Jump to content
USWE SPORTS ACTION HYDRO PACKS GIVEAWAYS!!! Read more... ×
Sign in to follow this  

XR400 smoking suddenly, replace plug, adjust valves or fuel mixture?

Recommended Posts

Hey fellow XRers,

 

My 03, which I've recently installed a FMF Q4 pipe on, has decided to start putting out white smoke. The area behind the pipe is quite "sooty" (black) and she is surely smelly. The pipe has been on for over 2 months now with zero issues. All of a sudden, stinky white smoke (I guess all smoke could be described as stinky, haha) when I rev after warming up.

 

Now, I haven't had the valves adjusted for years, but she usually starts up well (2-4 kicks using the proper starting tech) and runs like a champ. A buddy told me that if you don't have to use the decompression lever then the valves require adjustment/tightening. Not sure about that....your guys opinion?

 

Perhaps the bike finally "adjusted" to the new air flow w/ the Q4 (previously I had a white bros loud as Fk pipe) and now requires a change in the fuel screw?? FMF said no adjustment was needed. Something else to consider: I live and usually ride at 6,000-8,000 ft elevation.

 

It's like a math equation, just have to enter all the values and figure out the best answer. Any advice would be greatly appreciated. (yes I did searches and yielded nothing specific to my direct question....or I suck at searches :)

 

Landcrab

 

Share this post


Link to post
Share on other sites

One thing you can check is to make sure the manual decomp release is not stuck on, holding the valve open just a little.

 

Smoke after warm up can be rings. Do you have oil dripping from the crankcase breather or anything? Make sure that isn't plugged with dirt at the bottom. Also see if there is any oil in the intake tract, if there is (I assume one end of the vent goes down by the drains and the other goes up to the airbox? Someone correct me if I'm wrong, I might be thinking about my KTM) it could just be the plugged crank vent and a slightly overfilled oil level.

 

Might want to get a leakdown test done and see what's going on if you can't find something obvious.

Edited by michigan400

Share this post


Link to post
Share on other sites

Any way you look at it, Probably time for a valve spec inspection/adjustment.

Don't believe FMF when they tell you no fuel screw change is needed with the install of a new/different exhaust. You ALWAYS retune/verify the fuel screw is adjusted optimally for the new system.

Share this post


Link to post
Share on other sites

Thanks for the advice and knowledge folks. Yep, valve adj inspec in future. I thought it ran fine until just recently. Maybe now I'll get even more pow outa her.

Share this post


Link to post
Share on other sites

Now, I haven't had the valves adjusted for years, but she usually starts up well (2-4 kicks using the proper starting tech) and runs like a champ. A buddy told me that if you don't have to use the decompression lever then the valves require adjustment/tightening. Not sure about that....your guys opinion?

 

If your bike starts in 2 kicks, you don't need a valve adjustment and your compression is likely OK.  Does the smoke go away after a while?  If it goes away, don't worry about it.  If it always smokes a little after you rev, it could be the start of your rings getting old.  When you let off, you pull a big vacuum, which could pull oil past the rings (or valve seals - but one would expect a poof of oil-smoke at startup).  My CRF has always blown a little oil smoke when winding down after a hard rev, which is normal for their loose ring structure.

 

Incidentally, I took my decomp lever off of my XR400 in 1998 and still haven't missed it.  

Share this post


Link to post
Share on other sites

My xr4 smokes now on start up and is suddenly consuming 4oz. Of oil a day. I have adjusted valves and still can lift the front tire 1-3rd with just a twist of throttle. I wouldn't worry about the smoke if it weren't using so much oil. my question would be should I go ahead and do piston and rings if already I need a valve job done?

Share this post


Link to post
Share on other sites

What happened to me once is a valve seal which popped out of an intake valve guide. I was able to put it back in place with small screw drivers through the valve springs.

Share this post


Link to post
Share on other sites

I would definitely check valve stem seals. The seal leaks and oil settles in there when the bike isn't running and after you start the bike, the oil that leaked in causes the white stinky smoke. (If it is in fact valve stem seals)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×