[Mikat02600]

I had the same thing on my 02 600 after I rebuilt the carbs. Turned out when I put it all back together, I had the vacuum lines mixed up and it was starving it for fuel once it got hot. I also had the idle sensor a bit out of place. Had to learn the hard way on that one and pay a local shop to find it for me. Maybe that'll help.

[Solavenenum]

Thanks Mikat. Can you please tell me more about the vacuum line issue you encountered when you rebuilt you carbs?
What was messed up so I can double check at my end. Cheers

Hi all, I have now adjusted valve clearance and mix screw (back to 2.5 turns out)

A bit better but still a bit of hesitation when the bike is warm.
I have posted the video below where you can hear the engine behavior

https://youtu.be/qPArzwCqkwc

As a matter of pure luck, I have tried the same exercise with the tank off and just enough fuel in the bowls to run on idle for a short while.
The link for the second video is here

https://youtu.be/OueDAmWLV6Y

Unbelievably, the problem completely disappeared????
Is there an issue with the petcock then... I'm baffled.

Thanks in advance for your help.

Cheers

[skjeflo]

Petcock or kink in fuel line or vacuum line when tank is in place?

[Solavenenum]

Yes the kink in the vacuum line must be it... but in the meantime I cannot see it. I'll surely check again
For the Petcock is there any other way to test it than just opening the tap?

I have dismantled twice already to clean and check the oval ring and inner flat square gasket. Nothing to report there, the filter is also extremely clean.

Does anyone knows the main purpose of both fuel tank pipes that run under it? I have to admit that I never paid lot of attention to them and must certainly be kinked at the base. Would it have any consequence on the fuel delivery somehow or in the tank inner air pressure?

[92xjunker]

Those are drain lines. The tank vents at the filler neck. There have been instances of that Being clogged. You would hear and pressure/vac relief when you open the cap, if that were the issue.

[Solavenenum]

No noise when I open the lid unfortunately. I was aware of that issue so I also tried to run the engine with the cap opened. Do you think I should still look into this too?

[92xjunker]

Nope, slim to none that is the issue.

[Smoke-Dog]

As a matter of pure luck, I have tried the same exercise with the tank off and just enough fuel in the bowls to run on idle for a short while.
Unbelievably, the problem completely disappeared????
Is there an issue with the petcock then... I'm baffled.

Have you tried running it with the petcock set to prime? That will confirm that the vacuum line is pinched...

[Solavenenum]

Hey Guys

Sorry for the long delay in replying to your threads

I have (sadly) found the main problem since....
Following (another) compression test, yes you guessed it right: PISTON RINGS

Cylinder 1 and 4 are showing 88 and 91 psi. Jump to 155 with a dash of engine oil in the cylinder!
2 and 3 are alright at circa 150

I can't really be too upset since it is most likely my fault anyway:
it was my very first carbs stripping, cleaning, rebuilding, etc...
When I fiddled with the settings at one point the engine backfired very bad 2 or 3 times, like a loud "bang"
No surprise that has had a fatal consequence on the pistons

Love that bike so much that I'll strip the engine anyway and learn more from that

Please feel free to let me know your thoughts on this analysis.

Thanks again for your help

[92xjunker]

After fire won't damage rings, piston damage is possible. Most likely they were going anyway. Flooding the cylinders would cause the wear, due to cylinder walls being washed with fuel. Strange that it would be just the outside cylinders. Ring job isn't difficult or expensive unless the cylinders are damaged or worn. Boring or honing the sleeves isn't readily done at home, due to the material used when they were made.

[Solavenenum]

Cheers mate, really appreciate the advise here.

I'll try to think of taking pictures for better diagnosis on what might have happened

I'll keep in touch

[arsenic]

Cheers mate, really appreciate the advise here.

I'll try to think of taking pictures for better diagnosis on what might have happened

I'll keep in touch

What happened is 25 years.

[Solavenenum]

Yeah that's so true!

Sometimes you forget that and just hope that it will run like new straight away.