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Thread: Carb overflowing ?

  1. #1
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    Carb overflowing ?

    I have a 94 yz125 , with bunch of work done its a 151 know per the builder . Problem i have is the carb is overflowing mainly when its reved up ! At idle it doesnt seem to overflow. Carb is clean and it has a new needle . Float has been set and adjusted .

  2. #2
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    I have a 1/4 nipple in side of intake by reed cage . I have seen a high dollar pump around modification for carb overflow issues i dont plan to buy it though ! Im wondering if u all may have some pointers to help me fix . Its me n my sons first uas build

  3. #3
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    Im not sure if its a lot of vacuum suckin fuel pased needle and float , or just the carb . But been playin with carb a while know and kinda think its to much vacuum causing fuel overflowing but i dont know for sure

  4. #4
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    Runnin a fuel pump? If so you need to run a tee and return to the tank or have your carb modded so you can run a pump and not overflow the carb....

  5. #5
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    Yes i have a walbro square fuel pump

  6. #6
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    Man thank you for the info ! I will give it a try

  7. #7
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    Send it to pro kart i had the same problem . it had no tee in it.

  8. #8
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    You can't just run a tee. You have to have a restriction in the return line so that it still prefers to send fuel to the carb. A clone jet works if you take your time to get it the right size. We used a shut off valve on one of ours. Just gotta make sure it's closed when it's go time. But these were both idle /low speed condition. In your case, if you are revving it on the stand, it may not be loading the engine enough to make good vacuum to pull the fuel that the pump is pushing. I would try adjusting the float a bit. The pump is forcing fuel in and the floats being set for gravity will allow too much fuel as well. So if you lower that a bit, it may increase pressure on your inlet needle and stop the over flow issue but you won't starve the carb because the pump is pushing the fuel unlike gravity in the bike.

  9. #9
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    I never had issues without restriction with the 125. I have added a needle valve inline for the 250 Jimmy. Thinking about going a different direction with carburatation so will end up not being needed.

  10. #10
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    I tried the t today however ughh !! Before i tried to start n see if it work i checked float and found it had broken , just above the needle so i need. New float ! I also found a tear in the intake boot from carb to reed cage . So i have a few things to get before i can see if t or a clone jet or shut off works . The float and intake boot was good before we went to practice it though . Lots still to figure out . But im getting great ideas from u all .

  11. #11
    Honda part#18381-ZH8-800, Its an inline bypass valve. The pump will over pressure your carb, this little gadget will fix your problem.

  12. #12
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    We have had very good luck with the Mikuni SBN 38mm carbs on both the yz125, and the Yz250f...
    You can pick them up for a good price from older SLT 750 jet skies...

    As a option...

  13. #13
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    Quote Originally Posted by scottargo331 View Post
    Honda part#18381-ZH8-800, Its an inline bypass valve. The pump will over pressure your carb, this little gadget will fix your problem.
    A Honda muffler gasket won't be much help here....

  14. #14
    Well let me double check my parts list, the part I'm referring to is a bypass valve that was used on 1980s Honda Odysseys.

  15. #15
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    The T without a restrictor should work fine, provided you place the tee return at a high point so gravity always favours the carb. I had a restrictor in mine but it still pushed past the seat at idle, so I kept enlarging the restrictor untill I threw it away.

  16. #16
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    All Great info guys , thanks ur saving me a lot of time and headaches ��

  17. #17
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    Did the odysseys bypass valve require voltage ? I use a electric start . No battery is on kart

  18. #18
    Try this part## 16710-VMO-770 just found it on Bikebandit parts, it wont pull it up if you just search part#. Check the parts list for 1980 Odyessy its listed as a 3way fuel valve #2 on diagram. It does not require elec....

  19. #19
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    Quote Originally Posted by scottargo331 View Post
    Try this part## 16710-VMO-770 just found it on Bikebandit parts, it wont pull it up if you just search part#. Check the parts list for 1980 Odyessy its listed as a 3way fuel valve #2 on diagram. It does not require elec....
    Thats awsome thanks i like that ill order one ! Need some carb parts anyway !

  20. #20
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    You need the right needle and seat. Bike carbs are set up for Gravity feed fuel not pumped so you use different seat size . No need for all that jacked up bypass stuff just do it right

  21. #21
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    Quote Originally Posted by Sjg22 View Post
    You need the right needle and seat. Bike carbs are set up for Gravity feed fuel not pumped so you use different seat size . No need for all that jacked up bypass stuff just do it right
    I already ordered a 3way valve like suggested of a honda pilot 15.00 . Where would i buy the seat u speak of ? Or are u talkin about modding the seat i have to restrict fuel ?

  22. #22
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    You didn't mention what type of carb it is but you should be able to get them from the carb manuf. Snowmobiles and watercraft use float type carbs with a pump just like yours. Be it a Keihn or whatever you will be able to get the needle and seat you need.

  23. #23
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    If you tank has more than one fitting make one feed with fuel valve . Make second one with also a fuel valve . Then you won't have too have a restrictor, in return line. You can restricted fuel pressure by closing valve << Or lower it by opening it .

  24. #24
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    I like to keep things simple. I use a return line with a restriction devise. I use a small aluminum insert I made in a lathe with a .080-.125 hole. I also use the larger round Mikuni pump with two outlets. I just send one back to the tank. No T in the line anywhere. Has worked great for a few years now. Lots of options here. Pick the way you want to go and Good luck. -50

  25. #25
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    What Phiddy said - the larger round Mikuni fuel pump has a pulse line, a inlet line, and two outlets, one to the carb and one for a return to the fuel tank, simple and reliable.

  26. #26
    Sjg 22 answered earlier. Search for a smaller needle and seat. They are offered in many sizes. They nearly always have the size listed on them. The bike sizes are large due to gravity feed. When similar carbs are used on sleds the inlet needles are reduced due to the pumps over powering the needle and seat. Less lines creates less opportunities for leaks. JMO.

  27. #27
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    Well I definitely asked in the right place thanks ! Prob be a few weeks before we run it . Gonna go practice on sat night first for a test n tune ill update after ! I appreciate all the info a lot thanks fellas

  28. #28
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    Quote Originally Posted by Riggy View Post
    I already ordered a 3way valve like suggested of a honda pilot 15.00 . Where would i buy the seat u speak of ? Or are u talkin about modding the seat i have to restrict fuel ?
    what carb???

  29. #29
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    Use the proper needle/seat. The fuel pump is pushing fuel past the needle that is currently set up for gravity feed

  30. #30
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    Quote Originally Posted by daveydogg View Post
    Use the proper needle/seat. The fuel pump is pushing fuel past the needle that is currently set up for gravity feed
    if his carb is overflowing, wouldnt that mean the seat isnt big enough to take all the fuel it is trying to feed it?

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