Yamaha xj750 running issues,

Hello, I have a 1982 Yamaha xj750 seca and it backfires occasionally and just cranks, now it doesn’t even backfire. To give some context I bought the bike without it starting cleaned the carbs and a new battery and it would idle super rough and wouldn’t rev up at all, so I cleaned the carbs again a little more thoroughly and checked my diaphragms 3 are good one is bad, I then tried to start it again with some starting fluid and it almost idled on it so I checked my floats fixed them and it idled and revved pretty rough after that, I noticed it was running pretty rich and that only 2 exhaust pipes were warm so I know it’s missing on two cylinders, so I pulled the spark plugs and 2 were wet on the missing cylinders. Now when I jump it just cranks backfires a little or doesn’t backfire at all and the weirdest part is that it won’t even sputter on starting fluid.

 

My best theory is that I was cranking it to much and the battery got low so the cylinders weren’t firing and the spark plugs got wet and won’t fire now.

 

First, if a diaphragm is bad, how bad? If it has a pinhole, it needs to be patched. If it can't be patched, it needs to be replaced. You can't expect the engine to run well with one or more bad ones. Which cylinders are not firing? It could be a bad coil that is connected to those cylinders. No spark = no firing. More info is needed.

 

Yeah, I’m not sure how bad the diaphragm is I can’t find any holes I know the ring on top was broken so I did my best to glue it back together, cylinders 2-4 are not firing.

 

You can stretch the material with a light on the back side to see if any pinholes show up. One coil connects to cylinders 1 and 4 and the other connects to 2 and 3. Could be a bad wire on each coil, maybe.

 

Yeah, I think for right now I’m gonna let the cylinders and spark plugs air out and cross my fingers for tomorrow morning

 

You can at least unscrew the caps from wires 2 and 4 and inspect the ends for corrosion. if there is any, clip off about a 1/4 inch and also inspect the screw-like part in the cap that screws into the wire. Clean it if corroded. Reassemble and test.

 

I will also try that tomorrow morning unfortunately I’ve got to be at work shortly. Thanks for the advice so far!