[benroot]

I have a 2004 400ex. It has a White Brothers Full Exhaust. I have a uni foam air filter on it with the air box lid on. Carb has a 155 main and 42 pilot jet. Everything else is stock however I have the air/fuel mixture at 3 turns as it runs better there than any other position I tried. Everything in the motor is stock and valves are in spec. I am having problems with getting it running correctly. It starts right up with or without choke, however without choke it backfires and pops and cuts out with throttle but will stay running at idle. With the choke turned on it runs good with only a slight pop in the exhaust when you really give it throttle. Sometimes the idle will suddenly slow down for 5 seconds and then go back to normal. Some other things I’ve noticed is there is a sort of whistling noise happening somewhere that sounds like it’s around the top of the engine. And finally I’ve noticed that the quads idle goes way up with the choke off and lowers when the choke is on which is the opposite of any of my past experiences on other quads. I am really looking for any thoughts on what is happening. Obviously it seems like it is starving for gas but it seems like my jets are plenty big and I’ve seen lots of other people running the same set up.

 

[benroot]

I have a 2004 400ex. It has a White Brothers Full Exhaust. I have a uni foam air filter on it with the air box lid on. Carb has a 155 main and 42 pilot jet. Everything else is stock however I have the air/fuel mixture at 3 turns as it runs better there than any other position I tried. Everything in the motor is stock and valves are in spec. I am having problems with getting it running correctly. It starts right up with or without choke, however without choke it backfires and pops and cuts out with throttle but will stay running at idle. With the choke turned on it runs good with only a slight pop in the exhaust when you really give it throttle. Sometimes the idle will suddenly slow down for 5 seconds and then go back to normal. Some other things I’ve noticed is there is a sort of whistling noise happening somewhere that sounds like it’s around the top of the engine. And finally I’ve noticed that the quads idle goes way up with the choke off and lowers when the choke is on which is the opposite of any of my past experiences on other quads. I am really looking for any thoughts on what is happening. Obviously it seems like it is starving for gas but it seems like my jets are plenty big and I’ve seen lots of other people running the same set up.

Also I forgot to say that when I take the carb off after the engine is warmed up to adjust the air/fuel mixture lots of steam comes out of the intake side of the engine where the carb is removed.

 

[Eric the red]

I'd check the rubber intake tube for a crack and the petcock to see if its flowing lots of gas. You either have a air leak or are starving for gas.

The steam coming from the intake is normal.
I used to adjust the fuel screw on mine with a short bit out of a multi bit screw driver and a 1/4 wrench, get the bit in the fuel screw first with your fingers then turn it with the open end of the wrench. It's slow going but much easier than taking the carb off. You can also change the main jet through the drain bolt in the bottom of the carb if you ever need to re jet.

 

[benroot]

Thanks for the reply! I checked the intake boot and there was no cracks. I ordered a larger main jet. We will see if that does the trick. As far as the whistling noise is it possible it could be the oil pump?

 

[CantFeelMyLegs]

Thanks for the reply! I checked the intake boot and there was no cracks. I ordered a larger main jet. We will see if that does the trick. As far as the whistling noise is it possible it could be the oil pump?

 

[CantFeelMyLegs]

Did you find the cause of your issues?

 

[benroot]

Did you find the cause of your issues?

Ended up returning to stock jetting and raising the clip on the needle valve a notch. (May have lowered It one notch I actually don’t remember it was awhile ago) but after that it ran perfect. Still makes that sucking noise not sure what that is but doesn’t effect how it runs.