When running, gas very slowly drips out of the small clear carb overflow tube on the very bottom of the carb. I have tried three different float bowls, including different float height adjustments. I've tested the float bowls to confirm they float properly and not damaged. I've even gone back to the original float bowl. I've tried different needles and seats as well....same outcome. The carb is a Mukuni BST40. Something is causing it to still leak gas. If you were to completely rule out the float height, needle/seat, and the float assembly altogether, what could be another cause of the float bowl overfilling with gas.....what am I overlooking? Could something in the diaphragm area, the jet needle, or needle jet be the culprit?

 

Either you got something wrong with your rebuilds or the problem is dirt in the tank. Dirt comes through and gets stuck between needle and seat. You clean it out, then some more comes through and gets stuck there. You start to think it wasn't dirt, but a fault, and fit new parts, makes no difference because same happens again as more dirt comes through. Did you buy genuine parts? I have the same problem with a couple of Honda 300s, haven't changed seats or floats but am beginning to wonder if the non genuine needles I fitted to both, are faulty.

 

Are you replacing the needle seat and o ring in photo#33 below some the o ring will bypass fuel and cause overflow issue or if you did replace seat o ring may double check and make sure it did not get torn while installing

 

Polaris ATV 2004 OEM Parts Diagram for CARBURETOR | partzilla.com

 

Also if you are or have not may try to buff the inside of the seat [where needle sits] sometime the brass gets dirty and make un even surface I use value lapping compound on q tip and install q tip in drill an buff BUT please makes sure you clean and wash compound out GOOD because its qritty and could cause engine damage and some people uses tooth paste also new seats sometime didnt get machine good and not even or smooth and the compound will buff it smooth and always turn fuel off and crank engine with fuel off and let engine run until engine quits from running out of fuel this will cause engine to surge a little bit and jam the needle into the seat and make it seal may have to repeat a couple of times and they can be headache sometimes if do the third time twist throttle a little [half throttle way] an cause engine to back fire an this should jam needle.

 

Hi merryman, thank you for your comment, much appreciated. If I had to choose between the two I would lean towards your first option, something went wrong with the rebuild. Not to suggest it's not dirt in the tank, it's just that I thoroughly cleaned/washed out the gas tank and replaced the fuel filter.

 

Hi papa hogg scoot, thanks so much for your comments, much appreciated. Yes, I replaced the needle and seat (with o-ring) 3 times now, same result. Not to suggest the o-ring is not the culprit. Perhaps I'm getting the wrong size o-ring each time. Also, I read over on the Polaris forum that the brass overflow inside the bowl has been known to split or crack, which would also cause gas to leak out. Have you ever heard of this happening?

 

Great idea on turning the fuel off so that the engine quits, will give that a try. After trying three different needles and seats with the same result, I’d be hesitant to think this is the cause, but I’m surely not against giving it a try.

 

Yes you can put chainsaw fuel line over the crack brass tube that will reseal that issue if it is you also can remove bowl a fill bowl with fuel and see if bowl in leaking to do away with that guess. yes I have had that issue on alot of different models also can you shake the float an see if fuel inside of it I just trying to give you so ideals also I have had a few carbs through the 40 years of repairing atv and motorcycle that had isses like this and I found pitting in the seat surface[carb body] right where the o ring mates