I find that not all eggs are created equal. With grocery store eggs (very generic) I find that I can't use as much oil or it gets thin (as you described). The only fix is how was described above, use another egg yolk and slow beat your mayo into the new egg yolk. If I use "farm eggs" I can use more oil and it still stays thick.
As far as the taste, not a ton you can do about that at this point. I don't mind mayo with EVOO but it is definitely a different taste than made with a more mild oil.
Using EVO is not a good idea if you are using a machine. The Polyphenols in the oil are dispersed and lead to a very unpleasant bitter flavor.
If you want to use Olive Oil this is great place for a lower quality one. Otherwise a more neutral oil should be used as others have mentioned.
The typical ratio or Mayo is 1 yolk to 9oz of oil. Your problem with thickening is probably your oil to yolk ratio.
Also remember that Mustard, Garlic or Lemon all help encourage and stabilize the emulsion.
You can make mayonnaise in a mason jar using a stick blender in about 10 seconds.
Homemade Best Foods/Hellmanns Mayonnaise using stick blender
1 whole egg, medium or large size
1 Tablespoon lemon juice (bottled ok)
1 teaspoon distilled white vinegar
1 teaspoon dry mustard (or 1/4 tsp prepared yellow mustard)
1/4 teaspoon table salt
pinch white pepper
1 cup vegetable (canola) oil, room temperature
Break egg into bottom of 1-quart canning jar or other tall narrow jar that allows you to immerse the mixing blades of a stick blender all the way to the bottom. The jar should be only slightly
wider than the end of the stick blender.
Add lemon juice, vinegar, mustard, table salt and white pepper.
Add 1 cup of vegetable oil.
Place mixing blades of stick blender (turned off) all the way to the bottom of the jar, pressing
down over the egg.
Turn stick blender on high speed, hold in place at bottom of jar for about 5-seconds until you see mayonnaise form under stick blender's mixing blades.
Slowly pull running stick blender upward until the mixing blades reaches top of jar, taking about 5 more seconds. The stick blender will turn the oil into mayonnaise as it is pulled slowly to the top of the jar.
After chilling in the fridge, this mayonnaise gets slightly thicker and tastes very much like Best Foods/ Hellmann's Mayonnaise.
Makes about 1-1/3 cups of mayonnaise.
That's the ratio I use for mayo, and it usually works out alright.
Like Chinon00 asked, have you made this in the past? And how are you making it? I've found a few things to be particularly important for mayo:
1) For me, making mayo by hand is much more foolproof than using a food processor or standing mixer. The only time I've had mayo break is when using a food processor.
2) Did you add the oil in really, really slowly in the beginning? I'm talking about a couple drops at a time, and waiting for them to incorporate. If you add the oil too quickly at the beginning, it can get runny at the end.
As far as taste goes, I find that mayo usually needs an acid component, so you might want to add a little lemon juice to brighten it up. If all else fails, you can turn it into aioli by mincing a couple cloves of garlic and then turning them into a paste with some salt and the back of your knife.
Bring an egg yolk to room temp or warm it in a baggie in warm water. Whisk the yolk however you were making the mayo in the first place--whisk, food processor, blender, whatever. Add the broken mayo--very, very slowly, by teaspoonsful at first--and continue to whisk or process until the mayo "catches." Since you didn't care for the flavor of the EVOO, once the mayo catches you may want to add the broken mayo alternately with a neutral flavored oil such as grapeseed or even canola.