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View Full Version : 400ex bogs and shoots flames at high RPM's


h400exrydr
10-12-2005, 08:37 PM
Well i was at practice today, and like the last 10 laps my 400ex would bog and then backfire and shoot flames. It would always happen coming out of a corner or jumping. Not a pretty thing. I checked the gas...plenty, airfilter...clean,i am not sure what it could be. But then when i checked my airfilter i noticed that there was 2 little brackets on the stock air box that broke. Then i realized that the boot was a little loose on the carb and if i wobbled it a little it would come off. Do u think that it might b bogging because it sucked in some dirt? any help is appreciated!!
exracer131
10-12-2005, 09:54 PM
you might have a valve train problem. in order for an engine to back fire the exhaust valves have to be open when the fuel in the cylider ignights. you may have a bent or damaged exhaust valve. i would get a leak down test done on the top end. this will answer alot of questions about the motor. now it is possiable that you sucked some dirt into the top end with that loose intake boot, and the dirt could have damaged your piston rings and or valve seats. like i said a leak down test will answer alot of questions. i also see you have a 11:1 piston. predetination could be your problem. you might want to try some higher octane gas, above 93 octane.
h400exrydr
10-13-2005, 10:34 AM
Alright i geuss i will bring my quad to janssen racing. right now my motor is making a really loud ticking niose right where the valves are. do u think my valves might b bad? also with my gas i am running a 50/50 mix. i am using turbo blue 110 octane with shell v-power premium that is 93 octan i think. thaks for the help!!
tater_kamik
10-13-2005, 10:54 AM
try adjusting our valves first, but i would not run it for very long ( a few seconds) since that ticking very well could be the valves tapping against your piston...
h400exrydr
10-13-2005, 11:03 AM
well i jus rebuilt it and it has been ticking since the rebuild. I got about 10 hours on it now and the ticking just started getting louder. I already re adjusted the valves. If it is the valves is there a good place to get them?? Thanks for the help!
exracer131
10-13-2005, 07:58 PM
was the timing chain replaced???
h400exrydr
10-13-2005, 08:07 PM
no...do u think it could be stretched out or something??
exracer131
10-13-2005, 10:29 PM
is the ticking sound louder at idel than with the engine under a load ( going down the street half throttle) streatched timing chains with make an engine sound like it is about to come apart. the easy way to check this is: removed valve cover and see if you can lift the timing chain off of the gear that is attached to the cam. you should have no movement what so ever with the chain. no there is a slim chance the tensioner is froze up. it is located on the left side of the cylinder kind of under the carb.
h400exrydr
10-14-2005, 10:18 AM
ya..when it is idling it is very loud. But when i am balls to the wall ridin i cant even tell. Thanks for all the help!
h400exrydr
10-14-2005, 11:13 AM
is there a certain chain that i should try and get? because my friend has a Honda CRF 250f and if it is the same chain then i could probably get one from him. Do you think that a chain from a CRF 250 F would fit?
tater_kamik
10-14-2005, 04:12 PM
i dont know about that, but there is an heavy duty chain available for the 400 if i remember right
h400exrydr
10-14-2005, 06:25 PM
alright thanks, ne body know about the crf chain??
exracer131
10-21-2005, 05:07 PM
d.i.d makes a real good timing chain. i would recommend using one.
2004exrider
10-21-2005, 05:37 PM
anyone else think that since the boot on the carb was wobbling that its getting an air leak which is making it run lean and have it shoot out the flames. with it ticking it could be the cam, but it could be since its running lean that its running hot and causing preignition? Id check that first before paying a lot of money to get it checked out.

Jimmy
BLACKeR
10-22-2005, 08:56 AM
it could be since its running lean that its running hot and causing preignition? Id check that first before paying a lot of money to get it checked out.

my first thought, but im no thumper genius...
h400exrydr
10-22-2005, 10:52 AM
well..last night i had to race. so all this week i have been fixin her up to race.i re adjusted the valves and alot of the ticking went away. The first moto it ran awesome...i mean i was runnin in the front wit the 450's. Then at the start of the 2nd moto i was sittin at the gate and revvin to bout 3000 rpm's and all of a sudden, CLUNK, and it quit. i tried to start it and i could hear the starter motor goin but the piston obviosly wasnt moving. Then i tried to push start it and it was in 2nd and i popped the clutch and it jus kept movin, the piston didnt even move. I am geussing that i blew the connecting rod and/or the crank. Any help is really appreciated.