Mixing screws

[Luckydog]

Hi Everyone,
So, I've got my 83 650 (with 34's) running pretty good, I'd say I'm about 95% happy with how's she's running but there is this last little 5% or so that's been keeping me busy tweaking it here and there. Lurking around this site I've seen how important it is to have those little O rings in the bottom of the mixing screws to be in good shape. So last weekend I removed the screws and could not find any O ring or even the small washer that sits on top of the O ring. PO Even took some mig welding wire with a small hook at the end but could not feel or see anything there - nothing! To be honest though it made my day, finally I was closing in on this remaining 5%. The inconsistent rps"s, hanging throttle now will be a thing of the past. So I ordered new the kit (screws, springs,washers, O rings from Mikes and installed it (3 turns out). Took her out and she ran horrible - lost he giddiup. Turned the screws back in to 2.5 - horrible. Turned them out to 3.5 - horrible. Kinda stumped and any help would be appreciated.

 

[angus67]

Are u sure they are 34's? 38's don't have the oring. Other than that, maybe some crud plugged up your pilots

 

[Brassneck]

I think I read somewhere that some of the 34's mix screws that you can get aren't the same size...may be a factor?

 

[angus67]

Yes. I think early 34's are stepped, 81 and later are not. Don't take my word for it. Ask siri

 

[sweet_ride_55]

Luckydog,I received the idle mixture screws from Mikes, and found the mixture screws were about 4 mm shorter than my original '83 XS650 screws.
I contacted Mikes but they could not help me. I ended up putting the original BS 34 mixture screws back in.

 

[5twins]

All the BS34 mix screws had the stepped tip. That's an E.P.A. mandated type screw. I see Mike's sells two different versions of the BS34 mix screw. One looks original with a stepped tip. The other has a tapered tip like older non-E.P.A. carbs used. If you got that tapered tip type, the 3 to 3.5 turns out probably won't apply to it. It probably needs to be set leaner. I would start it around 1.5 or 2 turns out and fine tune from there.

 

[Luckydog]

They are definitely 34's and Mike's new needles look to be exactly as the stepped originals. Since I found no O rings when I removed the original screws I'm wondering if Angus's suggestion of possibly crud (disintegrated original O rings?) might have lodged itself down in the orifice. I've believe I've read here that compressed air could work for clearing out debris here. Would this be okay to do?

 

[5twins]

Well yes, compressed air is the best for cleaning carb passageways. But, I'd do some further investigating. The BS34 mix screw goes straight down into the carb main bore from the top. With the carbs off and the screw removed, you should be able to see right down through the hole if it's clear.

Also, if you run the mix screw all the way in so it gently seats, you should be able to see the tip sticking out of that hole in the main bore a little bit. You should be able to feel it with your finger. If the tip isn't making it out the hole then my best guess it you didn't get the old washer and o-ring out of there. Sometimes those parts are so mashed in there, the washer looks like part of the hole. What's left of the o-ring could be covered, or it may have broken apart and be all gone. But still, just an extra washer in there would probably mess things up.

 

[Luckydog]

Thanks everyone. An update. After installing my new mixing screws, springs washer and O ring I could not get the bike to run properly. To the eye the mixing new screws look to be identical as the old ones. As 5twins suggested I took them out to triple check that I didn't stack a new washer and O ring on top of old mashed one's down there. I used a mig wire with a tiny hook to fish around but could not get anything else out of there. I also made sure that the lightly seated screws just barely came through, just enough to feel with your finger, and they did. Frustrated I put the original screws back in and took it for a spin which got me back to being 95% happy with the way she runs. I don't want to say anything bad about Mike's mixing screws just wanted to share my experience.

BTW I still believe there were no washers or O rings in there when I first removed the original screws. I did use the new ones, but with the old screws.

I am learning a lot and appreciate this forum.

 

[5twins]

Did you happen to compare your old screws to the new ones? Yes, the new ones are stepped but were they the same size (length) steps? Really, you can't beat original parts. Many of the repros aren't quite the same. In the case of a precision fuel metering part, a little off could make a big difference.

 

[Luckydog]

I compared them but just by eyeballing them. They looked to be exact but apparently something was off. I'll take a closer look at the distance of the steps and post later.