72 xs2 bogs down and backfires out of carbs, out of ideas

[Its been a long time]

If the timing chain is badly worn the ignition timing will be retarded. If I read it correctly, the case here is that it's too advanced and the available adjustment has run out. There's a simple way to check the camshaft timing shown in the shop manual using a DTI on an inlet valve. One tooth of mistiming is 10 degrees, so it's pretty obvious to see. Here's a thread from when I asked myself if my valve timing was correct or not. Mine was fine but I had to check it to be sure. I used the method documented in the shop manual this thread is how I did it.

https://www.xs650.com/threads/camshaft-timing-is-my-engine-timed-one-crankshaft-tooth-out.66347/

 

[AUTOMAN]

Snap a pix of the timing light flashing on timing marks

 

[RaceCar1983]

Cam chain tension is good, advanced timing looked off as well. I will get a friend to help and get video of the timing light this weekend. I will check the timing chain in the meantime. The cam chain guide and chain looked mint when I did the top end last year, and it is a low miles motor (9000 miles when I bought it). Would the tension still be perfect if the chain was badly worn?

 

[Its been a long time]

Cam chain tension is good, advanced timing looked off as well. I will get a friend to help and get video of the timing light this weekend. I will check the timing chain in the meantime. The cam chain guide and chain looked mint when I did the top end last year, and it is a low miles motor (9000 miles when I bought it). Would the tension still be perfect if the chain was badly worn?

Even if the tension is good, a badly worn camchain retards the ignition timing.

 

[RaceCar1983]

Alright I did another start with the timing light (my phone failed to record cause it fell when I started the engine) bike started and idled perfect,

I confirmed the timing at idle and it was spot on. I revved the engine but my timing did not advance regardless of RPM. I am going to pull and lube the advance rod again as well as check the cam chain indexing.

 

[AUTOMAN]

Alright I did another start with the timing light (my phone failed to record cause it fell when I started the engine) bike started and idled perfect,

I confirmed the timing at idle and it was spot on. I revved the engine but my timing did not advance regardless of RPM. I am going to pull and lube the advance rod again as well as check the cam chain indexing.

So far so good!
Nice next move.

 

[RaceCar1983]

Bad news, my cam chain is definitely off the mark. I have started the process of pulling the engine to replace it. Now I have 2 questions: where do I find a cam chain for my 1972 motor? (I only can find 74 and later online) and since this problem arrived so suddenly is it possible my cam chain skipped a tooth?

 

[Wingedwheel]

https://xs650direct.com/products/cam-chain-tsubaki-bf05t-x-102
I like to order from here.

 

[Jan_P]

Not read through but it says in the first post you are running a PMA
Kan the PMA rotor have moved on the shaft ( rotated )
The stock Alternator rotor uses a key if that is not there even the stock alternator rotor can twist ..
If adjust timing after that now shifted rotor and it can go wrong

I have a rewound stock rotor with the timing marks off ..cant use them

To check if the rotor and piston are in sync one can use a wooden stick in the spark plug hole turning to get piston at Top DC
and then inspect the markings on the rotor if it lines up

If the machine runs one can move the ignition in small increments to listen for changes
at idle ...More knocking to advanced --Shooting in exhaust to late

 

[RaceCar1983]

did that already, it’s still good

 

[RaceCar1983]

I ordered my cam chain, master link, gaskets, and cam chain guide. Gonna pull the engine this weekend. Any tips on how to remove the chain without cutting it, Will a normal chain breaker fit?

 

[JOHNDADDY]

I ordered my cam chain, master link, gaskets, and cam chain guide. Gonna pull the engine this weekend. Any tips on how to remove the chain without cutting it, Will a normal chain breaker fit?

After you take off the head slacken the chain adjuster all the way out, slide the cam bearings off the ends and that will give you enough slack to slip the chain off the sprocket. Tie the chain up so it doesn't fall into the crankcase.

 

[RaceCar1983]

After you take off the head slacken the chain adjuster all the way out, slide the cam bearings off the ends and that will give you enough slack to slip the chain off the sprocket. Tie the chain up so it doesn't fall into the crankcase.

I still have to break the chain to remove it from the crank though right? I know that trick from when I did my top end before but I never broke the chain.

 

[JOHNDADDY]

Misread your post, yes I've seen pics on the forum of chain breakers being used.

 

[AUTOMAN]

Are we sure the chain is toast?

 

[RaceCar1983]

Are we sure the chain is toast?

See my picture above, if it’s not toast then it skipped teeth, either way the top end needs to come off to check it out.

 

[Wingedwheel]

Always a good idea to change it anyway. Yes a chain breaker will fit. If you ordered the chain from my link I believe you have to break that one too and it should come with a new link. I’m not home to take a pic but I swapped out a bolt for the sleeve in the breaker and used it to flare the pins on the new master link.

 

[RaceCar1983]

Update, I replaced the cam chain and got the engine back together and in the frame using a homemade engine lift tool, should be another week or so before she’s all back together for a test ride.

On another note, my front motor mount lines up on the bottom but not the top 13mm bolt hole, any tips besides wiggling and lifting?

 

[JOHNDADDY]

Try loosening all motor mounts up then push bolts through,
might give you more wiggle room.

 

[RaceCar1983]

Try loosening all motor mounts up then push bolts through,
might give you more wiggle room.

Worked like a charm thanks!