can somebody point me to an st90 carburator?

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Drew_P

New Member
I've fought my little st90 for a while, and I've solved most issues, EXCEPT, I'm really struggling with the carburetor. the more I work on it, the worse it gets. I can't hardly get it to start now, and it's leaking gas. I'd love to just buy a cheap carb off the internet and solve all my problems (if it works that way)

I've read the dr_atv page about the carburetor, and I'm confused about what he's talking about. http://dratv.com/atc70st90carb.html
can I just bolt something like this on and be good to go? https://www.ebay.com/itm/Carburetor...623695?hash=item364b9a174f:g:hQsAAOSwOFFeIoJj it says it just bolts on ready to ride, but it's the internet, so I take everything with salt.
 
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b52bombardier1

Well-Known Member
I'd probably try either carb but I've found that my bikes run better with a 72 main jet and a 38 idle. The Ebay bike carb does not list jet sizes that I could find so you get what you get. For that price, it would be worth a try.

They both appear to be the required front-to-back length to allow the re-use of the stock ST90 air cleaner. So many of the previously listed EBay ST90 carbs required a spacer between the intake manifold and the manifold flange to reach the stock ST90 air cleaner.

And both of these show the choke knob on the correct riders left side. Many others previously had it on the right - burned fingers time against the exhaust system.

Rick
 
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Drew_P

New Member
I received the ebay carb above today. It installed perfectly on my st90, and fired up on the 2nd crank. I had to increase the idle speed using the adjustment screw up to keep it running, but 20 seconds with a screwdriver and I was in business. It's raining today, so I haven't been able to drive it more than the length of the driveway, but so far, so good.
 
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Drew_P

New Member
well, after successfully starting the bike with the new carb I let it sit the weekend while I was out of town. Now I absolutely cannot get it to start. of course, I couldn't get it to start before the new carb either.

I have spark. I have 6V at the battery. I've removed the air filter. I de-rusted the inside of the tank as best I could and put on new fuel lines. It's frustrating.
 
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Drew_P

New Member
I don't know the definition of good flow, but fuel certainly drains out. not in a dribble. I also put in a new battery today. Just a little 6V deer feeder battery from tractor supply, but that was what was in it before. Anyway, it tried to start once on the 3rd kick, but then nothing.
 
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Drew_P

New Member
maybe I can just clean this one? it's got about an hour on it. I replaced it late last year. I couldn't even get it to start by taking the air box off and spraying starter fluid down into the carb.
 
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Drew_P

New Member
ok, starter fluid directly in the spark plug hole fired the bike right up! I drove it around for 5-10 minutes, and it ran great. other than having to set the idle higher than it should be to keep it from dying at rest, and occasionally i'd have to rev it just a bit to keep it alive. I turned it off for a minute and it started right back up again. So, what do you think is happening?
 
OLD CT

OLD CT

Well-Known Member
Sounds like a air/vacuum leak at the head to intake or intake to carb. Spray some of that starter fluid, if that is all you have ''carefully'' around the intake to head, intake to carb, when the bike first starts COLD to listen for a change/INCREASE in the idle. Do this when the engine is COLD away from the exhaust head pipe or sparkplug! I prefer brakekleen or carb spray, wd40...

So you don't start a fire! No change means no leak... You really should have a in line fuel filter if you have a metal gas tank. You may have sh*t in the tank also!
 
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b52bombardier1

Well-Known Member
What is your engine running DC and AC volts measured at the battery with a good multimeter? Try this at idle, half throttle and with the headlight and tail light on.

Rick
 
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Drew_P

New Member
I'll give the leak test a whirl later this week. I also have brake cleaner, wd40, all kinds of stuff.

How/where are y'all installing the inline filter? I tried one, but the fuel line was so long to get it to fit that the filter wound up flopping and dangling. a picture would be amazing.

I'll test the battery too.
 
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Steve R

New Member
Drew_P said:
I've fought my little st90 for a while, and I've solved most issues, EXCEPT, I'm really struggling with the carburetor. the more I work on it, the worse it gets. I can't hardly get it to start now, and it's leaking gas. I'd love to just buy a cheap carb off the internet and solve all my problems (if it works that way)

I've read the dr_atv page about the carburetor, and I'm confused about what he's talking about. http://dratv.com/atc70st90carb.html
can I just bolt something like this on and be good to go? https://www.ebay.com/itm/Carburetor...623695?hash=item364b9a174f:g:hQsAAOSwOFFeIoJj it says it just bolts on ready to ride, but it's the internet, so I take everything with salt.
Click to expand...
I ordered carburetors for both my 1970 CT90 and my 1982 C70 from Dr ATV. Except for the fuel outlet selector being on the other side for the C70, they were exactly the same as the Honda parts they replaced. I was very impressed with the quality as well. I ordered one-size-up and two-sizes-up jets for both when I ordered the carburetors. I opted for one-size-up on each because this miserable stuff that passes for gasoline in California is nothing like the vintage gasoline that the stock jetting was designed around. Both carburetors have worked flawlessly since installation, and I'm very happy with the purchase, and I thought the cost was very reasonable.
 
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Drew_P

New Member
well I took the cab apart and cleaned it. It looked clean, but at least it started when I tried it again. Runs like garbage though. it kept lurching across the parking lot. like it's not getting enough gas or something. I wish one of my brothers in law was something useful like a small engine mechanic rather than a useless job like a salesman or something.
 
Tripod

Tripod

Well-Known Member
Kinda late to this thread. Make sure you have a good 6v on your battey. My CL70 would fire and idle, then barely be able to get out of first gear. I think the battery had 3.2v. New battery and it ran great!
 
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Drew_P

New Member
zombie thread: found a local guy who looked it over. He found a wire that had kinked, been exposed, and was shorting out of the frame. it's working again!!
 
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