Back at it again... Carbs to lean (1980)

[NewestOnTheBlock]

I've been working on my 1980 xs650 for awhile now. I think I have most of the issues worked out, except for one last thing. The bike is running lean. I pulled the plugs and they are black, and all the issues that are associated with a lean bike are present.

I went out and got a clymer manual. Its great, but I'm slightly confused.... In the book it describes in detail the dead cylinder method. It talks about adjusting the idle mixture screw and all. However later on in the book, it says "All 1980 and later models have no idle mixture adjustment method". So what I am interpreting that statement as....is that the dead cylinder method that is described early on in the book, does not apply to the 1980...Is that correct. If so, how would I go about addressing the lean carb?

Secondly. My idle mixture screws seem......well.....weird? When screwed in (down) all the way, one side seems fine (as in where it should be). While the other side screws in a significant amount more....almost double. Is this normal? or did the previous owner do something to it? Threading is fine, just it goes in almost twice as much as the other.

 

[5twins]

Starting in 1980, the mix screws came from the factory capped over with a brass plug. That's probably why the manual is telling you they can't be adjusted. But if you remove the plug, they can be. It appears that has been done to yours. The screws should go in the same amount. Here's a pic of the screw assembly. Note the small washer and o-ring at the bottom .....

A P.O. may have replaced those without removing the old ones first on that screw that won't go in as far. Worth pulling and investigating. Also note the needle or pin tip on the screw. Fully screwed in, that should poke out the mix screw outlet hole in the main bore a little bit .....

 

[NewestOnTheBlock]

Great, getting ready to pull the carbs off now. I'll take a look at that.

So with that information, moving the cap off. I should be able to to use the dead cylinder method?

 

[NewestOnTheBlock]

So I pulled the mix screws... I found 2 things...

The first. is that right side, the first centimeter of threading is gone. As in it looks like someone drilled it out, so I can now see why it has to go in farther than the other side.

Secondly.....one side had 2 (both) orings in it, the other had none...... How does this effect performance/everything? or is it rather minor?

 

[5twins]

No, that's important to proper mix screw function. It seals the screw tip in the hole. Note the assembly sequence in the pic above. The o-ring goes in the hole 1st with the little washer on top, or else the spring will dig into the o-ring and tear it up. The BS34s like their mix screws set between 3 and 3.5 turns out from lightly seated (closed).

 

[gggGary]

I'm thinking you would put it back together with one o-ring on each......

 

[NewestOnTheBlock]

Gotcha. I have changed it so each one has 1 oring now.

Something I noticed. The right side seems to have a longer mix "tube"....as in the metal casing that the screws gets into. When I measured it...its a few millimeters longer that the left. Not much diffrence, but still noticable to catch my eye.....This might explain why that side seems to not have any threading right at the top?

 

[NewestOnTheBlock]

Another thing....on the weird/odd side. even though it screws it farther than the other. The tip of the screw does not come out of the hole, as seen in the pic above. When screwed in all the way, are the tips on Both sides supposed to show? or just one side? because on the "normal" side everything is functionally like everyone/the book says.

 

[5twins]

You should see them both. The "tower" that the screw goes into may have been cut down on that low side. Most people are total idiots when it comes to working on bikes. They do some strange and terrible things to them. This is why we so much love to hate those P.O.s, lol.

 

[NewestOnTheBlock]

Well F***. that make any since then. If the "Tower" is cut down more than the normal side. Shouldn't the tip of the screw stick out even more? The thing though is that no screw is sticking out at all....

wtf.

 

[NewestOnTheBlock]

I'm gonna take apart again. I'm curious to see if I switch the screws...will both tips stick out?

 

[NewestOnTheBlock]

Measuring the screws, they are exactly the same. So I took the brightest shop light I had lit the inside of the "tower" up. Sure enough, some random gunk that was preventing the tip from showing. Cleaned it out. now it shows.

 

[gggGary]

The thing is; if the rest of the idle circuit hasn't been properly cleaned (it hasn't) you aren't done yet, just say'n.

 

[NewestOnTheBlock]

The thing is; if the rest of the idle circuit hasn't been properly cleaned (it hasn't) you aren't done yet, just say'n.

Right. My next step is that I'm going to tear the carbs down, and do a thorough cleaning. I have my clymer book, and I also found these 2 youtube videos....

Somethings are simple screw-apart, then screw back together. While some other parts I need to be very specific about. Which parts are those?

 

[5twins]

Yes, a proper carb cleaning sometimes takes several tries before you get it right. You must insure that the mix screw outlet and the 3 by-pass holes ahead of it in the bore are clear. They flow the fuel/air mix from your pilot jet which controls the low speed running.

 

[gggGary]

Look through the carb guide then go through it again, and again then carry on. Use great care with the small holes in the pilot jet, there is one in the center too. I like a single strand of copper from a motorcycle electrical wire for this job. Make sure the rubber caps for the pilot jet are in good shape and in place. Be certain the choke passage at the bottom of the float bowl is clear. Replace the o-rings on the float valve body they are always hard and allow fuel to leak by the valve.

I like to bump the tapered needle up with a small washer to get rid of the pesky just off idle hesitation the BS34s are noted for.

 

[5twins]

That guy in those videos is a carb cleaning MORON. Find some better ones. He doesn't explain or tell you what any of the parts and passageways are, what circuits they feed, etc. I'm pretty sure the mix screws are still capped on that set too. You can't do a proper cleaning with the mix screws still in place.

 

[NewestOnTheBlock]

Lol good to know. In that case I'll stick with the carb manual and my clymer book.

 

[NewestOnTheBlock]

So one of the things I have come across....

"The BS34 float needle is retained by a screwed-down tab, and it is
Viton-tipped; avoid contact with solvents. The BS34 seat is push-in type, sealed and
secured by an O-ring. There is a fuel screen above the needle seat in many BS34
carbs. Be sure it's clear. Clean with solvent and compressed air. Again, keep seats and
needles paired"

One of the fuel screens....is "frayed" the fine metal mesh netting is slightly parted, almost looks like a hole from a distance, but its just kind of messy. Should I replace this or is it something that is alright as is? how much would this affect performance?

Additionally, what would cause such a thing? just on one of them and not both...

 

[gggGary]

A "frayed" screen should not bother anything, I like to keep the screens on as a last stop from crap hitting the float valve. It's kind of hard to get them off and back on the body. The o-rings are much more important. They need to be soft and a snug fit in the carb body.
Remove them, if they break they were too brittle.