400ex. Help!!!

[Zillafreak]

Hey guys, so Today i was ridin for about 45mins-1hour on tight trails and in a pit. it was running great when i left the house and i was riding in the pit for a little and it started doing this thing..anything thing past half throttle and it would bog/sputter but if i kept it at 1/4 it was fine and rode regular no stuttering or bogging...it puffs black smoke when I rev it but not alot. It runs on race fuel. It has a 42 pilot and a 190main jet. Today's the first day I ran it with triple t protection 15w30 rotella oil. Let me know what you guys think? Jetting issue? Please help. Thanks appreciate it!

[Mtndew99]

Did the choke turn on mine will if I bottom out or enough vibration will make the choke lever come on

[DragonGunner]

Clean the air filter, its getting dirty and cutting the air flow and making it run rich. Thats where I would start.

[HondaRacing83]

Sounds like the chokes on to me

[01boneless]

needle clip could have fell off

[Zillafreak]

The carb somehow got disconnected from the boot :confused:. what about the black smoke when i rev it from idle?? is it bad?

[Stickman400]

I've had my airbox boot pull off my carb. before after I hit my tabletop and landed really hard, it happens. Might I ask why you're running race fuel? Is it stock bore and compression? There's no need to waste your money on it if it doesn't need it. You could run 120 octane in a stock machine and it wouldn't gain a thing.

[Zillafreak]

I was just cruising when it came off.. The guy I bought it from gave me 5 gallons of vp and I run my shees on race gas so it's not a problem. It's bored to a 416 or 426. It's way faster than a stock 400

[Stickman400]

You can still run 93 on a 10.5:1 or 11:1 piston though, bore size doesn't have anything to do with fuel octane. No need to waste the money.

[2001400exrida]

11:1 on pump gas is pushing it with an air cooled 400ex motor. I run 100 octane in my 11:1 because i was pinging.

[Stickman400]

Damn nearly everyone on here has that setup and runs 93, maybe 1 or 2 guys are paranoid and run 100 octane, nobody else has had any problems. I guess if you got the money then by all means spend it however you think is the best.

[DragonGunner]

11:1 on pump gas is pushing it with an air cooled 400ex motor. I run 100 octane in my 11:1 because i was pinging.

Years back mine started pinging with 93 also, I was at that time a pilot and got 100 octane aviation fuel, best stuff out there period. After 2 yrs. of hard riding and racing the piston and cylinder was super clean, later as 100 octane got more I would mix 50/50 with 93. In recent yrs. if I buy 93 octane from a Sunoco station it doesn't ping......maybe the gas got better in recent yrs. or its just the station.

[Mtndew99]

I've had a lot of respected motor builders tell me 93 is fine just make sure it's jetted right

[Zillafreak]

The race fuel gets expensive. I'm gonna start mixing it with 93 pump. Should I bump my main jet up to a 220-230? I read on a forum post that it wakes up the big bores. I'm currently running a 42 pilot and 190 main

[DragonGunner]

The race fuel gets expensive. I'm gonna start mixing it with 93 pump. Should I bump my main jet up to a 220-230? I read on a forum post that it wakes up the big bores. I'm currently running a 42 pilot and 190 main

Doesn't work that way, jetting is determined among other things with the amount of air coming in, and how dense or thin that air is. To big of jet and sooner or later you will loose performance and it will bog. Racers usually try and jet for as lean as they can wthout being lean.

[Stickman400]

Jets-R-Us recommends putting bigger and bigger jets in until you get a sputter at WOT, then back it down 1 size. Then your main is jetted perfect.