synching carbs -strange gauge behaviour

[mr blackstock]

Hello,

I recently dismantled the carbs as the bike was idling horribly and popping under load etc...and I gave them a really good clean, etc.  I used a sonic bath etc.  SO they are really clean... all passages blown out with air, emulsion tubes clear.  I then manually balanced the carbs off the bike, installed them, then used my gauge set to complete the job.

All was going well until the gauge on no.4 cylinder dropped and indicated late ignition timing.  I swapped the gauge tubes around, no change so the gauge was reading it correctly.  I swapped out the ignition box, no change.  I considered the coils, but cylinder no.1 was fine, and it runs off the same coil as no.4 Carbs 3 and 4 were close to being balanced too, when I try to adjust by turning the screw to get a balance, it makes things worse... SO I think there is an issue outside of being out of balance..

I made a short video of it, see link below:
https://youtu.be/uKpgYCLUgsA

I am considering swapping coils out with some dynacoil spares, in case it is the sparkplug lead.  I will also check valve clearances in case there is an issue there... trouble is it happened suddenly, the bike was running pretty well, now this.  The carb rubber is installed correctly..

I am hoping others here may have seen this and point out a really simple fault??

Cheers, Gareth

[Pat Conlon]

Low intake vacuum, check valve clearances. check O ring on manifold-head joint. Check compression possible burnt valve...low compression? Do a leak down..listen on the exhaust port and intake port for the tell tale hiss.

[mr blackstock]

Thanks for the tips, I have to get an adaptor for my compression tester... I will be shattered if it's a burnt valve... sigh

[mr blackstock]

So until I can get hold of a compression tester adaptor, I did a finger compression test, and it did'nt go to well.  While I realise it is not a scientific method, I hope it would give me an indication. So I jammed my finger into the spark plug holes of pots 1, 2, 3, and when turning over the engine, the compression from the cylinders was pushing past my finger, no matter how hard I pushed my finger in.  On cylinder 4 however, the compression was at least 30% less, I could keep my finger in the hole with moderate effort.

Bugger. 

So I guess next I will check the valve clearances, but I doubt them being out will explain the sudden change.  Next I gotta research if I can remove the head without removing the engine.

[Sparky84]

Bugger. 

So I guess next I will check the valve clearances, but I doubt them being out will explain the sudden change.  Next I gotta research if I can remove the head without removing the engine.

Good Luck ..

https://www.fjowners.com/index.php?topic=11511.0