Question: Cycling larger tank with water from old tank?

Hello most knowledgable members of caudata.org, please help a newbie out.

My three axies have been in their small 10g tank since they were tiny, but they have now grown enough to warrant an upgrade.

So I've acquired a 40g tank - and I've been trying to cycle it for a few weeks now, to no avail.

I placed only 4 guppies in it (that's the most I could get my hands on, my LFS is... not that great), but still ammonia, nitrite and nitrate all register at 0.

Then I had an idea - maybe instead of dumping the water from the water changes in my current (cycled) 10g tank, I could put it in the larger tank, thus helping to kickstart the cycle... Is this a good idea?

Alternately, I could attach the 40g's canister filter to the 10g - I'd have to seriously reduce its flow (not sure if that is healthy for the filter, it is rated for a whopping 650 liters or 170 gallons so it is quite overpowered even for the 40g), but then it'd have some actual filth to filter. Would this help?

Help appreciated!

Can you use a piece of old filter out of 10 gallon to jump start your new tank. I have double sponge filter in cycled aquarium i take out one filter with bacteria on it switch with new one. So i have two double sponge filters each with one used and one new filter. Put one in old aquarium and one in new aquarium new aquarium usually is cycled within 3 days. They say cycled aquarium water does not cycle a tank. The substrate filter and decorations hold the bacteria last i read up on it.

I only have one sponge filter in the old, smaller tank so I can't move it to the new one (without breaking the cycle in the old tank).

My question is this - I think the problem with the new tank's cycle is that 4 guppies aren't creating enough ammonia for a 40g tank, but if I move 2g of old water from the old tank every week, I think that'd help start the cycle.
Is this true?

It may help but it would be very, very minimal. If you could use some filter media from an established tank is your best option to jump start. What you want is used/dirty media. If you can't do that from your old tank to the new one then ask your LFS if you could get a hunk of used filter media (floss,sponge or whatever they have)