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Post subject: Backfire question...
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KX3  Mmm, Fully Synthetic! Joined: 02 Oct 2006 Total posts: 1383 Location: Québec |
I started my F2 while the air was cold and very humid and the right plug
was about to die when the engine stopped. I restarted the engine and
since the plug wasn't completely fooled, a big explosion went out
the right exhaust (I saw a big flame at the end of the can...).
I'm wondering if a single (loud) backfire can be harmful for a little engine such as the RZ?
Or should I just put new plugs and restart it without bothering?
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Posted: Tue May 20, 2008 12:58 am
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jante350 RD/RZ Jedi Master Joined: 05 Aug 2003 Total posts: 5372 Location: Bergen, Norway |
It doesnt matter at all.. its just a weak explosion (compared to what goes on inside the engine) of unburnt fuel in your pipe. Worst case scenario is that the pipe splits open in a weld, but that very rarely happens.
Dump a new set of plugs in and give it a go! 
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Posted: Tue May 20, 2008 7:54 am
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Post subject: Re: Backfire question...
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| jmw |
| KX3 wrote: |
I started my F2 while the air was cold and very humid and the right plug
was about to die when the engine stopped. I restarted the engine and
since the plug wasn't completely fooled, a big explosion went out
the right exhaust (I saw a big flame at the end of the can...).
I'm wondering if a single (loud) backfire can be harmful for a little engine such as the RZ?
Or should I just put new plugs and restart it without bothering? |
What's happened is that the engine couldn't burn the charge that well due to engine temp and atmospherics etc.. so it dumped the unburnt vapour into the cold exhaust pipe as every 2 stroke would do.
The fuel condenses almost instantly and you get liquid fuel collecting.
At the first available opportunity - flame from the last coughing misfire leaving an exposed exhaust port, you get a back fire that from the ignited fuel in the pipe resulting in the flame and noise you observed.
Its quite beautiful at night to be honest.
This is one of the reasons why reed valves are about - they close the tract back to the carb on a negative pulse - with no reed valves that bang you heard could potentially blow back through the cylinder and crank case and out the carb - you can imgine the potential implications of that hoo haa....
Ever seen a car misfire and then go up in flames - old Weber down draught carbs spit back from this sort of thing and if there's no flame trap or air filter case in place, you can get big problems.
Clean the plugs, turn it over a few times by hand incase it was something more sinister like a piston crown letting go and if all sounds well - run it up.
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Posted: Tue May 20, 2008 8:57 am
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