It gets worse before it gets better (mini rant)

[sethhope]

So after the whole pickup carb mystery on cylinder 3, the bike was running great. She drove like a dream for about 100 miles. Then, out of nowhere, died at a stop light... no problem, i thought, i probably stalled it. Crank the starter a couple times. Nothing. I pull it to the side of the road to inspect it. I did do some wire replacement on the p/u coils... maybe thats it? I take the cover off. Yup, broken wire. No problem, just a quick solder job and i should be off. I solder the wires. Great now she starts, but shes backfiring like crazy and idling real rough. A look at a carbboots reveal a nasty crack in 2 of them... guess im replacing those now... with luck thatll solve my engine problems.

[BA80]

I'll bet you still have a problem with the pick up wires. The cracks in the boots generally don't go all the way through, hey just look bad.

[sethhope]

Im sure its problems with the boots. I can see one of my large cracks pulsing open as the engine runs...

[BA80]

http://www.ebay.com/itm/Yamaha-78-81...FXI6kz&vxp=mtr

[TopCatGr58]

Im sure its problems with the boots. I can see one of my large cracks pulsing open as the engine runs...

Hey Seth,

As was stated, even though you could see the intake boot pulsing, they are double walled, and it's quite rare for the cracking to get to the inner layer. They will flex and such with the engine running. There are several techniques folks have used to make them look better, from applying many layers of liquid plastidip, to plumber rubber sealing tape, to black RTV applied like cake frosting, etc.!

But now with them as low a price as what Greg showed in that ebay advert, they aren't too expensive to replace vs. the $125+ OEM prices !

As to the PU coil wires, they are OLD and fragile, so instead of just trying to splice them back together, you will be better off replacing them with multimeter test lead wire, otherwise they will just keep breaking due to the flexing/bending, especially at the solder junctions!

T.C.

[sethhope]

Hey Seth,
...
Snip
...

As to the PU coil wires, they are OLD and fragile, so instead of just trying to splice them back together, you will be better off replacing them with multimeter test lead wire, otherwise they will just keep breaking due to the flexing/bending, especially at the solder junctions!

T.C.

Thats exactly what i did, only instead of multimeter wire, i uses some high strand wire i had on my bench (its specifically for this kinda thing). Where i had problems was where i soldered the wire to the coil. I didnt do it right and it bubbled and broke. So i redid it and it seems like itll hold.

As for the boots, i still think they are a problem. Just in case, i ordered a cheap set from eBay (thanks Greg!). Its really heating up 1 and 2, and not so much 3 and 4, so to me thay screams carbs. Given ive just cleaned, adjusted, and reset my carbs 8 times (i have a thread on that....), im guessing its not the actual carbs, but the boots.

I still could be very wrong, but we'll find out i guess

[BA80]

i ordered a cheap set from eBay (thanks Greg!).

Don't use the paper gaskets that come with them, they will fail. Just clean up the surfaces on the head and use a little ThreeBond or YamaBond to seal them.

[sethhope]

Don't use the paper gaskets that come with them, they will fail. Just clean up the surfaces on the head and use a little ThreeBond or YamaBond to seal them.

Thanks for the heads up!

[CaptonZap]

I'm guessing its not the actual carbs, but the boots.

I still could be very wrong, but we'll find out i guess

Here is a way to check it. Start the bike, and let it idle as slow as it will idle smoothly.
Take a propane torch, light it, set it for a low flame, turn it off, counting the turns of the knob, open the knob the same number of turns, and play the unlit tip of the torch around the suspected cracks.
Any increase in RPM's will indicate a crack.

CZ

[HalfCentury]

I don't know about the XS, but the XJ intake boots come stock from the factory with gaskets installed.

I just removed my boots to replace them. The gaskets in place were in tatters. If you have gaskets on your boots and if they are old, they have probably at least partially disintegrated. A great place for undesired air to leak into the manifold.

If you do the propane torch test, try at the manifold-to-boot joint.

[TopCatGr58]

Also the synch port caps can be bad....hardened from age/heat and even though they might pop/snap down over the enlarged nipple end, they can actually be loose fitting around the nipple shaft and leak there!

T.C.

[Rasputin]

Also the synch port caps can be bad....hardened from age/heat and even though they might pop/snap down over the enlarged nipple end, they can actually be loose fitting around the nipple shaft and leak there!

T.C.

I agree with TC about the port caps as I have had issue with them before.
Another thought would be valve clearances as that is important in how these old ladies run as well. If you have not checked it yet, then might be an idea.
Also a quick re-assess of the carb balance may be in order.
The pick up coils are not so much suspect if you have repaired them correctly and the differences are between 1,2 and 3,4.
Just for fun here is a link to a thread where I cut apart an old set of carb boots. Takes a lot to make them leak unless you use the paper gasket (which I agree with BA80), should not be used. Good Luck.
http://www.xs11.com/forum/showthread.php?t=30603

[sethhope]

Ill check the sync caps as well... the guy who owned the bike before me removed the carbs... hard... he pretty badly damaged the boots when he did, so they should be replaced either way.

Ill check valve clearance if the boots dont fix it.

[DiverRay]

Ill check valve clearance if the boots dont fix it.

No, you need to check the valve clearance FIRST! Valves MUST be correct in order to properly sync the carbs per the book. A full tune, check cam, check valves, check timing, and then sync.