Head Gasket Replacement

With the ignition on and the kill switch set to run check the supply voltage at the red wires with white stripes on your ignition coil connections.

 

Remember the compression figures specified by Yamaha will be with the air filter fitted.

 

Yes it will provided it is in neutral (and the neutral switch is working.) Bike will start just fine with sidestand down, then die when you drop it in gear if the stand is down.

 

Well, I think I may have figured out the solution. It turns out my compression tester was the culprit for the previous bad readings. I rented one from a local auto parts store for a piece of mind and it tested much better and within range across all cylinders. I was thrown through a loop because my tester was working just fine on my car and my friends motorcycle. It still, however, didn't solve the issue as to why the bike is running so poorly. I did a bunch of tests with electronics and found that one of my ignition coils is shot, so I was essentially running on two cylinders. I'm going to replace that along with the valve cover gasket and see what happens.

 

Good point. I installed the new filter and ran the compression test with it instead.

 

Hopefully the new coil will fix it and you know the piston rings, bores and valve seats are in good condition by your latest compression test. You can double check the coils by swapping the harness connectors going to the coils. The spark will move to the other pair of cylinders and vice versa.

On the subject of ignition coils here is and alternative setup for your Yamaha.

https://xjbikes.com/forums/threads/cb-750-coils.88468/

 

Glad to hear it, because I tried the exact same thing by swapping the connectors and still saw no results. I came across a replacement nearby so I'm going to try it out and see how it runs. Fingers crossed!