New VMs - won't run (XS500)

Here's the deal:

I got this 78 XS500E that I rode once about 3 years ago. Idle raced to 3k when warm - which is unnerving, so I got a set of VM34s off a sled so I'd be the one in charge, not some worn out old vacuum system. Anyway, I've now got these things rigged up and everything seems like it should be dandy. Thoroughly cleaned - new jets in the ballpark of what's reported on XS650s.

Ran when I parked it. New battery, new plugs (one with newly-repaired thread insert), plugs show blue spark when grounded.

Carbs are puking fuel out the overflow tube, which is obviously not great, but shouldn't prevent it from running, right?

Any thoughts?
Thanks

Did you take the 1.5 needle and seat out and put in a 3.3? Brass floats and maybe one is heavy[took on fuel]? Float level spot on?

Your floats are stuck. It certainly wont help.

Shut off the fuel, drain the carbs. Close the drains.

While holding a plastic handled screwdriver, open the fuel again as you tap each bowl with the handle end of the screwdriver, sometimes pretty firmly but within reason. This will usually free the float valve and allow the float to rise, thusly stopping the pig rich condition and the overflow problem.

If this doesn't work, either your floats are WAY off, or you'll need to clean your carbs again. Sometimes I like to spritz a little pb blaster in the seat, keeps the float valve lubed until startup.

Post your results.

Thanks for the thoughts guys.

What's the difference between 1.5 and 3.3 needle/seats? I just cleaned up what was in there with very fine grit paper. Whatever float needle is in there is not retained by a clip.

Didn't do anything with the float level. Cleaned very thoroughly once, all new jets. I didn't do anything with the needle jet/jet needle. I think it said something like P6, which is what I found for xs650s, so I just left it (on middle clip).

I tapped the bowls with a few small pieces of wood I had laying around. I think it might have loosened up the float needles.

These are black floats - foam or something, so I don't think they can take on fuel like the hollow ones. Double-checked plug gap and spark - still good. Plugs are new and still look very clean/dry. I think maybe I'm not getting fuel. I did get one little pop-over today before fuel ran totally dry.

Will post updates as I get 'em.

Thanks again


ETA: Looks like Mike's XS recommends the #2.5 for VM34's:
https://www.mikesxs.net/product/48-8021.html

Black plastic floats are good,those don't go heavy. If the carbs are off a sled they have small needle/seats because they use a fuel pump. Bikes are gravity fed and need a larger combo.

Thanks Jimmer. Ordered the larger float needles/seats. Will wait to proceed until those arrive. Worst case I guess the stock carbs go back on and I figure out the racing idle issue from scratch.

Got 'em in the mail, but couldn't get 'em in the carbs. Bolt size on 2.5 needles/seats does not fit the one for mine which are marked 1.5. I reset the float levels and let 'em have gas, which dumped right out the overflow tubes. I think these "VM34" carbs from the Arctic Cat are just not going to work. I've sunk enough into these to have just bought a kit and have nothing to show for it. I think it's probably to do with the gravity feed vs pump like you mentioned. I don't think the float needle can seal off the pressure. Would not recommend someone to buy cheap snowmobile VM34s. In my experience at least, they will just not work. I think especially since even the kits will require work to get tuned, avoid the hassle and go with something that is sure to work from the start.

Going to scrap this idea and go back to BS38s. Can I clean them up without buying new gaskets?

Put the stock CV Mikunis back on - fired right up. Will do valves, timing, tensioner adjustments and it's probably all good. VM34s going on ebay.

Thanks for the help though guys - do truly appreciate it!