2011 YZ450F Camshaft Question

I have been having some problems with my used 2011 YZ450F dirt bike. I checked the valved gap and one was out of spec so I took the cams out and noticed that the intake camshaft is stock but the exhaust camshaft has a Web Cam marking with Grind number 943. According to Web Cams website this is a very agressive grind. Can anyone think of why someone would have just changed the exhaust cam only? And why with a Stage 4?

I'd be speculating, but yes, I can.

Can you be more specific? What does it help? And could it be making my bike start a lot harder.

It could be causing hard starting, yes. Let me start by saying I'm not familiar with the cam grind in question, and I'm not going to go to the trouble to look into it, but most people don't imagine themselves qualified to make decisions like that without some advice on one level or another, so it would most likely have been on some sort of recommendation (remember, I'm speculating). Maybe they saw it in a magazine, or in an Internet forum, or maybe that was what Web recommended.

As to why a stage 4, the term "stage 4" means nothing to anyone except to make it very likely that there were 3 other ones at least, presumably less aggressive than the 4. In the case of the YZ450 and the products available from Hot Cams, the HC Stage 1 was very nearly the same as the OEM YZ450 cams was in '03-'05. When Yamaha upped the ante in '06, the Stage 1 would have actually slowed that bike down, so to do a mild hop up on an '06, it's quite logical to have used a Hot Cams Stage 2 exhaust with the stock intake. Yamaha progressively made the cams in each year from '06 to '09 more aggressive than the previous model, and now we have the Third Generation 4 valve YZ450, which is probably already at a level equal to somebody's Stage 3 grind.

Changing only the exhaust is a perfectly valid way to add performance, and is, in fact, exactly what the difference between YZF and WRF models was from '99 up through '05, when the WR finally had to use its own cams on both sides of the head. So changing to a Web Stage 4 doesn't sound unreasonable on its face until we have some information to make it sound like a bad idea.

Not fact, necessarily, but that's how I see it. You can probably get something more specific from Web. Starting troubles can come from too aggressive of a grind causing through flow troubles at cranking speeds, but before I blamed that, I'd try the usual things people have been recommending for getting the EFI bikes to start easily first, just as if it were stock.

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