89 yz 125 boggs down at wide open throttle


Jul 16, 2006
18
0
The bike I just rebuilt has alot of mid range power and it seems to be hitting the power band but then when you try to go full throttle and really get the revs high it boggs down. Almost like fuel is completly shut off. Is this a jetting problem?
 

fit04

Member
Apr 9, 2007
21
0
I had the same problem with my dr200...I cleaned out my carb and it was better...but its back again so I have to figure out what else to do.
 

84cr125

Member
Apr 8, 2007
292
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cdorsey50stang said:
Almost like fuel is completly shut off. Is this a jetting problem?

Ya i think your on to it. Have you adjusted your float level before on your bike? While you have the carb out check the reeds for and cracks.
 
Jul 16, 2006
18
0
I should note that the carb is dumping fuel out the bowl overflow constantly. This makes me think maybe the float needs adjusted. How do I go about that? How do I know where to adjust it to? Thanks
 

IndyMX

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Jul 18, 2006
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cdorsey50stang said:
I should note that the carb is dumping fuel out the bowl overflow constantly. This makes me think maybe the float needs adjusted. How do I go about that? How do I know where to adjust it to? Thanks


Get a service manual for your bike.
 

84cr125

Member
Apr 8, 2007
292
0
cdorsey50stang said:
I should note that the carb is dumping fuel out the bowl overflow constantly. This makes me think maybe the float needs adjusted. How do I go about that? How do I know where to adjust it to? Thanks


then for sure its your float level, get yourself a manual and it will show you exactly how to do things, its a liitle difficult to explain but a manual with diagrams will help you out.
 

76GMC1500

Uhhh...
Oct 19, 2006
2,142
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No matter how many times you try to set the float level, it will continue to overflow if the needle valve doesn't seat properly. On a bike that old, the needle valve and seat could be worn and may need to be replaced.
 
Jul 16, 2006
18
0
With the bowl overflowing would this be the cause of the bogging problem though? Say the needle does need replaced, would it be a good chance that the bogging would stop?
 

76GMC1500

Uhhh...
Oct 19, 2006
2,142
1
Yes an overflowing float bowl can cause carburetion issues which lead to bogging. I don't know that you need to replace the float needle valve yet. If you try to set the float but it keeps creeping higher, then you do. But, you need to try setting the float level first.
 

Jul 16, 2006
18
0
Ok, I set the float level and there is no longer any fuel coming out of the bowl which is good. The reeds look good......everything looks good.....I just thought of something else, I'm running 89 octane fuel, I know you are suppose to run 93 octane... would the octane level make that big a difference? By the way, thank you for all your help so far!
 

84cr125

Member
Apr 8, 2007
292
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unless your compression ratio hasnt been changed, by say adding a doomed piston or shaving the head i wouldnt worry about running 89 octane. But i would run higher octane to be on the safe side, better safe than sorry.
 

Nevada Sixx

Member
Jan 14, 2000
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Hi, i also have a 1989 yz125.
Maybe your main jet is too lean, maybe water in gas, clogged carb/jets, dirty air filter, or i guess it could be an air leak. Make sure it is in fact a 89 model if you are gonna order parts, if it has gold rims or drum brakes, then its not an 89, its older. Make sure the tubes that hang out the carb isnt stopped up also.

tip, if your stator ever goes out,, but the stator and the wiring harness all in one.
 

Jul 16, 2006
18
0
Ok, I've set the float level and the carb no longer dumps fuel. There is still a bogging problem. The jets I have yet to change. The only things done to the bike are: It's bored .020 over with a wiseco piston kit, and it has a pro circuit silencer. The header pipe is stock. With only these things different from stock, would they require the carb to be rejetted from stock jets? I hope that makes sense. :coocoo:
 

76GMC1500

Uhhh...
Oct 19, 2006
2,142
1
Have you tried changing the spark plug? Cracked insulators can cause weird problems. At WOT, compression pressures are high and there is much more resistance between the electrodes of the spark plug. This tends to cause it to try to arc elsewhere like between the insulator and the side of the plug. Any small cracks or some odd traces of carbon or metal on the plug insulator can cause it to short circuit, which will be especially pronounced at high rpm or when operating near the peak torque output of the engine.
 

burgunder

Member
Oct 3, 2006
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I don't know if this is the case here, but when you over bore a cylinder, it raises the intake and exaust ports. That is why when you over bore, you need to have it ported. Raising the exaust port will increase bottom end and take away from the top. But, if you have the original reeds in the bike from 1989, I would replace them. When it revs out, is the bog a blubbering sound or is it a dry baaaaaa sound? If it is blumbery, try a leaner main. If it is a baaaaa sound like the engine isn't getting air and breathing hard, get a richer main.
 
Jul 16, 2006
18
0
It's more of a blubbery sound, like it wants to rev out but won't. I did look at the plug and the White part is black, so I know I'm too rich. I bought a new jet today. Stock is #280 and I found that the carb had a #140 in it. The #140 however, has been drilled out or filed out or something because it is alot bigger hole when held up to a new #140. I will try the correct jet today and let everyone know what happens. If this doesn't work I will try to reeds. Thanks for everyone's help!
 

Ol'89r

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Jan 27, 2000
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cdorsey50stang said:
It's more of a blubbery sound, like it wants to rev out but won't.QUOTE]


Sounds like jetting.

Do a plug reading. Take your bike out somewhere that you can run wide open. Run the bike wide open in 5th gear and hit the kill button. DO NOT close the throttle. Keep the throttle wide open until the engine stops turning over. Be careful not to let the clutch out until you are completely stopped. If the engine turns over you will get a false reading on the plug.

Remove the spark plug and inspect it. It should be a light brown to tan in color. If it is too dark you will need to go leaner or smaller on your main jet. If it is white or has little shiny dark specks on the porcelain, it is too lean and needs a bigger main jet.
 

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