1978 kz650c starting problems

If the #2 carb has no vacuum port someone has swapped carbs; all 1978 KZ650 models came with the vacuum port on #2. PLEASE post a picture of the upper part of #2 carb and of the side of the carbs; maybe someone can identify them for you. Assuming there is no vacuum port you can just leave the petcock in Prime while riding and then switch it to Run when you park it, OR you can run a vacuum line from a carb holder sync vacuum port and see if that will permit the petcock to pass fuel when it is in Run and the engine is running. Ed

I'll get a picture but it probably won't be until this weekend since school is back in session now.

nch_2018 wrote: I'll try the clear tube method but in response to the vacuum port on carb 2, I've found other forums mentioning this, it isn't on my carb. Where there should be a vacuum port there is an indent that is solid, no port or even a hole to cover. The petcock is manual and I put it on prime then on to start. This is why I am stumped as to why I can't get fuel through.

"Prime" doesn't need vacuum. Being in "Prime" position is supposed to allow fuel flow from inside the fuel tank through the petcock and on through the fuel line from the petcock to the carburetors.
Where Prime position doesn't allow fuel flow through the petcock, the petcock is probably clogged (screen inside the fuel tank or internally inside the petcock), or maybe there's no gasoline inside the fuel tank.

On carbs that don't have a separate vacuum nipple for the petcock, a vacuum nipple on one of the carb holders may be used to attach a hose that runs to the petcock's vacuum nipple.

Good Fortune!

650ed beat me to the punch!

Gas tank definitely has gas and I rebuilt the petcock if it was clogged I wouldn't get any fuel in the fuel filter.

Welcome! (:

The pods will most likely be an issue if you want the bike to run as good as possible, but that can be fixed later. The missing vacuum line also doesn't matter, as long as you use PRIME on the petcock. When it runs on starter fluids it has both air and spark, so you only need to get the gas issue fixed for now.

Did you try the clear tube method? If it doesn't have any fuel in it when you do or it is adjusted correctly, the carbs need cleaning.

There are good guides on here but you really need that factory service manual. Some can be downloaded, but it don't know about yours.

Edit:
Forgot you had cleaned the carbs already. A lot does it incorrectly though so you could try looking at the guide Patton often posts and see if you did it good enough if the clear tube method doesn't fix it.

Also, are you asking what jetting is? If yes, it is adjusting the air to fuel ratio by swapping out the jets with smaller or bigger ones. There are some really good jetters :lol: in here.

You can check if fuel is getting to the carbs by opening the carb bowl drain screws, one at a time, catching any fuel that comes out with a small cup.
Sometimes fuel filters get clogged and stop flowing, so even though the filter looks full, it may not pass gas :laugh: well enough.

here is some info on how to clear/clean carb passages, and a set of VM24SS carbs (not CV) showing where the vacuum port is (green line).
I suspect you have a set of '77 carbs.

img.photobucket.com/albums/v494/rstnick/...s/cleaning_paths.jpg

CV type carbs:

Mine look like the latter picture(just pods instead of an airbox). I've started to unscrew the drain screws and gas comes out that's why I'm really scratching my head here. I'm no master mechanic but I've got a better grasp than most my age and I know that something ain't right.

Pics of the plugs and the bike?
Steve

If your carbs look like the latter ones (the ones labeled "CV") someone has removed the original VM carbs and put those on it. SO, which CV carbs did the guy install (there are various sizes), and how long did it take him to give up on trying to rejet them after ditching your airbox and installing pods? You have your work cut out for you for sure. If that was my bike I would start by installing the correct VM24SS carbs and installing an airbox (if I could find one). Then I would perform a full tune up and get the bike running as it should. If after that is done and you have established a baseline from which to measure performance you can then install pods (if for some inexplicable reason you feel compelled to do so) and you will be able to compare the performance of the stock airbox and stock carbs to pods and stock carbs. Ed

nch_2018 wrote: I read on another forum that an issue is that it has "cv carbs" with pods instead of an air box. The bike had pods when I purchased it, so I don't know if it originally had an air box or not. I don't know what a "cv carb" even means but the forum said cv carbs and pods don't mix well and the carbs will either need an air box or "jetted". Can someone explain what this means and whether or not it will be an issue?

All KZs came from the factory with an air box. Pod filters and an aftermarket exhaust system were popular hop-up modifications back in the day. What has since been learned is that, especially on a stock engine, there is no power to be gained by going to pod filters. The stock air box and filter will flow as much air as the engine can use. Even with a mildly modified engine, a slightly modified box and a low restriction filter will net the most power.
CV is short for constant velocity. These carburetors are designed to keep the incoming air at a constant velocity across the main jet, which will provide a very consistent air-fuel mixture over a wide rpm range. Pod filters significantly alter the velocity of the air coming into the carburetor, reeking havoc on the delicate balance needed. This usually results in erratic idle speed, seriously lean mid-range mixture and rough transition from the low speed circuit. These problems can usually be overcome by changing the fuel metering jets, changing the low speed mixture settings and sometimes the main jet needles.
It is important to be absolutely sure that the valve adjustments are correct, the ignition system is functioning properly, and that the fuel is flowing and that the fuel level is correct in each carburetor before diving into the jets.

nch_2018 wrote: ... started to unscrew the drain screws and gas comes out that's why I'm really scratching my head here....

Fuel is entering the float bowls. Would suspect blockage in pilot circuits.

Here's a typical cv carb pilot circuit.



Good Fortune!