Engine/Frame VINs Don't Match?

abyssmaltailgate

Greenhorn Mechanic
Messages
148
Reaction score
8
Points
18
Location
Chicago
A few months ago I purchased one these beloved Yammies under the impression it was a '77 XS-D (U.S.). The title matched the VIN stamped on the neck tube, and using the attached .pdf (readily found in several threads), I confirmed this to be true. Although the bike was fairly stock, the previous owner had swapped out a handful of components making ID with the Haynes manual fairly difficult. It was only after hauling the non-running bike from Milwaukee to Chicago that I realized the VIN stamped on the engine differed from that on the frame! Looking at the same chart, I identified the engine as a '74-'75 XS-B (U.S.).

While browsing our forums for answers, I've come across threads about some models not having matching VINs, which furthered my confusion. My question is twofold:

1) Are my engine and frame from different bikes? (I'd say yes since the #s are not within the same model ranges) and...

2) Which specs in the Hayne's manual should I follow? I know to follow those for the engine when setting up the engine; however, Haynes lists specs for an XS1 B and an XS650B but does not mention an XS-B. Based on the chart, my hunch is to assume those for the XS650B since it already specifies an XS-1B but not the former.

Thanks in advance, as I look forward to any help!
 

Attachments

  • Yamaha XS650 VIN # ID Chart.pdf
    802.9 KB · Views: 355
In answer to your questions:

1. Yes they are from different bikes. When the bikes are this age, some swapping is common.

2. Re the specs - For the engine stick to the 74 specs. For the remainder, stick to the 77

One point to note - carbs. They could be from anything and may not be 74 the same as the engine. Pop some pics up or do a search and we can help identify them
 
One point to note - carbs. They could be from anything and may not be 74 the same as the engine. Pop some pics up or do a search and we can help identify them

All I know is that they are Mikuni Carbs, and the previous owner claimed they're "original". Attached are some pics to better help. Additionally I took one of what I think is the starter motor (?); I thought this might help as well.

Also, when you say stick to the '74-'75 specs, do you agree that I should follow those for what Haynes list as the XS650B as opposed to the XS1 B?
 

Attachments

  • 2015-12-02 13.35.05.jpg
    2015-12-02 13.35.05.jpg
    209.4 KB · Views: 329
  • 2015-12-02 13.38.17.jpg
    2015-12-02 13.38.17.jpg
    201.1 KB · Views: 318
  • 2015-12-02 13.38.37.jpg
    2015-12-02 13.38.37.jpg
    202.3 KB · Views: 313
  • 2015-12-02 13.38.50.jpg
    2015-12-02 13.38.50.jpg
    193.1 KB · Views: 306
  • 2015-12-02 13.34.12.jpg
    2015-12-02 13.34.12.jpg
    182.4 KB · Views: 298
Those carbs look to be the 76/77 carbs. Carbs changed every 2 years so it is important that any jets or needles are the right ones for that particular set of carbs.

Early models 70 XS1, 71 S1B, 72 XS2, 73 TX Have a different engine to the later 74-83. Use the settings for 75B engine, doesn't make any real difference from 74-83 so any of those settings will work.
 
Yes they are BS38's. BS38's were used on all XS/TX650's from 70-79, and they changed every 2 years. That is why it is important to Verify what year BS38's you have before doing any work to them.
 
Yes they are BS38's. BS38's were used on all XS/TX650's from 70-79, and they changed every 2 years. That is why it is important to Verify what year BS38's you have before doing any work to them.

Thanks! But how do I go about determining the exact year of these BS38 carbs? I'm looking through the carb guide that was posted earlier and it seems like I can figure it out by identifying certain components used in the carbs (i.e. mixture screw or pilot jets); however, being my first time doing this, it's all Greek to me. What resources are out there that make it easier to identify carburetors and better help me with this process?
 
The early carbs were not linked with the braces top and bottom.
The later replaced the vent lines with molded passages that were vented back to the intake bell. You would see those holes at 3 & 9 clock positions in the intake bell.
 
Yes you should be safe using hte 76-77 carb specs.

From what you have said no part of this bike is an XS1B and that is a good thing. The engine would be XS650B AKA the 1975 XS650 There are few differences between engines 75 to 79 they are all points ignition, 447 motors with one grounded brush in the charging system.
 
The early carbs were not linked with the braces top and bottom.
The later replaced the vent lines with molded passages that were vented back to the intake bell. You would see those holes at 3 & 9 clock positions in the intake bell.

Weekendrider, are you referring to the holes seen in this pic? I would call that 4 & 8 o'clock... is that what you were referring to, or are these different from that?
 

Attachments

  • 2015-12-02 13.38.37.jpg
    2015-12-02 13.38.37.jpg
    202.3 KB · Views: 301
Yes you should be safe using hte 76-77 carb specs.

From what you have said no part of this bike is an XS1B and that is a good thing. The engine would be XS650B AKA the 1975 XS650 There are few differences between engines 75 to 79 they are all points ignition, 447 motors with one grounded brush in the charging system.

In that case I suppose this pic will help confirm your suspicions? I knew my ignition was points based, but fortunately I had already started going through my charging system and it looks like there is only one brush on this stator. Thanks for your help!
 

Attachments

  • 2015-12-03 15.23.56.jpg
    2015-12-03 15.23.56.jpg
    172.6 KB · Views: 304
Yes that is the correct stator

two brushes there, you can see them from the back, check lengths.
measure ohms accross the slip rings after you clean them with very fine sandpaper, should be 5.0-6.0 ohms. find the charging guide. When you get to needing to troubleshoot.
 
Back
Top