operate the bike up to 4k. get a couple of carb kits from sirius online, they are in canada but excelent service. THey are also on ebay.

try bikebandit.com for xs as they have tons of OEM stock

By "Sirius Online" do you mean these guys?

I'll check the condenser, but as I thought about it more and more today, I think (I hope) it's a jetting issue. It ran fine on Sunday afternoon and Monday afternoon; as both days warmed up, the bike ran fine. Both afternoons were in the 60s. The only real trouble I had was when the temperature was below 50. I think that can be traced to the mains being too lean. They may be 42.5, I might want to try 45 in the cold weather, then swap back as the days warm up. We'll see.

I remembered today that the headlight does dim each time the blinker lights up. It kind of oscillated in kind with the cadence of the blinkers. Again, we'll see what that's all about. It's not bad, just a slight dimming I noticed. I'll bet it's normal.

Thanks for reading this and all the suggestions. I get frustrated sometimes, but it'll all be worth it when it runs well. 60 MPG (Yamaha) will beat the hell out of 13 MPG (Ford F-150), especially what with gas being consistently over $3.00 now. This summer it's supposed to be mid- to high- $3.XX. I can't wait.

By "Sirius Online" do you mean these guys?

I'll check the condenser, but as I thought about it more and more today, I think (I hope) it's a jetting issue. It ran fine on Sunday afternoon and Monday afternoon; as both days warmed up, the bike ran fine. Both afternoons were in the 60s. The only real trouble I had was when the temperature was below 50. I think that can be traced to the mains being too lean. They may be 42.5, I might want to try 45 in the cold weather, then swap back as the days warm up. We'll see.

I remembered today that the headlight does dim each time the blinker lights up. It kind of oscillated in kind with the cadence of the blinkers. Again, we'll see what that's all about. It's not bad, just a slight dimming I noticed. I'll bet it's normal.

Thanks for reading this and all the suggestions. I get frustrated sometimes, but it'll all be worth it when it runs well. 60 MPG (Yamaha) will beat the hell out of 13 MPG (Ford F-150), especially what with gas being consistently over $3.00 now. This summer it's supposed to be mid- to high- $3.XX. I can't wait.

them's the guys, the kits are comprehensive and I got needle and the air corrector jets etc in mine.

80% of engine failures are due to electrics according the the AA. I figure that would be the easiest to eliminate first then go for a thorough carb clean (ultrasonic) and new carb kits from sirrius.

I can't see why you would need a larger pilot jet due to weather, its altitude which affects carburetion (ie air density) and then there are not many roads 1000's of feet up.

try a plug chop to confirm.

them's the guys, the kits are comprehensive and I got needle and the air corrector jets etc in mine.

80% of engine failures are due to electrics according the the AA. I figure that would be the easiest to eliminate first then go for a thorough carb clean (ultrasonic) and new carb kits from sirrius.

I can't see why you would need a larger pilot jet due to weather, its altitude which affects carburetion (ie air density) and then there are not many roads 1000's of feet up.

try a plug chop to confirm.

I would have to say I experience better performance and such on warmer days. IIRC, while air fuel mixture doesn't change based on temp, the ideal does. 1980 XS400's come extremely lean from the factory, and the needle is NOT adjustable (idle mix is not adjustable either). Every time I check my plugs they show lean (and always have). BTW, it's 100% stock, stock air filters, plugs and exhaust are all stock. I found I was able to compensate by raising the fuel level in the carbs slightly, which made off idle circuit running much better, but idle is still way picky. I'm planning on getting the idle jet kit from MikesXS so I can adjust the idle properly and replug the jets.