HMF jetting specs

[meanyellow03ex]

I just bought a HMF slip on for my 2003 400ex Honda. I was trying to figure out how to jet it. I am a member of exriders.com and looked on there. It seems your specs are too rich. Most everyone with a HMF slip on , airfilter, and or airbox mod use a keihin 155 main jet. I have a dynojet kit which is different from keihin jets. I found a dyno test online of various pipes including your HMF and they determined a 148 dynojet was correct with the airbox lid on. And that was tested on a dyno with an air/fuel analyzer. It seems you guys might recc. a higher jet size to be safe. Is this true or did you actually see an improvement with jetting rich as your recommendations? Thanks

I did a search of your forums and found a post about the 2004 400ex having a bigger carb and you changed your specs down to a 152main with a full system and no airbox lid. Thats a big difference. as far as I know, the 2004 400ex has the same carb as 1999 on. Honda changed the specs on their web site, that was it. Honda shop manuals listed the carb on the 400ex as a 38mm since 1999.

[DD/HMF]

The '04 does have a bigger carb. We just had one in house and saw first hand. The jetting that we recommend is what we used to get our machine dialed in. Remember that so many factors affect jetting that what works for one person might not work for the other. Always do a spark plug check to verify whats going on inside the motor. Give us a call at 866 HMF PIPE if you have any more questions.
Dan/HMF

[meanyellow03ex]

Had the 400ex dyno tuned today. It took a 170 keihin main jet to correct the air/fuel ratio. The quad also put out 27.3 horsepower at the rear wheels. Thanks HMF