Electric bike has very stiff steering when in motion

I have a 350w electric motor on my front wheel and when under power the bike becomes difficult to steer-more so when I go full throttle.
If I reduce power the difficulty decreases-however even then the bike is difficult to steer-not nice to ride on
With the bike at rest the front forks are free and move easily.

I have a thornproof tube in the front wheel and a tyre that has a full tread.

It seems the spinning front wheel provides resistance to the rider steering the bike. I have another bike with a 350 w front wheel drive motor that steers easily-however the front tyre is worn smooth(bald as we say over here)
If I take my weight off the front handlebars there is a slight improvement in the stiffness of the steering.

If 2 words sum up the problem it is steering stiffness.
What is the problem here?

Thanks

Peter

Something in the headset is wrong, likely loose, then when the wheel pulls forward on the fork its jamming it up. Even when racing 50 mph with 4000w of power on the front wheel, I never felt a stiff steering. Other effects at that power level sure, but not stiff steering.

Adjust and lube should do it, assuming you don't have a wrecked bearing in the headset.

What kind of headset is on the bike? Have you tried loosening it up a tad to see how the bike responds?

EDIT: dogman dan beat me to it but i think it's an issue with the tightness or looseness of the headset. Try playing with the adjustment to see how the bike responds. I've had this issue before on non-ebikes.

Also, i'd be curious to know it it's a Cane Creek Headset?

Thank you for that information. I sprayed the headset bearings with WD40 and took the bike for a ride-very much improved so i upended it and soaked the bearings with engine oil-now really good.

I realise that the oil is not a long term answer and the headset will have to be dismantled and the bearings cleaned and greased.

This site is really helpful-thanks for sorting this out

Peter

Took the headset apart to grease it-the lower bearing was caged and only bit of the cage left-bearing balls missing or chewed up. Surprising that it still turned. A new set of bearings cost $5. They probably won't have a long life as the places where the bearings seated are worn-but one big improvement!

See if you can smooth the race out.
Is this a (B)icycle (S)haped (O)bject from any department store?

Holy cow... The bearing race is worn down? How man turns would it take for that to even happen? Well how many impacts from the front would that take too? I'd think the fork would break or spokes on your wheel would snap before bearings wear out... Ive got a bike from 2002 and I used to beat the crap out of the front ridged fork and the bearing still look great and the bike turns nice.

I wonder if you also have a little bit of a reaction wheel effect with the front wheel acting as the drive wheel...if it's unbalanced I'd expect it to be even worse.