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4 wheeler backfire on start

I rebuilt the carburator on a 00 Yamaha 250cc Big Bear. When i start it it runs rough. When I give it some gas it sputters and then backfires. Not sure why this is happening. Any information would be of great help. Thanks

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  • 39 Answers

Incorrect air fuel mixture or a leak check for damage to the intake boot or airbox

i need to know more about how its running at low mid and high rpm to help you troubleshoot and you need to check for leaks especiely the intake boot if the intake boot is leaking that will need to be fixed before running the bike asumeing that is ok or fixed run the bike listen to it at idle standing is it surgeing with a good fast acceleration off the line with you siting on the quad ? or just realy rough ticking over with little guts off the line ?

midrange rideing how does it feel is there a bwarrr noise as u accelorate hard or does the engine roar up fast

is it reaching a good top end with good pulling power or poor pulling power

are the backfires constant or mainly whyle slowing down from high revs

if all are effected but there are no leaks then it may be float / fuel level that needs ajustment fuel level in ur float bowel effects all stages of rpm low mid and high

A rich problem gets worse as the engine heats up.



A lean problem gets better as the engine heats up.



hope this helps if u dont fix it your self first try and do them little rpm backfire tests for me itl tell me a lot

Posted on Dec 05, 2012

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Posted on Jan 02, 2017

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SOURCE: Won't Start

do you have compression? for a engine to run you need clean air,compression, good fuel(make sure the fuel has not been there 3 months or more as it will deteriate) and good spark as well as good exhaust as this will cause a back fire if the exhaust valves are not set right.

Posted on Apr 21, 2009

  • 126 Answers

SOURCE: Yamaha Grizzly 600 leaking gas

if the carb was really cleaned out, then i would suspect the float is not set properly (where #14 in the pic meets #19, assuming it is adjustable), the float (#14) has a hole in it and is no longer "floating" which turns off fuel to the bowl when it raises #19 (needle valve) or the needle valve is not connected properly to the float (common problem when reassembling a carb.

http://partsfinder.onlinemicrofiche.com/atlanticcycleandpower/Yamaha_OEM/YamahaATV.asp?Type=18&A=268&B=11&Action=O

one way to check is to remove the float bowl and with your finger, push the float up (it pivots) and turn on the petcock. if fuel still pours out the needle valve, then the needle valve may not be connected properly to the float or the needle valve is worn. if it doesn't pour out, then i would replace the float as it is no longer floating (one way to also tell is if you see fuel inside the float if its plastic) to turn off fuel or adjust the float tang (assuming the float is brass. if its plastic, then there is no adjustment). good luck.

Posted on Jan 30, 2009

  • 4 Answers

SOURCE: Misfire and backfire at low rpm, runs rough at low rpm

You did not say whether or not this was a carburater engine but from the sound of it one of your jets may be sticking, a good cleaning of the jets will most likely fix the problem, the likely cause is a small build up or piece of debris on the jet.

Posted on Jan 02, 2009

  • 72 Answers

SOURCE: spits sputters and backfires

carborator needs to be cleaned and the float needs to be reset

Posted on Aug 24, 2009

  • 1 Answer

SOURCE: have a 04 yamaha big bear 400. hard to start wont

I have an 01, and it started doing this. I don't remember the circumstances. It's just dirty in the carb I think.

1) Check for water in the gas.
2) Turn off the petcock and drain the carb. turn it back on.
3) Try it.
4) Start it with the choke on and put your hand over the air filter hole. Will cause some back flow.
5) Try again.

Worked for me. Might be dirtier on yours, or have mud in it or something.

Posted on Dec 02, 2009

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