A mystifying set of carbs

[pmurphy]

Hey, Fellas! Court and I are working on our bikes, both 80SGs, and there are some very interesting differences in the carbs. Court has posted some questions, but I now have some data re: my jet sizes etc.
They are the newer carb body, in fact carbs 2 and 3 have "3U900 E9Z2" stamped on them. They have the plastic floats, newer drain bowls, original metal needle valve/seat combination.

Court's carbs have viton tips and wire keepers on his needle valves, so we figure his carbs have been rebuilt.

My carbs 1-4 are all the same:
Main jets 137.5 (same as 79 SF)
Pilot Jets 45 (can't find any year with them)
Air pilot jets 185 (80 SG specs)
I have been searching all kinds of combinations, and have yet to find that setup.
The bike ran strong when last running.*


My question: Is it possible this is all factory, or has someone been playing with the setup? I am running the standard airbox, btw.

Thanks for any help/ideas.

[DGXSER]

Sounds like you have the early model carbs. Look at your mixture screws, on the front of the carbs at the engine side. Are yours down inside a tunnel, or exposed? Do you have an extra set of Ts at the top of the carbs between 1 and 2, and 3 and 4, these would be the vent Ts.

For the bike to run much at all with those jets, it would need to be the early carbs. Not all that unusual for folks to put the early carbs on the 80-81 bikes.

[Courtney]

No, he's got the late model carbs identical to mine, with plastic floats, not the brass ones. He has the tall mixture screw towers, as opposed to the exposed screws. He has 81 SH bowls with the angled screw drains while mine has the center brass drain bolt. This is weird.

[DGXSER]

Stock exhaust? Those mains are huge for those carbs. Should maybe be 120s.

[pmurphy]

Yep, stock exhaust. No idea why it's set up this way.

[Courtney]

$100 !! :-)

[pmurphy]

You forgot one zero on the end, Court!

[motoman]

No, he's got the late model carbs identical to mine, with plastic floats, not the brass ones. He has the tall mixture screw towers, as opposed to the exposed screws. He has 81 SH bowls with the angled screw drains while mine has the center brass drain bolt. This is weird.

Possibly the "bastardized" carbs used on the late 80's models. Pull one of the bowls and see if there is a crossover tunnel casting between the main and idle circuit like the early model carbs have. Likely they are the early carbs since they have the center brass drain bolt, and the bowls do Not interchange between the two model carbs. If that be the case, your jetting corresponds with that.

[pmurphy]

Mine are the new bowls, with the sideways drain screw, and plastic floats. I'll check for the cross over, but I doubt there is one, as everything else points to new style carbs.

[natemoen]

Mine are the new bowls, with the sideways drain screw, and plastic floats. I'll check for the cross over, but I doubt there is one, as everything else points to new style carbs.

If they are truely from an 80g the those bowls have been forced onto the carbs. The newer side drain bowls DO NOT fit onto the older style carbs, not even the 80 bastard carbs. The brass tube the sticks down onto the bowl is moved ever so slightly off to the side so that it cannot fit.

You need to see if that crossover passage is there, I am nearly sure that it is not. So if there is no crossover you need to jet it for the later style carbs instead of the early model carbs.

[pmurphy]

Just checked. No crossover, the bowls fit perfectly over the brass tube. Tall mixture screw towers, extra hole in the bell (4 in total), plastic floats. Definitely new style carbs, but strange combo of jets.
The bike ran well with this config, but I am contemplating re-jetting back to stock. I think the PO must have been diddling with the innards.
BTW, anyone have a spare set of 110 mains, 42.5 pilot jets?

[Rasputin]

Does one, or the other, or both, have the rubber plugs in the bottom of the pilot jets? Just thinking about possibilities here.

[DGXSER]

Sounds like you have the 81 carbs on your bike. 110-120 mains should work fine along with the 42.5 pilot jets. Also, make sure you check the float heights to be 23 mm +/- .5 mm. I have gotten into more than one set of carbs where a PO jetted them up like that apparently to compensate for dropping the fuel level to low.

I have ordered the jets form the local shop for about $3-4 each before.

[pmurphy]

No rubber plugs at all.
I am thinking of going to 110's across, as that was the original specs, along with 42.5s
Thanks

[natemoen]

The 110's were a little lean for emission requirements. Then with the crappy "gas" nowdays you might be better off with 112.5's or 115's.