94 Yz250

dirtynogood · 09-23-2007, 09:11 PM

i recently bought this bike from my cousin,a 94 YZ250,he has ran it alot,but has also taken good care of it. i was resently out riding when in the middle of the ride it wouldn't hit the powerband anymore. it runs fine and revs up fine in nuetral.when i try to crack it ,all it does is bog a little and through a little black smoke.it is almost like the choke is stuck.i have changed the reeds, cleanded the power vaulve.my cousin just changed the piston,rings,and all the inside so iknow those are in good shape.i do have to change the head gasket. but other than that i am stumped.lif anyone has any thought on the matter, any info would be helpfull,thanks

Garryese · 09-23-2007, 10:10 PM

Black smoke is indicating a carb problem. Check the choke cable free play and check that vent lines are open. If these check out then remove the carb and clean it; check/set the float height when re-assembling.

Why does the head gasket need changing?

How many hours since the new topend? What kind of piston and rings?

How many hours since crank seals were changed.

What color is the spark plug? Can you do a cutoff test with a new plug?

Do you have the ability to do a compression test and a crankcase vaccuum test?

dirtynogood · 09-23-2007, 11:19 PM

it is leaking out the shifter side,about a half inch break in the gasket. the top end is new.i had to use some crappy oil to mix with the gas i hope that wouldnt be all it is? but i will take the carb apart thanks for the input.

dirtynogood · 09-23-2007, 11:21 PM

the sparkplug was a little bunged up not to bad but i chaged it anyway

dirtynogood · 09-23-2007, 11:22 PM

im not sure what a cuttoff test is and i dont have a compressin gauge

Garryese · 09-23-2007, 11:53 PM

Cutoff test:

Warm up engine with an old spark plug. Install new plug. Get machine into high gear quickly and then hold throttle wide open for 1/2 to one mile. While still hold throttle wide open use kill engine with kill switch. Remove spark plug and check color on insulator. Also check for forgien deposits.

A one half inch hole in the head gasket will cause your problem. Actually, I am surprised it runs with that big of a hole.

Top end being new is relative. OEM piston and rings might last 15-20hrs; Significant losses at 8-10 hrs. Competition piston and rings will last 5 - 8 hrs max, with significant losses at 2-3 hrs.

dirtynogood · 09-24-2007, 08:34 PM

thanks for the info garryese.i figured it out when i took the carb apart. the jet on the bottom had unsrewed,well at least i hope thats what it was,im sure it was.i just cant check it till i get the head back on.

09-23-2007, 09:11 PM	#1 (permalink)
dirtynogood Member Join Date: Sep 2007 Location: canada Posts: 5 Casino Cash: $53500 Thanks: 2 Thanked 0 Times in 0 Posts No Classified Ratings	94 Yz250 i recently bought this bike from my cousin,a 94 YZ250,he has ran it alot,but has also taken good care of it. i was resently out riding when in the middle of the ride it wouldn't hit the powerband anymore. it runs fine and revs up fine in nuetral.when i try to crack it ,all it does is bog a little and through a little black smoke.it is almost like the choke is stuck.i have changed the reeds, cleanded the power vaulve.my cousin just changed the piston,rings,and all the inside so iknow those are in good shape.i do have to change the head gasket. but other than that i am stumped.lif anyone has any thought on the matter, any info would be helpfull,thanks

09-23-2007, 10:10 PM	#2 (permalink)
Garryese Member Join Date: Jul 2007 Location: Edson, Alberta Posts: 522 Casino Cash: $533175 Thanks: 61 Thanked 207 Times in 142 Posts No Classified Ratings	Re: 94 Yz250 Black smoke is indicating a carb problem. Check the choke cable free play and check that vent lines are open. If these check out then remove the carb and clean it; check/set the float height when re-assembling. Why does the head gasket need changing? How many hours since the new topend? What kind of piston and rings? How many hours since crank seals were changed. What color is the spark plug? Can you do a cutoff test with a new plug? Do you have the ability to do a compression test and a crankcase vaccuum test? __________________ Garry Past President Edson ATV Club Aging is inevitable... growing up is optional 07 Scrambler: Aaen Stage III, Trail Tech Vapor, Bear Claws, Clutch tuning. NOS to come 07 Scrambler: Bear claws, Trail Tech Endurance, Clutch tuning. 98 Sportsman: 20,000 miles when the speedo quit in '05 08 F350 SD CC LWB 6.4l

09-23-2007, 11:19 PM	#3 (permalink)
dirtynogood Member Join Date: Sep 2007 Location: canada Posts: 5 Casino Cash: $53500 Thanks: 2 Thanked 0 Times in 0 Posts No Classified Ratings	Re: 94 Yz250 it is leaking out the shifter side,about a half inch break in the gasket. the top end is new.i had to use some crappy oil to mix with the gas i hope that wouldnt be all it is? but i will take the carb apart thanks for the input.

09-23-2007, 11:21 PM	#4 (permalink)
dirtynogood Member Join Date: Sep 2007 Location: canada Posts: 5 Casino Cash: $53500 Thanks: 2 Thanked 0 Times in 0 Posts No Classified Ratings	Re: 94 Yz250 the sparkplug was a little bunged up not to bad but i chaged it anyway

09-23-2007, 11:22 PM	#5 (permalink)
dirtynogood Member Join Date: Sep 2007 Location: canada Posts: 5 Casino Cash: $53500 Thanks: 2 Thanked 0 Times in 0 Posts No Classified Ratings	Re: 94 Yz250 im not sure what a cuttoff test is and i dont have a compressin gauge

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09-23-2007, 11:53 PM	#6 (permalink)
Garryese Member Join Date: Jul 2007 Location: Edson, Alberta Posts: 522 Casino Cash: $533175 Thanks: 61 Thanked 207 Times in 142 Posts No Classified Ratings	Re: 94 Yz250 Cutoff test: Warm up engine with an old spark plug. Install new plug. Get machine into high gear quickly and then hold throttle wide open for 1/2 to one mile. While still hold throttle wide open use kill engine with kill switch. Remove spark plug and check color on insulator. Also check for forgien deposits. A one half inch hole in the head gasket will cause your problem. Actually, I am surprised it runs with that big of a hole. Top end being new is relative. OEM piston and rings might last 15-20hrs; Significant losses at 8-10 hrs. Competition piston and rings will last 5 - 8 hrs max, with significant losses at 2-3 hrs. __________________ Garry Past President Edson ATV Club Aging is inevitable... growing up is optional 07 Scrambler: Aaen Stage III, Trail Tech Vapor, Bear Claws, Clutch tuning. NOS to come 07 Scrambler: Bear claws, Trail Tech Endurance, Clutch tuning. 98 Sportsman: 20,000 miles when the speedo quit in '05 08 F350 SD CC LWB 6.4l

09-24-2007, 08:34 PM	#7 (permalink)
dirtynogood Member Join Date: Sep 2007 Location: canada Posts: 5 Casino Cash: $53500 Thanks: 2 Thanked 0 Times in 0 Posts No Classified Ratings	Re: 94 Yz250 thanks for the info garryese.i figured it out when i took the carb apart. the jet on the bottom had unsrewed,well at least i hope thats what it was,im sure it was.i just cant check it till i get the head back on.

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