Honda ATV Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
TL;DR: 400ex runs for a little, maybe a minute or so and then stops dead like the engine has locked up. You can (with some force) get it unlocked by turning it over by hand and then it seems to turn over fine. If you start it, the whole process repeats.

I have a 400ex that I'm trying to get running after sitting most of the winter. Just put a new starter on and new spark plug. Fuel is fresh and the fuel that was in it over the winter was treated. Vent cap on gas tank is clear. I was having some issues with the battery not having the power to crank and that seems to be resolved for the moment. (Has some very janky wiring.) Has had some "fueling" issues in the past--it's been jetted but would still run it on partial choke. Discovered that the spark plug that was in it all last season was for a Kawasaki (previous owners didn't give a crap about it). Engine oil definitely needs to be changed.

When it's running, it sounds good. No odd engine noises to indicate trouble. And then without warning--full stop, you're done.

This happened to me at the end of last riding season. I had some trouble getting it going but then started ripping around and headed out on the trail. I wasn't far out when it locked up. That time, it absolutely wouldn't start on its own (the starter was on its very last leg). So we resorted to old faithful and pushed it with another vehicle. It would start, run for a bit and then lock up. The odd thing is that the process could be repeated--start it, run it a short distance, lock up.

As I'm typing this out it feels like it's been quite stupid to keep starting it when I know the end result is that it will lock up again.

This spring, thought it was time to get it in shape--new sprockets, chain, rear bearings, etc. are ready to go on for a good season. But since the starter was crap, decided to start there + hopefully fix the iffy carb. Put the new starter on hoping it would just crank right up and that brings us up to speed. I've read every forum and post I can find with no luck.

Send help. The trails are calling.
 

·
Registered
Joined
·
421 Posts
Easy way to tell if it's piston to cylinder that's seizing. The crank will rotate back and forth ever so slightly taking up and slop between the rod and crank and the rod to wristpin. If the crank had no free movement at all look at the bottom end.

You may also have a cam not getting lube. This situation will act like a piston seizure but with more crank rotation before it binds.
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #3 ·
Easy way to tell if it's piston to cylinder that's seizing. The crank will rotate back and forth ever so slightly taking up and slop between the rod and crank and the rod to wristpin. If the crank had no free movement at all look at the bottom end.

You may also have a cam not getting lube. This situation will act like a piston seizure but with more crank rotation before it binds.
Okay, thanks! That gives me a great place to start from.
 
1 - 3 of 3 Posts
Top