1977 KZ1000 VM26 questions

Just had a thought. Probably silly, but what the heck.

If you cap the vents, as you use gas it would create a vacuum. The easiest place to relieve the vacuum is through the fuel line. If the floats are a little sticky, it could provide enough force to open them up. Also, once you get the fuel level in the bowl set the way you want it, capping would tend to keep the level at that point, so you'd (theoretically) always have the right amount of fuel. If the floats were loose, the increased pressure in the bowls would resist the flow of gas into the bowls.

Of course, I doubt it would actually work that way - chances are that people that used this trick (if that's what it is) just got lucky with the operation of their floats.

Patton wrote:

kaw-a-holic wrote: ... What are the air vent ports for?

Serves basically the same purpose for gasoline in the float bowl as vent in the fuel tank cap serves for gasoline in the fuel tank.

Good Fortune!

this makes sense as I have always had a slight air bubble in the fuel line. I will remove the caps.

Cynjut wrote: Just had a thought. Probably silly, but what the heck.

If you cap the vents, as you use gas it would create a vacuum. The easiest place to relieve the vacuum is through the fuel line. If the floats are a little sticky, it could provide enough force to open them up. Also, once you get the fuel level in the bowl set the way you want it, capping would tend to keep the level at that point, so you'd (theoretically) always have the right amount of fuel. If the floats were loose, the increased pressure in the bowls would resist the flow of gas into the bowls.

Of course, I doubt it would actually work that way - chances are that people that used this trick (if that's what it is) just got lucky with the operation of their floats.

I think of it the opposite (but I've been wrong before). A proper size fuel line can carry fuel faster than the engine can use it. The carb has air in it. Fuel from the tank needs to displace that air to fill the bowl. The air cannot escape through the fuel line because it is pressurized by the weight of the fuel. So, if the air cannot escape through the vent or the fuel line the fuel coming into the top of the bowl will pressurize the bowl, and the pressure may reach a point where the fuel cannot continue to fill the bowl. If the fuel coming from (let's say a full tank) creates enough pressure in the bowl it may even push fuel out of the bowl through jets which could cause a rich condition. As I said, I've been wrong before, but I wouldn't block the vents. Ed

I agree. The vents should definitely be open. I can't imagine a scenario where capping them would work reliably except through sheer luck and possible elven magic.

Slightly enriching pilot circuits will often reduce or eliminate popping on deceleration, say ⅛~¼ turn each.

This presupposes clean pilot circuits, correct fuel levels, decent sync, adequate clean fuel supply, and no air leaks.

Good Fortune!

That's what I'm hopefully going to get to this weekend. I ordered the next bigger pilots and have those on hand too. Honestly, now that the muffler is properly packed and I cleaned & oiled my K&N's, it's sounding pretty damn good. I don't think I'm going to need to go bigger, but we'll see. I am going to double check my float levels, and re-sync, since I've had the carbs off since last time.

Not sure on VM carbs, but on CV carbs this is the rule:
If stock aribox is present, run vent tubes under the airbox, open.
If running pods, leave vents open with no tubes on them.

Do you think it reduced the popping that much or just cant hear it as well now? If it really did reduce it that much than that makes me think I could have a problem with my exhaust. Insufficient back pressure causing it? Just kinda guessing here. But I'm betting my exhaust is leaking at the head, pipes have been off at least a few times I know of without gaskets being replaced.

I have a new set of gaskets from Z1E, just haven't gotten around to installing them yet. Maybe this weekend I'll put 'em in and see what happens.

It definitely seems to have reduced it that much. I still get a little bit when engine braking / hard downshifts, and between shifts under (heavier) acceleration. But I personally think that is to be expected and nothing to worry about. Definintely a good idea to replace your gaskets at the head. I had the same problem on my LTD, except that was clearly a backfire due to an air leak. Lots of popping and backfiring, all the time. The exhaust gaskets surely helped a lot, but for me, the carb holders at the head solved it completely. If you don't know the age of the holders, I would definitely hold them suspect as well.

Today I happened upon this this document from Mikuni's website. Some good info

www.mikuni.com/tg_backfires_in_exhaust.html