cooter wrote:
> I just bought a 1990 KX 125 and it has a very noticable power loss
> compared to the other 125's i have ridden. When i go out to ride
it
> usually runs alright until i get out on the road after about 2 hours
> of riding and start opening it up.
Where do you live that you can ride a KX125 on the *road* for long
distances? An MX bike, even a water-cooled one like the KX125 really
isn't meant for constant operation at high RPM for 2 hours. That's
punishment, is what it is...
Early MX races used to require the riders to race for 45 minutes
without stopping, wait for a few other races and then race for another
45 minutes.
But the little water cooled MX bikes sold today usually race for 20
minutes maximum on a tight narrow MX course where they don't get run at
full throttle for more than a few seconds, it's mostly on and off
throttle...
Even if a *roadracer* had a little 125cc MX engine in it like was used
for
little 125cc roadracers years ago, the racer would only be riding it
full throttle flat out for about 20 miles and he would expect to tear
it down and re-ring it and install a new rod bearing after punishing it
like that for half an hour...
> then it just starts losing power and bogs then dies and locks up.
> while im sliding i downshift and try to roll start it but it
> stays locked.
YOU SILLY FOOL! That's NOT bogging! It's engine destruction about to
happen!
The piston is getting too damned HOT from excessive heat buildup, it's
EXPANDING in the watercooled cylinder bore! When the engine starts
"losing power", it's *begging you* to stop PUNISHING it! Trying to bump
start a seized engine by popping the clutch may result in breaking the
connecting rod, because the piston has stopped moving, but the
crankshaft keeps going.
It's YOUR crankshaft, keep doing that, and you'll be splitting the
cases to pull out a bunch of broken parts...
You are due for an engine teardown to see what you've damaged. Plan on
it before it gets really expen$ive!
I helped some guys build a big 2-stroke watercooled Suzuki triple for
endurance racing. It was fast, it had power on everybody riding
4-strokes that Saturday morning on Ontario International Raceway. I
rode the bike a little. It sounded sour, but it revved easily like a
2-stroke should and popped little power wheelies and then it overheated
and quit. Our rider took the triple out on the track for qualifying and
was humiliating some well respected club riders, and then he didn't
come around again...
The engine had seized on of the cylinders because it was running
incredibily hot. In fact, the piston was melted. I saw that the spark
plug was filled with melted aluminum. We pulled the head off, looking
for damages. There was a big hole melted in the piston. I pushed on the
top of the piston. It moved a quarter of an inch. It shouldn't have
moved without the crankshaft turning. I knew a rod was broken. When I
got the engine completely apart, I found that the water pump wasn't
pumping water because
the water pump housing was full of some radiator anti-leak compound
that had solidified there. Fortunately, the broken rod hadn't destroyed
the inside of the crankcases while the crank spun around and around as
the motorbike rattled to a stop from 120 mph...
That engine ran again, in a closed highway race from Tijauna to San
Felipe, in Baja California...
> i have to wait about 10 minutes before it will start again and i have
> to roll start it. i think its something to do with the carb. but im
> not sure
There are a number of things that could be wrong, starting with the
rider's knowledge of how a 2-stroke piston port engine operates. The
piston going up and down opens and closes the exhaust port. On the
KX-125 it looks like you have a power valve on either side of the
cylinder that's operated by 2 worm gears on a shaft that runs across
the engine. Are those valves opening and closing properly, or are they
seizing up when they get hot and holding too much heat in the cylinder?
Is your expansion chamber carbon free all the way through? A silencer
on the end of the stinger that's blocked up with carbon will trap heat
in the cylinder and you might or might not hear the tinkling noise of
pinging as the spark plug glows cherry red and pre-ignites the fuel air
mixture...
I had the carbon plugged silencer problem on the expansion chambers of
my
Yamaha 250cc cafe racer. It drove me absolutely NUTS for a few months,
trying to figure out why the engine ran OK when it was cold and then
would try to burn holes in the pistons when it got hot...
Yeah, you *could* blame the carburetor. Maybe somebody who thinks he's
a hotshot tuner has changed the main jet. That's what they think of, is
main jets, they might also raise or lower the jet needle a notch or two
and tweak the idle mixture screw to adjust for the previous fuck up on
re-jetting...
They get "main jet" locked into their heads and they think they need
huge mainjets for continuous wide open throttle running on really long
straights, and then they don't ride wide open on long straights, they
fool around on little half mile long MX tracks with 20 turns and they
are averaging ~40 mph at part throttle and the engine loads up on
fuel/oil mix and the rings seize in their grooves...
If your fuel/oil premix is too rich on oil, or if you use something
like racing castor oil instead of a thin synthetic oil, your piston
rings will stick in their grooves and the next time you start the
engine, it will be down on power, because it won't be able to compress
the fuel air mixture properly. Hot combustion gasses with leak past the
stuck rings and the piston will get hot and grow larger and can seize
in the cylinder bore...
I had the stuck ring business happen to me when MX first came to the
USA and I was out riding on Saddleback Park's MX track. The Husqvarna
factory team showed up, and the international MX stars were asking ME
questions about the track and my setup, and my 250cc Yamaha was running
like a 125 with stuck piston rings...
The only way to to know where you stand with the carburetor is to pull
it apart and read the numbers on the jets, check the jet needle clip to
see what position it's in, and put it back into the 2nd from the top or
the middle position, and go down to your friendly Kawa$aki $tealer$gip
and ask the part$ geek behind the counter to look up the main jet and
pilot jet sizes for you, so you can compare them to what you have in
order to make the decision whether to go back to stock, or if you
already are stock, as regards jets...
You might check the parts fiches at www.buykawasaki.com or
www.partsfish.com to see if they tell you what jets should be in your
carbs...
Other possibilities that can lead to the engine seizures you've been
experiencing are lack of coolant in the radiator, a water pump that's
not turning, a thermostat that's not opening (been there had that
happen once),
a plugged up radiator, a pressure cap that doesn't hold pressure, or an
electric cooling fan that doesn't work when the thermoswitch closes...
krusty kritter wrote:
> cooter wrote:
>
>>I just bought a 1990 KX 125 and it has a very noticable power loss
>>compared to the other 125's i have ridden. When i go out to ride
>
> it
>
>>usually runs alright until i get out on the road after about 2 hours
>>of riding and start opening it up.
>
>
> Where do you live that you can ride a KX125 on the *road* for long
> distances? An MX bike, even a water-cooled one like the KX125 really
> isn't meant for constant operation at high RPM for 2 hours. That's
> punishment, is what it is...
>
> Early MX races used to require the riders to race for 45 minutes
> without stopping, wait for a few other races and then race for another
> 45 minutes.
> But the little water cooled MX bikes sold today usually race for 20
> minutes maximum on a tight narrow MX course where they don't get run at
> full throttle for more than a few seconds, it's mostly on and off
> throttle...
>
> Even if a *roadracer* had a little 125cc MX engine in it like was used
> for
> little 125cc roadracers years ago, the racer would only be riding it
> full throttle flat out for about 20 miles and he would expect to tear
> it down and re-ring it and install a new rod bearing after punishing it
> like that for half an hour...
>
>
>>then it just starts losing power and bogs then dies and locks up.
>>while im sliding i downshift and try to roll start it but it
>>stays locked.
>
>
> YOU SILLY FOOL! That's NOT bogging! It's engine destruction about to
> happen!
>
> The piston is getting too damned HOT from excessive heat buildup, it's
> EXPANDING in the watercooled cylinder bore! When the engine starts
> "losing power", it's *begging you* to stop PUNISHING it! Trying to bump
> start a seized engine by popping the clutch may result in breaking the
> connecting rod, because the piston has stopped moving, but the
> crankshaft keeps going.
> It's YOUR crankshaft, keep doing that, and you'll be splitting the
> cases to pull out a bunch of broken parts...
>
> You are due for an engine teardown to see what you've damaged. Plan on
> it before it gets really expen$ive!
>
> I helped some guys build a big 2-stroke watercooled Suzuki triple for
> endurance racing. It was fast, it had power on everybody riding
> 4-strokes that Saturday morning on Ontario International Raceway. I
> rode the bike a little. It sounded sour, but it revved easily like a
> 2-stroke should and popped little power wheelies and then it overheated
> and quit. Our rider took the triple out on the track for qualifying and
> was humiliating some well respected club riders, and then he didn't
> come around again...
>
> The engine had seized on of the cylinders because it was running
> incredibily hot. In fact, the piston was melted. I saw that the spark
> plug was filled with melted aluminum. We pulled the head off, looking
> for damages. There was a big hole melted in the piston. I pushed on the
> top of the piston. It moved a quarter of an inch. It shouldn't have
> moved without the crankshaft turning. I knew a rod was broken. When I
> got the engine completely apart, I found that the water pump wasn't
> pumping water because
> the water pump housing was full of some radiator anti-leak compound
> that had solidified there. Fortunately, the broken rod hadn't destroyed
> the inside of the crankcases while the crank spun around and around as
> the motorbike rattled to a stop from 120 mph...
>
> That engine ran again, in a closed highway race from Tijauna to San
> Felipe, in Baja California...
>
>
>>i have to wait about 10 minutes before it will start again and i have
>
>
>>to roll start it. i think its something to do with the carb. but im
>>not sure
>
>
> There are a number of things that could be wrong, starting with the
> rider's knowledge of how a 2-stroke piston port engine operates. The
> piston going up and down opens and closes the exhaust port. On the
> KX-125 it looks like you have a power valve on either side of the
> cylinder that's operated by 2 worm gears on a shaft that runs across
> the engine. Are those valves opening and closing properly, or are they
> seizing up when they get hot and holding too much heat in the cylinder?
>
> Is your expansion chamber carbon free all the way through? A silencer
> on the end of the stinger that's blocked up with carbon will trap heat
> in the cylinder and you might or might not hear the tinkling noise of
> pinging as the spark plug glows cherry red and pre-ignites the fuel air
> mixture...
>
> I had the carbon plugged silencer problem on the expansion chambers of
> my
> Yamaha 250cc cafe racer. It drove me absolutely NUTS for a few months,
> trying to figure out why the engine ran OK when it was cold and then
> would try to burn holes in the pistons when it got hot...
>
> Yeah, you *could* blame the carburetor. Maybe somebody who thinks he's
> a hotshot tuner has changed the main jet. That's what they think of, is
> main jets, they might also raise or lower the jet needle a notch or two
> and tweak the idle mixture screw to adjust for the previous fuck up on
> re-jetting...
>
> They get "main jet" locked into their heads and they think they need
> huge mainjets for continuous wide open throttle running on really long
> straights, and then they don't ride wide open on long straights, they
> fool around on little half mile long MX tracks with 20 turns and they
> are averaging ~40 mph at part throttle and the engine loads up on
> fuel/oil mix and the rings seize in their grooves...
>
> If your fuel/oil premix is too rich on oil, or if you use something
> like racing castor oil instead of a thin synthetic oil, your piston
> rings will stick in their grooves and the next time you start the
> engine, it will be down on power, because it won't be able to compress
> the fuel air mixture properly. Hot combustion gasses with leak past the
> stuck rings and the piston will get hot and grow larger and can seize
> in the cylinder bore...
>
> I had the stuck ring business happen to me when MX first came to the
> USA and I was out riding on Saddleback Park's MX track. The Husqvarna
> factory team showed up, and the international MX stars were asking ME
> questions about the track and my setup, and my 250cc Yamaha was running
> like a 125 with stuck piston rings...
>
>
> The only way to to know where you stand with the carburetor is to pull
> it apart and read the numbers on the jets, check the jet needle clip to
> see what position it's in, and put it back into the 2nd from the top or
> the middle position, and go down to your friendly Kawa$aki $tealer$gip
> and ask the part$ geek behind the counter to look up the main jet and
> pilot jet sizes for you, so you can compare them to what you have in
> order to make the decision whether to go back to stock, or if you
> already are stock, as regards jets...
>
> You might check the parts fiches at www.buykawasaki.com or
> www.partsfish.com to see if they tell you what jets should be in your
> carbs...
>
> Other possibilities that can lead to the engine seizures you've been
> experiencing are lack of coolant in the radiator, a water pump that's
> not turning, a thermostat that's not opening (been there had that
> happen once),
> a plugged up radiator, a pressure cap that doesn't hold pressure, or an
> electric cooling fan that doesn't work when the thermoswitch closes...
>
He said he opens it up on the road AFTER two hours of riding (i assume
the two hours are on trails or a track) It sounds like it is seizing due
to the contiunous hi speed operation (bogs and then locks up and then
has to wait 10 minutes to free it up). My jet ski does this same thing.
Runs fine until you hold it wide open for too long and then it partially
seizes. Wait a few minutes and it runs fine (I hate to see what the bore
looks like)/ You may have a slight air leak, lean carburation or too
tight piston to cylinder clearance. I have never figured it out on my ski.
--
Rob Munach, PE
Excel Engineering
PO Box 1264
Carrboro, NC 27510
Rob Munach wrote:
> My jet ski does this same thing.
> Runs fine until you hold it wide open for too long and then it
partially
> seizes. Wait a few minutes and it runs fine (I hate to see what the
bore
> looks like)/.
You probably can't blame the cooling system, if the water pump is
squirting the usual jet of water out the back it has to be pumping...
One difference between PWC's and outboard or inboard powered boats and
motorbikes is that the former have an unlimited supply of 55 degree
cooling water. The motorbike has to carry all of its coolant onboard
and the radiator has to reject waste heat to the atmosphere, so the
more complicated cooling system has to work right...
(Many years ago, there were articles in some of the sportscar
magazines about a racer who was using Mercury 4-cylinder and 6-cylinder
outboard engines in his little sports racing cars. The light weight
Mercury 2-strokes sounded like just the ticket, and I was getting
interested in building my own little race car until the builder of the
cars admitted that the water passages and water pumps were sized for 55
degree water and he was frying his engines...)
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> compared to the other 125's i have ridden. When i go out to ride
it
> usually runs alright until i get out on the road after about 2 hours
> of riding and start opening it up. then it just starts losing power
> and bogs then dies and locks up. while im sliding i downshift and try
> to roll start it but it stays locked. i have to wait about 10 minutes
> before it will start again and i have to roll start it. i think its
> something to do with the carb. but im not sure. Any help would be
> greatly appreciated.