Discussion:
runaway idle speed on two stroke?????
(too old to reply)
Jason
2004-07-06 23:14:09 UTC
Permalink
Hi all,

My friend has a two stroke that gets a runaway idle sometimes after it
warms up from riding. What happens is even if the throttle is
"closed" the idle speed picks up significantly. What could be causing
this?

Thanks.

Jason
roost4u
2004-07-07 00:01:22 UTC
Permalink
Check for an air leak. Spray carb cleaner around the intake boot and carb.
If the running speed changes then you have an air leak.
--
Rick
2000KX250
1993KX250
1992XR100
Post by Jason
Hi all,
My friend has a two stroke that gets a runaway idle sometimes after it
warms up from riding. What happens is even if the throttle is
"closed" the idle speed picks up significantly. What could be causing
this?
Thanks.
Jason
whenindoubt
2004-07-07 00:14:17 UTC
Permalink
Yep, air leak between the carb and the engine.
Post by Jason
Hi all,
My friend has a two stroke that gets a runaway idle sometimes after it
warms up from riding. What happens is even if the throttle is
"closed" the idle speed picks up significantly. What could be causing
this?
Thanks.
Jason
CrashTestDummy
2004-07-07 03:51:28 UTC
Permalink
Post by Jason
Hi all,
My friend has a two stroke that gets a runaway idle sometimes after it
warms up from riding. What happens is even if the throttle is
"closed" the idle speed picks up significantly. What could be causing
this?
In addition to checking for an air leak, you might also check to
ensure that the throttle cable isn't being "stretched" or kinked. This
often happens when the cable isn't routed properly, and is usually
apparent when turning the bars one way or the other. I had this happen
on a little GT-80 back in the day when I had the cable poorly routed.
It would start and idle fine. It would even idle okay when turning
right. But when you turned left, whoa boy! But since you specify that
the problem occurs after "riding," I suspect the others are right when
they suggest air leak. (Though I imagine crud in the carburetor could
also be feasible). Good luck!

Fred B. - DFW Area
'85 RM 250
'81 DT 80
dobypinch
2004-07-07 04:34:13 UTC
Permalink
H
Check the water in the cooling system to make sure it is full. I had the
same problem and it turned out that the coolant had escaped to somewhere.
Most of my free advice was jetting related.

fran
Jason wrote in message ...
Post by Jason
Hi all,
My friend has a two stroke that gets a runaway idle sometimes after it
warms up from riding. What happens is even if the throttle is
"closed" the idle speed picks up significantly. What could be causing
this?
Thanks.
Jason
Chris Buckley
2004-07-07 18:56:10 UTC
Permalink
dobypinch wrote:
H
Post by dobypinch
Check the water in the cooling system to make sure it is full. I had the
same problem and it turned out that the coolant had escaped to somewhere.
That would indicate an engine problem, either a leaking head gasket or
seals.
unknown
2004-07-07 22:04:03 UTC
Permalink
On Wed, 07 Jul 2004 18:56:10 GMT, Chris Buckley
Post by Chris Buckley
Post by dobypinch
Check the water in the cooling system to make sure it is full. I had the
same problem and it turned out that the coolant had escaped to somewhere.
That would indicate an engine problem, either a leaking head gasket or
seals.
I've seen a leaking head o-ring give high idle symptoms.

I've also seen a too high idle set give the same steadily increasing
idle symptom also. A two stroke ideally should have the idle speed set
just high enough to get your goggles on without the motor dying.


MX Tuner
IdaSpode
2004-07-07 22:50:30 UTC
Permalink
Post by unknown
A two stroke ideally should have the idle speed set
just high enough to get your goggles on without the motor dying.
You state that as fact, when it's really just your opinion. My opinion
is that only a poorly engineered or improperly jetted engine/carb
combo needs to be adjusted as such.

My KTM 200 starts with one or two kicks, hot or cold, will idle all
day, yet has excellent response right from the get go all the way to
WFO. I haven't fouled a plug since my 2000 model. I usually change the
plug once a season, just because. I basically have three jetting
"realms", winter (cold, low altitude desert), spring (medium temps,
mid level altitudes) and summer, (hot and high).

Ride our mountain TST terrain with a bike that will not idle with the
clutch in and in gear and you'll hate life as the rest of the pack
rides away from you.

Maybe things are different down there in Georgia. Maybe that's why you
dislike KTMs so much, they don't need (or respond to) your tuning
methods like the Jap bikes do... <G>
Post by unknown
MX Tuner
DJ
spodely
2004-07-08 01:22:06 UTC
Permalink
Post by IdaSpode
Post by unknown
A two stroke ideally should have the idle speed set
just high enough to get your goggles on without the motor dying.
You state that as fact, when it's really just your opinion. My opinion
is that only a poorly engineered or improperly jetted engine/carb
combo needs to be adjusted as such.
My KTM 200 starts with one or two kicks, hot or cold, will idle all
day, yet has excellent response right from the get go all the way to
WFO. I haven't fouled a plug since my 2000 model. I usually change the
plug once a season, just because. I basically have three jetting
"realms", winter (cold, low altitude desert), spring (medium temps,
mid level altitudes) and summer, (hot and high).
Ride our mountain TST terrain with a bike that will not idle with the
clutch in and in gear and you'll hate life as the rest of the pack
rides away from you.
Maybe things are different down there in Georgia. Maybe that's why you
dislike KTMs so much, they don't need (or respond to) your tuning
methods like the Jap bikes do... <G>
Seein' as I'm in the South (note that it is capitalized), I'll add that I
cannot stand to ride a bike that will not idle. My bike is on the same plug
as it was in November, and it will idle until it runs out of gas. If I let
off the throttle and it dies in the time it takes me to put on my goggles,
something needs fixin'. I refuse to ride a downhill run or let off the
throttle and it die on me.
Post by IdaSpode
Post by unknown
MX Tuner
DJ
I have often wondered who started the idea that a 2-stroke should die after
a few seconds off the throttle. I have a weed eater and a chain saw that
seem to idle until I hit the kill switch, why should the motorcycle be any
different?

John.
whenindoubt
2004-07-08 01:45:49 UTC
Permalink
I tend to like bikes that idle too.
Post by spodely
Post by IdaSpode
Post by unknown
A two stroke ideally should have the idle speed set
just high enough to get your goggles on without the motor dying.
You state that as fact, when it's really just your opinion. My opinion
is that only a poorly engineered or improperly jetted engine/carb
combo needs to be adjusted as such.
My KTM 200 starts with one or two kicks, hot or cold, will idle all
day, yet has excellent response right from the get go all the way to
WFO. I haven't fouled a plug since my 2000 model. I usually change the
plug once a season, just because. I basically have three jetting
"realms", winter (cold, low altitude desert), spring (medium temps,
mid level altitudes) and summer, (hot and high).
Ride our mountain TST terrain with a bike that will not idle with the
clutch in and in gear and you'll hate life as the rest of the pack
rides away from you.
Maybe things are different down there in Georgia. Maybe that's why you
dislike KTMs so much, they don't need (or respond to) your tuning
methods like the Jap bikes do... <G>
Seein' as I'm in the South (note that it is capitalized), I'll add that I
cannot stand to ride a bike that will not idle. My bike is on the same plug
as it was in November, and it will idle until it runs out of gas. If I let
off the throttle and it dies in the time it takes me to put on my goggles,
something needs fixin'. I refuse to ride a downhill run or let off the
throttle and it die on me.
Post by IdaSpode
Post by unknown
MX Tuner
DJ
I have often wondered who started the idea that a 2-stroke should die after
a few seconds off the throttle. I have a weed eater and a chain saw that
seem to idle until I hit the kill switch, why should the motorcycle be any
different?
John.
unknown
2004-07-08 23:03:08 UTC
Permalink
Post by IdaSpode
Post by unknown
A two stroke ideally should have the idle speed set
just high enough to get your goggles on without the motor dying.
You state that as fact, when it's really just your opinion. My opinion
is that only a poorly engineered or improperly jetted engine/carb
combo needs to be adjusted as such.
Let me rephrase that. On most all two strokes that I've had the
pleasure of jetting (more than a couple- and yes, plenty of KTM's),
you can get it to run okay with an idle speed. The lower you have the
idle speed set, the better throttle response you *can* get with the
proper jetting. I never said anything about the bike fouling plugs
with or without the idle speed set high or low. This is especially
true of bikes with a Keihin carb.
Post by IdaSpode
Ride our mountain TST terrain with a bike that will not idle with the
clutch in and in gear and you'll hate life as the rest of the pack
rides away from you.
I rode all my enduro days with a bike set up not to idle. Plenty of
hills around here. I can't ride a two stroke effectively with the idle
set up.
Post by IdaSpode
Maybe things are different down there in Georgia. Maybe that's why you
dislike KTMs so much,
I don't dislike KTM's at all. I just don't wear orange underwear like
quite a few RMD'ers. I'm not brand loyal. I ride a Honda... right now.
I'm not against owning a KTM. One of the best 4 stroke mx'ers I've
ridden was a 525 (very similar to my CRF). KTM's have a good market.
Funny how all the KTM owners say their bikes come with all the good
parts.... and then proceed to change most of them. I used to be big
into Yamahas recently until they started treating their customers like
shit. I won't be buying a Yamaha anytime soon.
Post by IdaSpode
they don't need (or respond to) your tuning
methods like the Jap bikes do... <G>
No, they respond very well, just like the jap bikes. After all, they
have the same carbs. And I have jets for all of 'em.




MX Tuner
dirtfirst
2004-07-07 23:41:11 UTC
Permalink
Post by Chris Buckley
H
Post by dobypinch
Check the water in the cooling system to make sure it is full. I had the
same problem and it turned out that the coolant had escaped to somewhere.
That would indicate an engine problem, either a leaking head gasket or
seals.
You may have a leaking crank seal too. Pressure testing is the difinitive answer.
DF
john
2004-11-03 04:39:27 UTC
Permalink
On Wed, 07 Jul 2004 18:56:10 GMT, Chris Buckley
Post by Chris Buckley
H
Post by dobypinch
Check the water in the cooling system to make sure it is full. I had the
same problem and it turned out that the coolant had escaped to somewhere.
That would indicate an engine problem, either a leaking head gasket or
seals.
Doh did he blow a seal?
john

James
2004-07-07 19:27:12 UTC
Permalink
Float level might be too low.

A quick little test that may give you a better idea if it is the float
level is to let the bike warm up until it does this. Immediately shut
it down. Tilt it sideways until fuel leaks out the overflow tube so
you have a pretty good idea as soon as the bowl is full again. Start
it. You'll want to start it again as soon as you can so the engine
temp. is about the same as it was when it was idling fast before.

If it idles fast immediately, it's probably an air leak. If it idles
fine until approximately the same amount of time passes as did the
first time, it's probably the float level.

Of course, this isn't a sure fire diagnostic, just something free and
easy to maybe give you a little better idea what the problem is.

James
00CR250
Post by Jason
Hi all,
My friend has a two stroke that gets a runaway idle sometimes after it
warms up from riding. What happens is even if the throttle is
"closed" the idle speed picks up significantly. What could be causing
this?
Thanks.
Jason
Loading...