QuestionHi there. I noticed all your awesome diagnosis's and decided to give you a try with a few questions. I just picked this bike up with 9000 miles. I have never worked on anything larger than my last yamaha tw200. This bike has trouble starting cold. With the battery charged and using the electric start, the motor doesn't turn over. it sounds like it tries though with subtle pops from the exhaust. Eventually, after trying and waiting and trying, it will start. Once started, the idle will either go too low causing it to stop or it will rise to about 2500 and stick. If I loosen the throttle screw it will lower itself back down. What should I do and check to produce a quicker start and to even the idle out? Also, when it starts, one of the cylinders takes much long then the other 3 to produce heat at the exhaust manifold. But, it does eventually get real hot.
Thanks for any insight you may have. I am new to these, but I want to learn how to maintain it myself.
Kyle
AnswerKyle, Any time you get involved with a 30 year old bike with 9k miles, it is obvious that it has sat idle a lot more than it was driven. The chief problem is almost always contaminated fuel system and plugged up carburetor jets and passageways.
Before you get going in that direction, you must check the rest of the engine over.... Adjust the valves, adjust the timing chain, then remove the point plate and inspect the mechanical spark advancer. Often the advancer sticks in one direction, causing idle problems and power loss. Mark the advancer where the point cam slips on the end, then remove the point cam, clean the parts and lightly lubricate with high temp grease. Reassemble that, then you can work on getting the point gaps in around .014" max, then you have to adjust the backing plates so that the Left point set just opens at the F mark, then the same with the right side at the F mark. You will see two sets of markings ... 1-4 and 2-3. The coils fire both cylinders at the same time, one on the compression stroke and the opposite cylinder is getting a "wasted spark" on the end of the exhaust stroke. You can use a 12v test light to statically check the point open moments or a volt meter.
Once you have the valves set, timing adjusted and then we can move onto the carburetors. One route is to go to the Yamaha store and find their carb cleaner, which you mix with gasoline and then drizzle it down the fuel lines into the float bowls, which you have already drained out. Let it sit there overnight and then drain that mix and see if it will fire up on a fresh tank of fuel. Do be sure that the fuel in the tank is clean and/or drain it all out, remove the petcock and check for screen contamination. If all else fails, you get to wrestle off the carb bank for a good cleaning. It isn't a particularly fun job on these old bikes, but it may have to happen anyway.
When you have finished all the cleaning and tuning, the bike should fire up with the full choke, then back off choke about 1/4 or 1/2 way and continue to let it warm up. All four pipes should be hot all the time. Do replace the spark plugs with fresh ones and check the spark plug caps for the same resistance values.. around 5k ohms. The caps unscrew from the ends of the plug wires for testing.
Hope that gets you going in the right direction..
Bill Silver
