Hydrolock test and plug gap

[Jet86]

Okay at 67k i did the hydrolock test per this site and cyl#4 was a hair low, so low that i had to do the test 3 or 4 times to be sure, any way the bike now has 73k and runs just fine, but sometimes when i hit the start button i hear a knock that sounds like its coming from cyl 4 but im not 100% sure, i am going to install new spark plugs soon and was wondering if i should Gap/adjust #4 plug. 
I have always just thrown the plugs in without gaping at all, i just look at them and if they all look the same they go in with no adjustments, so is there anything i should do to help cyl4 ??

The knock i hear at startup only seems to happen when the bike is warmed up, i never hear it from a cold start.

[Steve in Sunny Fla]

you should always check the gaps when installing new plugs. Changing anything on one cylinder isn't a good idea. steve

[T Cro ®]

Always gap new plugs; myself I prefer the narrow end of the spec as the gap only opens more as the plus ages. If your piston height difference was so "little" that you had to measure several times just to make sure that you saw what you thought you saw. I would pull a compression test to see if your low cylinder is within 10 % of all other cylinders and if so I would do nothing. As in truth true top dead centers are difficult to measure without special devices and skills. Namely if you find that the engine is still running without issue I would not worry further.

[Jet86]

Ok thanks, i have a round coin gaper in my tool box, i will use it from now on, i am still wondering where that knock is coming from? can a bad fouled plug cause a knock at startup? once its running its fine its only when i hit the start button. or could the knock be coming from the starter tensioner?
I know this kind of problem can be hard to tell without hearing the bike start for yourself.

what should i gap plugs to' can you give more detail. thanks

I still need to buy a compression tester, i can get them cheap at Harbor fright.

[T Cro ®]

Yes that small knock coming from the right side could be from the starter chain.

Spark Plug Gap 0.024" to 0.028"

[Jet86]

Cool thank you for that information..