Is there any search engine or price alert engine that let you specify a specific flight or set of flights and receive alerts when the price goes up or down?

All sites I know let you do this but it is a generic from A to B but sometimes this A to B (on long haul) the cheapest flight is such a bad combination (like 40h long journey) that you don't really care about it, the worst is that these flights are usually the cheapest ones and they just pollute the search results and fare alert as you'll mostly be receiving alerts when those flighs go up or down and not when the flight you really want to take goes up or down.

Something like: Alert for AF7625 + AF276 + AF279 + AF7630

EDIT: Seriously, how can someone mark this question as duplicated when I'm clearly asking for a price alert engine for specific flight numbers within a route from A to B and NOT a general price alert for A to B where we will get 40h long flights that only a suicide guy would take. Where the real 15h long flights are the real flights to take in consideration for the alert engine and therefore we need to somehow just specify them and filter out those cheap 40h long journeys that no one will ever take.

I even gave an example on the original question and replied to the comments stating this is not a duplicate question and explaining why.

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    Yes, Kayak, Skyscanner, Google Flights, Momondo and Hipmunk are the main ones I use – user13817 Nov 6 '16 at 21:20
  • @JonathanReez That question is in no way related to my question. I want price alerts for a specific set of flight numbers and not from point A to point B. – user13817 Nov 7 '16 at 21:30
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    Aren't flight numbers from point A to point B? – Mark Mayo Nov 8 '16 at 0:04
  • The duplicate asks about a specific flight between A and B, not all flights between A and B. – JonathanReez Nov 8 '16 at 5:42