400ex questions?

[zack221]

I have a 2000 400ex and I was just out riding today and noticed it running weird so i brought it back home and turned it off. Ater I turned it off there was blue smoke still coming out of the exhaust it wasnt blowing out real hard but it was coming out of the exhaust. So I checked the oil and sure enough it was very low on oil. I had just changed the oil about 3 weeks ago and i only have about 4-5hrs ride time on it since then and it probably burrned over a quart of oil. It also sputters out when climbing hills and it seems like here lately it is kind of bad to foul a plug. Could this all be caused by one problem or do you think it is valve seals causing the smoking and jetting causing the sputtering and fouling plugs?

Also Merry Christmas to everyone.

[zack221]

Also forgot to mention it used to only smoke on start up but now it smokes pretty much all the time.

[JOEX]

Probably rings and valve seals. If the cylinder & piston specs out ok you may get away with just a re ring and hone along with valve grind & seals. If the cylinder is too worn you'll need a bore job.

[josh31]

I second JOEX. It may be worn out or stacked rings. Your best bet if this is the case, would be a new piston. I would suggest an .080 over. That makes it a 416 and they run great! Just a thought.

[zack221]

No I dont want a 416 but maybe while I have it down I will do some motor work too it. But I really dont need any motor work because it is fixing to be my trail bike and i will have a lt250r to race and stuff with. Is there anything you all suggest that I should do to beef up the motor a little while it is apart. I rode a friends kfx with a dvx motor in it (I know they are the same motor) and I liked the torque and bottomend it had. What could I do to be able to beat a dvx. I really want a little more power but i dont want to go crazy.

[josh31]

a 416 is a very reliable motor that runs good. I had a 416 in my 400 ex that I motocrossed. It needed freshened up and I made it a 426, .120 over. It ran alot better, more low end. I have since then changed it over to my woods bike. It runs just as good as the others. Some simple things to do are: make it a 416 (.080 over), or a 426 (.120) over, lighten the flywheel, advance timing (changes the stock flywheel key to a modified one, just a few dollars), and exhaust. Keep in mind that if you put an exhaust on and/or make the engine better you will need it to be jetted properly. A different cam is nice too. That will make it run very strong. This is what is done to mine, TC ported head, 426 piston, advacned timing, TC woods cam and HMF exhaust. Not telling you to do this or that, but with my experiences with the 400ex engines, the 416 and 426 are reliable and run great.

[zack221]

If I do bore it I am going to make it a 426. I will also put a hotcam stage 2 in it and a rev box. What does TC stand for? Maybe the woods cam would be better than the hotcam?

[JOEX]

Originally posted by zack221
If I do bore it I am going to make it a 426. I will also put a hotcam stage 2 in it and a rev box. What does TC stand for? Maybe the woods cam would be better than the hotcam?
I'd rather do a 416 than a 426. With a 426 bore the cylinder wall gets very thin. Some builders prefer to resleeve the cylinder when going to 426cc which add to the cost.

[kawiefan]

i say do the 416. my cousin has it done along with the TC woods cam and a LRD exhaust. he beats on it pretty good and it still runs like a champ.

Originally posted by JOEX
I'd rather do a 416 than a 426. With a 426 bore the cylinder wall gets very thin. Some builders prefer to resleeve the cylinder when going to 426cc which add to the cost.

x2 416 will probaly be the highest i will ever bore my 400ex out to if i do bore it. I want basically the same reliability as a stock 397cc motor. People say oh if you build the motor right it will be just as reliable as stock but theres no way. Take a look at how thin the cylinder walls are on a 440.

[zack221]

Actually a 440 sleeve is not that thin because it is designed for a big bore piston. I used to be one of those ppl that swore if you bored a motor it would never be reliable. But I think I am going to take a chance and bore it out.

[josh31]

I have never had trouble with the cylinder walls getting to thin on a 426. I have even bored out a brand new sleeve to a 426. It is all what zach221 wants to do.

zach221--TC stands for Tom Carlson. Very good engine builder, if you haven't heard of him. Owner of TC Racing.

[zack221]

Does tc have a website?

[josh31]

tcracingengines.com

[03Blaster]

If your not wanting to rebuild it right away just add the oil every ride... My buddys 400ex from factoryh burned oil and it progressivly got worse.. it turned out to be buring 1 quart of oil every 2 hours.. constant oil being burned.. thats from 1999 to 2005.. still ran when it stopped being rode b/c the trans broke a shift fork.. tore the engine down and the rings were shot.. it didnt harm anything but the person behind you..lol

in my own opinion just keep riding it.. it will need rebuilding anyway just wait..

[RATPACK Z400]

Sounds like valves blowing oil ,not seating properly,if you wont that 400ex to beat a Z,kfx,etc you need at least a 440kit or more! 440 will put you with Z that has pipe,rev,jetted.