‘78 XS650E total rebuild

Niels B

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A while back bought a lot of xs650’s, 2 of those were in good running condition with minor issues, while the 3 others were either in pieces or partly in pieces. One of the ‘78 was 80% assembled but in need of a total overhaul. After cleaning the bike I polished the tank - dismantled everything and renovated as I took it a part. The engine was ugly but after a good clean in the vapor honer and partly in the ultrasonic cleaner it turned out ok. Transmission now installed with new bearings and seal, next step flywheel and closing up the cases.
Meanwhile I got friendly help to get the frame painted up - hopefully engine will be ready when the frame returns. Have a good weekend you all.
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A while back bought a lot of xs650’s, 2 of those were in good running condition with minor issues, while the 3 others were either in pieces or partly in pieces. One of the ‘78 was 80% assembled but in need of a total overhaul. After cleaning the bike I polished the tank - dismantled everything and renovated as I took it a part. The engine was ugly but after a good clean in the vapor honer and partly in the ultrasonic cleaner it turned out ok. Transmission now installed with new bearings and seal, next step flywheel and closing up the cases.
Meanwhile I got friendly help to get the frame painted up - hopefully engine will be ready when the frame returns. Have a good weekend you all.
View attachment 213380
You had better watch out for those painters!
 
Slowly and steadily moving along, had 3 sets of starter motors - all between terrible and rusted up to somewhat salvageable. One was so rusted up that I wasn’t sure how to proceed,(should have taken pictures before I attacked them). Anyhow got one back to life and another one back to life except missing the long stags bolts that holds the end together. The third one I believe I can make work too but also missing the stags. Tomorrow the one I plan on using will get new seals etc. had 2 sets of carburetors in awful condition - one set is now useable, however need to check I have the correct jets and needle for the ‘78E ( think it’s jetted for my ‘75.
Here is a few pick ( all parts have been through light cleaning in my vapor honer using super fine glass beads and thereafter 30-60 minutes in the ultrasonic cleaner @60C, to get all the sediments and remaining dirt out. Here’s a few pictures of the progress. Have a nice evening out there.
 

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It looks like you have a '74-'75 carb set there so that's what you will need to base your jetting on.
 
Yes, you jet these carbs, or base your re-jetting on the year of the carb set, not the year of the bike you're putting them on. The main and pilot jet sizes are tailored to the needle and needle jet sizes and chosen to work with them.
 
Yes, you jet these carbs, or base your re-jetting on the year of the carb set, not the year of the bike you're putting them on. The main and pilot jet sizes are tailored to the needle and needle jet sizes and chosen to work with them.
Got another question to the jetting if I may :). Since this is a BS38 I see in the stock carb specs that thenjets differ between each year, I.e a ‘74/75 runs a main jet 127.5 and a pilot jet 45, while a ‘78 runs a main 135 and pilot 27.5. If jetting goes with the carb year and not the model bike year what then makes the difference ? And how can I tell if the BS38 is from ‘70/74 or any other year they ran the BS38? Would like to get the jets as accurate as possible before I mount the carbs. I’m running stock air filter box and exhaust as well as the bore is standard. Rgds Niels
 
Since you have two throttle cables (not linked throttle shafts) they are before 1976
The 70-73 have a raised floor at the venturi ( note the Z6 LONG needle jet) used in the 70-73
While the 74-75 use the Z6 Short


650carbspecsreducedsizeey7.png

See that flat raised section below the slide on these 70 carbs?
XS1  early carbs 006.JPG

Your 75 set
1653687315765.png


Also the 74-75 were the only years with a choke on only the LH carb, the rich mix was sent to the RH carb via a rubber crossover tube. All other years have a choke on both carbs.

unlinked BS38s.JPG
 
thanks for that clarification, so now it's determined it's a 74-75 year carb, does that mean i have to jet it as Main 127.5 and pilot 45 ? although they'll run on a '78. and why did the '78E run with a different both main and pilot while still running a BS38 - because of the small modification on the choke and single cable throttle ? i baffled why they changed the jets on same type carb unless it had something to do with EPA and maybe different exhaust set up etc.
 
The main jet size is chosen to match up with and work with the needle jet size. Larger needle jets are paired with smaller mains, larger mains get smaller needle jets. You can see this reflected in the chart Gary posted. Your '74-'75 carb set has Z-6 needle jets paired with 127.5 mains. The '78-'79 carb set gets smaller Z-2 needle jets because of the larger 135 mains.

A local 650 guy told me that Yamaha bumped the mains up on the '78-'79 carbs in an effort to give the 650 more top end and high speed performance. Guess it makes sense although I've tried both '76-'77 carbs with their smaller mains and the '78-'79 ones, and honestly, I don't find much difference in the top end performance. Midrange is stronger on the '76-'77 set due to it's large Z-8 needle jets (biggest put in any 650) but the '78-'79 set is more refined (spring-loaded needle) and gives nicer, smoother low end performance.
 
Next step - fuel it up and get it off the lift. Hopefully it’s all in good order and it’ll start up - always a little concerned when it comes to my carb work and the refurbished electric system - anyway all seem to work when I’m testing the electric circuits.
 

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Clutch activator pin leak.
So the bike has been done for a while now, just only had time for a couple of smaller rides. Yesterday i decided to go for a longer ride!
Bikes running great, however returning home i realize that i have an oil leak between the clutch activator pin and the oil seal (not between the seal and the case itself). The activator pin is the original type, it's not bent and there are no visible corrosion. Did i just get a crappy seal ? Or is the push rod the culprit ?
I think I've seen that you can get a single long activator pin rather than the two type rode with the ball in the middle.
Any suggestion ? who sell the best seal ? obviously it looks like i need to replace the one i got in spite of it's new.
 
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