Vacuum pulse near air intake troubleshooting

[Ryan G]

Hello! Towards the end of my clone swap but having issues with fuel and the vacuum setup I purchased from Vegas Carts. In the picture you can see the billet aluminum port to pull vacuum. I had it hooked to fuel pump, attempted to start but would not. I took the house off and put my hand over the port while cranking and there is little to no vacuum. Anyone else have this setup? Was hoping to do this rather than drill through valve cover.

[CP241]

In the ones I’ve done, the nipple needed to be between the carb and the motor. Looks like you’ve got your setup on the outside of the carb?

I didn’t buy anything fancy, just a threaded vacuum fitting from tractor supply for a buck. Then drilled a hole through the plastic spacer between the carb and the motor and threaded it in. Worked perfectly. This was on the 420/460 clone setup. Not sure about a v-twin

[Ryan G]

This is on a lifan 420cc swap. Should have mentioned that! And yes, this is on the outside of the carb between the carb and air filter. Was hoping I could get this to work but may have to go that route.

[Fairtax4me]

The pressure drop happens on the inside of the butterfly because it blocks airflow when it’s closed. Pressure Outside of the butterfly is same as atmosphere.

[Ryan G]

anything on inside of air filter should be pulling vacuum. Atmosphere is on outside of filter.

[crash12888]

The outside of the carb will pull and have vacuum but you need a pulse to operate the pump preferably from the crankcase.
If your air filter is free flowing to much there will be no "pulse".
The hose just below the fuel line, is that coming from the valve cover? you can use that.

[meimk]

As everyone has mentioned you need something like this
https://vegascarts.com/products/isol...-pulse-fitting

[Ryan G]

Originally Posted by meimk

As everyone has mentioned you need something like this
https://vegascarts.com/products/isol...-pulse-fitting

Yep just ordered one. Thanks!

[CP241]

Originally Posted by meimk

As everyone has mentioned you need something like this
https://vegascarts.com/products/isol...-pulse-fitting

That’s what I did, but I just used a vacuum fitting from tractor supply and drilled a hole in the one on the motor. The brass fitting threaded into the plastic nicely, but I still put a dab of epoxy on the threads to make it permanent before installing it back to the cart.

[raydhd]

Another note. The fitting you used is for the crankcase venting such as off the valve cover on stock clones where the rubber hose usually ends into the air cleaner.