400ex has erratic RPM

[RezoD]

Well, it seems that my bike only runs weird in the mid-upper RPM range. It will accelerate fine, and decelerate fine, but if you hold the RPM's constant for a couple seconds it will act as if it's bouncing off the rev limiter, only not as predictable. It feels like an air leak, but I've sealed all of my connections, so I don't think it can be that?

It's an '00 416, 39 FCR carb, full LRD exhaust, and FST's cam... It's been running great until about two weekends ago. One thing I haven't checked is my spark plug, but I'll be effed if it's that.

Any more info needed?

Travis

[underpowered]

sound to me like it has leaned out. has the weather changed there? did it do it when the weather got colder? if so, a jetting change is needed, if not then sounds like there is possibly somthing clogging the main jet in you carb.

[RezoD]

The weather has changed, but it's running very rich still. If you jump on the gas, it blows black smoke (yes black, not blue/purple). I guess it could be a clogged jet.. didn't think of that.

I think yo ushould check your cdi. My quad would run good but after half throtle it would loose power and just pop and feel like its hitting rev limiter. Turned out to be just bad connection to the cdi.

[RezoD]

Well, I went riding yesterday and it seemed to clear up after about 30 minutes, and hasn't been back yet. It seems to me that it was probably just some crap stuck in the carb somewhere... It's running tits now! :D

[pit/wood]

Originally posted by RezoD
Well, I went riding yesterday and it seemed to clear up after about 30 minutes, and hasn't been back yet. It seems to me that it was probably just some crap stuck in the carb somewhere... It's running tits now! :D

I can say that is true,saw it myself.

I bet ya mine is runnin better, Travis....ol Buddy.:blah:

[RezoD]

You know what Joe... You name the place, and I'll race ya. I'm not afraid to lose, and I'm almost positive I will! :) That guy that came out with his kid last weekend, Kent, he loves to race. That's the FIRST thing we did when I went out to his place.. Next time he's out, ask to "touch 'em" and he'll get on it!

Have you raced Nate? Nate's quad seemed like it would just walk away from mine :rolleyes: I need a 450!

:devil:

[pit/wood]

Nate has something workin for him that you dont, another 90 pounds of traction.

I rode in the rain last night,before the sun was up this morning and 2 times during the day. practice,practice,practice.

You may give an old man a lesson but that is how I learn. I think I can get you to go off the sand-cliff.

[RezoD]

I don't think it's 90 pounds... but if you're saying I don't look fat in my riding jeans, thank you! :o

You need to take it easy on me Joe, I just started going up the steeper hills you have last weekend! Nate said something to me that just made sense, "You'll make it, I know you will. Just nut up, it's all in your head." So.. I started following him, jumping down your hills (that's a weird feeling seeing the earth fall away from you, without hitting a jump :eek2: ) and I went up that hill you had us start going down the weekend earlier! Now I just need to hit the creek jump and I'll be as :cool: as you!

[Ronald Gosse]

Hi! I have a 300EX that is having the same problem. Have tried the following without success and wanted to know if anyone helped you. First tried to seperate between fuel delivery or electrical problem. Rebuilt carburator, new jets and needle valves etc. Cleaned petcock assembly. No change. Checked all wiring connections. All seemed to test fine. No change. Replaced CDI. No change. Replaced Rev Inhibitor Box. No change. Replaced Stator and Pulser coil. No Change. Checked static timing. Set to manual. No Change. Stiil seems to be an electrical issue due to puff of black smoke as soon as the engine kicks in once the rpms have decreased.It's too consistent to be fuel. Have not been able to figure out how to test if the spark is being cutout such as would occur by a rev limiter. I'm stumped! Has anyone been able to help you? I just can't figure this out! Starting to get desperate and feel that I've already wasted too much time and money. Looking for help!

[pit/wood]

Ok,ok heres an old secret diognostic procedure that has worked well in the past.

Now dont give it away to anyone.

Get ahold of an old timing light. attatch it as described to the battery and plug wire.

Now run the wires so they can be tie-wrapped in a way as to keep them safe. Attatch the timing light in a way that you can see it and ride away. if it cuts out and the light goes out you have an ignition problem . If it cuts out and the light still blinks it is fuel or air. Do not forget the air.

You need to list all mods that have been done to your machine also. along with a description in your own words as to what it is doing and when.;)

[bwamos]

Originally posted by Ronald Gosse
Hi! I have a 300EX that is having the same problem. Have tried the following without success and wanted to know if anyone helped you. First tried to seperate between fuel delivery or electrical problem. Rebuilt carburator, new jets and needle valves etc. Cleaned petcock assembly. No change. Checked all wiring connections. All seemed to test fine. No change. Replaced CDI. No change. Replaced Rev Inhibitor Box. No change. Replaced Stator and Pulser coil. No Change. Checked static timing. Set to manual. No Change. Stiil seems to be an electrical issue due to puff of black smoke as soon as the engine kicks in once the rpms have decreased.It's too consistent to be fuel. Have not been able to figure out how to test if the spark is being cutout such as would occur by a rev limiter. I'm stumped! Has anyone been able to help you? I just can't figure this out! Starting to get desperate and feel that I've already wasted too much time and money. Looking for help!

Yours is the reverse limiter kicking in. Disconnect the Reverse switch wire from the terminal behind the foot brake pedal, under the sheetmetal cover. Use a multimeter (set to ohms) and put one end on the teminal, the other on frame ground. You should have a short when the reverse is not engaged. If you have any resistance your CDI thinks you're in reverse and you are getting capped at like 3800 rpm.

The big wire harness connector right above the coil is also a culprit of fried connections.

[RezoD]

have you checked for air leaks? possibly a cracked/torn carb boot? when I initially replaced my valves, I didn't set the carb-to-boot close enough (it was fully engaged, but not by much), and had a leak... ran like arse.