Could this be carb or something more serious

[user11235813]

OK recently checked piston pressure because of suspected leak due to carbon on seats because of valve clearances getting larger on exhaust. Pressure was 110 on left and 120 on right but this was with cheap tester and has not been verified. Bike was running well good acceleration etc...

However a problem has developed and I do not know if it is related to the above, or if it is entirely unrelated and due to carburettors. It feels like something to do with the carbs, but then it might be the valves. I did put some valve cleaner through which may have caused this by dislodging some carbon, but it does feel more like a carburettor problem.

It idles perfectly, no stuttering or starting problem and constant rate and also drops back to good idle after blip. However what is happening is that after a short while it is stuttering and dramatically losing power. Tacho swings wildly, starts at about 3000. It has developed gradually over a few days and it now quite bad.

Any suggestions on the best way to proceed from here, to confirm if it's a valve problem or a fuel problem?

[yamahonkawazuki]

Possibly a carbon issue but tbh its doubtful. This bike runs fine and responds fine until it heats up? Beginning to wonder if it perhaps might be a mmagnet/coil issue?
Aaron

[user11235813]

Took it out for a tentative ride trying to pinpoint if it's rpm related or throttle position. Seems to be both. I was able to cruise at a low speed and low rpm without problem and while it did seem to get worse when warm, that could just be the intermittent nature of it because there was a point coming home when it would not go past 4000 rpm and opening the throttle would just make it die more, then after continuing at low speeds when I got almost home in 3rd gear I was able to crank the throttle open up to 7k without issue but that didn't last long.

I guess this has got to be some sort of a carburettor blockage now. Is there an easy way to rule out the coil? When you say magnet/coil are we talking stator or some other component.

[mr72]

You will not be able to diagnose or fix anything until you fix the compression problem. It's as simple as that.

The carbs operate using vacuum, which depends on compression. And poor compression causes poor combustion plus a hundred other things cause poor combustion so no use trying to fix the 99 things it might be until you fix the one thing you know it is.

I know this is not good news but it's the most likely real cause. This is precisely the road I went down. You can read about it in the archives if you want, same thing. And the guy I bought the bike from? Little did I know but he was also on this forum and had the same problems, chased them in the same way, likely came to the same conclusion as I did that it needed a top end rebuild and sold it instead. His posts are also in the archives.

Low compression = runs bad. Fix the compression problem first, then worry about what's next. You might have more than one problem but you know you have at least one problem, fix it first.

[The Buddha]

Took it out for a tentative ride trying to pinpoint if it's rpm related or throttle position. Seems to be both. I was able to cruise at a low speed and low rpm without problem and while it did seem to get worse when warm, that could just be the intermittent nature of it because there was a point coming home when it would not go past 4000 rpm and opening the throttle would just make it die more, then after continuing at low speeds when I got almost home in 3rd gear I was able to crank the throttle open up to 7k without issue but that didn't last long.

I guess this has got to be some sort of a carburettor blockage now. Is there an easy way to rule out the coil? When you say magnet/coil are we talking stator or some other component.

That sounds an awful lot like starvation to me.
Cool.
Buddha.

[user11235813]

@72, top end rebuild is a bit extreme as a starting point as this seems like a separate problem, as it was running well it makes more sense to get the carb sorted and then monitor the compression and valves. I'll check the clearances again soon.

@Buddha, do you think I should just bite the bullet and pull the carbs apart? Or can this be a float bowl problem?

[mr72]

@72, top end rebuild is a bit extreme as a starting point as this seems like a separate problem, as it was running well it makes more sense to get the carb sorted and then monitor the compression and valves.

You're the expert

[user11235813]

@72, top end rebuild is a bit extreme as a starting point as this seems like a separate problem, as it was running well it makes more sense to get the carb sorted and then monitor the compression and valves.

You're the expert

I f.ucking hate forums sometimes.

[mr72]

I f.ucking hate forums sometimes.

Well, I hate wasting my time trying to repair phantom stuff on my motorcycle that could easily be avoided if I someone was willing to help me figure it out.

So I'll put you on hide once I remember how, that way I won't be tempted to help you out anymore.

[rg500gamma]

this  is what  I did  , took carbs off bike  , took carbs  to get  ultrasonic  cleaned  $ 125.00  Whittier  Kawasaki  .  then  put carbs back on bike .   valves  were  in  range  .   sometimes  carbon build-up can   cause rings to stick  causing low compression  as this happened  to one of my other motorcycles .

[user11235813]

Update: After installing almost new carbs which fixed the main problem which was the press fit carb insert gradually coming loose and finally detaching completely, and then fixing the residual problem caused by bad contacts either on the ignition timing plug or the CDI plug (not sure which one caused the problem) everything is now perfect.

So I put through another tank of Liquid Moly, Carburettor and Valve cleaner, I check the PSI again, and the readings on the bad one has gone up now they are reading 125 and 127, so it probably was carbon caused by the carb being very funky. Those readings were cold too so maybe a few more pounds warm. Still slightly out of range but more importantly they are equal now.

Will be looking forward to checking the valve clearances next service.