'81 Midnight Special carbs?

[bikerphil]

Make sure there is no crossover passage as shown in the pic...

[robbo]

Paint

Ooops, missed the edit timeout, and should also have said that I had the forks re-chromed and painted the lowers, fitted new headstock bearings, re-greased the swingarm bearings and painted the swingarm.
Still needs a few things cosmetically but winter is about to arrive here so I've time do it.

Hi Alex. What paint did you use on the swinging arm and is it a good match for the rest of the frame? Only my swinging arm could do with repainting, but the rest of the frame is quite good, so was looking for some paint that would blend nicely with the factory stuff

Cheers Rob

[FJ111200]

Make sure there is no crossover passage as shown in the pic...

Thanks for the tip, but pretty certain there isn't.
What I have found though is that there is a shim under each jet needle, is that right?



Quote:

Hi Alex. What paint did you use on the swinging arm and is it a good match for the rest of the frame?
Cheers Rob

Just some Hammerite Smooth Black and 8 coats of it.

[3Phase]

Thanks for the tip, but pretty certain there isn't.
What I have found though is that there is a shim under each jet needle, is that right?

The only emission control plugs are the metal anti-tamper plugs for the idle mixture screws. I have not checked the two different inside diameters of the pilot fuel and mixture screw towers but it may be possible that someone tried to use the anti-tamper plugs that come with some carburetor kits for the Pilot towers and then had to drill holes in them. The engine won't want to start and run without fuel for the pilot circuit so for the main jet to work all alone you'd have to tow the bike up to speed and pop the clutch or drop it from a bomber.


There is one washer for the jet needle in the slide assembly but just so we're all on the same page it's item #33 on the Yamaha online catalog:-

Yamaha Street Motorcycle Parts | CARBURETOR - XS1100LH - 1981

#33 3F7-14952-00-00 WASHER, PLATE (7Y2) $0.88 4 ea.

Quote:

Hi Alex. What paint did you use on the swinging arm and is it a good match for the rest of the frame?
Cheers Rob

Just some Hammerite Smooth Black and 8 coats of it.

Cool! Was it rattlecan, brushed, rolled, or sprayed?

The ate-up, acid-damaged, swing arm from my XJ1100 has to be repainted and rolling on multiple layers of Rustoleum is how I'd planned to do it.

[FJ111200]

There is one washer for the jet needle in the slide assembly but just so we're all on the same page it's item #33 on the Yamaha online catalog:-

Yamaha Street Motorcycle Parts | CARBURETOR - XS1100LH - 1981

#33 3F7-14952-00-00 WASHER, PLATE (7Y2) $0.88 4 ea.




Cool! Was it rattlecan, brushed, rolled, or sprayed?
[/QUOTE]

Thanks for the info on that and it was a rattle can spray on paint. I find with Hammerite that the longer it's left to cure the harder it becomes and less likely to chip and crack. I've got a parasol stand in the back garden which is left out in all weathers, all year, which I sprayed with Hammerite Smooth about 5 years ago and it's still as good as the day I did it. The secret is try and do the spraying in warm conditions. Should also say it's Smooth Gloss Black.
That's messed up quote but I hope you get the gist.

[3Phase]

Those right-hammered quotes worked fine, no problem! Well, five years from now I'll be scratching my head and thinking, "I don't remember any of this!" but that'll be from senility, not quoting.

Some paints do get better with time. I had some patio chairs that shrugged at aircraft paint stripper (methyline chloride) and just sat there while it cooked off in the sun down to a sticky, water and UV-resistant shell.

[FJ111200]

After piddling about with this pig of a bike for weeks now, I think i'm on the home straight.
Under those plugs that I managed to remove were some unmarked pilot jets with no jet size stamped on them and they had eight bleed holes.
So I've bought some 42.5 size pilot jets and the ones with six bleed holes.
I'm fairly certain this has been holding me up after doing research on this forum.
The carbs also had 125 mains across all four which I've changed for 120's.
What's the reckoning on these changes?
Picture of the new and old pilot jets.

[TopCatGr58]

Hey FJ,

We can't tell much from the photos of the jets. The # of bleed holes is a bit of a red herring. We thought they were important with regards to how rich/lean the jets behaved, but that's not the case. Yamaha came up with a newer style of pilot jet that actually doesn't even have any side holes, they were first made for the XJ1100 carbs. However, they will work for XS11 carbs also....because the way the pilot jet tower/chamber is built...there is NO ...I repeat...NO venting air supply port feeding the tunnel that the pilot jet screws into. The Jet seals against the bottom of the tunnel with the cone shaped tip, and the threads, seal the other end IN the tunnel...and there is NO way any air gets to the SIDE of the jets, so the bleed holes are redundant. I cut several carb bodies completely in half thru the pilot jet/main jet towers, and it revealed that there were NO air ports in that area of the pilot jet towers. Also, George/GLOWEVA put in the no side holed pilots into his XS carbs, and they ran and tuned just fine just like the vented pilots.

What does cause problems is using OFF brand/Generic K&L jets which are sized and metered totally different than Genuine Mikuni jets. The K&L's run excessively rich and are why folks can't get them to tune/idle properly, get black plugs, etc.!

SO....regrettably you didn't say what BRAND of pilot jets you got, but if they weren't MIKUNI, then you may still have problems trying to get it tuned....UNTIL you get genuine mikuni jets.

T.C.

[bikerphil]

The ones with 8 holes are the VM type and have the wrong spray pattern.

[FJ111200]

SO....regrettably you didn't say what BRAND of pilot jets you got, but if they weren't MIKUNI, then you may still have problems trying to get it tuned....UNTIL you get genuine mikuni jets.

T.C.

Thanks for the info.
I've bought genuine Mikuni mains and pilot jets.
I've had a look down the tunnels with a light and magnifying glass and can't see any air ports. I used TourMax float needles but they are sealing good at 23mm float height.
I'm starting to give up with this pig.

[TopCatGr58]

The ones with 8 holes are the VM type and have the wrong spray pattern.

And here's the diagram borrowed from MikesXS website that demonstrates this.



The metering orifice on VM's are near the threads, the BS are near the nipple/cone end.

T.C.

[leggman1]

My 81 special takes rubber plugs held in by the float bowls.

[motoman]

Hello there, long time no post.
I've tried searching but not found anything like. So anyway, I've bought this 4W1 '81 Midnight Special and it's come with these carbs that seem to have some of the jet orifices blocked by something.
Is this right or what? Also the main jets are 125 across all four.
Anybody shed any light on what's happened and what I need to do? Thanks in advance.

With a magnifying glass, if those metering rods have 5GL16 stamped in sides of them near the top, 110 main jets ARE what is needed, as long as they are Genuine Mikuni with the curly loop line next to main jet size. If those carbs do in fact have the 5GL16 metering rods, even 120 mains are way to big.

[motoman]

Thanks for the tip, but pretty certain there isn't.
What I have found though is that there is a shim under each jet needle, is that right?



Quote:

Hi Alex. What paint did you use on the swinging arm and is it a good match for the rest of the frame?
Cheers Rob

Just some Hammerite Smooth Black and 8 coats of it.

FJ, that IS correct, the special shim washer under each main jet......and again, 110main jets across all four IS stock main jetting from factory, and needs to be left as such. Stock pilot jets ARE 42.5, and need to be left that way also.

[TopCatGr58]

My 81 special takes rubber plugs held in by the float bowls.

Hey Leggman,

IF they are truly 81 carbs, then somebody put the rubber plugs in by mistake, because the pilots need to feed from the float bowl. So...check your carbs to be sure they are 81 series, and do NOT have the sharing tunnel between the main and pilot jet towers.

A PO may have swapped an earlier model of carbs on to your bike, it's happened before. You can run any year XS11 with any year of carbs, just have to have the carbs jetted for the year of carb, not the year of engine.

T.C.