Okay, this will probably be a long descritption so please bear with me. I have a 1999 Honda 400 EX. It was bone stock, that is until today. I bought a rev box on ebay. It was supposedly a White Brothers, brand new, but it didn't have any White Brothers labeling on it, which I thought was wierd. It did however, have a "WB" etched on the plastic casing with some tool. Anyway, I installed the rev box, did nothing else, and I ran it for awhile, 5 minutes max,... everything seemed to be fine. I drove my truck into town to get gas and filled up the EX when I got back. I then went for a 3-4 mile ride and to be honest I had it topped out pretty good for most of the time, until it stopped. I was going up a hill in 5th gear and I was losing speed (I think that the engine may have quit at this point, but I am not sure as it happened so fast) so I downshifted into 4th. Now the engine quit for sure. I pulled off to the side and noticed that there was smoke coming from the engine. The exhaust was so hot that it was making popping noises. I took the lid off of the airbox, took the dipstick out of the engine, and took the spark plug out in an attempt to cool the engine down fast. I was really low on oil and the spark plug was gray from all of the heat (I think this means that I was running lean). After 20 minutes of cooling I tried to start the EX back up to see if it was just overheated. It wouldn't start. I checked to see if I had spark and I did. It turned over and it was not seized up. I could hear it trying to turn over (the foomp foomp foomp sound from the exhaust). I know little about this engine but it seemed as if it didn't have much compression, (I put my hand over the exhaust and tried to start it). What I felt was not overwhelmingly strong but I could definitely tell that it had compression. What is my problem? Why did this happen? What needs to be replaced? Cost? EXPERT ADVICE IS GREATLY APPRECIATED.

 

sounds to me like you toasted some rings or maybe a valve

 

Polaris500HO4x4, I want to say thanks for reading that long post and replying. Someone told me that it might be the rings so that is what I was thinking. If it is the rings or the valves how difficult are they to replace? How much would it cost to get it fixed at a shop and how much for the parts? What should I do with the rev box so that this doesn't happen again? Will this happen again once I get it fixed? If I rejet my carb will this help to keep the engine running cooler by having more gas enter the engine? Any suggestions on what I should do to prevent this from happening again? Thank you, your help is very much appreciated.

 

what i might suggest is a top end rebuild.. saying that u ran it with low oil you may have scorred the piston and sleeve. for a complete top end rebuild valves,seats,rings,gaskets i would estimate around 300 400 dollars. u will have to ask someone else about that

 

yeah your probably either fryed the rings if that happened you'll need to resleeve your cyclinder and if you droped a valve or something get them replaced so i suggest a top end rebuild

 

how about the gas, a guy i know got bad gas it ruined his f-350 and his prarie 360, but he got them both repaired. major$$$$$$$

 

Thanks alot guys. Oh, by the way I don't believe it was the gas because I always buy my gas (premium) from the same place (Amoco/BP). I have never had any problem with the gas before.

 

What about a 440 big bore kit...what are your thoughts there? Would it be able to hold up to the rev box or should I get rid of it? Do you think that my rings/valve(s) were weak and ready to go anyways? I didn't notice the engine lacking power or acceleration and it kept up with my buddy's piped 400EX. Ironically I just checked today, the price for a 440 kit being installed. NO JOKE. It was around $600. I'll probably go that route. Do you know any cons of doing so other than the price tag and having to run premium, which I already do.

I guess the moral of the story is "Go big, bore go home" right? Hope you get the joke.

 

if you have to repair the top end then go for the big bore
I mean if it hurt the rings and sleeve then it needs to be bored anyway go 440
just rejet and pipe it and have way more power besides

 

Have you tried to put it back to stock? remove the rev box?
Do a compression test , and youll know if its lost compression.
Have you tried a new spark plug?
Was it really low on oil when you started out...or ended up really low?