2004 400ex Carb Issues

[staab7803]

I am brand new to these forums and brand new owner of a 2004 Honda 400ex. I bought this 400ex on ebay and the guy said it was perfect condition and just serviced by honda. I put a bid on it and got it for a price that I thought was really good. I drove 4 hours to get it and lets just say it was not in perfect condition. I am 27 and my dad and I have been racing cars since I was born so we have knowledge in the automotive industry. My dad knows a lot about the honda 250r as we had one back in the day. Anyways I got the quad and I had to buy all new brake pads, front inner tie rods, rear brake rebuild kit, misc bolts that were missing, had to put a new top end in, new crank and rod, timing chain, carb rebuild kit, new seat, new swingarm bolt, and axle bearing case.

We rebuilt everything and the quad was running well. After a few weeks of some small short rides around the yard and fields it would not start. The plug looks like it has been wet fouled when we take it out. We take the plug out, clean it, put it back in and it starts and rides fine. Then the next day it wont start again. Everything on this quad is stock besides the top end which we just bored .020 over to a 85.50mm piston. We had a 152 main jet in it and we went back to a 148 and it still does the same thing. The carb has been gone through 3 times now and the only part missing is the baffle plate, in which we dont think that is the problem. Timing is good, valves have been checked and adjusted twice, air filter is clean, carb is not clogged up all jets are good and hoses are clear, has good gas in it, the plug has been replace and gapped accordingly to the clymers manual.

I need some help as we are both stumped.

Thanks

Jason

[01boneless]

befor you put it up at nite turn your gas off and see if that helps any at all. it sounds like the carb is flooding the engine out when it sits

[staab7803]

Thanks for the reply...gas gets turned off every night after riding. I have had the gas tank off and full of fuel and the switch for on/off/reserve works and it does not leak when in the off position.

Thanks

Jason

[CJM]

So it just wont start, even if you pump the throttle 3-5x before hitting the button?

Air filter is clean right and not overly oiled?

Float is good and float needle is clean and working properly?

Try this: Adjust the air/fuel screw (small screw on underside of the carb next to the idle screw arm). Turn it all the way in GENTLY and then turn it out 2.5 times.

FWIW: brand new 400's I have dealt with have issues starting up, they refuse to run unless you hold down the throttle for a good 3-5 mins to keep gas flowing once you get it to initially start. We remedied this by installing a larger pilot jet as they are way to lean from the factory. Went up to a 42 pilot no issues.

What plug are you using btw, should be DPR8Z iirc.

[staab7803]

CJM to answer your questions the 400ex will not start. It will turn over all day long, but once we take the plug out and clean it and put it back in then it will start. The air filter looks clean, when we took the quad apart to rebuild it we cleaned the stock air filter in the parts cleaner and let it sit outside and dry completly before we reinstalled it. The quad was at my dads house last week and he took the carb apart again and everything was good. The float needle is in good working order and he said that he could not find a way to adjust the float but the float was working properly as he blew air into it and it performed the way it needed to. Is there a way to adjust the float? I am using the correct plug as I bought it from the honda store here locally. We adjusted the air/fuel screw to 1.5 turns out which is what the clymers manual said. When I get home I will adjust it out to 2.5 turns and see if that does it.

Thanks for you reply and let me know if think of anything else.

Jason

[CJM]

Everything seems right but the 1.5 turns of the air/fuel screw. Ive never seen one run well at that setting, min 2.25-2.50 turns out imho.

Other ideas are you may have not adjusted the valves properly. When you adjust them the T mark must be lined up on the notch with the case and the rockers MUST be movable. If you can grab the rockers and they wiggle good, no wiggle turn the crank again till they do.

Does it push start?

Also when you redid it did you make sure if your using the stock cam to put the spring and plunger in for the decompressor-no decomp it wont start really at all.

[staab7803]

We changed the air/fuel screw to 2.5 turns out and we will see how that runs. It will take a few days to see if does the same thing. We have not tried to push start it so I cant answer that question. When we adjusted the valves last week we took the cam out and took it to Honda to make sure the decompressor was functioning properly and they said it was perfect so I know that is not the problem. I will have to double check with my dad on how he adjusted the valves as I was not there when he did that. I will update you guys in a few days to see if that works.

Thanks

Jason

[staab7803]

Update...

I changed the air/fuel screw to 2.5 turns out and installed the baffle plate in the carb and we are still having that same problem of it not wanting to start. Some more history on this atv is that we rebuilt it all and it ran strong for 1 month. It would start real quick and easy and we never had a problem with it. We did no changes to it then all of sudden we are having this starting problem. I did replace the plug when we orginally had this problem and it started for a few times then back to the same ole problem. The atv just turns over and over and it never evens trys to start. We are starting to look at the ignition system. Could anyone give me some quidance on what typically goes wrong with the ignition or even if that is causing it.

Thanks

Jason

[xX-Clutch-Xx]

Ok, put a new plug in, then take it out and ride it like you normally do, let it cool off, take it out again (same day) 3 or so times, then look at the plug and it should be white at the very tip and black around the base, or tan. If its all black your mains too high and also is it stock piped? if so i think stock is either k146 or k148. i wanna say 146

[staab7803]

Hey Guys

I am still having no luck on getting this wet fouled plug problem fixed. I have stock jets in there 148 and 38. Should I go even smaller on the main jet to see if that works? We live in Indianapolis Indiana and feel that the altitude is in the range of a 148 jet. Cam is good, timing is correct, rockers are adjusted and like I said I have not had this problem before. I rode the atv for a good month and never had a problem starting it up, then one day it would not start. We have to take the plug out and clean it and put it back in for it to start. We get a day or two of it starting then it wont start after that. Like I said it was running perfect then one day it does not run and we did absoluetly nothing to it. Dad and I have been through the carb plenty of times and nothing wrong with it and the petcock on the gas tanks shuts off and not fuel goes in the carb in the off position. Does anyone else have any more suggestions.

Thanks

Jason

[CJM]

It could be the gas is leaking past the rings and not getting burnt.

Does your exhaust smell like gas? Perform a compression test-100-128 psi is normal. Less than 100 you got a ring issue.