I had a slanty that would do that cause of a clogged up filter..full of rust
start out and be going then drop off and die if you gased it
when it stummbled, and you let off and let it coast and slow down it would catch up and go about 1/8 mile and start dieing again
drove it under 30 mph all day but 45-55 was out the window and would die off till slowed down
so yea a dirty filter could cause it, and just cause I could blow through it,didnt mean zip
it was a metal one,I cut open and had a hand full of rust powder and the filter media was clogged full of it
swap on a filter and it ran fine for about a yr and then again it was clogged
scratchin