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Author Topic: Help! Yellow Honda ST90 "Big Bird" Idling problem  (Read 566 times)

Offline TheCoffeeGuy

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #10 on: Aug 12, 2018, 13:23:52 »
soak in Pine Sol
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1968 Harley Aermacchi ML 125 Rapido, restored
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Offline thrillseeker

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #11 on: Aug 12, 2018, 13:31:07 »
soak in Pine Sol
Pine sol? Really? Is that better than a bucket of carb soak?

I got the carb back on the bike this morning. I think cleaning helped. Now it runs better with just the mixture screw out. It doesn't need the altitude knob pulled out anymore. I'm thinking there may still be some gunk to clean out.


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Online irk miller

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #12 on: Aug 12, 2018, 15:19:42 »
I clean all of my carbs and carb parts in an ultrasonic cleaner filled with Pine Sol.

Offline Maritime

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #13 on: Aug 12, 2018, 15:59:30 »
+2 on pine sol. Shit works well. Has to be the regular one, not one of the new flavors they make. And I use a sander duct taped to a tupperware container as a redneck ultrasonic cleaner and it works too. 
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Offline thrillseeker

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #14 on: Aug 12, 2018, 22:51:25 »
I did some searching on this method and it seems people use 50/50 pine sol and water. is that what you guys use? I do have a bottle of original pine sol so I could probably do this tomorrow.
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Online irk miller

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #15 on: Aug 12, 2018, 23:10:44 »
Personally, I use straight Pine Sol.

Offline datadavid

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #16 on: Aug 13, 2018, 02:59:56 »
You know, usually when you up the displacement and use the same size carb you get a higher carb vacuum, sometimes requiring stock or smaller fuel jets. Because the bigger piston is sucking more fuel from the jets.

Offline thrillseeker

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Re: Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #17 on: Aug 13, 2018, 09:16:13 »
You know, usually when you up the displacement and use the same size carb you get a higher carb vacuum, sometimes requiring stock or smaller fuel jets. Because the bigger piston is sucking more fuel from the jets.
Thank you! This is the type of info I've been looking for. This was my theory but I've been having the hardest time finding info online to verify. I looked for a 32 idle jet but the smallest they make in this style is the stock size 35. I did find one similar with all measurements the same except a longer head. Maybe I'll order that, try it out, and cut it down to size if need be. For now I'll let my carb sit in cleaner for a couple days and see if it gets any better.


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Offline thrillseeker

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Help! Yellow Honda ST90 "Big Bird" Idling problem
« Reply #18 on: Aug 14, 2018, 22:54:01 »
Cleaned the carb really good. soaked for 48 hours, and then plugged mixture screw passage so carb cleaner and forced air had to blow through the unreachable passage. Put her back together and it's running better than ever. Now I realize how important and difficult it can be to thoroughly clean a carb that had been sitting full of gunk for 20 years. Went for a ride and got Big Bird up to 50mph. Was only able to reach 45 before. Some more fine tuning and I'll be able to hit the highway. Ha


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« Last Edit: Aug 15, 2018, 08:14:22 by thrillseeker »
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