Why does my mercruiser 4.3 sputter and backfire after hot
After the engine has been running and it is hot, if I slow down and then give it gas again, the engine sputters and backfires. it does not quit. but I have to speed up slowly through the sputtering to get up to cruising speed.
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Re: why does my mercruiser 4.3 sputter and backfire after...
It sounds like a fuel vapor lock, check that the fuel line to the carb is not coming contact with any metal surfaces of the engine for this will boil the fuel in the line before it enters the carb. If this is the case, just stand the fuel line off from where it is touching. I hope this helps....GOD BLESS....Randy...
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Electric choke? Try retrofitting a manual choke. I think the electric choke is closing over a hot engine, thinking that the engine's cooler than it really is. A manual choke will allow you to start it with no choke at all when you know the motor's already warmed up.
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
Sounds like your carb needs the fuel/air mix adjusted..uses all the gas at high speed but has excess at low speeds...find your adjusting screw and at med throttle slowly screw it clockwise until the engine starts to sputter then back it out until it starts to sputter again then continue to do this until you reach ideal mix where it runs the best it can..then go slowly through the throttle up and down..when set..unjust your idle speed screw to your ideal idle speed..if this dies not fix ..carb will bed cleaned or rebuilt. Good luck.. Note always push or pull your throttle handle slowly to position avoids gas load up causing sputter and backfire.
I am not sure what you mean on the "running fast" statement. If idle speed then turn the idle screw outward to slow down the idle.
The backfire is caused by turning off the ignition key when the bike is at high revs. let it idle down THEN turn it off. The backfire is there because the carb idle circuit is active anytime the piston is in motion. Gas goes into the cylinder as the bike revs down then a hot spot in the exhaust pipe finally ignites the built up gas. There is your backfire.
Is the running fast question answered? Give me more information on the problem if it isn't.