About a month ago, i performed my 100K maintenance. Everything except the timing belt, water pump.

I also replaced my spark plugs.

I noticed my car running smoother, but i always get this burnt smell, esp when i go uphill. I thought i was breaking in the spark plugs or something, but after a month, the smell is still here. What could be the problem?

Also when i start my car, it sometimes sounds like a little struggle before the engine starts, versus the engine starting up smoothly.

Thanks.