JNaws Carburetor Adventures

[5twins]

Yes, you will need to lube the advance unit occasionally. After a ride, while it's still warm (or hot), I just dribble some foaming chain lube on the posts and springs. I do it on a warm engine so it penetrates better.

To lube the bushings that the advance rod turns in, you'll need to pull the rod out, but it's not difficult. Just remove the little disc from the advance side and pull the rod out the points side with the points cam still on it. Then clean the old grease (if there is any left, lol) out of the grooves in the I.D. of the outer bushing in each end of the cam, and pack them full of fresh grease. The factory shop manual recommends a grease with moly in it ......

Luckily, this doesn't need to be done often, only like every 5 years or so, but it does need doing. Most of these haven't had it done since they left the factory and are looooong overdue, lol.

 

[JNaw]

Took the cap vent out, bike is still leaning out on highway (verified with choke)

I wish I had a bowl drain that I could attach a hose to and check while riding.

This is occuring at 5-5.5k rpm on the highway, literally any other roadway runs perfectly fine.

If this isn't a fueling supply issue, I'm wondering if I gotta run a 150main or something, though when it Bogs, it'll continue to bog even around 3k rpm, especially worse at 1/8th throttle.

(This is a 73 tx style tank with the two piece gas cap)

Edit, I just had a revelation, do I have this outer seal on backwards? flipped it around, I bet you that's the darn issue. It was sealing inside the cap and couldn't let air through....

Flipped:

EDIT 2: Whats odd is the tx650 parts diagram shows it with the flap facing the cap, as in the first photo, Though to me this almost seems like it seals better having it backwards, maybe i am back to square one..., though i did notice the diagram shows a hole in the seal which mine doesn't have.

I will try it out again tomorrow with the seal flipped and see if its any different.

 

[JNaw]

Yup that didn't help at all. Still scratching my head. Guess I still will have to take the petcocks apart.

Edit: confirmed it's lean. Sparkplugs are whiter than photos can show. This is after 40min highway and 5-10min city at 3-4krpm previously with the 145main and needle clip at #3 it was completely black.

Gap was tad high at 0.032", set it at 0.028.

And a theoretical question here, what's the possibility a long z6 can be cut to match a short z6? Is the difference inside the carb body length or is it after the carb body into the bowl?

If I base the measurements off the length with a z2 I wonder if I can make it work.

 

[member43148]

The color actually looks close. Lean a bit but not black or oily. The plug body looks to be pretty old ?
What plug are you running ? NGK BP7ES is what I’ve run in several XS’s

 

[JNaw]

The color actually looks close. Lean a bit but not black or oily. The plug body looks to be pretty old ?
What plug are you running ? NGK BP7ES is what I’ve run in several XS’s

Sparkplugs are a couple years old but the bikes sat outside in the rain a fair bit (as my garage/shop isn't attached/near my house unfortunately)

Got bpr7es, with no resistor in the plug caps.

Here's some better photos. I'm having a brain fart right now, we are looking at the electrode and porcelain color correct? Should be tan or grey?

First two are right bank, second are left bank

 

[member43148]

Oops, a 4 cylinder sumpin. I don’t know what plugs lol..

 

[JNaw]

Oops, a 4 cylinder sumpin. I don’t know what plugs lol..

Nah it's the 2cyl twin still, just two different angles of the plug haha

 

[JNaw]

I don't wanna say much but I think adjusting the gap to 28thou fixed the stumbles. I'm gonna try raising the needle and see if it continues, as I believe I'm probably too lean now if it was a spark issue.

I think when I richened the mixture with the choke, it allowed the weak spark to ignite better, and with it being a high load on the highway is when it would only appear.

Only a theory though. I got z8 and z6 needle jets coming Thursday, will do a bunch of testing this weekend.

In theory, the 4n8 needle with the z2 jet should be good cause the bs38's apparently come rich in midrange from factory.

Will keep everyone posted.

 

[650Skull]

Burning to hot. Can see contaminants from something breaking down.

In the old days, and still do it if i haven't a plug on hand, when checking plugs, seeing one in this condition, (without contaminants), with a rounded electrode, (per pic), i would file the face flat, regap and reinstall

 

[JNaw]

Burning to hot. Can see contaminants from something breaking down.

In the old days, and still do it if i haven't a plug on hand, when checking plugs, seeing one in this condition, (without contaminants), with a rounded electrode, (per pic), i would file the face flat, regap and reinstall

View attachment 328972

I think it is burning a little bit of oil. I plan on doing a rebuild in the near future but just trying to get it running properly first.

New jets and needles came in. Looks like modifying the z6 long needle jet is out of the picture without a lathe. (Even then, my only concern would be the o-ring sitting too far in the carb body after machining the seat of the needle jet)

I'll try running the z8 with matching needles and hopefully I can find a #130 main jet somewhere, or open up a 127.5 slightly.

That is if the 142.5 main is too much, which I assume it is. I also think that the needle jet will affect the main jet size as they would both be supplying fuel at full slide lift?

 

[Jim]

Burning to hot. Can see contaminants from something breaking down.



View attachment 328972

Those look suspiciously like little aluminum ball deposits you get when you're starting to get a little detonation.

 

[5twins]

You won't get any higher than the mid 130's on the mains for a '76-'77 carb set due to the large Z-8 needle jets.

The higher o-ring groove on the long Z-6 needle jet wouldn't be an issue. The groove on the Z-2 needle jet is even higher than that I think .....

However, what would concern me is the thicker flange on the long Z-6. It may stick down too much and not allow the bowl to seat.

 

[JNaw]

You won't get any higher than the mid 130's on the mains for a '76-'77 carb set due to the large Z-8 needle jets.

The higher o-ring groove on the long Z-6 needle jet wouldn't be an issue. The groove on the Z-2 needle jet is even higher than that I think .....

View attachment 329174

However, what would concern me is the thicker flange on the long Z-6. It may stick down too much and not allow the bowl to seat.

It's near impossible to find a 130main without paying $60 in shipping right now haha, but I do agree It most likely wouldn't work with anything larger.

Yeah that thicker flange was what I was referring to as the seat. My photo above is the z6 on the left, z8 on the right.

From that flange bottom, to the bottom of the jet, the length is the same, I'd just have to machine it down where it contacts the carb body, and shorten the part towards the slide.

My father has a lathe that I may try this experiment with.

My other thought was opening the holes on the z2 pilot to resemble a z6, with my acetalyne torch tip cleaners. Crude, but as long as I'm slow I shouldn't oval out the holes.

Also, if you look at the two upper holes on the z8, they are Infact larger than the z6 long, so they aren't entirely the same unfortunately. Unless the z6 short style has slightly smaller holes, technically making it a z8?

 

[5twins]

Here's a good deal on a 4 pack of 130 mains from eBay .....

https://www.ebay.com/itm/313150761736

But, on the two sets I've used, I run 132.5 mains. They're the biggest I could go. I tried 135's but they caused break-up in the upper midrange even with the needles leaned a step.

Those rows of holes down the sides of the needle jets are air bleed holes. They let the air in from the air jet to mix with the fuel coming up from the main jet. As far as shortening the long Z-6 needle jet goes, I don't know if it's possible. You'll need to take a look in the top of the jet. Here's some Z-2's. Notice the step about 1/8" down into the jet. That's the metering orifice. Check the long Z-6 to see where it's metering orifice is. If it's near the top just like on the Z-2, then shortening it would remove it and wouldn't work .....

 

[JNaw]

Here's a good deal on a 4 pack of 130 mains from eBay .....

https://www.ebay.com/itm/313150761736

But, on the two sets I've used, I run 132.5 mains. They're the biggest I could go. I tried 135's but they caused break-up in the upper midrange even with the needles leaned a step.

Those rows of holes down the sides of the needle jets are air bleed holes. They let the air in from the air jet to mix with the fuel coming up from the main jet. As far as shortening the long Z-6 needle jet goes, I don't know if it's possible. You'll need to take a look in the top of the jet. Here's some Z-2's. Notice the step about 1/8" down into the jet. That's the metering orifice. Check the long Z-6 to see where it's metering orifice is. If it's near the top just like on the Z-2, then shortening it would remove it and wouldn't work .....

View attachment 329232

Yeah I checked the inside and it's got the step near the top. Although with the right measuring I'm sure it could be copied when cut.

Then again that's alot of work when a z8 and 4m1 needle would work fine lol.

Thanks for link I'll look into that and probably pick them up, I gotta check what I've got for main jets in my drawer at the shop too, I maaay just have a #130 sitting around.

 

[JNaw]

So, to me the z2 and z8 metering holes look to be the same size, if anything. The z2 internal metering size is slightly larger than the z8, which seems counter intuitive to me?

 

[JNaw]

Fitted the z8 and 4m1 needle/jet at 2nd clip position with a 135 main (smallest I had) with new bpr7eix plugs at 28thou.

Also honed the bronze bushings I installed, with a brake cylinder hone, as they were super tight with the pivot tube, and installed a grease nipple for feeding the new bushings.

Set ignition timing as it was super advanced after adjusting cam chain tension.

Preliminary results are good, much more midrange torque. I am expecting for it to breakup on the highway due to it being too rich, but revving up to redline on the street seems to be clean.

Will order 127.5-132.5 mains and see where that takes me.

 

[JNaw]

So, mains arrived off Amazon.

#130 had major breakup/cut in and out at 5k even with lowering needle (slot #3 to #2 on a 4m1)

#127.5 still has breakup/cut in and out but slightly less severe.

After 5k it runs like a rocket all the way to redline

I'm gonna try the #125 next, I'm wondering if these jets are slightly oversized as they aren't genuine mikuni. (Although they have the mikuni logo on them)

Lowering the needle brought with it a lower level of power from idle to needle transition, so I'm hoping I can use a #125 with the stock needle slot position but I'm unsure. I'm already at #30 pilots with 1-1/2 turns out

Feeling defeated here lol.

Edit: I also wonder if the needle jets aren't fully seated, I was having issues getting them to seat but after a few light taps they fit in. I'll have to check that if the size down on the main again doesn't do anything.

 

[5twins]

Stock pilot size for a '76-'77 carb is a 25, so you're two sizes up at a #30. Maybe try a 27.5?

Yes, it's difficult to get the needle jet to seat what with it's o-ring groove being so close to the shoulder. I just lube it up real good and install the float bowl. The float bowl pushes it in fully and eventually the o-ring will work it's way in.

You're kinda in uncharted waters here, what with running the old style slide in the later body. I don't see why it won't work but who knows. You may not be able to get the carbs perfect set up like this. What with you having to downsize the mains, they're not acting like the two '76-'77 sets I've used. Mine both took 132.5 mains no problem, and one set was even adapted from an XS500. I wasn't sure how that was going to work out but it was fine.

 

[JNaw]

Stock pilot size for a '76-'77 carb is a 25, so you're two sizes up at a #30. Maybe try a 27.5?

Yes, it's difficult to get the needle jet to seat what with it's o-ring groove being so close to the shoulder. I just lube it up real good and install the float bowl. The float bowl pushes it in fully and eventually the o-ring will work it's way in.

You're kinda in uncharted waters here, what with running the old style slide in the later body. I don't see why it won't work but who knows. You may not be able to get the carbs perfect set up like this. What with you having to downsize the mains, they're not acting like the two '76-'77 sets I've used. Mine both took 132.5 mains no problem, and one set was even adapted from an XS500. I wasn't sure how that was going to work out but it was fine.

View attachment 330146

Haha I'm in uncharted waters that's for certain.

I'm gonna have to do some more brainstorming, another option is having my 502 needle machined to proper length and running a z2 needle.

I'm second guessing myself with lean vs rich conditions, but my thoughts may be that the unofficial #122.5 may be sized the same as a #130 genuine main jet. I'll keep going down mains and monitoring performance and see where that takes me. I have a range from #110-#130 now.

I'm with you that I don't see why I can't make this work, unless the airjets in the later carb are smaller than that of the 76 model carbs. I don't have a way to measure that though. Do you?