XR4 Bogs/Chokes

CPT Jack

Subscriber
Joined
Jun 27, 2000
Messages
485
Likes
0
#1
Yes my '98 XR400 is anything but snappy. It chokes if I try to roll on the throttle too fast.:think I don't think it used to do this which may be beside the point, but probably indicates that all I need to do is an adjustment of some sort. I'd rather not pay for a pumper carb. Can anyone give me some recommendations for alleviating this. Thanks.
 

mtngoat

Lifetime Sponsor
Joined
Jun 12, 2000
Messages
314
Likes
0
#2
If it didn't do it before; here's the most likely culprits I've found:
air cleaner
dirty carb
valves (but I doubt it if you haven't noticed more valve noise)

Just out of curiosity, what main/slo jets are you running?
 

ochster

Lifetime Sponsor
Joined
Mar 11, 2000
Messages
690
Likes
0
#3
Don't let the lack of "valve noise" be an indication. As the valves sink into seats, they actually become tighter. Thus it is not allowing the valve to seat completely. This is very common on these.
 
Joined
Jul 14, 2000
Messages
51
Likes
0
#4
CPT, have you done any modifications such as removed restrictors on the intake or exhaust? I jetted mine too lean once and it would almost die when I rolled on the throttle and then would take off.
 
Joined
Apr 11, 2001
Messages
1,298
Likes
1
#5
CPTJack: Vector Opinion Needed

Say Jack: let’s hear your opinion on the Vectors in the Product Evaluation Fourm.

Re: your 400, have U (or the 1st owner) changed the jetting @ all or is it stock? Seem like XR owners have a need to change things a bit to make them respond better, like remove the airbox lid, then to a 152 or 155 main jet, 55 pilot, A16A needle in the middle & 2 turns out on the air screw.
 

mtngoat

Lifetime Sponsor
Joined
Jun 12, 2000
Messages
314
Likes
0
#6
ochster, Wow!
I'm a little new to thumpers and never considered that a valve seat could wear enough to practically offset/exceed the lash adjustment (.004/.005, which I thought tends to increase as valve components wear, ultimately causing noise if not re-adjusted). And, as the seat wears, wouldn't it increase lash? Maybe I'm looking at this all wrong, but I'd like to know, since I do the valves on multiple XRs. Thanks.
 

ochster

Lifetime Sponsor
Joined
Mar 11, 2000
Messages
690
Likes
0
#7
mtngoat, You are partly correct. If the wear is taking place on the rocker arms and or cam, your lash will increase, being "noisier". If the wear is taking place on the face of the valve, as in a groove being pounded into the valve face by the hardened seat, your lash will become tighter, or less. The oem valves are known for being "soft". Both these scenarios are common to most air cooled 4 strokes. Honda seems to have had some quality issues with certain batches in recent years. On older, ill maintained motors, you see more of the actual cam/rocker wear. It is also caused by performance cams, and heavy valve springs.
 

SFO

Lifetime Sponsor
Joined
Feb 16, 2001
Messages
2,001
Likes
0
#8
KLX's are particularly noted to go to zero lash due to crap-ola valve material.
I used to make all the valves for Larry Roeseler at KMPI.
He wouldn't even run them(OEM) in brand new bikes.
With one piece stainless valves in place, valve clearance fluctuation became history.
The XR is air cooled as well, so the thermal retention could be a problem.
We used to run our z50 to zero lash riding it so much.
It would slowly get slower.(imagine that)
Then it would stop starting,
because the valves were actually hung open to far,
to have enough compression to start.
 

Shaw520

Damn Yankees
Joined
May 14, 2000
Messages
1,082
Likes
5
#9
Cpt,
If the valves have not been adjusted in some time, you'd best start there, these valves do seat over time and in most cases zero lash is the result, causing starting problems and off idle flat spots.
Then proceed to the carb, if no mods have been done, just a good cleaning of the bowl and main/pilot curcuits. Check float level, and finally set air screw. If everything is stock it wont hurt to go 2 sizes fatter on the jets,(main and pilot). If there are airbox and/or pipe mods, you will need to jet accordingly.
 
Joined
Nov 2, 2000
Messages
249
Likes
0
#10
Need more info for suggestions. Is your bike stock.modified etc..If stock go by owners suggestion,and change main & pilot jets 2 steps per time.:cool:
 
Joined
Feb 6, 2000
Messages
295
Likes
0
#11
I know this is probably a no brainer, but you didn't leave the choke lever in the middle detent while riding did you? I did this once and the bike seemed to suddenly run like crap and had no power. When's the last time you cleaned the arresstor screen?
 

mtngoat

Lifetime Sponsor
Joined
Jun 12, 2000
Messages
314
Likes
0
#12
Thanks!

I have to say, this is why I love this site. Never would have considered the "lash-loss" scenario.

ochster, I really appreciate the "education". Next season, I plan to service the head on my ole 96 XR4 (valve seals are going). I should probably consider replacing valves.
 

CPT Jack

Subscriber
Joined
Jun 27, 2000
Messages
485
Likes
0
#13
Thanks!

Great help all around!. Sorry, I can't answer too many of these questions off the top of my head. I'm the 3rd owner of this bike and I haven't changed any intake/emissions/jetting. The snorkel was already removed and the jetting (I'm told) was changed to whichever needle is recommended for the White Bros. pipe that is currently fitted. I'll have to start monkeying around to find the details.

Tex, your description is right on, but it never used to bog like that, so unless it's a seasonal issue, I'm thinking it must be something else. I'll probably look at all the recommended solutions.

PlaceLast - O.K., I'll put up a review ...AlpineStar probably won't be too thrilled though. I had to supplement them with duct tape last time out!:think