Pokémon Platinum: Gym Leader Wake help!

I would say yes, by raise only Infernape to high levels it leaves your team with a weak point, especially with water types. For now, focus on Pichu Carnivine and Roselia.

You should definitively train Infernape, along with everyone else. What I do is give Infernape/Empoleon/Torterra the EXP.Share that you receive from Dawn's/Lucas' father and just fight with everyone else on my team.

Whoa, whoa, whoa. Your Infernape's Lv. 40 and the others aren't even Lv. 30 yet? I'm not from your region and I STILL know that's a HUGE mistake. You shouldn't raise one Pokemon really high and forget about the others. Secondly, you're using a Ponyta against an experienced Gym Leader specializing in Water-types? Maybe using another Grass- or Electric-type instead? So, basically, train your friends, help them get better, and maybe let Ponyta rest for a bit. Also, don't depend on your Infernape so much, because when it faints, you've pretty much lost the battle.

-Plasma Grunt Katie

It's a really good idea to evolve pichucause electrics are super effective against water and flying, both types mushed together plus gyardos stats equals the unpredictable......
Teach it discharge or volt tackle, i SUGGEST YOU DON'T TEACH IT THUNDER because my Luxray ALWAYS MISSES when it is versing a Staraptor. Tip: Train it with love, don't giveup onit after I did-your not the only one with a pichu attempted to train. Though soon enough it was too weak so I finally agreed to ditch it at the daycare. I can't remember what happened after that, I think I transferred it ti poke white or something......

ok here's what i would do first i would try to evolve pichu into a pikachu and obviously level it up to around 38 or 34 something like that :L and as a back up just encase he faints level up carvine as well, or you could just buy loads of revives and hyper/super potions and defeat him that way :P

I say level up your grass types, evolve your Pichu, and replace your fire types (if you have good leveled pokemon in your storage).