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Discussion Starter · #1 ·
Hey guys, I'm new here and I'm finally throwing up my hands and asking for some help. I fix these things and others for a living so I usually know what I'm doing but this one has me stumped. 96 QR 250 2wd, I rebuilt the carb, put on a new fuel pump and all the basics that go with that. It starts easily and runs great for a few seconds but then the carb floods. When I bench test it off of the bike it does great. No leak at the valve seat whatsoever and can withstand a good bit of pressure in the fuel line but as soon as I hook it up to the fuel pump it floods. I've changed float needles, adjusted the float many times and everything else I could think of, all to no avail. Anyone who's worked on these knows what a pain it is taking it off the bike and getting it back on and I've done it countless times now. I even bought a new knock off carb from ebay that was supposed to work great but it doesn't fit. You only have so much room in there and it was too wide from front to back. If anyone has dealt with this flooding issue I would greatly appreciate any advice. Also, if anyone knows the correct slide carb I could replace it with, I'm not against going that route.
 

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Hey guys, I'm new here and I'm finally throwing up my hands and asking for some help. I fix these things and others for a living so I usually know what I'm doing but this one has me stumped. 96 QR 250 2wd, I rebuilt the carb, put on a new fuel pump and all the basics that go with that. It starts easily and runs great for a few seconds but then the carb floods. When I bench test it off of the bike it does great. No leak at the valve seat whatsoever and can withstand a good bit of pressure in the fuel line but as soon as I hook it up to the fuel pump it floods. I've changed float needles, adjusted the float many times and everything else I could think of, all to no avail. Anyone who's worked on these knows what a pain it is taking it off the bike and getting it back on and I've done it countless times now. I even bought a new knock off carb from ebay that was supposed to work great but it doesn't fit. You only have so much room in there and it was too wide from front to back. If anyone has dealt with this flooding issue I would greatly appreciate any advice. Also, if anyone knows the correct slide carb I could replace it with, I'm not against going that route.
Welcome to the forum. I take it this is an OE carb you are using? I would advise against an aftermarket replacement. Those typically do not produce consistent positive results.

What fuel pressure are you testing with ? What pressure is the pump producing on the ATV?

Does that machine have a gravity feed option?
 

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So you are saying that fuel floods the carb bowl and comes out the vent over flow? You have to set flat height at the same angle that the carb is mounted on the bike. It's a pain in the ass i have done it a few times and it is frustrating.

You could try building something out of wood to hold it at the proper angle to set it not attached to the bike. Or just bend the flat tab a little bit and keep mounting it back ont he bike and hooking the gas line to it and see when it stops. But you really need to use a piece of clear fuel line and measure the height of fuel in the bowl to make sure it's not too low.
 

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Discussion Starter · #4 ·
Welcome to the forum. I take it this is an OE carb you are using? I would advise against an aftermarket replacement. Those typically do not produce consistent positive results.

What fuel pressure are you testing with ? What pressure is the pump producing on the ATV?

Does that machine have a gravity feed option?
Hi John, thanks for the reply. No gravity feed option on this one. Terrible design in my opinion. I don't know how much pressure the pump puts out but its not much. Just a steady pulse just like a lawnmower. When I do it on the bench I used a large syringe with a tube on it and there's no way the pump puts out more pressure than I did so I'm really stumped
 

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Discussion Starter · #5 ·
So you are saying that fuel floods the carb bowl and comes out the vent over flow? You have to set flat height at the same angle that the carb is mounted on the bike. It's a pain in the ass i have done it a few times and it is frustrating.

You could try building something out of wood to hold it at the proper angle to set it not attached to the bike. Or just bend the flat tab a little bit and keep mounting it back ont he bike and hooking the gas line to it and see when it stops. But you really need to use a piece of clear fuel line and measure the height of fuel in the bowl to make sure it's not too low.
It has yet to actually come out the overflow. It may be going into the motor. The angle is a little confusing because it doesn't mount straight up and down. Hard to tell exactly where the level should be
 

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Hey guys, I'm new here and I'm finally throwing up my hands and asking for some help. I fix these things and others for a living so I usually know what I'm doing but this one has me stumped. 96 QR 250 2wd, I rebuilt the carb, put on a new fuel pump and all the basics that go with that. It starts easily and runs great for a few seconds but then the carb floods. When I bench test it off of the bike it does great. No leak at the valve seat whatsoever and can withstand a good bit of pressure in the fuel line but as soon as I hook it up to the fuel pump it floods. I've changed float needles, adjusted the float many times and everything else I could think of, all to no avail. Anyone who's worked on these knows what a pain it is taking it off the bike and getting it back on and I've done it countless times now. I even bought a new knock off carb from ebay that was supposed to work great but it doesn't fit. You only have so much room in there and it was too wide from front to back. If anyone has dealt with this flooding issue I would greatly appreciate any advice. Also, if anyone knows the correct slide carb I could replace it with, I'm not against going that route.
Sounds like the new pump produces too much pressure for the needle to hold back.
 

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Maybe it's not the carb. If the gas isn't all getting used or makes it to the cylinder. And sits in the carburetor, could that be a possibility ?
If the timing was off n the intake value isn't opening enough, could there be a possibility. Have you checked the valve clearance n timing ?
Hole or cracks in the rubber boot between the carb n intake. Replace the o ring under the boot connecting to the carb n head?
Just spitballing here but it seems that the air fuel may be issue. Your positive the correct high speed jet is in the carb?
Thinking through, check the o ring between the head n carburetor boot. If it's suckling air, after it has started. When not running the gas flows correctly n it gets a little to start. Then can't produce the vacuum needed to get to the cylinder.
Good luck, just a machine
 
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