1999 vmax 225 ox66 rpm problem

[skeeter 21]

My engine runs just fine in the morning, but by late afternoon when it hot out the engine retards the rpm's to 4100 from 52-5400 that I was running.If I let off the gas just a little the engine picks right back up and runs fine for 30secs- 5mins before retarding rpms agian. I've replaced the waterpump, thermostats, fuel filters,checked the water overflow,checked the hp fuel pump for water, and running super unleaded for fuel. This problem only happens in the afternoon when I'm trying to get back to the ramp.I would like to check a few more things before taking it to the shop. Any help would be great.

[jb123]

i didnt look up your motor, but if its an 0x66 efi then you SHOULD have an 02 sensor that either needs to be cleaned,tested or replaced and those are the symtoms they cause when dirty or bad.
Also, check your pump ball when this happens cause it sounds like it COULD be some fuel restriction.