Carb question

[DavePlum]

Will the carbs from a 82 XJ work on a 80SG? I know they are different manufacturers and the main and pilot are different sizes but are they completely different animals?

[BA80]

The XJ uses the Mikuni BS34 also but the choke setup is different. The XJ uses a cable.

The mains are pretty much the same size as the XS, 112.5s, but the pilots are larger,47.5. Also the pilot and main air jets are different than the XS, 170 & 140 respectively.

The engine and cams are the same as an 80 - 81 XS though, just reconfigured flow rates on the fuel and air jets. They should work just fine and I think the choke can be modified to work also.

[DavePlum]

Thanks for the info. The carbs on my 80SG project bike are a disaster and there's a possibility I can pick up a full carb set from a 82SJ so wanted to ask before moving forward towards the purchase.

[3Phase]

Dave,

I put a set of XJ carbs on my '80G and rode it from California to North Carolina for the XSSE rally, then back home in a meandering sort of roundabout way. I got good performance and decent mileage; didn't have to do jack nothing to them, they just worked.

So, XJ carbs should work fine on your 'SG, if it's still stock they'll drop right in and you just need to make something to pull out and hold the Enrichener to start the engine and let it fast idle for a bit. I used an old drip irrigation emitter stake because I had one and it had a fork in it:-


Dig Drip Irrigation Garden Micro Kit Sprinkler Spray Stake Emitter 2 Pack

[DavePlum]

3Phase...That's good to hear that they will drop right in, how long is that irrigation stake and where do you store it on your bike? Do you think $90 for a full set of XJ carbs is a decent deal? I'm assuming they will need a rebuild but the carbs that came with my project 80SG need way too much to bother with.

[kboehringer]

Good Deal!

Do you think $90 for a full set of XJ carbs is a decent deal?

YES! I personally paid $100 for an XJ set and mine had been put up full of fuel and sat for probably ten years on a shelf in the junk yard. I thought I got a KILLER deal at $100 even considering the rebuild kits, replacement Mikuni Jets, and about million hours of cleaning... They are finally my SPARE set... Ready to Roll!

YES. Assuming all the float posts are solid and someone didn't break any of the mixture screws off in them....That would be a killer deal.

Kurt

[DavePlum]

YES! I personally paid $100 for an XJ set and mine had been put up full of fuel and sat for probably ten years on a shelf in the junk yard. I thought I got a KILLER deal at $100 even considering the rebuild kits, replacement Mikuni Jets, and about million hours of cleaning... They are finally my SPARE set... Ready to Roll!

YES. Assuming all the float posts are solid and someone didn't break any of the mixture screws off in them....That would be a killer deal.

Kurt

Those are exactly the problems with the carbs that came with my 80SG and I still spent quite a few hours cleaning up the float bowls and diaphragm covers before I decided to go with plan "B". Btw...It's actually going to be $110 after the $20 shipping fees so you already did better than me...lol

[kboehringer]

Those are exactly the problems with the carbs that came with my 80SG.

Dave,
Unless the XJ carbs came off a bike that was running perfectly yesterday, you will need to spend the time cleaning, replacing gaskets, checking float levels, synchronizing, etc. Even if they DID come off a bike that ran perfectly yesterday some of that work still must be done...

Unless you have something broken in your carbs.... Maybe finish the work of Plan "A" is the better idea? Those new purchase XJ carbs are not going to be install & ride deal.

I own two SG's and one SH. Having a nice spare set of BS34s is a no-brainer for me.

[DavePlum]

Yeah, I know I won't be opening up a box and installing these carbs. I know the XJ they are coming off sat for quite some time. I just enjoy doing this kind of stuff as a hobby so I know there's work ahead. I'm in no big rush since I'm taking my 80SG down to the frame.
My 80 carbs came with...#4 has a broken float post, 2 & 3 have a stripped out pilot jet that won't budge, one diaphragm has a tear and the others look like wilted flowers. Two of the four main nozzles look as if someone grabbed it at the top with needle nose pliers and rocked them back and forth bending the metal at the top. (I'm a novice with carbs so does that bend at the top really affect the function?) The throttle plates were stuck shut and in each carb the two screws holding the plates to the shaft have quite a bit of rust on them. Filters are MIA from all four valve seat assy's, and there is a few other missing parts. The bores need cleaning and whatever else to get them smooth again. Bottom line is if the 82XJ carbs are complete and undamaged I think I'll be way ahead. Seller claims they are in good condition...we'll see.
Btw...does the 80SG carbs use the rubber plug...does the 82 XJ?
Thanks

[TopCatGr58]

Hey Dave,

The 80's were the transitional year between the early and later style carbs, and so IF the 80 carbs have the main Jet NEEDLE/emulsion tube with the sharing tunnel and port to the Pilot Jet Tower, then they use the rubber Pilot Jet tower plug caps. IF there is NO sharing tunnel, then they do NOT use the pilot jet tower cap/plugs. The 78-79 carbs had threaded sections that are sealed with large head screws. The Later carbs do not use a sharing tunnel, and the pilot jets feed directly from the float bowl just like the main jet.

T.C.

[DavePlum]

Hey Dave,

The 80's were the transitional year between the early and later style carbs, and so IF the 80 carbs have the main Jet NEEDLE/emulsion tube with the sharing tunnel and port to the Pilot Jet Tower, then they use the rubber Pilot Jet tower plug caps. IF there is NO sharing tunnel, then they do NOT use the pilot jet tower cap/plugs. The 78-79 carbs had threaded sections that are sealed with large head screws. The Later carbs do not use a sharing tunnel, and the pilot jets feed directly from the float bowl just like the main jet.

T.C.

Okay, I'm a novice with carbs so bear with me here. I'm looking at one of the carbs now, (diaphragm side down, float posts towards me) there are 3 towers, the lowest being the main jet, the highest being the main nozzle, and pilot jet is 4mm lower) if I look down into the bore of the main nozzle I should see a tunnel to the pilot tower...if there is one...correct? If I'm understanding this correctly what I'm calling the main nozzle is what you're calling the main jet NEEDLE/ emulsion tube.

[3Phase]

Dave,

The stake is a little longer than a Popsicle stick and I kept it tucked between the speedometer and the warning light cluster. Most of the time I just used my fingers to pull the Enrichener, I only needed the stake when it was really cold or I if I didn't feel like standing there like a goof holding the Enrichener for half a minute while the engine warmed up.

Yes, you will see a hole between the main and pilot tower if you've got the early mixed-style carburetors.

In Mikuni-speak the main jet screws into the 'needle jet' and the needle in the slide is the 'jet needle'. It's usually just called the emulsion tube or the nozzle and slide needle unless you're trying to work with someone using the Yamaha parts fiche.

[DavePlum]

Thanks 3Phase, that makes sense now.
One more carb related question for you gurus out there. While sorting thru all my carb parts I got with this project I've got 4 screw-in type jets I've yet to ID.
They look much like the main jets but while they are very close to the same length as the mains these are smaller in diameter at the slotted end only. Main jets measure 8mm at the slotted end and these measure 6mm at the slotted end. I've looked at parts illustration in my service manual a couple times and still haven't spotted them. What are they? There's always a chance they don't belong to my 80SG at all since when I got the bike the carb bodies and related parts were just sitting in an old plastic toolbox. Thanks

[red bandit]

What's the number on the face of the slotted end? Might be your air jets???

[DavePlum]

What's the number on the face of the slotted end? Might be your air jets???

Really hard to read but it looks like 185, main jets are stamped 110.