splutter problem
 

my XR400 has a problem with spluttering/fuel. It will not tick over easily until the choke is on at least halfway or full. The bike when reved past halfway will splutter and as soon as the choke is turned off the bike slutters and dies. When the choke is on it still does if I try to rev it past about halfway.

Is this too lean/rich and do main jets get blocked without the pilot jets blocking up first?


[This message has been edited by martync (edited 26 February 2006).]

Probably too rich if it runs with the choke and doesn't without.

Pilot and main jets could block seperately, but jets don't normally block unless you've been using dirty fuel. The problem is likely to be somewhere else.

When/how did the problem first occur? That would be useful to know, as well as if it's a intermittent problem or has got worse over time. Also, how is the idle?

If you haven't already, check/clean your air filter.

I'm not sure how long as I just bought the bike (Sh*t!) although it ran fine the week before when I test rided it.
It's not the air filter which i checked and the problem is bad (won't tick over without chock or run for that matter and when you rev it with the chocke on it splutters after a quarter throttle, it seemed to get worse as i tested it) after i got it home. Is there anyway of telling/testing if it's electrical(CDI) surely this would occur right through the rev range, it just seems as there is either too much or not enough fuel getting into the engine but I'm open to suggestion

From what you describe, either the carb is way out of wack or it's likely to be something else. Did the previous owner switch carbs or exhausts after your test ride? as it would take something of that magnitude to send a carb that bad within a week.

The CDI is always a pain to diagnose. Mostly the bike stops pretty much dead, but sometimes all sorts of intermittent running problems occur, including problems similar to yours. There's not much difference between an intermittent spark and a really bad carb as far as run is concerned.

It's possible that the CDI is broke, but the only way to check that would be to replace it. Worth doing, as playing with all the different carb components can really take some time.

Side stand switches are always good for a laugh when it comes to causing running probs.

Phil

Martync
Did you check the rubber union between carburator and upper head?(don´t know the name in english)but a small crack or a little hole or a loosen screw could do this.Air is getting in there?
KH

rubber described in the previous post had a bit missing, there was also water in the CDI connection, I haven't managed to get to the spark plug (lack of specific tool) but will replace it. I rebuilt the carb and will refit next week to see if the problem has gone.

Hi martync,XR400s are generally very reliable so it does not sound like anything serious.
It might have an air leak {very lean mixture}.
First replace spark plug with new one,check rubber O ring between the inlet rubber and the cylinder head,then check the pilot screw at the bottom of the carb the standard setting is one full turn out from fully seated.
See how you get on with that.