OK, just got back from a race weekend. I won my division on Saturday (bike ran great)
, and then ended up in third on Sunday because of a recurring, but inconsistent, mechanical difficulty
. I could definitely use help diagnosing this, as I don't have the time or money to get a full engine rebuild...
Here's what happens - at 13k or 13.5 rpms, under full acceleration, the engine starts to "stutter" and won't go to redline (and beyond). The first time this happened, I had just put on pair valve block-offs, new spark plugs (Brisk AR12-zs), a PC quickshifter and PC ignition module. None of this should cause stuttering - but I quickly removed the ignition module and quickshifter with no change. Then I put in different fuel (switching from VP100 to pump gas) and the problem disappeared.
I had assumed that the problem was with the upper injector bank, since they only switch on at 13.5k rpms. My assumption was that I had accidentally got gunk/dirt in the fuel line to the upper injectors when I tore my bike down for the pair valve replacement, and that the new fuel had dissolved it - or something.
So, two race weekends later (all on pump gas with the bike running well) and I switch back to VP100 between Saturday and Sunday. Problem recurs, and now it is happening at lower RPMs (can't tell how low because I'm hanging off the bike driving out of curves when it happens).
The bike isn't burning oil; makes great power when it's not stuttering; nothing else seems to be wrong. (My PCV map was done on pump gas, by the way.)
Question - would the fuel really cause this problem? (VP claims the 100 is a direct replacement for pump gas.) Is there something I'm missing?
Thanks in advance for any help - I really want to get back on the podium!