Just finished a pretty extensive build on my 2021 YFZ450R. Athena 97mm cylinder, JE 12.5:1 piston, and some Hot Cams Stage 3 for the YFZ450R (P/N 4098-3E and 4097-3IN). Replaced the crank, timing chain, guides, all new OE gaskets, bearings, oil pump, head studs, full valve job, basically a fresh engine.
But the weird thing is, it's incredibly difficult to kick over. I've had it pop a few times and even idle beautifully for a bit, no leaks or anything. But actually getting it to fire up from cold is a serious workout, and it just doesn't want to light off most of the time, just a puff from the exhaust. I timed the cams to the two dots as per OEM spec, everything seems perfect. However, I noticed there are also lines on both the exhaust and intake cams. I also checked the stock exhaust cam against the new Hot Cams one, and the decompression pin on the stock cam is visibly longer.
Could this be the root of my problem? Is the shorter decompression pin on the Hot Cams causing such high compression that it's nearly impossible to kick over? If anyone has suggestions where else I should look into or how to fix this, please drop a message!
But the weird thing is, it's incredibly difficult to kick over. I've had it pop a few times and even idle beautifully for a bit, no leaks or anything. But actually getting it to fire up from cold is a serious workout, and it just doesn't want to light off most of the time, just a puff from the exhaust. I timed the cams to the two dots as per OEM spec, everything seems perfect. However, I noticed there are also lines on both the exhaust and intake cams. I also checked the stock exhaust cam against the new Hot Cams one, and the decompression pin on the stock cam is visibly longer.
Could this be the root of my problem? Is the shorter decompression pin on the Hot Cams causing such high compression that it's nearly impossible to kick over? If anyone has suggestions where else I should look into or how to fix this, please drop a message!
