Hard starting 400ex when cold?

[RezoD]

My 400ex recently had a couple problems... Basically, I roasted my exhaust valves, and had to replace them. My timing is dead nuts, and the plug is new. I have an aftermarket rev limiter, but the stock rev limiter starts the same, so I don't have the WB rev box it seems. The bike will turn over for about 30 seconds before it even starts sputtering.. I have to bump the throttle (about 1/8th throttle) and let off real quick, then it tries to start. To me, it seems like it's not getting gas... But, for about 10 seconds after it starts, the RPM's are lower than it should be for the throttle being given to it. For example... start it up, and give it gas to about 1/3 throttle.. it stays at around 1/4 throttle RPM's for a while, then it will catch up and run fine. Also, the bike sputters if you jump on the gas from an idle, seems like the top end is a bit fat (blows some black smoke and backfires).

While the bike is in motion and the motor has load on it, it runs PERFECT! Couldn't ask for a better running bike, and you wouldn't know it just took over a minute to get it started.. So wtf?

Seems like a carb problem.. but I didn't adjust anything other than the idle (I lowered it a bit).. Oh, I did recently switch to premium gas, but it was running fine on it before I did the valves.

Where do I start?

Travis

[Reggie44]

Try replacing the stock pilot jet with a 42. That will help it start better if nothing else is a factor.

[RezoD]

Sorry, forgot to mention the mods in case it makes a difference..

416 kit with new cam
Full LRD exhaust
CR Carb
Aftermarket Rev Box

...I think that's all as far as the motor goes.

[†2005 400ex†]

Definately get a 42 pilto jet, you should also let it warm up for a while before you get hard on the throttle. All 400exs are hard to start when they are cold, or at least everyone iv encountered. Once you switch the pilot though it starts fine.

[RezoD]

I know enough to not jump on the throttle while it's cold, so no worries there :D

So a 42 pilot jet will fit with my CR carb? Does anyone have any links or names of what kind of jet I'm looking for? Thanks guys.

Travis

the 400ex seems to take a little longer to start and get warm enough to idle..others may take 5 minutes where the 400 will take 7...just example times nothing measured...
the sputter could be from the carb going form closed to wide open real quick...the accel. pump needs to catch up...a larger (42) pilot will help this

[RezoD]

I'm confused as shiz now... Couple of you are telling me to try a different size jet?

Like I said, the quad started and ran PERFECT before my valves went tits up, but since I've redone them, it's taken a long time to start... I hope it's something like a gas flow problem.

Travis

[Warrior-mx]

Ok Now u said it started fine B4 the new valves. Are u sure the clearance was set correctaly. And make sure all your jets are cleaned out well ur entire carb in fact this could help ur so called "fuel Flow Prob". NOw about wat these guys are saying about the "piolot jet'. U seemed confused on this.? There are a number of jets in ur carb. THe main ones are the main and piolot jet. And chaning the Piolot jet to a 42 will help it out on starting. And maybe affect ur bikes performance off bottom end. UR pilot jet controls ur throttle all the way up to 3/8 open then the main jet takes over. hope i helped u

[cals400ex]

it probably won't take a 42 pilot jet if you are using a different carb? dont you know what carb this is? does it say cr on the top of it? if so, i bet its a FCR because the FCR carbs say CR on the top. however, i have no idea if it is a FCR 39, 40, 41, etc....

[RezoD]

Figured it out, but first...

I know what the jets are, and I wasn't confused on that.. Just confused about people suggesting two different sizes.

The carb is a FCR 39 Keihin.

Now for the problem. The PO had a cheap plastic fuel filter on it... it was clogged pretty badly. Also, the quad didn't like premium fuel. It fouled out the bike today (wouldn't even sputter). I changed the plug, drained the gas and filled up with regular, and after it spit and kicked the premium that was in the bowls out the pipe, it ran perfect! :D Runs much better than I remember it running.

Thanks for the help guys, I appreciate it.
Travis

[red426ex]

i have a 2000 400ex with a 426 kit that i ice race stock carb with a 160 main jet and a 52 pilot jet plug looks fine and everythg runs great and i never use my choke even my quad starts the best of anything i think ive ever owned it can be 20 degrees below zero out and she will start and idel perfect with no choke or nothing even after its been outside on the trailer drivign 3 hours to get to the race.