Motorcycle Repair: 82 yamaha seca sputtering engine cuts out, different climates, yamaha xj550

Question
I've got an 82 yamaha xj550. It starts up fine, but even after warming up, it sputters and cuts out altogether. It'll start up fine again, but it sputters out shortly after putting it in gear. The volt meter also reads strong. What's the problem and the fix?

Answer
Hey Les, well, it could be one or more of a few things here. But initially the voltmeter reading I wouldn't think has a direct influence to the fault, it is merely showing you the charge circuit is running OK and the battery is being charged, which you prob know anyway. As to the fault, well, initially the most obvious is the mixture of the fuel/air in to the engine. Once warmed and popped into gear, the motor will cut out, or die, as when the mixture is too rich, i.e. too much fuel to air ratio. Now there are a few things in the carb that might cause that, first, have you or anyone changed the settings recently? did the fault start recently after a change or refit of component, obviously that would point you in the right direction. Or, take the carb apart, and check the float level with the spec in the manual, if you don't have a manual, the spec will be online somewhere. reset to correct height if necessary. Also, check out the jets and airways in the carb, check the jet sizes, number stamped on jet, to the spec in the manual. Bear in mind that different locations can have different affects on the carb settings to performance. For instance, different altitudes, and different climates make a difference, and also weather conditions, now in the colder months, in the northern hemisphere anyway, certain carb settings may not work as well as they did in summer months. Also check out the air filter, and seals between carb and engine, any leaks around the seals will cause the ratios to alter in a big way, and a clogged up air filter, will of course restrict the air intake, and subsequently the mixture will enrichen. Now that is much of the carb/fuel side, you then have the ignition side of things to contemplate. When an engine starts and idles OK then load applied, this can cause an increase on the draw from the ignition components, and if there is any breakdown of insulation, the increase in amperage may cause the spark to run to earth easier. Check first of all your wiring to the coil, to the cdi unit, to the stator, check in particular the HT leads, are they brittle and old, check the plug and the plug cap, or in america, the boot. Have a look at your spark, remove, connect to HT lead, earth against engine, by touching the metal body of the plug to the metal part of the engine, please don't hold it! or you will light up. Crank the engine a bit to observe sprk with ignition on of course. You want a nice fat blue spark, a weak white yellow spark indicates less than satisfactory conditions. It would start the bike, but as more fuel mixture is pushed into the cylinder, the increase in pressures and explosion will cause the spark to fail, it is a very hostile environment during the ignition sequence of an internal combustion engine as you can imagine, it needs to be a fat good spark. Even if there is a good spark, it may be disappearing during normal running, which would at first point you to the coil, again there are test parameters for your coil in the manual, it tests the resistance by ohms, through both the primary and the secondary circuits. Maybe you have a tester, or can borrow one, to be honest they are handy things to have around, and aren't expensive. If so far everything checks out, you would be moving on to the cdi unit, which can only really be swapped out with a known good one as they are usually sealed, and not adjustable. However, to tell you the truth, I would suspect that your fault lies in some of the aforementioned, and you won't get as far as the cdi unit, they are quite robust after all. Check the easy things first, the ignition connections, the overall condition of the plug, cap, HT leads, low tension leads etc.
test the coil, nice and easy, then move on to the carb, check through potential leakage, blockage air filter etc. then move into the carb for good clean and check jetting and float heights.
Should be enough for you to be going on with for now.