Thanks for the comments! I'll give it more time and rework the entire pixelart ;)

the idea for this piece is nice, but I agree with onek, the lineart needs review... You better check some tutorial in the link section of the site and study the way to create non jagged lines, because that's the basic of a pixel art...

check this tutorial ... Also this composition looks more like an isometric one and for this reason you may have to take a look to isometric way of creating shapes. Try to start with raw and simple shapes (cubes, pyramids, circles, etc...) and than adjust them by slicing and smoothing some pieces...

your lineart is  weird... you shouldnt overlay the lines like you did, try to clean them up, also try to use selective outlining, ..

i made an edit to show you what i mean,... i also added some shading......

(step1:original >> step2: lineart >> step3: cleaned lineart >> step4: colors >> step5: define lightsource >> step6: shading) 

another thing that i recognized are some suspicious leftover pixels in th rear lights, which make it seem like you downsized and traced this....

And have some work on the wheels. 

Nice, but you should add some shadows and lights. :x :)