Issue only in first gear and only underload??

[Manbearpig1]

Hello, I recently purchased a 1978 Yamaha XS650 from an estate sale it appears to be pretty much stock. It was last registered in 1991 I cleaned the carbs and cleaned and adjusted the points and she fired right up.
The issue I'm having is that in first gear only if I accelerate somewhat at a normal rate and especially if I'm going uphill as the bike hits 2,500 - 3,000 rpm it almost feels like the clutch slips then re-engages and it'll continue to do that at about every 1000 rpms consistently after that. Shift into second no issue, no issue in any other gear after that. I thought it was probably a clutch issue, so I opened clutch cover and checked the plates and replaced the springs and readjusted the clutch this had no effect.
If I'm going downhill or flat ground and very slowly creep up on the RPMs it doesn't do it?

Any suggestions would be greatly appreciated!!!

 

[kshansen]

Well if it was a clutch problem I would expect it to be worse in the higher gears. Are you sure it's not jumping out of gear when this happens? Hard to really diagnose from a distance but I would probably start by cheking things related to the shifting mechanism. Maybe the shift cam and the screw that holds the detent pins to it.

Not sure if those terms are correct but there is a star shaped retainer that holds the pins in and has a long screw that holds the assembly on the end of the shift cam. I had one or two bikes that had a shift problem that was traced to the long screw either breaking of coming loose.

 

[jetmechmarty]

Disengagement of the clutch is a smooth action. Disengagement of the gears clatters.

 

[Manbearpig1]

Thanks for the responses!!

I checked the screw that holds the star plate on the shift cam last night all looked good.

Another way of describing the problem is that it almost like it's hitting a rev limiter (if it had one). Just at every thousand or so RPMs it increases but only in 1st gear and it happens consistently, but I can make it not do it if I slowly creep up on the RPMs and it's not going up hill.

Is it possible it's an issue with the auto advance mechanism?

 

[Jan_P]

What is strange is that it is only in first gear
If it was fuel / rpm related it would be the same all gears
If it was clutch The test is usually high gear and throttle up it will slip

If strobe light available a quick timing check would be a first
can also give info on the advance unit.
I am thinking pilot jet dirty or small ( others here knows more )
One test could be pull out the choke when it hits the " Wall " se if it gets worse or better
+ Using the Pri position on the petcock if available.

I have never heard of XS 650 gear box malfunction

Maybe go for new points and condenser

 

[Grimly]

Very possibly rounded-off dogs on first gear.

 

[Jan_P]

Very possibly rounded-off dogs on first gear.

I believe it would clonk making noise gear shifting

 

[nj1639]

I'd be inclined towards the advance, though I don't and haven't run the points setup. It wouldn't hurt to make sure the rod is lubed and your weights and return springs are in order....from what I've gleaned reading the forum.......

 

[YamadudeXS650C]

My take on this is to ride it for at least 200 miles. At that point you will know what the issues really are. Be patient. Ride it.


.

 

[JOHNDADDY]

Check airflow, slides move smoothly
Or pinholes in a diaphragm?

 

[Grimly]

I believe it would clonk making noise gear shifting

Nope. When dogs are rounded, the gear will select normally, but be spat out under pressure (load).

 

[Jan_P]

Nope. When dogs are rounded, the gear will select normally, but be spat out under pressure (load).

? Will it Jump in again ?

2,500 - 3,000 rpm it almost feels like the clutch slips then re-engages and it'll continue to do that at about every 1000 rpms consistently after that.

 

[Grimly]

? Will it Jump in again ?

2,500 - 3,000 rpm it almost feels like the clutch slips then re-engages and it'll continue to do that at about every 1000 rpms consistently after that.

In the early stages of 2nd gear defectiveness on my GS, it did that.
Not for long, though. Within a few hundred miles of town use it was just jumping out and staying out.
The accursed PO caused it with his clutchless shifting.

 

[Manbearpig1]

So I'm fairly certain it isn't a carb/fuel issue as I've been into the carbs several times and I've tried the prime, on, and reserve settings on the petcock with no change. I recently picked up an electronic ignition system from offerup for $50 bucks I figure that should completely eliminate the ignition system as a possibility. And if that doesn't change anything I guess I'll be tearing into it and having a look at the transmission.... I was really hoping not to have to get that far into it.

Again thanks for all the input!! Much appreciated!

I'll report back after I get the electronic ignition put in.

 

[Jan_P]

Again the CSF Rule ---Cheapest Simplest First -- .I have had worn dogs between first and second on a Honda and that one clonked shifting .Never jumping out if gear- .And certainly never in again Never heard of it before .But can happen maybe.
Not saying it cant do so.
My View is that it would be noticeable otherwise than smoothly jumping in and out
But I have been wrong before .

But even if I am wrong now the CSF rule makes it rational be sure it is not anything else.
Maybe one can inspect the gears from under via the sumplate hole with a borescope
But if not it is a lot of work and costly tearing the motor out and Into parts.
Dont remember if one can do it from Underside

New Ignition is one way forward please ensure the right Voltage and Ground
And wiring so it is not shorting somewhere intermittently

I Probably would test other jets in the carburetor before anything else CSF rule But I don't know much about carburetors
How does the plugs look
Perhaps the experts on that can have an opinion
Taking the engine out and repair the gearbox
Lot of work and ? $ 300 --400 --..500 Costs

 

[JJames]

The motorcycle was never intended for use by MANBEARPIG! Best of luck.

 

[Its been a long time]

Sounds suspiciously like worn gear engagement dogs to me. It will get worse until it jumps out of gear everytime. I recall similar issues with 2nd gear and 4th gear dogs on some Sportster gearboxes. At least they were cassette gear boxes and easy to repair though.

 

[Jan_P]

Sounds suspiciously like worn gear engagement dogs to me. It will get worse until it jumps out of gear everytime. I recall similar issues with 2nd gear and 4th gear dogs on some Sportster gearboxes. At least they were cassette gear boxes and easy to repair though.

I hear what you gentlemen say But I cannot remember hearing about any gear box problems on a XS 650. Never ..
Would be surprised .But everything is possible. There is a first time for everything

 

[Its been a long time]

I hear what you gentlemen say But I cannot remember hearing about any gear box problems on a XS 650. Never ..
Would be surprised .But everything is possible. There is a first time for everything

I agree with you. There's a first time for everything though. Very difficult to diagnose remotely.

 

[Bruno_c]

In my opinion, the symptoms as described do not lead to any logical conclusion.
If the bike runs ok on all gears except first, I would ride it as it is until better understanding.