Bicycle Mechanics - Freewheel spins freely forwards?

I'm fixing up an old 10 speed for the neighbor kid. I've noticed that sometimes the pedals spin freely forwards before the freewheel engages. What causes this? It only happens when starting from a stop or if you have been coasting.

I assume it's a freewheel, not a cassette. It sounds like the pawls are not engaging. Probably gunked up with old lubricant. I'd probably try dripping some oil in the body. Or just replace the freewheel.

I assume it's a freewheel, not a cassette. It sounds like the pawls are not engaging. Probably gunked up with old lubricant. I'd probably try dripping some oil in the body. Or just replace the freewheel.

It's an old Huffy 10 speed bike, 5 speed freewheel. Not really worth spending money on parts. Will 3 In 1 oil do the trick?

It might, but I'd try to wash things out with some really light lubricant such as WD-40. Then drip in some regular oil once the pawls engage ok.

+1, I use penetrating oil in a spray can. Spray liberally into the gaps around the edge of the freewheel and let it soak in good, laying it horizontally. Go ahead and let the excess drip out after it has soaked for an hour or so and then put some 5W-30 or similar engine oil into the freewheel. Should do the trick.

If you have the correct freewheel remover, take off the freewheel and toss it into a can of solvent - kerosene, diesel fuel, mineral spirits, or napatha. Let it soak overnight then continue the next day agitating and lifting and draining then re-dunking from time to time. This is overkill, but doesn't realy take much time.

The goal is to flush any old dried grease and oil from the freewheel. When finished it should be what I call "rattling clean" and the pawls engage cleanly every time. Drain and dry it completely. Naphtha and mineral spirits will dry completely on their own, diesel fuel and kerosene requiring a bit of heat so put it in a warm place for a while. If it's warm out, put it on a pan inside your car parked in the sun with the window cracked open slightly for a few hours.

Re-oil with a 30 weight or higher oil (not that it needs heavy oil, but thin stuff spins out) or Chain-L or Phil tenacopus (if you have them). To apply, drip the oil on the upper gap, spin to work it in a bit, and lay the freewheel on a paper towel to drain. If none drains out the bottom, repeat, and keep adding until some drains through.

I suggest the remove and soak method, because an effective cleaning and oiling on the wheel will make a mess and have you wiping the spokes for days.

On a bike of that age it's also possible that the freewheel is gunked up with rust. But you won't know if it's salvagable or not until you flush it out with some solvent using the dunk n' drain methods already described. If it cleans up then it was just old dried gunky oil or grease. If it stays rough and intermittent and sounds like it's got a handful of coarse sand in it after flushing with solvent then it is rust and it can't be saved.

The good news is that 5 speed freewheels are so cheap that it's worth replacing it even for an old Huffy. Or if there's some second hand shops around that specialized in old bikes you can often find a servicable used one for likely a fiver.