Later engine in older chassis

Well, it's a couple weeks later than my last post. I installed new, non vacuum petcocks, new clutch rod bushing and seal and tightened the nut on the Trans output shaft. Thanks 5 twins for the tip to check that. I thought it was tight, but I noticed the lock tab on the washer had not been folded up against the nut. Between tightening that nut and the new bushing and seal on the clutch rod, the oil leaks appear to be fixed.
Now there's a new issue. After running it around the block and back in the garage, and shutting it off, both the headlight shell and tail light lens were quite hot to the touch. Bike started running rough just before I got back to my driveway. Started it again and it ran poorly, then all the electrics shut off. I checked the fuses and all were good. Battery checked at 12.67v, but nothing works. Unless I'm missing something, I'm assuming it's a connection problem somewhere, first guess would be in the headlight shell. If it was a short I would think a fuse would have blown. Probably won't get to check it until the weekend. I know the bike is 44 years old, but it is frustrating. I've built British bikes from boxes of parts with less problems, plus the RE 650 Interceptor is calling to me.
Any suggestions are much appreciated.
Thanks
 
Electrical issues, as you describe, without a blown fuse would lead me to the ground side of things - especially the ground from battery negative to the engine cases.
 
Head straight to the battery ground strap. It's on my must replace list on every old XS through the shop.
Heat in head n tail light housing points to ground issues too. If they haven't already ground wires in the harness will melt and fuggle the harness.
 
Thank you both. I'll put that at the top of the things to check list. I just hope it's that simple and that nothing got damaged.
 
Thanks to jpdevol and gggGary. You nailed it. Problem was the ground strap. A little sanding on the frame, wire connector and dielectric Grease on the fastener and problem solved. That problem anyway. Still having issues off idle. When I had the carbs apart for cleaning, I replaced the pilot jet with a #30 and raised the needle clip up to the 2nd from the top groove. Here's a question for anyone. Should I go back to the stock pilot jet? Bike seems to run fine above 3k rpm. Playing with the mixture screws doesn't seem to have much affect once past 1 turn out. Hard to get a plug reading but they both look a little sooty. If it was a coil issue, wouldn't it be a problem through the whole rpm range. I think I'm pretty close with this bike. I just want to get it running right before riding season ends up here. Speaking of that, we're getting a little nervous about hurricane Lee. We're 2 miles back from the coast. Not worried about flooding, just the wind. We live in the woods with trees all around. Fingers crossed.
 
oldrider said:
I replaced the pilot jet with a #30 and raised the needle clip up to the 2nd from the top groove.
Click to expand...
Sorry more info needed... filters, pipes any other changes?
With stock airbox and pipes the stock jetting is VERY close.
A bit unclear; you went a slot higher lowering the needles?
Did you remove and clean the needle jets (emulsion tubes)? This is the number one not done but needed carb cleaning gotcha.
Per guides and 5T; if the mix screw doesn't change things you are off on the pilot.
BS38 float needles are fussy, old worn parts will leak making low speed operation flaky as all get out.
650carbspecsreducedsizeey7.png
 
gggGary said:
Sorry more info needed... filters, pipes any other changes?
With stock airbox and pipes the stock jetting is VERY close.
A bit unclear; you went a slot higher lowering the needles?
Did you remove and clean the needle jets (emulsion tubes)? This is the number one not done but needed carb cleaning gotcha.
Per guides and 5T; if the mix screw doesn't change things you are off on the pilot.
BS38 float needles are fussy, old worn parts will leak making low speed operation flaky as all get out.
View attachment 251081
Click to expand...
OK.
Exhaust is 2 into 1 of unknown origin, (came with the bike, it's all I have).
Uni pod filters.
#140 main jet, new
30 pilot jet, New
Z2 needle jet, new
Float needles and seats, new
Needles in 2nd groove from top, lowering needles. (The lower needles and bigger pilot jets came from a previous recommendation)
Float levels set per chart
Carbs completely disassembled and cleaned with carb cleaner then all passages cleaned with air
Bike runs fine above 3k or so rpm, crappy at lower rpm.
Plugs appear a little sooty, hence my thinking it's too rich down low and my reason for lowering the needle and thinking of going back to the stock pilot jet.
Timing is right on. Valve clearance set.
Honestly, this bike has taken a lot more time than I thought. I really want to get it sorted, but as the season winds down I'd rather spend the time riding the Interceptor 650 than scratching my head down in the garage.
Thanks for any help.
Gotta say though, I've learned a lot. I still have a 1977 xs650 standard, mostly complete except for gas tank. It needs a lot of TLC but it will run. Next year project.
 
Closely compare new and old needles and Z2 jets?
Varies by design but 2 into 1's often lean out the motor and scavenge strong enough to create tuning difficulties, as they pull mix right through out into the exhaust manifold.
 
Sure, try the stock 27.5 pilot jets. Carb re-jetting for mods is all about experimenting, and every one of these can be a little different, wanting slightly different jetting. Now usually, when you lean the needles a step to "fix" the too rich upper midrange caused by bleed-over from the larger mains, it can create a flat spot just off idle, hence the need for the larger pilot. What you have to keep in mind is that the 3 circuits in your carb overlap each other slightly, so changing one effects part of the one next to it. In the case of the midrange, moving the needle will effect both the lower part of the main and the upper part of the idle circuits, besides of course, the midrange itself.

Carb_Circuits.jpg
 
A quick update. I've gone back to a standard pilot jet and the needle clips are now in the center groove. Main jet is still #140. Bike now starts easily on choke when cold. It warms up in a couple minutes and with choke off idles about 1300 rpm. Throttle response is much improved. Still may need a little tinkering with the mixture screws, but overall, I'm pretty happy. It's not registered and will have to wait until spring for that. Plan is to clean up the side covers and tank and paint them. This is not, and was never planned to be, a pristine machine. It is a 44 year old bike and it's entitled to show it. All I want it to do is be a dependable and fun old bike. Where I live in mid-coast Maine, I have yet to see another one.
Thanks again to all who have contributed to it's resurrection.
 
Well, you won't be able to test the upper midrange to main transition area (about 3500 to 5500 RPMs) until you can get the bike out on the road and run some higher speeds and RPMs. Normally on the '78-'79 carb set, any increase in main jet size, even one, makes this area too rich and you get stumbling and break-up under heavy or full throttle application.

If you study my chart that Gary included in post #88, you can kinda see why this happens. The '78-'79 carb set got the largest mains of any of the BS38 carb sets. To do that, they had to reduce the needle jet size (Z-2, smallest put in any of the BS38s). But, this still had the upper midrange right on the verge of being too rich. That's why even one size up on the mains usually pushes the upper midrange over the edge, making it too rich and causing break-up and stumbling. The "fix" is to lean the needles a step, but that usually requires a step larger pilot as well. But your bike doesn't run right with that, and I think it can be attributed to that 2-1 exhaust. So, I'm thinking you may never get it tuned perfectly with that exhaust. My advice is to replace it with a 2-2 system, the 1.5" headpipes and the matching (1.5" inlet) Commando mufflers.
 
Exhaust change is still a possibility. The junker parts bike I have is, I believe, another 79 Special, and it has a complete stock exhaust. The condition is unknown as it's stuffed in a place that's hard to get to, 3 other bikes stored in front of it. Anyway, I did sneak the Yamaha out yesterday long enough to run up through the gears a couple times. It seems to pull fine in every gear, but I only had enough road to get to about 5k rpm in top gear for a short distance. At least the main jet is an easy swap. I think my time to do more on the Yamaha will be pretty limited until the spring. Any riding time left this year will be on the Enfield INT650. Lots of home and yard projects to catch up on before the snow flies!
 
Well, it's the end of January 2024 and time to start thinking about XS650 projects. A few more things to do on the 79 Special I got together last summer. It needs new front brake pads and then to get it registered. Probably April before I can get it out to ride.
Next project is to work on the 77 Standard. It's pretty much all there except for needing a huge amount of TLC. The bike shows about 8500 miles and the motor is free. The wiring is kind of a mess, but thanks to this forum, I'm not as intimidated as I was with the 79 Special. The biggest thing missing was the gas tank, which is one of the reasons for this post. I had been surfing around since last Fall with no luck. Anything I found at a "reasonable" price was in very rough shape. I did find one on Ebay from Showtime Power Sports in Delaware. The price even with shipping was very good, about half what I thought I would have to pay. The tank is in very good condition and it has only minor surface rust inside, nothing white vinegar won't remove. It came with a nice gas cap, but no key. Again, thanks to a 5twins post, it took about 2 minutes to open.
Last word, this is a great forum with a wealth of information.
Thanks
 

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