So I have a 1981 Yamaha XJ650H Bobber that I blew the #2 piston on last fall. Long story short, after a long night of mods and a clutch install I forgot to add oil and started for about 5 seconds. I found a 1983 XJ750J in decent shape but it hadn’t been ran in a while. I have the 750 motor out and am getting ready to replace the “Oil Pan” gasket. Next step is to put the motor in and get it running. I have 2 questions, 1. The Carbs from the 650 are in good shape and worked fine last year. I poured stabil in them to prevent gumming over the winter. Shoud I use thes carbs as is, rejet to stage 3.5 for the 750, or clean the crap out of the 750 carbs and use them. I plan to rebuild the 650 motor one day and use it in the 750 frame. I know this sounds crazy but I want to ride NOW and I have less money to spend on the motor rebuild. question 2: The ignitors for these 2 bikes are slightly different. They have different numbers and the pigtail on the 750 has a wire with a bullet connector on it that I am not sure wher it goes. DO I use the 650 Ignitor or the 750 Ignitor? ANY help would be useful!!
1 – If you already have the carbs on your bench you should probably just open them up and check that the jets are clean and the floats are moving smoothly. It only takes 15 minutes. You will need to upjet a bit to compensate for the extra 100cc of displacement – but I would be inclined to run them as is and make my jetting adjustments afterwards.
2 – The XJ650 and XJ750 ignitors have the same function, but are wired slightly differently.
Here is the XJ650 Ignitor wiring
Here is the XJ750 Ignitor wiring