Van Islander's TX650A - Quest for a Daily Rider

[TX650A Van Islander]

5T, you are a wealth of information - Thanks!!!
I'll check my float bowls after work and confirm. What makes me think the carbs are 76/77 vintage is the vacuum tube location is blocked off with the bolt.

 

[5twins]

There are a couple better "tells" that indicate these are '76-'77 carbs. First, the external float bowl vents which result in only two round holes around the edge of the intake bell. On the '78-'79 set, these vents were located internally, around the edge of the intake bell, and that puts 4 round holes there .....

The other "tell" is overflow hose nipples on the float bowl bottoms. In '78, they were eliminated, along with the brass pipe inside the bowl they connected to. I guess with the introduction of the vacuum petcocks in '78, Yamaha figured the carbs would never overfill or overflow, lol. That is true as long as the vacuum petcocks are functioning as they should, but now 40+ years later, that's not always the case. Here's a '77 bowl with the overflow nipple .....

..... and here's some '78-'79 bowls with the nipple removed, same casting just not drilled out for the nipple .....

 

[gggGary]

In '78, they (overflow tubes) were eliminated,

They had to be eliminated, with the float chamber no longer atmospheric, connected to the intake, the overflow tube would create an alternate air source.

 

[TX650A Van Islander]

So interesting how they changed. I definitely have the '76/77 carbs then. I have the VM22/210 float bowls.
I will order the appropriate 122.5 main jets and 25 pilot jets. Curious why the pilot jets would be so much smaller than the previous years. Is that due to them having 2 extra holes? Would it be a good idea to order the next size up as well, if for no other reason than just to experiment with potentially more power (or would that just foul plugs)?
Thanks again 5T!

 

[TX650A Van Islander]

Curiously, the 42.5 pilots someone had installed were the correct type for the float bowl, VM22/210. I only ran the bike with these for about 150 miles if that and it ran terribly for perhaps poor carb setup as well as the fact that it burned almost more oil than I could put in! I think it went through a litre in about 100 miles!

 

[5twins]

The jetting was very, very rich for those carbs and I don't doubt it ran bad. That super rich jetting may also explain some of the smoke you were getting and the excessive wear you found once you took it apart. Very rich jetting like that can wash the oil coating off the cylinder walls, causing smoke and excessive wear.

I was also going to explain the large change in pilot jet sizes as well. I wondered about that too when I first started studying these carbs. I mean, it was basically the same 650 motor throughout the production run. Well, if you study the pic of the two different float bowl types, that explains it. It has to do with how the air is fed to the jet and what the jet flows. The smaller sized VM22/210's (sized in the 20's) flow straight fuel and the air is added afterwards to the top of the jet. On the larger sized BS30/96's (sized in the 40's), the air is delivered to the bottom of the jet and mixed with the fuel before the jet meters or flows it. So, the VM22/210 flows straight fuel and the BS30/96 flows the already made up fuel/air mix. The resulting strength of the fuel/air mix that gets delivered to the pilot circuit ends up being about the same, it's just done in two different ways.

Now let's talk about the jetting you may need. Looking at that chart I made up, you can see that the stock 122.5 mains are the smallest put in any 650 carb set, and by several sizes. They do work fine on a totally stock machine but are easily outpaced if you make any mods. Now I understand that your machine is mostly stock but it looks like you have the freer flowing Commando mufflers on it. That may require bumping the mains up a size or two. Only running the bike and experimenting a bit will tell you for sure but it wouldn't surprise me if you needed bigger mains. Also, one of the first rules of jetting for mods is that when you think you're good, try the size above and below that to be sure. So, I would get 122.5's and 125's to start, maybe 25 and 27.5 pilots as well. If you end up several sizes up on the mains, that may make the upper midrange too rich and call for leaning the needles a step. If you do that, it could create an off-idle flat spot and that would need a larger pilot to correct it.

 

[TX650A Van Islander]

5T, Thank you so much for your input! I will follow those recommendations and let you know how it goes.

Interesting about too much fuel potentially causing that damage. Good thing I knew of this forum when I put it back together and went through the original carbs, following tech forum advice. Would have sucked to foolishly use those carbs without checking.

 

[TX650A Van Islander]

A question about throttle shaft seal installation. The carb guide states that the throttle plates must be removed and the shaft removed for seal installation.

Is this necessary - isn't it possible to pick the seal out and install a new one with the shaft in place? I don't have much play in these throttle shafts although the seal seems possibly worn. I bought new seals and am about to reassemble the cabs. This could be one of those times when replacing something which doesn't necessarily need replacement leads to heartache.

Further to this question, is this currently installed seal upside-down? The concave side of the seal is facing up.

 

[bosco659]

Looks correct to me. There’s one seal on each side so the shaft needs to be removed to get at the one side. Careful removing the screws. Booger up the head and you’ll have a project ahead of you. I grind the backs of the screw off and support the shaft from underneath (I believe some stick a dowel with a groove for the shaft, up through the carb to allow you to bear down on the screwdriver without bending the shaft) while removing the, using good downward pressure and a good JIS screwdriver.

Read here: https://www.xs650.com/threads/carb-tips-and-tricks-1st-throttle-shaft-butterfly-screw-removal.46423/

 

[bosco659]

If you pull the shafts, make sure they are deburred when reinstalling to prevent damaging the new seals.

 

[TX650A Van Islander]

Thanks Vic. I thought that would be the answer and I am afraid of buggering up those throttle plates. I'm going to give it a go the way it is before I damage something and see how it runs. As I understand it, if the seals are really compromised I will have excess air entry to the carb, correct? So that said, if it idles well without surging, it is ok and throttle shaft seals and all other seals are good, correct?

 

[Jim]

Yep.. everything Bosco said, and I'll add this. Some folk put a little red grease on the seals when they install them. I'm not a fan of that idea. Dirt and dust sticks to grease. Over time enough will build up that the grease can turn into a mixture akin to something like valve grinding compound. That ain't gonna play nice with the shaft and seals. I sometimes put just a dab around the outside of the seal to help in sealing, but don't get any on the lips of the seal.

So that said, if it idles well without surging, it is ok and throttle shaft seals and all other seals are good, correct?

Yes, correct. If the carbs give nice smooth idle with no surging or hanging idle, your seals are still in pretty good shape.

 

[5twins]

You can pull the seal out of that one side and examine it to determine it's condition. Give it the "pinch" test. These seals look similar to a normal oil seal but have no metal parts in them (spring or metal band). They are all rubber and very soft when new or still good. You should be able to easily pinch one down to an oval shape (try one of your new ones) .....

If it's all hardened up and in need of replacement, it won't easily pinch down .....

..... even if you pinch it really hard, lol .....

I'm one of those guys who packs the new seal with red rubber grease. I don't foresee any issues with dirt build-up because the seal is covered .....

 

[TX650A Van Islander]

So I did infact replace the throttle shaft seals, but just the ones easily done without removing the shafts. Good thing as they were not that soft. Hopefully that is ok in the end to leave those other ones in. We'll see.
I may have another issue though as I've realized that I have incorrect mixture screws, the 1970 to 1975 256 series, not the longer ones as shown in the attached screens hot from another thread about a year ago (thanks 5T)
My carbs look great but can I use these mixture screws I have? They seem like they are going to work. Carb guide says no. The other potential bummer is one of the mixture screws I pulled out and replaced was damaged and may have compromised the seat. Photo attached. Another wait and see how it runs situation.

 

[TX650A Van Islander]

May have answered my own question. There may not be enough thread on the wrong mixture screw to open it up as much as its supposed to be, without it vibrating out. Seems not tight enough on the left carb. That would explain why the thread is closer to the pointed tip on the correct screws.

 

[jpdevol]

I'm confused: you changed to an extra set of '76-77 carbs (584), but the pilot screws are (maybe) '74-'75 (256). Could it be a Canadian "76 set with 447 carbs that did run 256 screws?

 

[TX650A Van Islander]

It could be I suppose but the main jets in them were also totally incorrect, leading me to think whoever last assembled these carbs didn't know what they were doing, so they also may have used the incorrect mixture screws.
The screw sitting on my workbench in the previous photo came out of these carbs.

 

[jpdevol]

The US spec'd and the Canadian spec'd (everywhere else) BS38's differed greatly from the factory. IDK what you may have found your internals to be - of course there's always the possibility of other parts getting installed during PO. Maybe this will help resolve:

 

[TX650A Van Islander]

Interesting chart. I didn't know about those differences Canadian spec. vs USA spec. I had a bit of both. I think the PO messed it up a bit. Will confirm.

 

[650Skull]

Cross referenced that chart and things don't add up. Needle jet on the 74/75, (75/76 on the page), carbs with the Z-8 nozzle has the same part # as a Z-6 nozzle.

Also that chart references the TX75B and 76C carb as being the same.

Canadian 77D parts manual, (from xcafe part manual), #'s for carb jets. needle and nozzle are the same a the US 76C Carb part #'s from Biker.net fish file

cross reference http://biker.net/650parts_index.html with Partzilla and https://thexscafedotcom.wordpress.com/tag/manual/