My friends 400ex won't stay running. We put it in a heated garage - but when trying to start it, all it will do is run off the fuel that the accelerator pump put into it. It will fire, run for a sec, then die. The carb has been pulled off, cleaned, dried and reinstalled. If you spray fuel into the carb while turning it over it will fire, but again dies. Any ideas? Thanks all!

 

Has it been sitting? Are you sure the mainjet is clean? Is fuel flowing into the carb from the supply hose? Is the needle valve clean and working?

 

i assume the choke is in the proper position and the fuel is in the on position? did you mess with jetting lately?

 

Sounds like a clogged pilot jet to me.

Remove it, hold it up to a light and make you can see through it.

Scott
www.atvworks.com

 

All jets are clean and clear. The carb was remarkably clean. Fuel is flowing from the tank to the carb. The only time it will fire is when you use the throttle a couple of pumps to get the accel. pump to squirt some fuel in. This is really strange. There is some type of air valve on it, inside where the throttle cable is. Does anyone know about this - what it does - does it or can it fail? Thanks again all!

 

Its a fairly simple carb so dont spend time making it overly complicated.

If the carb is getting fuel, and your sure that it is clean (you did or need to re check this as more than once dirt has found its way into the carb while putting it back together) , and it will start so you know the accel pump is working and the fuel is there so the problem has to be someplace else.

IF the jets all check out clean then move on to the jet size v/s temp and especially the slow/pilot jet and then the fuel screw setting.

The one thing I am not sure of is if it wont idle or just wont run at all after the initial start, and this makes a big difference.

If its not idling then you need to look at or adjust the fuel screw, pilot jet size, idle setting and look for any head, intake or exhaust leaks. Now if it wont run you still need to check the others but also look at the possibility that the engine is either running rich or lean as this can produce the same symptoms etc.

hope that helps.

 

Change the plug.
JP

 

It's definately not the plug, changed it each time we took the carb off.

 

My turn again!

Check your float level, It's possible some fuel is getting to the carb but not enough to cover the pilot jet. Look at the little metal tab on the float valve and make sure it's not bent.

Scott
www.atvworks.com