Mikuni VM34 Fuel Starve Problem at the Dinner table..

[cleoncleon]

So.. Here's my pickle.

*It seems as though no fuel is FLOWING into my carbs.. When the carb bowls are on, the gas just stays in the lines.

I can get the bike to idle sometimes, but it takes a few staggered idle starts to get to that point. . But between that, Id have to put my mouth to the fuel lines and blow air into the line, pushing the rest of the gas into the bowl. Of course, when the bowls are finally full, I can no longer push air into the lines nor do any bubbles displace; so, i can confirm at this point, the bowls are full and the bike with then hold an idle. until that gas runs out of the bowls.

My float levels are good (I have the (2) independent floats, newer VMs)..
The float tangs are perfectly horizontal with the carb body. @ about 22 - 23mm.

Things Ive tried:
- It makes no difference when the gas cap is off or on.
- I connected just the carb body without float bowl to the petcock a turned it on, and the gas seems to flow fine. again with gas cap on or off.
- Petcocks flow fine. .
- Currently running without the inline filters as I thought they were to problem at first.

Havent taken the float needle / assembly apart..
Figured I'd see what you all could chime in before I did that.

 

[jayel]

are the atmospheric vents to the carbs open to outside air?

 

[cleoncleon]

@jayel, I think they are actually.. . open to the outside air that is.
So, Im assuming the vent/tube on the bottom is the only fuel overflow outlet?
What does that said, "air-vent" on the side do?

 

[ippytattoo]

What does that said, "air-vent" on the side do?

The air vent allow air to escape/enter the float bowl as the fuel level changes. If no air can get out no gas can get in.

 

[jayel]

yes bottom tube is either over flow or drain tube some carbs wil have a screw that can be opened to empty the bowls if needed... even running you would be hard pressed to see any flow through the lines once the carbs are full, you can run a ways on full carbs if you forget to turn the gas taps on, been there done that

 

[cleoncleon]

For sure .. Let me play with it today. I'll see what turns up .

 

[cleoncleon]

So, here's where I'm at. .. I kick and I can get an idle within 1 or 2 kicks but it only idles for a few seconds before it dies. . Then it'll fire every kick after but idle less and less at the fuel in the bowl gets used. As you can see this is how the lines look at that state , full of fuel.

Before this point, if I tried blowing air into the bowls while full, I couldn't .. After I ran the engine it'll the bowls were lean I could push air in the lines and further fill the bowls.

Info:
Pilots: 30

Also.. Not sure if this may be an issue but. Is it okay for my carbs to point up slightly ? I think my manifolds are the same but .. I could have missed that.

 

[ippytattoo]

Just out of curiosity what happens if you put a container under the carb and remove the drain plug in the bottom of the float bowl? Does the fuel flow through or do you still have to "blow" the gas through the hose?

 

[Paulrxs650]

Is your petrol cap vented? If not, try leaving the cap loose and see if the fuel flows.

 

[cleoncleon]

So here's where I'm at now. I just got done trying out that process, with the drain plugs. So, fuel flows with them off. I assume it was getting into the bowls too, So I then plugged em' back up and let em fill up.

I kick and kick .. Maybe 8-11 times and get a few rolls of idle, nothing that holds too long.

When I unplugged the fuel lines from the petcock, I blew into em like I had before. . Boom, I can hold a long steady idle. Long enough for me to go to the store today to pick up an external battery for the old Timing Light, and make sure Im at decent timing.

The timing was pretty damn retarded .. haha, @ about a little under half rotation of the Pamco plate towards Advance side.. I now have the timing right outside the fire mark at idle towards the retarded side, bike starts easier.

So what is it? it's 0dd.. What is it, floats? Vents? I can move air through the vents they aren't clogged. And as for the tank, the tank and petcock clearly flow well.


-----------

I found a new problem.. .

My ATU springs are weak.. So, I did some research on them. I cleaned em' and lubed em with engine oil for a quick good lube. It helped and my idle came back down a bit quicker from idle with just a tiny bit of throttle. Any 'usable' amount of throttle and it'll hover. So, I tried a test by wrapping a small rubber band around the weights. The bike would idle much better when i had the band on it, when it was off, my rpms would rise as the bike stood there idling/ even worse if i revv'd the throttle.

The way are now is I can wiggle em just a hair.. But they DO snap back. It's clearly not enough tension, but, i didn't imagine the weights to need that much resistance.. It's not enough to throw the bike out of timing and kick me back or advance too much at startup, but of course, everything else. . I'll end up taking a loop out before i buy some springs.

At this point, i think it makes sense to address my ATU first, instead of messing with the carbs/fuel..
Let me stiffen them up and ill report back.

 

[TwoJugs]

I had similar issues but in the end I found that it was not really an issue. Once running it would flow enough. It does not take alot of fuel to run at rest and the bowls do fill fast so you won't notice a flow.

 

[cleoncleon]

@TwoJugs.. Seems like this is turning out like so. . Not sure what was more retarded.. Me or the ignition timing.. -__-

 

[grizld1]

Don't be too hard on yourself. Sure, the Golden Rule of carburetor tuning and maintenance is simple--"Check everything else first." But the tendency to chase electrical or even valve train gremlins through the carbies must be hard-wired in the human brain, because expert or novice, wise man or fool, we've all done it some time or other. All you can do is fight the temptation.