1980 Special - Sticky Carbs?

[RadMax]

So I’ve been playing with my carbs, they’ve always been a bit “sticky”, and frankly? I’m tired of it. They’re just the standard USDM BS34s (“Bit Sticky”?)… I’m broke and I’m cheap, but I don’t mind spending money on performance if it’s worth it. What should I do? Buy new diaphragms? New slides? New carbs? Or should I say “Enough of this BS!”, save my money, and get something like these?

https://www.mikesxs.net/the-coveted-mikuni-vm34mm-carburetor-complete-kit-fits.html

I just completely rebuilt my carbs, and I’m sure the idle is wrong, but something tells me I shouldn’t be jumping to 3K with the choke on.

 

[RadMax]

P.S. I REALLY hate these carb boots.

 

[Jan_P]

I am not good at carburetors reason being having used 34 .s for 40 years without problems.
On 2 1980 ies but with European 34 s

Not saying running perfect all the time but no problems in comparison to other things
( Put it like this -- I am much better on the electrics --Lucas class amount of problems )
My guess it to high rev setting making it jump up with choke. Air leaks is another common problem.

Take a deep breath and post some pictures and the story behind the problem I am pretty sure someone
here with knowledge better than experts and friendly. Helpful persons Can give the right advice.

perhaps that helps

 

[RustiePyles]

What do you mean by sticky? Throttle return sticks? Throttle shaft sticks? Slides stick? They're covered in honey? "Sticky" cloud be anything from bad cables to a worn out shaft bore.

 

[5twins]

I feel that most carb issues can be attributed to guys not doing a thorough enough and 100% refurb job. The P.O. of my '83 said he always had some carb issues. I gave the carbs a 100% refurb and they've worked just fine for me. In doing so, I discovered the P.O. missed a couple things. He didn't replace the butterfly shaft seals or the little o-rings on the mix screws. Those items were hard as a rock from age and the mix screw o-rings were also all mashed flat and deformed.

 

[RadMax]

Well I replaced the cable, so that isn’t it.

 

[RustiePyles]

Well I replaced the cable, so that isn’t it.

Improperly adjusted cables can make throttle return very sticky.

 

[5twins]

Improperly routed cables too. If it's pinched or badly kinked somewhere along it's run, that can make it hang up. But ..... you haven't really explained yet just exactly how it acting, when it's sticking. Are you just dealing with a high idle issue or is it sticking at speed?

 

[RadMax]

I did a fairly thorough rebuild job, wasn’t able to

I feel that most carb issues can be attributed to guys not doing a thorough enough and 100% refurb job. The P.O. of my '83 said he always had some carb issues. I gave the carbs a 100% refurb and they've worked just fine for me. In doing so, I discovered the P.O. missed a couple things. He didn't replace the butterfly shaft seals or the little o-rings on the mix screws. Those items were hard as a rock from age and the mix screw o-rings were also all mashed flat and deformed.

Do you know where I can find some? MikesXS is sold out.

 

[xjwmx]

I just completely rebuilt my carbs, and I’m sure the idle is wrong, but something tells me I shouldn’t be jumping to 3K with the choke on.

If jumping to 3k with the choke on and the bike warmed up is the problem, that's normal (as long as turning off the choke takes it back to normal).

 

[650Skull]

If the slides are the problem then use some wet and dry 2000 grit sand paper and clean the slides and bore. Use water of something better like WD40 as a lube with the sandpaper.

Cruzinimage sell BS34 slides with the diaphragm cheap

 

[xjwmx]

BS34 slides have a polymer coating that you don't want to use sandpaper on. If everything is clean and undamaged and put together right, no reason for the slides to stick

 

[5twins]

If you mean the butterfly shaft seals, most of us use the Suzuki equivalent now, about $2 and so much cheaper than the Yamaha one, especially since they recently jacked the price to $18, lol.

https://www.partzilla.com/product/suzuki/13651-51010?ref=56effa58763ad658ef407e618a6d5738324b7135

For the mix screw o-ring, a 1mm x 3mm size fits and works well, no need to buy the actual part. I've been installing these 1 x 3's for years.

 

[toglhot]

BS carbs are alright, but VMs are a lot better. Just be aware they aren't cheap and some don't fit properly due to cables interfering with the taps using the supplied manifolds. Hoos sells rubber boots similar to the originals that take the VMs and site the carbs clear of the taps.
I was told by the Oz distributor that not all XS650s are built the same, so the carbs will fit without problems on some, but on others the carbs have to be angled or different manifolds used. Googling the subject does bring up a few complaints on different forums. I don't doubt that not all XS650s are built the same going on the build quality, the frames are absolute rubbish.

 

[xjwmx]

For the mix screw o-ring, a 1mm x 3mm size fits and works well, no need to buy the actual part. I've been installing these 1 x 3's for years.

What replacement BS34 mix screw works best? I remember years ago a replacement that had a different profile from the original BS34 for XS650 and it was a problem.

 

[5twins]

I discovered you can still get originals from Yamaha for less than $10. This is pretty much the same price as knock-offs so why buy them? Even though Yamaha never listed the mix screw for our 650 BS34s, they do for many other models running similar carbs .....

https://www.partzilla.com/product/yamaha/12R-14105-00-00

I found an auction on eBay for aftermarket ones that the seller provided detailed measurement pics .....

I compared these to an actual screw I had and they pretty much matched, so I took a chance and ordered some from Yamaha. So, I can confirm that this is our BS34 mix screw, a perfect match and fit.

 

[xjwmx]

Great. Thanks.

 

[RadMax]

I found seals for the butterfly shaft, screws for the butterfly, but I can’t find the butterflies or the shafts anywhere. If I drill out the screws, I risk damaging those. And I’d like to be assured I can get replacements before I mess with that.

 

[5twins]

You can't get the butterfly plates or the shafts, never could. Yamaha never sold those parts. Used ones are your only option. But, if you take care, things come apart OK with no need for drilling. It's very important that you use a properly fitting J.I.S. screwdriver or 1/4" insert bit. I use an insert bit in a T handle holder. I soak the screws with penetrating oil for a day or so, and apply some heat to them. Also, and I feel this is very important, I grind off the peened ends of the screws with a Dremel .....

 

[RadMax]

Update: I managed to drill them out on a spare (junk) carb without any drama. Taped off the holes, packed the carb with a paper towel, sprayed it down with a 1:1 mix of acetone and ATF… The heads came out, I got the shanks very carefully with a long pair of needle nose pliers, I’ll tell you what drill bit I used in a minute. The threads on the shaft don’t appear to be buggered at all! I checked the seals, they’re definitely old and worn, but… It seems weird that these would be my problem. Any air leak after the carbs is bad, sure, but like… What do you guys torque your carb boots to? They’re old, they’re hard, they’re a bear to get on… Should I get new ones?