Timing issue on my right cylinder and many other head banging issues

[clabedan]

Not for the faint hearted ;-)
Here we go

The bike is stuttering at mid revs and refuses to go any faster than 50miles an hour (xs2 with mikuni bs38 Solex carbs, megaton exhausts and Uni pod filters)...

Visible symptoms:
The spark plugs are completely black
The mixture screws are fully turned in (bike doesn't stall whatever set of carbs I use). The needle is positionned in the 3rd slot from the top(center position)

After changing the carbs to another set, cleaned them with ultrasonic bath twice, new diaphragms and brand new coils, the problem remains
I then started to check timing on both cylinder with a strobe light

The right cylinder is way off the F mark to the right (retarded) whereas the left one was advanced.

No problems getting the left cylinder in line with the mark but the right cylinder is still way off after moving the timing plate to the max... So nothing more I can do there to get it inline

Any possible issue somewhere else that can cause this on the right cylinder? Wear and tear somewhere that could cause this retard?

Any other idea about the plugs being black and the mixture screws completely turned in? Can all this be related?
Told you it wasn't simple

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[5twins]

What are the points gapped at? Specifically, the upper set for that right cylinder you can't get timed correctly. Making the points gap larger will advance the timing. Are the points old? Old, worn points can make setting the timing difficult.

You shouldn't set the bottom points timing until after you set the upper set. Setting the upper right cylinder set involves turning the large backing plate, which moves the bottom left cylinder set along with it, changing their timing setting as well. The bottom left cylinder points are mounted on a separate half plate attached to the main backing plate. It can be moved separately to adjust the left cylinder timing after the right cylinder is set with the main backing plate.

Turning the mix screws in all the way should stall the motor at idle. It might not if your float levels are set too high. I think you have both carb issues and ignition issues.

 

[Brian902]

Perhaps this will help ; http://www.xs650.com/forum/showpost.php?p=22218&postcount=3

Lots of good stuff in the XS650 Tech section.

 

[TwoManyXS1Bs]

Late (or retarded) ignition timing can be caused by any combination of:

A stretched camchain.
Worn fiber followers on the points.
Worn points cam.

Interrupted ignition, which can foul plugs, can be caused by:

Bad points condenser.
Bad coil(s).
Bad hi-tension leads.
Vibration-induced poor connections at the coil wiring.

Those are the most common causes. There's others that are more unusual, but check these first...

 

[clabedan]

What are the points gapped at? Specifically, the upper set for that right cylinder you can't get timed correctly. Making the points gap larger will advance the timing. Are the points old? Old, worn points can make setting the timing difficult.

You shouldn't set the bottom points timing until after you set the upper set. Setting the upper right cylinder set involves turning the large backing plate, which moves the bottom left cylinder set along with it, changing their timing setting as well. The bottom left cylinder points are mounted on a separate half plate attached to the main backing plate. It can be moved separately to adjust the left cylinder timing after the right cylinder is set with the main backing plate.

Turning the mix screws in all the way should stall the motor at idle. It might not if your float levels are set too high. I think you have both carb issues and ignition issues.

Many thanks for the reply
Gap is about 4mm... Not sure how old they are but I would assume pretty old. If i do change them, do i need to change the condenser as well?

Regarding the rich mixture setting... When you say 'set too high' do you mean they are lower than the recommended 24mm? I.e they go too high once the carbs are upside down in their normal position or do you mean the opposite (i always get confused with this)

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[clabedan]

Many thanks

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[clabedan]

Late (or retarded) ignition timing can be caused by any combination of:

A stretched camchain. Should't be as it's been set by a pro 2 years ago and hasn't run much since

Worn fiber followers on the points. not sure what these are...

Worn points cam. Probable

Interrupted ignition, which can foul plugs, can be caused by:

Bad points condenser. Probably... Looks quite old and could be original condenser... Any idea how to test it with or without removing it from it's position (stuck inside the frame over the top of the engine and not easily accessible)

Bad coil(s). Nope, brand new ones

Bad hi-tension leads. Pretty new too
Vibration-induced poor connections at the coil wiring.

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[TwoManyXS1Bs]

A stretched or worn camchain is not the same thing as a 'properly tensioned' camchain. Just like the rear drivechain, even though you can adjust its slack by moving the axle back, eventually the drivechain is too stretched/worn to be used. A stretched/worn camchain will have a lot of slack on the backside, adjusted by the tensioner, but the stretch on the frontside will cause the camshaft (including the points cam) to be retarded relative to the crankshaft.

The fiber follower on the points is that little plastic foot that rides on the points cam. If its leading edge wears down enough, it will cause the point action to be late (retarded).

The most obvious sign of bad condensers is visible sparking/arcing in the points gap while the engine is running.

Did this translate poorly?

 

[5twins]

By "set too high" yes, I mean the measured setting on the floats is lower than 24mm. That would give a higher fuel level in the bowls when the carbs are turned right side up.

If you don't know how old the points and condensers are then it would be best to replace them. Points are good for maybe 10 to 15K miles. Condensers can last a long time but 30+ years is a bit much to ask.

 

[clabedan]

Thanks again for the very detailed answers... I can see a lot more clearly and will check all these in the coming days... I'll keep you posted

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