New-Old XS650 Special journey - My initial problems

[ForestHasAnXS650Too]

I just bought a 1979 XS650 and got it home yesterday, I saw it on facebook and fell in love with the style, the simplicity, and knowledge of the power and reliability has me hooked on taking care of this pretty much entirely stock 650 from over 4 decades ago.

One thing I noticed while riding it for a couple miles for the first time, is there's a bit of jolting at low rpms when I give it throttle. I can't seem to roll on the throttle delicately and it jolts even in higher gears at low rpms. But I think I know my issue.

Upon inspection of the carbs, the right-side air filter was completely busted and open to the grime of the world.



I think as I took it for its maiden voyage, dirt got sucked into the carburetor, and now my float valve or some other part is stuck open. What this is also causing is gasoline to leak out of the air intake of the carb that had the broken filter, if that's what the float valve helps control? But this is a guess, I'm not too sure.



But the jolting can also be my chain? I'll attach a link to a video showing how much play I have; I'd like second opinions on all of this.

I got a new UNI filter that's coming in tomorrow, and I'll oil it. I think I'm going to have to go in and clean one of the carbs again. The previous owner had the bike sitting dry this winter and I had to replace the battery, he said he clean the carbs himself within the 400 miles he owned it for. So I feel like the carbs might be fairly clean, but I am unfamiliar with how they should look and feel in general, and generally what all the parts in them do. All I know is what they do, and how important it is they get clean air.

I'd like a second opinion on all of this.

 

[nj1639]

Hey Forest,
'78 and '79 bs38 carbs are the same for both years. I'm running '78's on my '77 and I don't see or can't tell if yours have the bevel at the bottom of the brass slide. It's either there, turned around OR a different year carb set. If it's turned to the front it will affect performance big time. Poke your finger in there and see if there's a bevel....it'll be obvious if it's there.

 

[ForestHasAnXS650Too]

Hey Forest,
'78 and '79 bs38 carbs are the same for both years. I'm running '78's on my '77 and I don't see or can't tell if yours have the bevel at the bottom of the brass slide. It's either there, turned around OR a different year carb set. If it's turned to the front it will affect performance big time. Poke your finger in there and see if there's a bevel....it'll be obvious if it's there.

I think I know exactly what you're talking about. It seems to round off and upwards towards the front of the bike on the underside of the brass you're talking about. Is it supposed to be facing the air intake?

 

[ForestHasAnXS650Too]

Hey Forest,
'78 and '79 bs38 carbs are the same for both years. I'm running '78's on my '77 and I don't see or can't tell if yours have the bevel at the bottom of the brass slide. It's either there, turned around OR a different year carb set. If it's turned to the front it will affect performance big time. Poke your finger in there and see if there's a bevel....it'll be obvious if it's there.

I think I know exactly what you're talking about. It seems to round off and upwards towards the front of the bike on the underside of the brass you're talking about. Is it supposed to be facing the air intake?

You just blew my mind. I checked the second carb, and it is the complete opposite but correct way, and it's so obvious like you said. The previous owner put the brass slide in backwards in one of the carbs!!! Thank you so much, I think this will solve my issues once I rebuild it.

^not actually sure about this^

 

[nj1639]

I had to replace the diaphragms on mine with some JBM replacements, and one of the slides would turn after a few miles of riding. JBM posted to put a spot of super glue or epoxy to hold them in place where the diaphragm meets the slide on the topside. The stock diaphragms have a tab that fits into a recess on the carb under the top cover to hold them in place, the JBM's don't have it.

 

[nj1639]

Looks like your chain could be tightened a bit.
There was some discussion, iirc, about having less than an inch slack ? while sitting on the bike......someone might chime in for better details.

 

[ForestHasAnXS650Too]

You just blew my mind. I checked the second carb, and it is the complete opposite but correct way, and it's so obvious like you said. The previous owner put the brass slide in backwards in one of the carbs!!! Thank you so much, I think this will solve my issues once I rebuild it

I had to replace the diaphragms on mine with some JBM replacements, and one of the slides would turn after a few miles of riding. JBM posted to put a spot of super glue or epoxy to hold them in place where the diaphragm meets the slide on the topside. The stock diaphragms have a tab that fits into a recess on the carb under the top cover to hold them in place, the JBM's don't have it.

Here's a picture of the left and the right one. I'm actually just unsure now, and I'm actually thinking it's not.

left
right

 

[Its been a long time]

You just blew my mind. I checked the second carb, and it is the complete opposite but correct way, and it's so obvious like you said. The previous owner put the brass slide in backwards in one of the carbs!!! Thank you so much, I think this will solve my issues once I rebuild it.

The assistance here is truly exceptional. Last week one of the members pointed out that previous owner had assembled the auto advance mechanism on my bike 180 degrees out. The bike would never have started and I wouldn't have had a clue why. Good luck with sorting the carburettors out.

 

[nj1639]

If there's no bevel on the one then you have a mix matched bastard set.

 

[ForestHasAnXS650Too]

If there's no bevel on the one then you have a mix matched bastard set.

There's a bevel on both. I'm thinking a leak in the float valve? Or my float is defective causing the bowl to fill up with too much fuel?

 

[nj1639]

Float could need a simple height adjusting or there may be a pin hole in it.

 

[ForestHasAnXS650Too]

I'll take out and look at its guts, because the bike might also be running a little rich. I'll post about it if I get it figured out.

 

[Jim]

Methodical... one thing at a time.

RE your drive snatch: Try tightening the chain first and see if the fixes (helps) it. Remember, you need to be sitting on the bike to check the chain. As the shocks compress, the swingarm moves up and pulls the chain tighter. If you don't have anyone there to help, tighten it a bit and sit on the bike and see where you're at. Repeat as required. Then ride the bike and see if that helps.

The next likely culprit would be the springs in the clutch basket. It's not unheard of for 'em to break. They act as a cushion (cush ) drive. If enough of 'em break, you'll get your driveline snatch. That's a bit more involved to investigate and fix though, so try the chain first.

Sticking carb slides is also a possibility. You can feel for that by hand, but that might not be definitive. Put the bike on the centerstand, start it and warm it up. Take the air filters off so you can see the slides. Start the bike and slowly add throttle. Watch the slides and see if either sticks or is jerky when you rev it.

You'll need to chase down the fuel leak out the carbs, but that's likely got nothing to do with the snatch.

Just remember, methodical, slow... and lots of research here before you try something. Then ALWAYS check for results before moving on to the next thing.

 

[Jim]

Forgot an easy one....

Sometimes with a new to you bike that you ain't used to yet, excess play in the throttle itself can feel like driveline snatch. With the throttle off, start twisting it and note how much play you have before the carbs actually respond. If you can feel more than just a hair, it's too much. Use the adjuster underneath the throttle and take all the play out of it... save for just a hair. See if that helps.

 

[ForestHasAnXS650Too]

Methodical... one thing at a time.

RE your drive snatch: Try tightening the chain first and see if the fixes (helps) it. Remember, you need to be sitting on the bike to check the chain. As the shocks compress, the swingarm moves up and pulls the chain tighter. If you don't have anyone there to help, tighten it a bit and sit on the bike and see where you're at. Repeat as required. Then ride the bike and see if that helps.

The next likely culprit would be the springs in the clutch basket. It's not unheard of for 'em to break. They act as a cushion (cush ) drive. If enough of 'em break, you'll get your driveline snatch. That's a bit more involved to investigate and fix though, so try the chain first.

Sticking carb slides is also a possibility. You can feel for that by hand, but that might not be definitive. Put the bike on the centerstand, start it and warm it up. Take the air filters off so you can see the slides. Start the bike and slowly add throttle. Watch the slides and see if either sticks or is jerky when you rev it.

You'll need to chase down the fuel leak out the carbs, but that's likely got nothing to do with the snatch.

Just remember, methodical, slow... and lots of research here before you try something. Then ALWAYS check for results before moving on to the next thing.

Forgot an easy one....

Sometimes with a new to you bike that you ain't used to yet, excess play in the throttle itself can feel like driveline snatch. With the throttle off, start twisting it and note how much play you have before the carbs actually respond. If you can feel more than just a hair, it's too much. Use the adjuster underneath the throttle and take all the play out of it... save for just a hair. See if that helps.

Excellent, incredibly useful information, thank you both. I am taking my time in general to learn this bike and deepen my understanding of motorcycles, and until my air filter comes in and the weather clears up, I'll be learning by word what to take care of.

I'll get the filter on, then see what I can do about the snatch since that's easiest right now, and get the bike physically ironed out.
Then I'll move on to the carbs, and I'll use the petcocks on both sides to make sure it's the left one (since they are both connected) that is leaking and check on the floater and float valve.
Then after that, some aesthetic stuff and getting some of the OEM parts like the grab bar etc.

One more thing- I'm having an extremely hard time getting it up on to it's center stand. Any tips?

 

[Jim]

The Specials can be a real ball buster. I wound up taking about an inch out of my stand.
Proper technique makes it less of a ball buster though.... Once the stand is touching the ground, raise yourself up and put all your weight (one foot) on the stand tang. Like you're trying to force the tang into the ground. At the same time, grab hold of the seat passenger grab bar and lift. Never pull back, lift straight up. Both of those at the same time and you'll find it's not a terrible ball buster, just hard.... but doable.

 

[nj1639]

Center stand.
On my old '83 I put some 10.5" shocks on for the slammed rear look. Yeah, it looked good to me but wasn't practical at all and it was a bear to get on the center stand. Now with the stock length shocks and what Jim has stated above it's normal for my Standard. With my old Special with the shorter shocks, placing a couple foot length of 2x6 on the floor and rolling the rear tire on it made it tolerable.
5Twins has some threads on adding zirk fittings to be able to grease the center stands shaft and help ease the situation.

 

[MrBultaco]

The way that I was told/shown to check the chain is...at the center of the rear sprocket,(about in line with the swingarm) pull the chain back, if you can see more than 1/2 tooth, then you need a new one.

 

[YamadudeXS650C]

One more thing- I'm having an extremely hard time getting it up on to it's center stand. Any tips?

There is an easy solution. Put a piece of 3/4" plywood or plank (approx. 6 x 15) in back of the rear tire and back up the bike onto the plank. With the bike now 3/4" higher, engage your centerstand as usual. The bike will lift easily.


.

 

[5twins]

Keeping the pivots well greased makes an amazing difference. If they're dry and rusty, the stand will bind up big time and be very difficult to operate .....