[Zzr600]

I might try some seafoam as a "what the heck, why not". But the gas is fresh, and I've also tried running it with the airbox completely removed so that I can see the intake manifold. So not gas/air.

 

[Zzr600]

Ran perfectly a month ago, then over a 2 week span it gradually lost power and then the next day I tried to start it and it does with throttle. Never had an issue with the bike before except a bad spark which was fixed with some new coils.

It very well could be a carb issue, but that wouldn't explain why the vacuum gauge was jumping around like crazy. I've taken carbs apart before on other bikes and outboard motors and managed to clean them just fine. I'm just hesitant because it's a pain in the ass on this one and I'm not 100% confident its a carb issue due to the vacuum guage

 

[Zzr600]

I forgot to mention I tried hooking it up to a big marine battery that I know is good and nothing changed. First thing I thought of trying too, but unfortunately it's not it. Thanks though

 

[Zzr600]

Where was this vacuum gauge connected?

It was at the synchronization junction. Disconnected it and stuck the guage on one of them. Tried both carb 2 and 3. Didn't matter if I plugged the other one. Also tested carb 1 directly where the synchronization tube would go if it had one. Removed the rubber seal and stuck it on. Same issue

 

[Zzr600]

Going to get a compression adapter as the bike's spark plugs are too small for the guage and check that, also going to pick up some seafoam and let that soak. Depending on compression results, I may be checking the head gasket and valves. Does anyone know if it's possible to do valves without dropping the entire engine out?

 

[Zzr600]

Gonna get the compression adapter on the weekend and test it. We'll see what happens. Hoping it's just a carb issue

 

[Zzr600]

Update: compression readings were all fine. Did a lot of work over the weekend on it.

1. Adjusted the valve clearances. They were within spec but had some variance between them. Engine ran better, as it wouldn't die, but still lots of hesitation

2. Disassembled and cleaned the carbs. No effect on the engine

3. Synchronized the carbs. They were within spec but I made sure that they became perfectly balanced using a homemade water guage. Fixed the hesitation issue. Engine runs good except for an idle speed that goes up and down a bit.

Summary, fixed by adjusting both the valves and the carb synchronization. Not 100% perfect, but definitely good enough where I don't notice anything under normal riding.