OK, With the compression readings as low as you have got, I'm not surprised the bike runs out of power. Interesting to note that the lowest reading is for the cylinder that has the plug fouling......maybe it is just part of the problem. However, check the emulsion tubes to see if they are worn, if they are oval, they are worn. Perhaps the rear one is worse than the front.
Several months ago I rebuilt the carbs since I suspected that the floats were sticking. Although I did not remove the emulsion tubes, I thoroughly cleaned the carbs. I cannot discount your suggestion that the tubes might be worn; but with only 25K km on the engine that would seem odd. As I mentioned earlier, I am not convinced that the compression readings are entirely accurate. I might re-check the compression using a higher output battery to hopefully get the engine to crank more rapidly. Also, the fact that the loss of power occurred instantly seems to point in another direction. If the problem persists, I would like to rule out the possibility that the culprit is one of the coils or the high-tension leads first. Hopefully there is a way to test these components without blindly replacing them.
There shouldnt be any significant bore/ring wear with the mileage covered.I be inclined to disbelieve the values on the comp gauge.Low compression wouldnt cause a drop in power"sometimes".There would be a loss of power permanantly.Hope you find the problem and its a cheap repair.
Thank you, Keith. I'll get to the bottom of this. Since engine diagnosis isn't my "day job" so to speak, it will take me a bit longer and...I'm not so proud to ask for help from those with more expertise.
In light of all the discussion we have had on my "loss-of-power" issue, I failed to mention something that might bear some relevance. Earlier in the year I started the bike after sitting in a heated garage for about 2 months. After about 15 seconds of cranking the engine, an eruption of fuel & oil spewed out of the crankcase breather similar to a Mt. Etna eruption. Obviously fuel had found its way into the crankcase. The logical assumption was that the carb floats had stuck open. Although I replaced the float assemblies & thoroughly cleaned & rebuilt the carbs, I could not definitively find the cause of the problem (other than an incorrect float height). So, I installed an external fuel petcock that I could shut off after riding. The fuel-in-the-crankcase issue seemed to be solved. I mention this since after the recent loss-of-power issue occurred, the rear spark plug was black with what appeared to be fuel. Maybe I am stretching logic here, but I am trying to see some association between the 2 issues. Your thoughts would be appreciated. Thank you kindly. Kit
First post mentioned sluggish throttle response and exhaust not sounding crisp would tie in with one cyl flooding heavily.
I wonder if, due to the flooding caused by the carb issue whether the oil might have been 'diluted' by fuel dumped into it ? If this is a possibility and you ran it with this oil then this could have caused some engine issues. Would seem strange to link this with 1 cylinder only but a possibility?
Immediately after the crankcase oil became contaminated with fuel, I emptied the contaminated oil, refilled with new oil, ran the engine just enough to circulate the new oil & the dumped the oil again. I did this 3 times. I might have been "grabbing at straws" when I raised the fuel-in-the-oil issue. In fact, I just might have stumbled upon the cause of the loss of power. When removing the ignition coils for testing this afternoon, I discovered that the spark plug cap on the rear cylinder was cracked. So the wet plug on that cylinder might have been the result of intermittent shorting to ground. That being said, any recommendations on aftermarket spark plug caps? So my fingers are crossed. But the celebratory bottle of wine has been selected. I will keep you posted. Thank you for your responses. Kit
Fuel lines in tank are fine (as is the tank breather). With the new plug caps installed, today is the test trial. Will report back.
Here is an update. After (1) replacing the fuel in the tank, (2) checking the fuel lines in the tank & to the carbs, (3) checking the fuel tank breather, (4) verifying the resistance specs on both ignition coils, (5) changing the spark plugs & (6) replacing the cracked spark plug cap (actually both caps), I ran the bike today. For 13 miles, it ran perfectly. Then suddenly without warning it appeared to lose spark on one cylinder. After I limped on home, I immediately checked the spark on both plugs. The rear plug had a faint spark at best. I then disconnected one spark plug lead at a time & hit the started button. The engine would fire on the front spark plug. However, it would not fire when only the rear spark plug was connected. So, clearly the loss of power is the result of the rear cylinder not firing. The problem seems to only occur after the engine has been run for awhile. To me, this suggests that I have an electrical issue associated with heat. Does this suggest a bad rear ignition coil? Anything else? Thank you kindly. Kit
First thing that now comes to mind is corresponding ignition pick-up failing or sometimes leads shorting or losing contact. More likely actual pick-up as they typically break down when hot once the body shows signs of cracking. I used aftermarket Electrex units last time I swapped a pair :- https://www.electrexworld.co.uk/acatalog/P8.html
It absolutely could be a coil, unfortunately, there are other options too, such as the ign pickups as mentioned by CHris. To be honest, the pickups are prob worth replacing as you go in to inspect them. Don't give up, you will get there!...
