1974 TX650A Restoration Project

Yes, UNI Pods do fit nicely behind the standard tins. Did it before on a 78 and gonna do it again in the future as well.
I am a fan..
which @Machine 's picture seems to help answer, is if the pods can sneak behind the tins. Seems like yes,
20190524_185121_IMG_0452.JPG
 
If you think about it, there's quiet a bit of R&D time (and money) that goes into tuning a stock intake system. Logic sez they wouldn't waste all that if a set of foamy's worked as good. Never tried it on an XS, but it's been my experience on other cars and bikes that aftermarket filters "sometimes" get you up to as good as stock... seldom better.
Fwiw... I'm running pods, but that was just because I had other plans for all that space and performance wasn't (isn't) an issue for me.
 
If you think about it, there's quiet a bit of R&D time (and money) that goes into tuning a stock intake system. Logic sez they wouldn't waste all that if a set of foamy's worked as good.

Yeah, I hear you Jim. There's a reason I rehabbed the stock airboxes and (over)paid for a set of the stock-repros the first time around. I agree it's silly to dismiss all the R&D that goes into making a stock machine work. That being said, I did just make those upgrades you mention, and beyond that I have to imagine the landscape of materials has evolved significantly over the last 50 years. That's me just supposing; and hey, maybe for this application - a filter is just a filter. I know in MY industry (drug development) we've seen pretty amazing developments in filtration media over even the last 15 years, so perhaps projecting a bit.

One benefit I would get straight away is a bit of space to rout my dumb crankcase breathers since I still have the dual-output breather and have two of them back there.
 
There is the reasoning that the airbox is infact an large undisturbed air chamber. Having both airfilters in the box does not isolate them. So actually each carb can suck air from the box which breathes with two air filters at once even.
I just like the Pods for ease and sound.
And my BS38 / Uni XS's run just great..
 
Agree, I think if you are going to run Pods, take advantage of cleaning up the crankcase vent system with a small single outlet breather which are hard to find on Ebay..
20200314_135546.jpg

I added the standard vent screen to the later breather by slight trimming.
It's working well. No real dripping going on.
 

Attachments

  • 20200131_120605.jpg
    20200131_120605.jpg
    76.9 KB · Views: 173
  • 20200131_120537.jpg
    20200131_120537.jpg
    203 KB · Views: 174
Last edited:
On the other hand... just remembered you went big bore and cam, so you're sucking more air than stock. So.... :shrug:

Yeah, I was thinking of my old Yamaha XT500 that I had bought new. The power was underwhelming when I got it. It had this heavy, restrictive two stage exhaust / spark arrestor on it, that I replaced with a lightweight high flow Super Trapp exhaust.
I removed the air box and hung a big K+N air filter on it.
I also bumped up the pilot jet, main jet ( one size up each ) and raised the needle jet one notch.
And finally changed the spark plug to a gold palladium plug.
That bike was absolutely transformed!
I gotta believe Somerville’s 750 with the big bore kit , the hotter cam and better flow intake and exhaust with the right jetting, that bike has got to feel stronger.
Might give ol’ Madness a run for it’s money! :D
 
I gotta believe Somerville’s 750 with the big bore kit , the hotter cam and better flow intake and exhaust with the right jetting, that bike has got to feel stronger.

After all this, I certainly hope so!!! :laugh:

Might give ol’ Madness a run for it’s money! :D
Now Bob....don't go stirring up any trouble!
 
Yes, switch to the UNI pods, they'll go hand in hand with all your other mods. If you get the all foam 4" long version (UP4200 for your BS38s) and not the shorter ones w/ end caps, I think they flow at least as good as the stock airbox, probably more and better.

Many claim the factory airbox works best but for years I couldn't really say because I ran my '78 from day one with pods. But recently, my newly acquired '83 came with the airboxes so I left them on because of what many said - for about a year, then I couldn't stand them anymore, lol. They may flow OK but they make working on the carbs a royal P.I.T.A., not to mention how difficult they are to remove and install, and all the space they hog under the side covers. So now I can honestly say the pods work just as well, maybe better even, than those monstrous airboxes.

Airbox design takes other things into account besides just air flow. That would be water protection and intake sound muffling. Accomplishing the 2nd two may sometimes require taking some away from the 1st one. The only down side I've encountered with pods is if you get caught in a heavy downpour. When you come to a stop at idle, like waiting for a light to change, the carbs may suck some water in and the bike will start stumbling or running rough. No big deal really, you can keep it running with throttle blips, and at speed, the rain doesn't seem to effect it. It must just blow by and not get sucked in. That being said, I think the benefits far outweigh this one drawback.
 
As far as re-jetting for your mods goes, yes, you will need to do some, but these bikes don't need huge increases in jet sizes. Your older carbs also came set up richer from the factory so shouldn't need as much as a later set might. The usual routine is 1 to 3 up on the mains, one up on the pilots, and lean the needles a step. I'd start with one up on the mains. If that induces stumbling in the upper midrange under heavy throttle applications, you'll need to lean the needles a step. That will often lean the idle to midrange transition area and cause a flat spot right off idle. Then a larger pilot will be needed.

Being a 750 now won't effect the jetting much at all. If you look at the carb jetting specs for the old TX750 twin Yamaha made in '73 and '74, you'll see it ran virtually the same jetting as the 650, and used pretty much the same BS38 carbs.
 
Thanks 5twins, good advice. While ideally I won't need to be accessing the carbs all that regularly, I think we all know that's wishful thinking lol. The ease of access is definitely an attractive feature.

One thing I just thought of....I suppose an additional drawback is that the carbs are not longer physically supported on both sides anymore, and are now solely hanging from the intakes. I just replaced my intakes with a new set of TourMax's since I had some pervasive air leaks last year that no amount of "snugging" could get rid of.....but that is a potential downside I suppose.

As far as re-jetting for your mods goes, yes, you will need to do some,
Haha, your new message just loaded as I'm writing this....and I was going to ask about the jetting. Thank you. I've seen your other posts on this issue and definitely heeded your advice. When I reinstalled the carbs for the 750 start up I put a 130 in the mains and 47.5 in the pilot. (So one up on each). (EDIT - I'm second guessing this...I need to double check if I upped the pilots or put 45s in...I bought both). The floats are set to 24mm and the needle is set to the stock #4 slot. Granted, I've run this bike now for 3 minutes (lol) but it sounded pretty good at start up. I will obviously have to do some plug monitoring when I get it out on the road.

So understanding I have some experimenting to do....any other feedback on jetting? I bought some 132.5 mains as well, but no other pilots. I don't have any other jets, so anything beyond what I mentioned I'd have to buy.



upload_2021-4-17_15-35-30.png
 
Yes, actual road testing will be needed to really dial in the carbs. Besides plug readings you'll need to observe how it runs at various RPMs. If there are "glitches", the RPM they occur at will direct you to the circuit or circuits that need attention. As I mentioned, a larger pilot may only be required if you lean the needles a step. These CV carbs are rather forgiving and can mask over minor jetting discrepancies because they work on engine demand. Whacking the throttle wide open doesn't necessarily mean the slide is lifting fully. It will only lift as much as the engine can use. For this reason, it's easy to over-jet them and still have the bike run halfway decent. To really test the jetting, you'll have to work the carbs hard, with big handfuls, or even full throttle through some of the RPM ranges. Only this will uncover any jetting "glitches", otherwise you wouldn't notice or see them. Now, I'm sure you don't normally ride like this, but you'll have to do some of it for jet size testing.

So, the usual routine when re-jetting these carbs is to start with the mains. Leave the needle setting and pilot jet alone for now (but you can leave that larger pilot jet in there, as you'll see). What you have to understand about a carb is the various circuits overlap so changing one affects the one next to it as well to a certain extent. In the case of the midrange, you will influence both the main and idle circuits .....

cC7PbUq.jpg


So, go up one size on the mains and run the full throttle upper midrange test. In 2nd or 3rd gear, starting around 3 to 3.5K RPMs, roll the throttle open fully and run it up to near redline. Watch for break-up or stumbling in the upper midrange, say from around 4 or 4.5K to 5 or 5.5K RPMs. If you get none, go up another size on the mains. Keep doing this until you do get the break-up and stumbling. Now lean the needle a step to fix that. You could try another size up on the mains but that usually brings the stumbling right back, so when this stumbling begins to occur, that's the big "tell" that you've gotten as big on the mains as you're going to. To go further up on the mains would require more radical changes to the midrange, like changing out the needle and needle jet for leaner ones, but those parts aren't available for the BS38s.

So, when you get to the point that you're getting stumbling in the upper midrange, and you fix it by leaning the needle a step, now you might need that larger pilot jet. That's why I told you you could leave it in there, you'd probably need it anyway. For idle circuit testing, find a large empty parking lot somewhere where you can tool around slowly in 1st gear. Take off easy in 1st then roll the throttle open. It doesn't need to go wide open, just a big handful. You want to put a load on the circuit to see how it performs, how it transitions into the midrange. If it gurgles, sputters, or stumbles, you're probably too rich. If you get a flat or "dead" spot, a momentary hesitation before it takes off, that's usually a lean indicator. Also, cruise around in 1st with the throttle just cracked open a hair. Watch to see if the bike runs smoothly or surges. Surging is a lean indicator.
 
Thank you for taking the time to spell all this out. Very helpful (to many I’m sure). Will use this as a guide once I get out on the road. My goal is to try to get 50 miles on the bike first thing, to help seat the rings and break in the cam, and then do an oil change and check the torque on the head. Hopefully it runs more or less well enough to do that, then I can start trying to fine-tune the carbs. Sounds like having a couple more sizes on hand for the mains and possibly the pilots isn’t a bad idea.

Cheers @5twins appreciate you sharing all that experience
 
I don't think you'll need any bigger on the pilots than one size but maybe the mains might take a little bigger than 2 up. But, I think I'd hold off until you test what you've got. 132.5's may be as big as the midrange settings will let you go. But then again, one of the first rules of jetting is that when you think you're right, try the size above and below to confirm it. With the mains, you usually keep going up one size at a time until you get too big, then step back down to the previous smaller size that worked well.

As I mentioned, it's easy to over-jet these CV carbs so something else you can keep an eye on is your gas mileage. Get too big and rich, and it will take a pretty big hit, like 5 to 8 M.P.G., even though the bike may seem to run good. When you finally get the carbs right, you may end up losing a mile or two per gallon (but maybe not), but I just consider that the price you pay for the better performance. Your mileage is still going to be way better than a car.
 
Been a minute. So, I finally got back down to my bike to button up the rest of my winter maintenance projects. I rebuilt the forks including some new seals and a set of progressive springs.
CFA3F994-D8D9-4451-B735-F16C77130A99.jpeg


I polished up the lowers a bit as well. Nothing super fancy, but an improvement....before/after
E3DC90AC-901B-480A-AEA8-CBBCD8D6CDAF.jpeg


Also flushed/replenished the front brake and added my Vesrah pad (and drilled my missing rotor hole @5twins lol).

I spent some time tweaking the mix screw and idle jet to try to get it idling well. I think it's still a little high, but it seems to be running pretty strong. Since I had about 20 minutes on the motor at ~2000 rpm breaking in the cam, I also took the opportunity to retorque the head bolts, since there had been 3 or 4 heat cycles (They did all tighten a little bit even after that relatively small amount of run time, FYI).

After some warm-up time and a blipping the throttle a bit to make sure I wouldn't get stranded, I took it out on the inaugural ride. Have to say, the bike feels AWESOME! Best way I can describe it is it just feels capable. The 8-plate clutch feels very precise and grabs just how you'd want it to. The motor feels hungry, and was very responsive whenever I gave a bit of throttle. It sounds great. The front end feels a lot less 'squishy' (although I really need to get some miles to feel this out). I did a nice little 18 mile loop or so with a lot of hard acceleration up to 3000-4000 rpm followed by release for some compression braking to help seat the rings. Very happy with how things are looking as of now (knock on wood). No visible oil leaks at the moment (@TwoManyXS1Bs confirmed that the cam covers are indeed seated, btw). I will need to really pay attention to the plugs to monitor the jetting, but have to say right now, it felt strong and didn't have any stumbles. Feel like I'm at least in a good starting place carb-wise.

Few pics. I'm already seeing some gold on my headpipes, probably from my idling/cam break-in without any sort of fan. Dumb on my part, but will try to polish out if I can. It may just be what it is.
07783580-A811-4ADC-9CCF-B1FB72970558.jpeg
88337CAA-AD5B-408D-A8D2-526CAF4429DF.jpeg


And because you asked @TX650A919 Van Islander - here's a little drive by video. It sounds better in person, but I think it gives you the idea.

Next steps....I'll head down next weekend for a couple more small rides to shake any bugs out, change the oil, then ride it back home to Somerville to get ready for the Distinguished Gentleman's Ride here in Boston on May 23rd.
 
Aftermarket single wall headpipes usually will turn colors on you eventually, even if the jetting is good. It's just the nature of them. Gold isn't that bad, blue is what comes next and from running hotter. If they went blue immediately, that might indicate being a little lean on the jetting, or a possible exhaust leak at the head. That's what happened with the MAC headpipes on my '78. They didn't seal well into the head and turned colors pretty much immediately. The right side turned more than the left because it was leaking worse. The MikesXS headpipes I recently put on my '83 are barely showing any color at all after several hundred miles, maybe just a touch of gold. I was quite surprised but they are thicker and heavier than the MAC ones.
 
Have to say, the bike feels AWESOME!

Your bike sounds awesome too! :geek: Very healthy indeed! I kinda like the gold on the header pipes, if it really bugs you there is a product called blue away that is supposed to remove it, I have even had luck with Blue Magic polish.
P.S. you live in a beautiful area. :thumbsup:
 
Aftermarket single wall headpipes usually will turn colors on you eventually, even if the jetting is good. It's just the nature of them. Gold isn't that bad, blue is what comes next and from running hotter.
I kinda like the gold on the header pipes, if it really bugs you there is a product called blue away that is supposed to remove it, I have even had luck with Blue Magic polish.
Yeah, that's what I've heard... I could live with the slight gold, I'm just hoping it's not on the way to blue. Time will tell I suppose. Bob - I did get something similar called "Blue Job" (har har), that's supposed to be pretty good. I'll report back.

The MikesXS headpipes I recently put on my '83 are barely showing any color at all after several hundred miles, maybe just a touch of gold.
I wonder if the ones I just got from yamahaxs650.com are the same as your Mike's 5T. I don't have a lot of context for comparison, but these new ones I put on seem to be pretty nice quality. Out of curiosity - how would one know if they have a leak around the exhaust header? I was careful to torque mine evenly and the gap between the mount flange and head is even...but other than that not sure how I could (easily) tell.

P.S. you live in a beautiful area.
Thanks! This is down with family on Cape Cod where my bike was stored for the winter. Spring has sprung here, so it is particularly beautiful this time of year.
 
Out of curiosity - how would one know if they have a leak around the exhaust header? I was careful to torque mine evenly and the gap between the mount flange and head is even...but other than that not sure how I could (easily) tell.
2 ways I know of....
Look for soot around the pipe and it's flange.
Move a birthday candle around the flange (cigarette smoke works too), rev the engine and see if it blows the flame (smoke).
 
Back
Top