[sjsmith8688]

Hello,
New to the forums.
I have a new to me '07 400EX (Just bought it 8/20/17)
It has a Sparks full exhaust system, and is supposed to be correctly jetted. Otherwise, I believe it is stock.
My Problem: It starts and idles very well. I can run it for quite some time until it gets warm/hot. The harder I run it, the faster the problem occurs. When warm/hot, it will start to severely bog-down when I apply throttle. When this starts to happen, it does not smoke, but it does sort of a slow lurching if I keep trying to apply throttle (which makes me think it is fuel related) and it can backfire. It does not die. If I let off the throttle, it will idle fine. When I park and put it neutral, I can rev it and it does not do the bog-down.

What do you think? Carb/jetting? Compression problem? Electrical problem? What should I try first?
I am waiting for a plug wrench to arrive so I can pull the plug, inspect it, and do a compression test.

Thanks in advance for any help.

 

[TRX2fiveO]

I would start by finding out what jets you have and get back with us.

Sent from my LG-US996 using Tapatalk

 

[sjsmith8688]

The main jet is a 150 and the pilot jet is a 45.
Sorry for the delay in getting back.

 

[SlammedRanger]

45 pilot jet for a stock internal quad is gunna be really rich at idle. And 150 main is 1 step up from stock. And for a full pipe will be way lean. Does it have an airbox lid? Any holes drilled? Stock yellow air filter?

 

[sjsmith8688]

It has a K&N filter with a foam Sparks cover. The problem I described above happened with the airbox lid on and off. There are no holes drilled in the airbox lid.
What jet sizes do you recommend?

 

[SlammedRanger]

42 pilot jet. Mixture screw 2 1/2 out from light seat. And a 165 or 170 main jet.

 

[sjsmith8688]

Airbox lid on or off?

 

[SlammedRanger]

That would be for the airbox lid off. If you were going with it on i would go 155 160. Same pilot jet and mixture though.

 

[sjsmith8688]

What needle jet clip position?

 

[sjsmith8688]

Dynojet kit says to use a 146 Main with the airbox lid on and the needle clip in position 3. How can there be so much difference between your 155-160 suggestion and the Dynojet suggestion? I am not questioning YOU, I am just confused at the amount of difference.

 

[SlammedRanger]

Dyno jets are on a completely different scale. No worries! Its gotten all of us at one point lol. And needle clip isnt adjustable on an 07 400ex. I had to buy a rebuild kit for a pre 05 to get an adjustable needle and i had to drop 1 clip when i did all the internal work.

 

[sjsmith8688]

OK. So, I put in the Dynojet 146 Main. I am waiting on a 42 pilot, so the 45 is in right now. I adjusted the mixture screw out 2.5 turns, and got the idle working well. It starts, idles and runs flawlessly running lightly, and running hard for about 20-25 minutes. Then, I am getting the same bogging issue when it gets very warm. I do not get the bogging when I am running very hard up and down a street. It only occurs when I am doing more trail-type riding, some ups and downs, rough terrain, and lots of low-then high-then low (etc.) throttle. Electrical problem when warm/hot?

 

[SlammedRanger]

That 45 pilot jet is most likely your issue. Have you pulled the plug at all to see what it looks like? And where was your mixture at before? Cuz the mixture i told you would be with the 42 pilot jet in. Your mixture is directly related to your pilot jet size. I would bet with a 45 you would want your mixture down at around 1 1/2 or less. Keep in mind im running a 45 pilot jet with all my internal engine work at 2 3/4 mixture. You are moving tons less air through your motor and at idle pumping almost the same amount of fuel in as me.

 

[sjsmith8688]

Plug was definitely on the black end of the spectrum. I will try the 42 pilot when it comes in. Any tips/tricks to setting idle when I install the 42 pilot?

 

[SlammedRanger]

Setting idle is done with the flat tip screw that can be turned by fingers if necessary at bottom or carb. If your talking about mixture that is done with a specialty tool made my motionpro that is a 90° flat tip screw driver. Its pricey but worth every penny!

 

[sjsmith8688]

My Dynojet kit came with the adjustable needle. Can I use that in my 2007 carb?

 

[SlammedRanger]

Yeah if im not mistaken you have to use the needle. The taper is different. I could be mistaken though because i have never wasted my money on a dynojet kit.

 

[TRX2fiveO]

Dynojet kit says to use a 146 Main with the airbox lid on and the needle clip in position 3. How can there be so much difference between your 155-160 suggestion and the Dynojet suggestion? I am not questioning YOU, I am just confused at the amount of difference.

Dynojet numbers run smaller. I buy individual jets from www.jetrus.com youll spend way less money. A 146 dynojet IS A 160 keihin. I agree with the 42 for sure. there is a jetting how-to in my signature that should help you?

Sent from my LG-US996 using Tapatalk

 

[sjsmith8688]

OK.
Yesterday I installed the 42 pilot jet and the dynojet needle jet with the clip on the third notch down. I set the fuel screw to 2.5 turns out. It started and ran very well. It was idling a bit high, but I could not get it to do the bogging issue. I was going to post to you all last night that everything was solved, but I thought I would hold off until I could see the same performance today.

Well, I could not get it started today. When I first attempted to start it this afternoon, it started and idled for perhaps 10-15 seconds, then died. I had to put the choke on to get it to do this. I attempted to start it again. It idled for a few seconds and died. I started moving the idle screw and the fuel screw, but could not get it to start. I took the carb off and reset the fuel screw to 2.5 turns out. I am not sure where the idle screw wound up. I changed the spark plug and it started (with the choke on) but idled for only a few seconds. I quit after 2.5 hours to watch the Chiefs/Patriots game.

Any ideas??

 

[SlammedRanger]

Sorry but i have to ask this. Is the fuel turned on and enough gas in the tank? Sounds like its running out of gas to me. What does the plug look like? Im watching the game also lol.