BS34 1980 XS650 Special Carb Mix-Match?

zodc

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Hello all! I'm new here and have been searching/lurking recently. I just picked up an '80 XS650 Special that had been sitting for a number of years.

Pulled the carbs to give them a clean and when I took out the diaphragm assembly, each side was different. Is that a common thing to see? Below is a photo of both assemblies.

upload_2019-11-2_22-21-15.png


Thank you.
Steve
 
No, that's not normal. The slide on the right in your pic is a correct type. The one on the left with the snap ring in it is from some other carb set and bike.
 
Thank you for the replies! I'll start searching for parts. I'm sure I'll be posting more as I work and ride this thing. Good fun!
 
Kinda interesting...............BS34 carbs and 2 different type of slides. The slide on the left, In the pic), isn't a normal XS650 BS34 slide. if it did/does fit into the BS34's they could be off a suzuki ?????. Would be interesting to know what the needle is and if it sits the same as the other slide...........may need to check the needle Jet as well, if the needle is different the Needle jet may have been changed to suit the needle..........

More pics and info on the needles and jets will help
 
Some other Yamaha models also used BS34 carbs with a slide like that (XS400, XS750 triple, XS1100).
 
Thanks! I pulled them off and cleaned the carbs last week. That's when I discovered the two differences. I actually put them back together and mounted them again just to see if the bike would start. It was successful in starting and holding an idle. However, the right side began dripping gas from the air intake inlet (I did not have air filters mounted). I have pulled them off again and will be taking them apart. I'll be sure to snap some photos.
 
Those valve slide diaphragms are expensive! And to think I'll be need to get jets and needles etc... probably should get a pair while I'm at it... seems more reasonable to buy a full set of rebuilt carbs.
 
Kinda interesting...............BS34 carbs and 2 different type of slides. The slide on the left, In the pic), isn't a normal XS650 BS34 slide. if it did/does fit into the BS34's they could be off a suzuki ?????. Would be interesting to know what the needle is and if it sits the same as the other slide...........may need to check the needle Jet as well, if the needle is different the Needle jet may have been changed to suit the needle..........

More pics and info on the needles and jets will help
Suzuki GS450!
 
upload_2019-11-6_22-36-13.png
OK, pulled the carbs off again and here we go...
Engine started up but right side as mentioned before, started dripping gas so I didn't keep the bike running long.
I pulled the diaphragm apart on the right side first.

upload_2019-11-6_22-38-54.png upload_2019-11-6_22-48-54.png
Pulled the main jet and pilot jet.
upload_2019-11-6_22-41-5.png upload_2019-11-6_22-41-28.png
Main Jet: 132.5
Pilot Jet: 42.5

upload_2019-11-6_22-47-42.png upload_2019-11-6_22-49-35.png
Pulled off the left side and the Main Jet and Pilot Jet are the same.

upload_2019-11-6_23-2-58.png
The only difference between the two other than the slide needles is the pilot air jet screw?
I'm not sure what it's called but the right side carb is 2.5 turns from bottom/closed and the left carb is 4.0 turns from bottom/closed position.
 
Kinda interesting...............BS34 carbs and 2 different type of slides. The slide on the left, In the pic), isn't a normal XS650 BS34 slide. if it did/does fit into the BS34's they could be off a suzuki ?????. Would be interesting to know what the needle is and if it sits the same as the other slide...........may need to check the needle Jet as well, if the needle is different the Needle jet may have been changed to suit the needle..........

More pics and info on the needles and jets will help
How do you determine the size of the needles?
 
The needles should have a number on the sides as well, but yours have been changed from stock. Stock ones didn't have any adjustment slots for the clip, just one slot. But the big thing will be how much of the needle hangs out the bottom of the slide when it's installed. That has to match side to side and may not with the 2 different slide types. If it does then those mismatched slides could possibly work.

For reference, the stock 5HX12 needle with the "fixed" clip measures about 50mm from the clip down to the tip. See if you can achieve that length with your adjustable ones in one of their clip slots. If you can, mount one in the original slide you have and measure how much hangs out the bottom of the slide. Then try to achieve that same measurement with the mismatched slide. It may require setting that needle in a different slot. Something else you need to know is that the needles are assembled differently in those two different slides as far as the spacer, spring, and washer positions go. Here's some diagrams, first the original .....

i3ZD5ra.jpg


..... and then that mismatched one .....

JBHxvr2.jpg
 
That adjustment screw is your mixture screw and controls the fuel/air amount in the idle circuit. Turning it out lets more in (richer), in lets less in (leaner). The mismatched settings could indicate the needle heights weren't the same and was an attempt to compensate for that. The main and pilot jet sizes you found are stock. Here's a chart I made up listing them .....

7wbHkpb.jpg
 
This is awesome information! Thank you so much. I’ll see what I can find on the needle lengths.
 
Your pilot jets look quite corroded.
My old pilot jets had slowly eroded larger over the years, making them more than the next size larger, making my idle a bit rich.
71XS1B-Carbs-PilotJets01.jpg


Need a set of pin gauges, or an #80-#61 drillbit set to try to determine the orifice sizes. Or, if in doubt, replace them. Per 5twins, try to use only genuine Mikuni jets...
 
Yes, I was going to mention the pilot jets, but more for the fact that the screwdriver slots in them look pretty bad. Put those back in and it may be very difficult to ever get them out again. I usually start with fresh jets when I'm renovating some carbs or a bike, they're not that expensive.
 
Thanks for the feedback! Yeah, mines are surely aged and will be replaced. As 5twins mentioned the screwdriver slots. It was difficult to remove. I'll be at it this weekend again so I'll measure the needles and also check to see if they both are the same lengths. On a side note, what about the jet-looking thing connected by a wire under the float. It has a rubber cone tip. Is that something that needs to be adjusted as well?

The bike is completely stock as far as I know and I won't be running aftermarket filters or exhaust anytime soon.
For now it's getting it running and dialed in correctly.
 
That's your float needle. The float pushes it into it's seat (the float needle seat) as the fuel level in the bowl rises and the float lifts. It shuts off the fuel flow into the bowl eventually so it doesn't over-fill and start leaking all over the place. There's no adjustment for it but there is for the float height. The float height setting controls what level of fuel in the bowl shuts off the gas flow.
 
I see. thank you. Again, great information. I am really appreciating the replies. This could be why gas was leaking from the carb. The float needle tip is ripped and the black rubber on it is just hanging there.
 
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