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Discussion Starter · #1 ·
Hello, first time post longtime lurker, Have new to me 250 tundra that is very boggy on low end and low idle speed. gets worse as it warms up, i replaced fuel, fuel lines and cleaned carb, everything looked good and in specs. ran it and same problem. Low end boggy and would run out good when you worked the throttle over half. You have to work the throttle to get it up to clutch engagement speed. Removed and went threw carburetor again and replaced pilot and main jet.retried and no change.have good spark and new plug and ran on a stand with loose track. No change. Stumped. on a hunch i removed the muffler and ran engine. idles at 1500 rpm and throttle response was snappy and immediately responsive/ put pipe back on and idle drops back to 900 and boggy comes back, So i think i have it figured out. When i examine muffler and blow air threw it doesn't appear to be obstructed. Not sure how to inspect inside? I'm past the age where loud pipes are cool and want quiet sled. What should i do next???
 

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By what you're saying the pipe is probably good if it is not blocked. You may check in the air filter as well especially if that sled sat for a few years. About the carb, did you test the inlet valve? Check in the gaz tank if the fuel line is still there in good condition with the filter at the end. And finally check the fuel pump if there is some dirt inside ,check the pulse line. Also check on the oil injection line to prevent cracks and leaks if the pump is still in place.
 

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Discussion Starter · #3 ·
I removed fuel tank and replaced inlet line and cleaned check valve. i will have to double check the check ball operation. I did my testing with air box disconnected. I dint check impulse lines and will replace tonight.

When i removed the exhaust it seemed to have plenty power and quick throttle response and when i reinstall it lays an egg. I am going to attempt steam washing out muffler today and see if that helps. Does anyone have picture of inside of old sled muffler?
 

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Sounds like a rich condition. With your airbox off and the front end up, blow in the tank to pressurize the fuel system. If gas flows out of the carb, replace your needle and seat. That's what the whole issue sounds like to me.

A bad needle and seat would cause too much fuel to flow into the carb and flood you out at low rpms. When you get the sled screaming, it will likely sound fine because the increase in fuel is now in demand.

Removing the pipe will allow the excess gas to flow through the motor due to a lack of back pressure from the exhaust which is required to hold the fuel in the engine.

If your plugs are wet after stalling out from the bog this is another indicator of a rich condition.

Did you have the needle out when cleaning the carb? The tip should not have much noticeable wear on it.

We're the floats empty when you took them out? If they are full of gas they will sink and not be able to close the needle.

Is your brass float arm properly installed? With the carb upside down and the bowl off, it should sit roughly level with the carb body. Your float arm spec is from 22-24 mm measured from the float arm to the carb body. The float arm will have a small wear mark where it contacts the needle. Ensure that the arm was not reinstalled upside down.

Have you checked your compression? Those 253s ran low to begin with. I haven't rebuilt one in a couple years but 110 seems to ring a bell. If it's any lower than 100 I would investigate the top end.

Your issue doesn't sound like a crank seal. Usually when they leak, you have power on bottom and bog on top. Hope this helps. Happy wrenching
 

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Discussion Starter · #5 ·
I did the suggested testing and the needle and seat were leaking and giving a full float bowl. I ordered and installed a complete carb kit with new jets and needles no more bog. When replacing the needle jet i did find an improvised C clip (small strand of wire) that wasn't holding needle in correct groove. Thanks for the help guys
 
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