How do you use と言ってた?

Question

I am reading Genki II. And I found a report sentence (a sentence that states what somebody else said) that ended with と言ってた:

チョコレートを食べすぎたって言ってた。
He said he ate too much chocolate.

I've got two questions:

1. Why is 食べる in its stem form (食べ)?
2. And, why are we using 言ってた instead of 言っていました?

Answer 1

1. The verb is in its "stem form" because that's the form 〜すぎる attaches to. This is what Martin refers to as the excessive in his Reference Grammar of Japanese (p.434):

   You can attach すぎる to the infinitive [stem form] of most (probably all) verbals, to produce a new verbal, the EXCESSIVE form with the meaning 'overly' or 'all too (much, many, often)'.

   In Japanese, what you call the "stem form" of a verb is usually referred to as the 連用形{れんようけい}, and if you look up 〜すぎる in a Japanese dictionary you'll see that it attaches to the 連用形 of verbs. From 明鏡国語辞典:

   ≪動詞の連用形、形容詞・形容動詞の語幹などに付いて複合語を作る≫
   物事がある程度をこえる。度をこえる。

   　「働き―・喜び―・みじか―・多―・静か―・危険―」
   　「自信がなさ―」
   　「あまりにも情けなさ―」
   　「ぎごちな(さ)―」
   　「人の意見を聴かな―」

   〔語法〕「…ない」に続くときは、語によって「なさすぎる」「なすぎる」の形になる。「情けない→情けなさすぎる」「つまらない→つまらなすぎる」

   This doesn't have anything to do with って言ってた, though. It just happens to be part of the quote in this case.

2. 言ってた is an informal contraction of 言っていた, which is the plain form corresponding to the polite 言っていました. It's a more colloquial way of saying the same thing.