Need help fast! Emergency jetting question!!

[Guy400]

My cousin and his friend just piped and rejetted a 300EX. They're running an HMF slip-on and a Dyno-Jet 128 main with a K&N. Here's their trouble. As soon as they reassembled the bike they blasted it up and down the street and it seemed to run perfect for about 2 half mile trips and then it started sputtering. Idle to half throttle the bike runs fine but more than half and it starts cutting out as if the rev limiter is coming in. Also, when the bike was running well it was backfiring a blue flame between shifts (this was at night). Does this sound it's running lean or rich? They had the lid off so I had them put it back on with no change so it would seem as if it's probably not too lean. Another detail to throw in--the owner of the bike replaced the rear brake pads just last night and now they say the bike won't even coast. It acts as if the rear brake is always about half on. I had them check the e-brake because I know that if that's engaged it'll activate the rev limiter. They removed the switch and pulled the plugs off it and still no change. Is this switch a normally open or normally closed switch? They're going to try and jump the two plugs together and see if that changes anything just to rule out the e-brake limiter. If anyone has any suggestions I'd appreciate 'em so I can relay the info to my cousin.

[inacoma91]

About the throttle running on half and then it sounds like the rev limiter comes on.........My 400 did that one day after i was jumping this double over and over again then after i landed one time it wouldnt run right. It did the same thing you described. It ended up being that my air box boot from the end of the carb came loose and was leaking making it run lean on the top end. So then it would run great to mid throttle then you would try to give full throttle and it would fall on its face. So you might want to check the that?????????? Sorry but thats probably not it though.........

[NVR2L8]

I think you have two different problems which are not related to each other. As far as the rear brake, it sounds as if something wasn't re-assembled correctly, or they used the wrong pads. FYI...I've seen that some of the aftermarket pads are a little too thick, and require that you remove some of the material for them to fit correctly. I'm not sure if the e-brake switch is normally open or closed, but I'm almost positive that what you mentioned about jumping the two pins on the connector is the way to bypass it.

I'd have to say you have a problem with the main jet since the problem starts once you get past 1/2 throttle...this is where the main jet circuit really comes into play. If too rich the cutting out at this point should feel like a "blubber"...like it's getting too much fuel and/or you have the choke on. If it feels as if it's an ignition miss, then it might be running too lean. From what you describe though, it sounds as if it's running too rich...some backfire on deacceleration is normal when running a properly jetted engine with a performance pipe, but when overly rich it'll backfire a lot cause unburnt fuel is being burned in the exhaust system rather than in the engine. If it's "missing" and/or backfiring on "acceleration" though, then this is an indication of running lean.

Lastly, since I don't know how Dynojet sizes correspond to Keihin jet numbers, all I can suggest is to work down on the main and see if the problem resolves itself...if not then go up until you find the size that gives the best performance and plug condition. Given the addition of the pipe and a K&N, you might also need to lower the clip on the needle to richen up the midrange circuit.

[MOFO]

Guy,


I know EXACTLY what the problem is...I've done it myself. His main jet fell out. Before a race, I changed my main jet, well I never really cranked them in, because the threads are fine. Well, one lap into the race and I lose 1/2 throttle and up. Sputtered real bad and back fired....I was pissed. Limped back to the parking lot and started to rip and tear. Ended up being that my main jet was just floating in my float bowl. I tightened her back up and it ran good ever since...


Eric

[skemp]

That's what it is.

Happened to me once and luckily, I checked that first before anything else. I was in a hurry to change out the jet, and I didn't bother to finish tightening it down. Ran awesome for 15 minutes, then I was going up a hill over some ruts, and it dogged bigtime and died. I started it up again and it ran fine until 1/2 throttle, then it would bog, or die if I kept on it. I thought it was the main, so I checked and sure enough, it was going for a swim in the float bowl. :D

[Guy400]

Hey guys, thanks for the info. I'm not the one actually working on this bike, my cousin is. He's at work until around 5:00 so I'll have to call him and have him check the main again.

Thanks!

[carlj75]

That shyt happened to me too, then I tightened the jet really tight and got a small brass shaving inside the jet, which made it really run like crap. I blew the shaving out and it ran fine.

[400exRacerX]

yea it also happened to my best friends 300ex we were changing the jets and he didnt bother to tighten the main jet down all the way and it ran fine for about 30 min then from 1/2 throttle and up it ran like crap, we tore it apart and the main jet had fallen out and was floating around in the float bowl.

[Guy400]

Just wanted to update you guys and tell you that the main did fall out. I called my cousin tonight and he said that right after work they tore the carb off and there it was, just laying in the bowl. The screwed it back in, tight this time, and now it the bike is running great.

[MOFO]

Glad to hear thats what it was. Atleast he wasnt at a race and got a big fat DNF.... :mad:



Eric

[4punksdad]

Originally posted by inacoma91
About the throttle running on half and then it sounds like the rev limiter comes on.........My 400 did that one day after i was jumping this double over and over again then after i landed one time it wouldnt run right. It did the same thing you described. It ended up being that my air box boot from the end of the carb came loose and was leaking making it run lean on the top end. So then it would run great to mid throttle then you would try to give full throttle and it would fall on its face. So you might want to check the that?????????? Sorry but thats probably not it though.........

same thing happened to me.........

[MOFO]

:eek2:

[Pappy]

hey guy400....post in the proper section or feel erics wrath:devil:

[JOEX]

Originally posted by Pappy
hey guy400....post in the proper section or feel erics wrath:devil:
It's OK, it was an emergency:scary:

[Mxjunkie]

Originally posted by Pappy
hey guy400....post in the proper section or feel erics wrath:devil:

:eek2:

[MOFO]

Originally posted by JOEX
It's OK, it was an emergency:scary:


Well, it is an emergency and the poor guy has yet to get a straight answer on the brake issue.... I mean, its been several years.

I guess those damn tech sections dont work. :confused:


;)

[Guy400]

Every one of you muthertruckers are getting banned:D

[AtvMxRider]

Originally posted by Guy400
Every one of you muthertruckers are getting banned:D

lol...

battle of the atv patrons :devil:

this is rele dumb but i thought it was funny...
dont mind the stupid post :)

[FreekShow]

Ummm ok.....