MNupnorth I think you're absolutely right. I have a 01 400 Explorer with the HSP speed kit and the 38mm carband v-force reeds setup in it. My bike will hardly run with lid on. It loses throttle response, bogs easily and doesn't rev out.Without the lid it runs awesome. Last weekend I replaced the lid with a car type filter to keeep the junk out but let air in and it worked ok. Not as well as an open lid or just having the filter on the carb though. Could you show me a picture of your lid?

 

It has been some time since I wrote an update on my 99 explorer 400 and its loss of power.After I fixed the jet cover bolt hole on the bottom of the carb it ran real good for about a week.Then it started to lose power and stutter again.I took it to dealer as it was getting to close hunting season and I was out of ideas on my own. They found a cracked piston and some of the lower end had piston fragments in it.I had it rebuilt for $1800.00 and change and took it out to a mud bog that afternoon. It had a bit of a knocking sound in it I had not heard before the rebuild ,but the dealer assured me I should should ride it hard and break it in with the oil gas mix in the tank.I was apprehensive but went mudding anyway and it ran pretty good.I took it home unloaded it and went to put it in the barn and it died with an impressive cloud of smoke. I took it back to the dealer and to there credit they ran it staright in to the shop and tore it down as I drove home with there loaner.They found the water pump seal was cut probably on the rebuild. The coolant leaked down into the counterbalance oil and they say it caused excessive pressure and sheered off the flywheel key. That in turn gouged the fly wheel and they replaced all of this. Wether or not this could all happen from a coolant leak I dont know but what I do know is they replaced it all at no charge and the machine sounds like new and runs like it.If anyone has any opinions or insight on that let me know I am still curious if this is really what happened. Take Care all and get out and ride!!!!!!!!!!!!