Re: Yamaha 250 loss of rpm
if you wish to splatter gun the troubleshooting be prepared to purchase pistons and machine shop time. its your choice. purchase the proper tools and tech manuals or repair the mechanical damage that will occur and continue trouble shooting. the yamaha diagnostic lamp is relativly cheap, less than a piston in the box on the counter. I have tried to assist you yet you have a steadfast refusal to believe me. if you spray raw gas instead of premix you risk a lean oil condition. my suggestion is not to let a friend that has no training in the V76 ign/fuel system to mess with your motor. they tend to make a simple repair an overhaul. I dont mean to sound harsh but if you dont read and understand how and why the systems work that motor will self destruct. the diagnostic lamp,commonly called the winky blinky can quickly rule out a sensor failure. the TPS can have an inrange failure but a simple run with a voltmeter attached can find it, the TPS is the main ign timing determinant on that system. the pump you refer to is the enrichment pump, it is on anytime the key is on. it supplies fuel from #6 fuel bowl to the 6 enrichment injectors. in certain conditions,cold start,rapid acceleration or knock detected, the computer allows more fuel via the enrichment circuits. thats why a cold engine at high speeds can drain #6 bowl and create a problem. to properly test the system will require 3 or 4 test harness's a peak reading multimeter and a digital multimeter as well as a service manual and a working knowledge of WTF.like I say I dont mean to sound harsh but so far this week I have 2 blown V6 yams that had routine maint issues that were incorrectly diagnosed and now once I repair the mechanical damage I can repair. the bill will go from a 300 or so to about 4K. post back all the electrical test results you have so far. the CDI output is simple to measure but requires a peak reading meter. takes no time to test. I also use a KV tester to test secondary ign output. the KV tester is about 130 dollars.<br /> but I do reccomend a reading session with the service manual. it wont detail how it works but will tell you what each sensor does, but ya have to teach yourself how and why. there were some stator failures in the engine range you have, but overall most yamaha problems with the V76 are fuel issues. there were a few issues with the TPS but with a voltmeter and a timing light they are easy to find. but I cannot understate that understanding the system is imperative to troubleshooting it. you will also find that yamaha electrical parts are expensive and no one stocks them. cause failures are very rare. I have given ya some test tips, follow them. dont re-engineer the system, the system works very well. but post back the results of the fuel system vacum test, the CDI output test and the TPS voltage. remember that if the TPS 5V reference is not correct the rest will be off as well. its a complex system but easy to test. but the testing must be done in a logical sequence or your sunk. the test and tune up spec book will prove invaluable. in my opinion the factory manual is somewhat lacking but needs to be read. the V76 is a complex motor but works well.
