Figured out my petcock issue....maybe

Ok so my bike (77 kz650) would die on me after about 10 miles of riding and also idles like crap (still kinda does). Anyways, some said I should try running the vacuum petcock on prime. After doing this, the bike ran a lot better. I just watched a youtube video that referenced a vacuum port on the carb specifically for the petcock. The po had just removed one of the caps on the carb holders and ran that to the petcock. Could this be my issue? maybe it wasnt getting enough vacuum? Im going to test the theory as soon as I get done with valve clearances and synching carbs but thats going to be a few days. What do you guys think?

If your bike is a 1977 KZ650 someone has changed your petcock. No 1977 KZ650 model used a vacuum operated petcock; they used a manual petcock, so the carbs on the 1977 KZ650 models do not have the vacuum port for the petcock. That vacuum port (for the petcock) on later models is forward of the carb vent port on the #2 carb. You may want to buy the correct petcock for your bike as shown in the image below. Ed

650ed wrote: If your bike is a 1977 KZ650 someone has changed your petcock. No 1977 KZ650 model used a vacuum operated petcock; they used a manual petcock, so the carbs on the 1977 KZ650 models do not have the vacuum port for the petcock. That vacuum port (for the petcock) on later models is forward of the carb vent port on the #2 carb. You may want to buy the correct petcock for your bike as shown in the image below. Ed

That makes a lot of sense now. This is just one of many things the po didnt really think about before he did it. This could also be whats causeing my idiing issues I hope?

I was going to post the same thing as I have my 77 KZ650 petcock sitting on my desk while the tank is away for it's repaint, it's a twin to ED's. Definitely no vacuum petcock on a 77, As I've commented before, while vacuum petcocks seemed like a great advance in the early 80's when they appeared, 35 years later with the age induced issues they suddenly make turning a petcock on and off, seem so simple and much safer for the bike, given you don't want to be riding with over weak fueling due to restricted fuel flow, or fill your crankcase with fuel when your 35 year old carbs decide to have a stuck float moment and your vacuum petcock is not stopping the fuel flow as intended.

I would find a modern one (like a Pingel) or period replacement of the good old fashioned on/off/res style particularly as what you have is not the correct one for the bike. It also seems rebuild kits are far more available for the manual ones.

If the vacuum diaphragm, is stiff, dried out, cracked etc. which after all these years it likely is. it's very likely you were not getting full flow when the engine was running and also it's not stopping the fuel supply when the engine is turned off. I would use it in the prime position in terms of getting the bike set up, for now,but look for a replacement long term. Be careful you don't get a problem while it's sitting, with your carbs flooding/leaking etc. if everything isn't quite as it should be in the carb department.