You only need to disconnect one. If the motor slows but continues to run or try to run, it was firing on both. If the motor stops immediately, it was only firing on that one. If it makes no difference, it was only firing on the other one. As Chris suggests, don’t keep it running with one plug disconnected
Are you suggesting that it would be preferable to simply put my hand lightly on (or near) exhaust header of each pipe rather than disconnect the plugs while idling?
you have it absolutely - hold hand near or even with a gardening glove and be ready to react quickly rather than burning hand of course. I guess the way we are moving technology-wise, maybe it will be become the norm to use a temperature probe instead if price not prohibitive. You get better at it by trying different approaches - when you have satisfied yourself that one cylinder is only "trying" (pipe is only warm, and can be touched/held near without burning hand) you can try and raise the revs on hand throttle just to see if "idle" related/pipe gets hotter. You wouldn't do this for long obviously as not good to leave bore with possibly unburnt fuel/diluted lubrication while running. Only speaking generally here, as I thought your engine was running on both cylinders?
Thank you for the suggestions. The first order of business is to change the timing belts which are long overdue for replacement. Although a visual inspection indicated that they were fine, I want to avoid a major catastrophe if a belt were to snap. Then I will start sleuthing for the low-power problem as per all of your suggestions. Thank you for working with me on this issue. I will definitely report back.
I finally had some time to try to locate the source of the loss-of-power issue. 1. Changed the timing belts. Not that these were suspect, but it was time. 2. Checked the spark plugs. The front plug was a light brown color, but the rear was black wet. This suggested to me that the rear plug was not firing properly. However, both plugs had a healthy spark. I replaced both plugs. 3. Checked fuel delivery from the tank to the carbs. That was fine. 4. Checked the fuel tank breather from inside the tank to the end of the breather hose. That was fine. 5. Checked whether both cylinders were firing. After the bike was allowed to warm up, both exhaust headers were very hot. 6. I replaced the fuel in the tank & the carb float bowls with fresh fuel. The next thing I need to do will be to run the bike & see of the problem persists. Maybe the problem was a faulty spark plug or bad fuel (although unlikely). Also, I wonder if the pilot jet in the rear carb was plugged? In any event, I will report back after a trial run. Thank you all again!
Pilot jet only comes into play at tickover and v. low revs Have you thought about replacing the ign coil - could be giving up the ghost at higher revs/loading.?
The problem with doing several things at once is that you don't know which did the trick. I'm not sure how hot a header will get simply from compression, not as hot as if it's firing of course but maybe enough to mislead? Debris or water in a float bowl would cause one cylinder to run poorly but then it would show as weak, ie a white plug. Maybe a poorly sealing needle valve would give you a wet plug??
Could be an HT lead breaking down if it is an original one, not a commin thing gut have seen it before.
Original leads are and were pretty much crap IMO............I always change my leads for copper core ones and fit NGK plug caps. (and always NGK plugs). Is the wet on the plug, oil or fuel? Does the exhaust smoke when the loss of power occurs, if so what colour smoke? Do a couple of compression tests on both cylinders, first one cold; second one hot.
It's my understanding that the pilot jets will continue to meter fuel even when the main jets come into effect. That is why I mentioned the possibility that that there might be an obstruction in the pilot jet.
The plug appears to be fuel-fouled. No apparent exhaust smoke with loss of power. I planned to check the compression, but need to get a different adapter for my compression gauge to fit the spark plug size. Does anyone know what the ideal compression reading should be? I can try to look it up in either the Hayne's manual or the cryptic Ducati manual.
Needle takes over from pilot jet from around quarter throttle and then main jet comes into play from half to wide open as a guide, pilot jet being blocked is extremely unlikely to have any effect. I would hope to see well in excess of 120psi, if lower then further checking needed. Others with specific experience/knowledge of your engine/carbs may give you different figures but not by much I would imagine.
Compression check indicates the following: front -- 111 psi & rear -- 109 psi. Considering that my compression gauge is of the auto-parts store variety. I cannot vouch for its accuracy. Also, the engine has always tended to crank rather slowly. So that might indicate readings on the low-side. I might add that the engine has about 16K miles (25 Kms). Although the readings might be lower than ideal, I cannot see how this could be the cause of the loss-of-power issue that I experienced in the middle of a ride.
Try a small amount of oil down the bored and see if the readings increase. Still think it's more likely coil or HT lead breaking down under load though.
Forgot to mention that I did exactly that. With oil in cylinders, readings were: front -- 119 psi & rear -- 114 psi. That tells me that there is some cylinder bore wear or ring wear. Once I run the bike again & if the problem resurfaces, I will look into the coils & HT wires.
Did you hold the throttle wide open when you checked the compressions? I reckon the readings you got are low and I would expect to see them around 150psi.
