choke lever and mixture screws

[ippytattoo]

The idea of checking for leaks with the carb cleaner is that when you spray it on area that is leaking (like around the carb boots) you will hear a change in the way the motor is running. Try searching for bs34 jetting, you should find alot of info.

 

[5twins]

Take my word for it, you need to re-jet. Go up one size on the mains and pilots to start. Eventually you may need to go up another size on the mains but only actual road testing will be able to tell you that. You also need to clean the carbs again. You'll need to uncap your mix screw and remove it, then clean the pilot circuit again. You can't do a proper cleaning on the pilot circuit with the mix screw installed. When you re-install the mix screws, set them at 3 turns out and fine tune from there. Your mix screws have a small washer and o-ring at the bottom of their hole. Make sure you remove that stuff before using the cleaner. Carb cleaner can destroy that o-ring.

 

[wilbur60]

I assume the mix screws are under that little brass cap up near the boots. It has a little hole in the center. I am not sure how to get that brass cap off. If I do get it off is it necessary to put the cap back on, or can I leave it off so I have access to the mixture screw.

 

[angus67]

take a stubby wood screw they have big threads, and screw it into the small hole. you might have to drill a slightly larger hole to get the screw to 'bite'. dont go too deep, the mix screw is literally , like, right there. once its inthere, use a pair of pliers to snatch the cap outta there. you dont have to put the cap back on. it was just a way to keep the general public from fixing there bikes on there own.
the screw will probably pop out a time or two, just keep trying. if you screw up the mix screws, mikes has them. no big deal.

 

[wilbur60]

I am running # 135 and 27.5 Main and Pilot jets. (I think) Not sure how to tell so I am relying on the service manual.
I live at 3200 feet so I know that has an impact on the jetting. The plugs are tan so I know it is not running rich, if anything it is running lean. Still starving for gas at 4500 + RPM.
Not sure which size jets to buy. Could buy 137.5 and 30, but not sure if that is much difference. What would be a good starting point.
By the way, the carb cleaner test works great.

 

[5twins]

If you really do have a 1980 then you're looking at the wrong carb specs. Stock for your carbs would be a 132.5 main and 42.5 pilot. The only way to tell for sure is to look in the carbs and read the numbers off the jets.

 

[wilbur60]

10-4. I am going to have to take the carbs off again to clean them thoroughly. The letter that came with the K and N filters said to increase the size of each jet by about 15 % and to raise the needle up a notch. Sounds pretty drastic but maybe I will go up by 10 for the main and 5 for the primary's. Not sure if that is enough or not.
I was having a hellava time getting one of the primary's out so I finally gave up before ruining it. 10 years of sitting with gas in it was like epoxying the parts together.
Where are the gas filters located? I am sure they are full of stuff, too. just need to locate them.

 

[5twins]

Those K&N recommendations are just a general "one size fits all" tip. What I told you is what's proven to work for your bike. But do what you like, it's your bike. The needle in your carbs is fixed and only has one slot for the clip. You can't raise it but you could add a washer under the clip and shim it richer. Most don't find the need for that, just increasing the mains and pilots is usually enough.

There is a screen on the bottom of the float needle seat and screens on top of the petcock up in the gas tank. That's it as far as filters go.

 

[wilbur60]

I looked at the picture and followed your instructions regarding removal of the mixture screw. I was able to get the mixture screw/needle and the spring out, but how do you get the "O" ring and the washer out of that tiny hole?

 

[wilbur60]

Never mind about the mixture screw/"O" ring question. I fished the "O" ring and washer out of the hole with a round toothpick. Whoever said the stock jets for the '80 XS were 42.5 and 132.5 were correct. I went with a 45 and a 142.5 for starters. I will let you know when they arrive. Thanks for all your help.

 

[jchrisk1]

5twins, the .5mm shims for the needles you use, do you source them through mcmaster- carr or is that something that could be found at a hardware store?

 

[5twins]

It's possible you could find them at a hardware store but I sourced them from McMaster-Carr .....

 

[jchrisk1]

Okay. Thanks for the part number. Probably easier to just order from them.

 

[wilbur60]

Just received the jets for my carbs. The 142.5 mains fit, the 45 pilots did not. Went ahead and put the carbs together with the new mains and the old 42.5 pilots.
It is still popping, especially on decel, (just on the right side). I tried the carb cleaner test and everything seems to be ok, no leaks. Will try adjusting the mixture screws some more, see if that helps.
The good news is the larger mains really made a huge difference on my top end!! Wow. It runs great at high RPM's. Just wish I could get rid of the popping on the right side. Maybe when the 45 Pilots arrive that will do the trick.

 

[wilbur60]

I have replaced the pilot, (42.5 to 45) and the main, (132.5 to 142.5). I have set the jets several times. I have taken out the mixture screws and thoroughly cleaned the carbs. Cannot think of anything else to do. Still have this popping on decel. It also pops intermittantly while it is sitting there idling. Have tried the carb cleaner test looking for leaks around the intake boots. Also have tried adjusting the mixture screws.
It runs very well, has good top end and satisfactory midrange.
I just don't know where to look for the cause of the right cyl popping.?? Any ideas??

 

[5twins]

Carefully check your float levels. The BS34s are very picky about them. Your brass float '80 carbs are set to 27mm. If you've changed the brass floats out for plastic ones, they are set at a different number, 22mm.

 

[wilbur60]

Thanks for the advice on the floats. My manual has been saying +- 24. Is a lower setting allowing more gas into the bowl or is a higher setting allowing more gas into the bowl? Not exactly sure. It would help to know.
The only other thing that I can think of is an airleak but I just cannot locate it.
I rode it about 50 miles today and it ran fine on the highway.

 

[jchrisk1]

Higher is less fuel and lower is more fuel. When upside down.

 

[wilbur60]

1980 xs 650, Brass floats
Checked my plugs, Both were tan and looked normal. I will try adjusting the floats again tomorrow from 24 to 27.
Where can I get the specs for my B34's? I do not have something on my mac that is needed to look at the sketches and adjustments, I guess. When I click on one of the buttons to open up a PDF file I only get a blank screen.
The specs or parts blow-ups sure would be helpful. Anyway I will try changing the float level tomorrow and see what happens. I will set them at 27 as five twins suggested. I will let you know if it helped.

 

[gggGary]

No one has mentioned synching the carbs, that needs to be checked. Also before doing carb work, cam chain and valves should be set.