I have a problem starting my EX when its cold outside.
Here is what I have in my quad. It's still a 400.

Stage 2 Hot Cam
11:1 comp piston, stock bore
Dynojet kit with a 170 main jet
Stock pilot jet
K&N air filter
Air box cover removed
Choke plate and bar removed
Ground out head pipe
HMF silencer
GWC high rev box

My problem is It wont start. I live in Minnesota, In the spring, summer, and fall it starts great. Now that it's winter here it dosn't like to start cold. The first two times it didn't start i cracked open the bowl and drained the gas, then it started. the next few times I tried this and had no luck. I had to have my brother pull start me. When it warms up it starts and runs great.

What is wrong??? Is my pilot jet or main jet to small? Is my neetle and seat leaking (floding it out)? Are my valves off? Is it because my choke is taken out? Or is it because my high rev box?

I've herd a high rev box will make it start hard in the cold.
Should I need the choke back in the carb, with the cold weather; normaly I just blerp the throtle once or twice and the excelerator pump starts it up just fine.

I resently cleened my carb, and the neetle and seat look good. Also my battery is fully charged. I run 92oct gas and some oct booster. Also reset my valves recently.

If anyone can help me with this problem Please post. THANKS

 

That's a fairly common problem. There is a short some where between the seat and keyboard. Good luck finding it.

 

'98RECOn what are you talking about?

 

Never mind. I loaded this page several times and nothing ever poped up in your post, just your signature. That is an expression my computer professor used when someone couldn't get their computer to work. He was saying that the problem was with the person. I don't know why it wasn't working for me before. It was my problem not yours.

Your porblem sounds like it is the rev box. Most rev boxes are just stock XR250 boxes. The problem is that they were designed to work with a kickstart which turns the engine over faster. The spark plug won't fire until the entine reaches a certain RPM to prevent kick back on a kick starter. The problem on the 400 is that the electric starter sometimes won't turn the engine over fast enough when it is cold to reach that RPM. There are sevral things you can try.
1) plug the stock box back up to start the engine and until the engine is warm
2) get a stronger battery. I use a Yuasa YT12A-BS. It is exactly the same size as stock.
3) try stabbing the throttle real hard to full throttle. The excellerator pump will squirt gas into the cyliner and may be enough to get it started.
4) put the choke back in
5) pull the air boot off the back of the carb and cover the carb's opening with your hand. Your hand will be acting as a choke
6) get a 40 or 42 pilot jet
If the problem is the rev box 3, 4, 5, and 6 probably won't do much to help.

 

Ditch the rev box for the winter, and change your pilot jet to a 42

 

Thanks 98

I'll give the stock rev box thing a try but thats kind of an inconvenience. With that new higher output batery will it start in the cold better and will I be able to leave my high rev box in? I work at a Motorsports shop so may be I'll charge one up and give it a try.

If I ditch the High Rev Box then I will hit my rev limiter to much, with the mods I have.

The choke plate and bar being removed doesn't hut it???

Anyone else feel free to confirm or help out, THANKS

 

It doesn't matter how much gas you put into it if it isn't firing, and that's what I suspect. To verify, catch it when it won't start, add a small battery charger to it, or jumper cables from your truck (don't start the truck, or you'll burn up your regulator). This should boost the starter and fire it right up if it's the rev box.

 

I'm pretty sure it will, but I can't guarantee it. It does not get as cold here as it does in Minnesota! It made starting my 416 a lot easier. Be sure to get the YT12A-BS, there is also a YTX12-BS that's output is the same as the 12A's but it requires some modification to make it fit since it is about an inch taller than stock.

Have you tried running it with the stock rev box? My setup is very similar to yours and I have no trouble with hitting the rev limiter. But, I also am running a 37 tooth rear sprocket so that may explain that.

I don't think that having the choke removed is hurting. I know of people with and without the choke that have had trouble with the aftermarket rev boxes.

 

You are not getting enough fuel to start the machine. You need to move up to a 42 pilot jet and pump the throttle a few times before you try to start it. If it still won't start remove the rev box.

 

I'm with them...In the cold the rev boxes make it harder to start, and I just delt with a non believer in the 42 pj today.. He was amazed about not having to use the choke to start it, and how much more smooth it idled while warming up.