1991 CR 125 Top End?? - Motorcycle-Journal Forums

fetch · 07-29-2008, 05:30 PM

Hey everyone,

I recently bought a 1991 CR 125, Runs pretty good, Starts first kick, but there are a couple of issues I was hoping I might get some help with.

1) There is quite a bit of Oil/fuel Mixture blowing out of the exhaust right next to the Flange, New gasket? or new top end? I have heard when compression is low the oil part of the mix will not burn off and it just sort of drips out of the exhaust, is that what I am seeing all over the front of the motor?

2) it seems the chain is very loose, Can I just loosen the rear wheel, and slide it back to tighten it up some?

3) The bike will not idle, you have to give it a small amount of throttle to keep it running. carb probably not adjusted properly, where should I look to
get enough fuel flowing to let the bike idle?

Thanks in advance for any help!!

the_privateer · 07-30-2008, 06:46 AM

if the bike starts first kick, it doesn't need a top end. most likely spooge is from being jetted overly rich. if it leaks out between the pipe and cylinder, you need a new exhaust o-ring as well.

to adjust the chain, is basically how you describe it except there are bolts and lock nuts to hold the axle back in the swingarm. they are pretty much self explanitory if you look at them.

adjusting the idle is done as so: first, turn up the idle with the idle speed screw. this is usually a phillips screw near the fuel line of the carb with a lock nut on it. turn it in until you get an idle. now use the air screw (flathead screw somewhere near airboot side of carb) to get the highest possible idle. now back out the idle speed screw to get the lowest sustainable idle.

I can elaborate on re-jetting but would need more description of how the bike runs in low rpm, mid rpm, and high rpm ranges as well as what the spark plug looks like

fetch · 07-30-2008, 08:33 AM

Excellent! Exactly what I wanted to hear! I already ordered the o-ring, and also the flange gasket just in case! I guess I will wait for my shop manual to come in before I adjust the chain, so I can get specifics on appropriate tension.
Now, re-jetting, I have seen a few walk throughs around the web, I guess I will need to take a closer look.

Thanks for the info!!

07-29-2008, 05:30 PM	#1 (permalink)
fetch Newbie Joined: Jul 2008 Bike: 1991 CR 125 - 1989 KX 125 Posts: 3	1991 CR 125 Top End?? Hey everyone, I recently bought a 1991 CR 125, Runs pretty good, Starts first kick, but there are a couple of issues I was hoping I might get some help with. 1) There is quite a bit of Oil/fuel Mixture blowing out of the exhaust right next to the Flange, New gasket? or new top end? I have heard when compression is low the oil part of the mix will not burn off and it just sort of drips out of the exhaust, is that what I am seeing all over the front of the motor? 2) it seems the chain is very loose, Can I just loosen the rear wheel, and slide it back to tighten it up some? 3) The bike will not idle, you have to give it a small amount of throttle to keep it running. carb probably not adjusted properly, where should I look to get enough fuel flowing to let the bike idle? Thanks in advance for any help!!

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07-30-2008, 06:46 AM	#2 (permalink)
the_privateer Clunked into first gear Joined: Jul 2006 Bike: 2000 yz125 race prepped Location: bentonville, arkansas, us Posts: 230	if the bike starts first kick, it doesn't need a top end. most likely spooge is from being jetted overly rich. if it leaks out between the pipe and cylinder, you need a new exhaust o-ring as well. to adjust the chain, is basically how you describe it except there are bolts and lock nuts to hold the axle back in the swingarm. they are pretty much self explanitory if you look at them. adjusting the idle is done as so: first, turn up the idle with the idle speed screw. this is usually a phillips screw near the fuel line of the carb with a lock nut on it. turn it in until you get an idle. now use the air screw (flathead screw somewhere near airboot side of carb) to get the highest possible idle. now back out the idle speed screw to get the lowest sustainable idle. I can elaborate on re-jetting but would need more description of how the bike runs in low rpm, mid rpm, and high rpm ranges as well as what the spark plug looks like

07-30-2008, 08:33 AM	#3 (permalink)
fetch Newbie Joined: Jul 2008 Bike: 1991 CR 125 - 1989 KX 125 Posts: 3	Excellent! Exactly what I wanted to hear! I already ordered the o-ring, and also the flange gasket just in case! I guess I will wait for my shop manual to come in before I adjust the chain, so I can get specifics on appropriate tension. Now, re-jetting, I have seen a few walk throughs around the web, I guess I will need to take a closer look. Thanks for the info!!

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