Encontrei um furo na câmara de ar.

Encontrei is the 1st person singular form of encontrar in the pretérito perfeito (simple past).

So it means I found.

Breakdown:

• encontrar = to find
• encontrei = I found

This tense is used for a completed action in the past, so the sentence is talking about a specific moment when the speaker discovered the hole.

In Portuguese, the subject pronoun is often omitted when the verb ending already makes the subject clear.

• encontrei already tells us the subject is I
• so Eu encontrei um furo na câmara de ar is also correct, but Eu is not necessary

European Portuguese very often leaves out subject pronouns unless there is a reason to emphasize them.

Um is the indefinite article and means a or an.

So:

• um furo = a hole / a puncture
• o furo = the hole / the puncture

Here, um furo is used because the speaker is introducing it as new information, not referring to a specific hole already known in the conversation.

Here, furo means a hole, and in this context more naturally a puncture.

Although furo can literally mean a hole in many situations, with something like câmara de ar, it strongly suggests a puncture.

A useful distinction:

• furo = a pierced hole, bore, puncture
• buraco = a hole in a broader, more general sense, often larger or less specific

So for a tyre inner tube, furo is the more natural word.

Câmara de ar is the normal term for an inner tube.

Literally, it is something like:

• câmara = chamber
• de ar = of air

But you should learn câmara de ar as a fixed expression meaning inner tube, especially for bicycles, motorcycles, and similar tyres.

Because Portuguese contracts the preposition em with the definite article a.

So:

• em + a = na

That means:

• na câmara de ar = in the inner tube

Other common contractions:

• em + o = no
• em + os = nos
• em + as = nas

Because de ar is part of the fixed noun expression câmara de ar.

Here, ar is being used in a general sense, not as the air in particular.

Compare:

• câmara de ar = inner tube
• o ar da sala = the air in the room

So do ar would sound wrong in this expression.

The accent in câmara shows the stressed syllable and helps distinguish pronunciation.

It is pronounced with the stress on the first syllable:

• CÂ-ma-ra

In European Portuguese, unstressed vowels are often reduced, so the full pronunciation may sound less clear than an English speaker expects, but the stress still falls at the beginning.

A broad European Portuguese pronunciation would be roughly:

Encontrei um furo na câmara de ar
≈ en-con-TRAY um FOO-ro na CA-mra d’AR

A few useful points:

• encontrei ends with a sound like ay
• um in European Portuguese is nasal
• furo sounds roughly like FOO-roo, but with a lighter final vowel
• câmara often sounds compressed, almost like camra
• de ar often links smoothly, almost like d’ar

This is only an approximation for English speakers, but it helps with the rhythm.

Yes, it is feminine, because the head noun is câmara, and câmara is feminine.

That is why you get:

• a câmara de ar
• na câmara de ar

Even though ar is masculine by itself, the gender of the full expression is determined by câmara, not by ar.

Yes, absolutely.

Both are correct:

• Encontrei um furo na câmara de ar.
• Eu encontrei um furo na câmara de ar.

The version without eu is more neutral and very common.
The version with eu may add emphasis, contrast, or clarity.

For example:

• Eu encontrei um furo, mas tu não viste nada.
  = I found a puncture, but you didn’t see anything.

Yes, it is natural and correct.

Depending on context, native speakers might also say things like:

• A câmara de ar tem um furo. = The inner tube has a puncture.
• Encontrei um furo no pneu. = I found a puncture in the tyre.
• A câmara de ar está furada. = The inner tube is punctured.

But your sentence is perfectly idiomatic and sounds normal in European Portuguese.

The sentence follows a very common Portuguese order:

• Encontrei = verb
• um furo = direct object
• na câmara de ar = location

So the structure is basically:

I found + a hole/puncture + in the inner tube

This is a normal and neutral order in Portuguese.

You could move parts around for emphasis, for example:

• Na câmara de ar, encontrei um furo.

But the original version is the most straightforward.