Help with VM20 carb on ace100

[[email protected]]

I have a carb VM20. I have replaced needles, floats, float valve and seat main jet, pilot jet all back to original and used factory settings. I can’t get the float bowl to not overflow. I took the carb off and put it on a ace90 and it doesn’t leak. When I put it back on the ace100 and turn on the gas and wait 15 seconds or so I see gas pouring out the overflow. I turn off the gas and start it up it runs beautiful. When I turn on the gas and it pours out the overflow it is really sluggish and quits starts up again but runs awful. Any thoughts would be appreciated

[viclioce]

It’s truly weird! It leaks out the overflow when mounted on the Ace 100 but does not leak out the overflow when mounted in the Ace 90. What would cause it on one bike & not on the other??? Victor

[matt glascock]

Make sure your floats actually float. Shake them and listen for fuel sloshing around or hold them under fuel and look for bubbles. Make sure the float arms are parallel to the gasket surface with float needle in place and the carb body held upside down so that the float arms are resting on the needle. Make sure the spring action on the needle is not seized. Make sure the needle and seat are in pristine condition. There are but a very few possibilities to check when troubleshooting a carburetor that overflows the float bowl. The operation of the carburetor properly filling the float bowl occurs irrespective of the model its mounted on. The needle/seat system has to be perfectly mated to stop fuel flow and maintain correct fuel height in the bowl.

[viclioce]

Matt. Alan is out for a ride. Here’s what we’ve discussed....

The 90 has a VM20 & so does the 100. Either carb overflows when mounted on the 100. Neither carb overflows when mounted on the 90.

So my thoughts are, it has to be something external to the carb on the Ace 100. I know it doesn’t make any sense, but it’s exactly what happens. Victor

[Bullfrog]

Yup. My money is on you finding that one (or both) fuel petcocks on the ACE 100 are leaking fuel. The fuel is likely flowing down the outside of the fuel line (and the fuel line is always wet/oily). If the fuel line touches the throttle cable, there is a path for the external flow of fuel down the cable into the carb and on into the engine. So - a quick check will likely show the ACE 90 fuel tubing is dusty dry on the outside - and the ACE 100 has wet/oily fuel tubing. Find where that fuel is coming from and you will have solved the problem.

Ed

[matt glascock]

Holy Craaaap. That never occurred to me. I've had plenty of leaky petcocks, the proceeds of which always ended up in a shop rag on the floor. Locked and loaded.

[viclioce]

I told him to check the petcocks. But, if it’s leaking down the outside of the fuel line, how, please, could that be overflowing the bowl? You can see it draining out the overflow tubing! If it were just the outside of the fuel line, it couldn’t make its way back into the bowl, could it??? Victor

[Bullfrog]

As mentioned in my previous post, if the fuel tubing touches the throttle cable, fuel will also run down the throttle cable and into the "cup" at the top of the cable adjuster. Then into the carb on the inside of the slide, down the needle through the needle jet and into the float bowl.

Ed

[viclioce]

OK. I see what you’re saying. It would also explain why it runs rich when it leaks! Hope he reads this and follows the path..... Victor

[[email protected]]

Thank you for all your replies. I think what I will try is to run a fuel line from a different tank to the carb on the ace100 and see what happens. Thank you all so much for your replies

Alan

[Bullfrog]

You might just try wrapping a dry paper towel around the fuel line on the hundred to see if it gets wet quickly.

Ed

[viclioce]

Alan. Since this became a sudden thing, use Ed’s idea with the paper towel to ID where and then replace the petcock gasket(s) and see if the fuel lines stay dry.... Victor

[viclioce]

Well, we figured it out! Alan’s original statement that the carb leaked on one bike & not on another was not a correct statement.

It turns out the brand new floats put into the carb we’re rubbing against the side of the bowl. It caused the floats to hang and therefore the fuel flow did not shut off when the bowl was full.

A simple bending inward of the floats to avoid the bowl edge was all that was needed. Here’s a before & after pic! See the right float. Victor