1995 XT600E; pre-fires at low RPMs; any ideas?

Hi,

I have a 1995 XT600E that I just got running, and I don't
know it's history. The bike seems to run well and smooth
at high RPMs, but at lower RPMs and at idle, it will pre-fire
back into the carbs; sometimes the engine will die as a
result. I either have an ignition problem or a carb
problem; which would be more likely for this bike?
The carbs were pulled and cleaned, but I could not
remove the float pin, so I was not able to properly
clean the float needle or seat. I just sprayed carb
cleaner as best I could though the float seat via the
fuel inlet pipe. I don't believe the ignition module
is the problem because I cleaned the air filter using
the spray carb cleaner, and installed it still damp
with the cleaner; the bike ran and idled perfectly until
the filter dried out. If it is the carb, is there any
gas additive that I could use that would help to clean
out whatever is causing this problem? I do not want
to remove the carbs again unless absoultely necessary;
it's a real hassle.

Thanks for any help.

 

It sounds like lean idle mixture or an inlet valve that isn't closing
fully. Check your valve clearances to make sure it has the minimum
clearance and check the compression to be sure you aren't getting
reverse airflow at low RPM.

An excellent carburetor cleaner is Berryman B12 Choke and Carb
Cleaner. You can get it from Wal*Mart or any good auto parts store in
either liquid or aerosol form

The solvents in B12 are strong enough to quickly clean out gum and
varnish, but they won't touch calcium carbonate deposits from water
that got into your gas and plugged up the tiny
orifices and passageways in your carbs.

 

Thank you for your help. I have a service manual for the bike,
but it isn't clear on what to set the pilot screw at (number of
turns out). I have tired everything from 0.5 to 2.5 turns, but
it doesn't seem to make much difference. Does anybody know what
a 1995 XT600E pilot screw setting is suppose to be? The manual
lists a 3UX carb as 2.5 turns out; but my carbs are marked 3UY
which is not listed in the manual. So if I have a lean condition,
does that means I need to turn 'in' or 'out' the pilot screw?

Thanks Again!

It sounds like lean idle mixture or an inlet valve that isn't closing
fully. Check your valve clearances to make sure it has the minimum
clearance and check the compression to be sure you aren't getting
reverse airflow at low RPM.

An excellent carburetor cleaner is Berryman B12 Choke and Carb
Cleaner. You can get it from Wal*Mart or any good auto parts store in
either liquid or aerosol form

The solvents in B12 are strong enough to quickly clean out gum and
varnish, but they won't touch calcium carbonate deposits from water
that got into your gas and plugged up the tiny
orifices and passageways in your carbs.

 

Timing over-advanced?...

 

Which carb are you fiddling with? The XT600E has two, you know, and
fiddling with them is not advisable unless you really know what the
function of each carb is.

 

It get the impression that you have California carburetors from the
parts diagrams at http://www.powersportspro.com.

The carbs shown have GAS screws, you turn them counterclockwise to
richen the idle mixture.

If you don't get any response from turning the screws, that indicates
the idle mixture passages and ports are clogged up.

 

It wouldn't hurt to check compression as well. You might
want to do this before you start trying to adjust anything.

Pull and ground the plugs.

Open the throttle.

crank the engine and compare compression for each
cylinder.

Always good to do full diagnostics before adjustments.
If a cylinder isn't quite right, you can drive yourself
crazy trying to adjust the carbs to fix the problem.