Backfired .....
01-02-2005, 09:43 AM
#22
Re: Backfired .....
Originally Posted by Formula Outlaw
Mike, you've probably got Rochester Quadrajets for carbs. Check a couple of plugs that are reasonably easy to get to and check to see if they are running lean. I'm guessing it's somewhere in the ignition system.
I tend to agree with the coil going bad idea. It might be just starting to break down a bit as it gets hot.
Except for wet sanding on the transom, got Outlaw finished up this afternoon. Gonna crank the motors over tomorrow on the hose and double check everything then try to drop it in at the local ramp for a little test run.
I tend to agree with the coil going bad idea. It might be just starting to break down a bit as it gets hot.
Except for wet sanding on the transom, got Outlaw finished up this afternoon. Gonna crank the motors over tomorrow on the hose and double check everything then try to drop it in at the local ramp for a little test run.
01-02-2005, 10:14 AM
#23
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Platinum Member
Re: Backfired .....
fuel starvation can cause a lean backfire at WOT.
bad coil will usually not result in a backfire, but more of a simple miss that gets worse with additional heat.
bad plug wires will result in a miss, and sometimes a midrange backfire, but not a wot backfire.
rotor and cap can cause just about any sort of pop, miss, or backfire.
weak or broken valve spring can result in WOT backfire.
that's a short list.
bad coil will usually not result in a backfire, but more of a simple miss that gets worse with additional heat.
bad plug wires will result in a miss, and sometimes a midrange backfire, but not a wot backfire.
rotor and cap can cause just about any sort of pop, miss, or backfire.
weak or broken valve spring can result in WOT backfire.
that's a short list.
01-02-2005, 12:02 PM
#24
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Re: Backfired .....
Don't forget to check the connections on the distributer module if you have the Merc thundervolt ignition. I had a backfire problem with one of my engines after a rebuild and the cause was a loose connection on one of the module post.
Good Luck!!!!!!
Good Luck!!!!!!
01-02-2005, 12:07 PM
#25
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Re: Backfired .....
Make sure the distributor is tight and didnt move. Check the ignition timing. Also check the timing advance at wot. You will need timing tape on the harmonic balancer or a timing light capable of reading advance. I once had a dist. a little loose and it turned just enough to lower the advance enough that it started poping at 4000 too.
01-04-2005, 05:17 PM
#26
Re: Backfired .....
Took the boat out today for some test runs ...Put Teressa in with the motors and made a few WOT runs .... Port motor ....it is thru the carb ...you have to be at 4900-5000 for a cpl of mins and pop ..... So i guess start swapping stuff out ... gona do Filters ,Cap and rotor ....see what happens ...This is sorta good news as this is the older of the 2 motors ..< 50hrs ... Starboard has about 10 or so ... There is another isssue with this motor ....burns or sumthin about 1/2 quart an hour ....it was full when we started and now shows about 2 quarts low ...we put between 4-5 hours ...This same motor got water in it this past summer and we pulled it ..had heads checked and valves done ...has new gil manifolds with Stainless marine pipes .... there are no leaks that I know of ..
01-04-2005, 05:26 PM
#27
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Re: Backfired .....
Mike:
What color are the spark plugs after the run?
If the center porcelain is beige or brown that's good. If they're white the popping is from a leaning-out. Compare the plugs to the other engine too. Should look similar.
Ed
What color are the spark plugs after the run?
If the center porcelain is beige or brown that's good. If they're white the popping is from a leaning-out. Compare the plugs to the other engine too. Should look similar.
Ed
01-04-2005, 05:46 PM
#29
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Re: Backfired .....
Call me stubborn but I still think it is leaning out. See how the plugs look now after the idling. If it started popping immediately at 4900 then that's one thing, but it took some time, as you described, before it started to happen. This tells me that it's either heat related to an electrical component or the demand is exceeding the supply of fuel. Keep me posted; I love this stuff.
Ed
Ed
01-04-2005, 05:49 PM
#30
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Re: Backfired .....
Originally Posted by offthefront
Took the boat out today for some test runs ...Put Teressa in with the motors and made a few WOT runs .... Port motor ....it is thru the carb ...you have to be at 4900-5000 for a cpl of mins and pop ..... So i guess start swapping stuff out ... gona do Filters ,Cap and rotor ....see what happens ...This is sorta good news as this is the older of the 2 motors ..< 50hrs ... Starboard has about 10 or so ... There is another isssue with this motor ....burns or sumthin about 1/2 quart an hour ....it was full when we started and now shows about 2 quarts low ...we put between 4-5 hours ...This same motor got water in it this past summer and we pulled it ..had heads checked and valves done ...has new gil manifolds with Stainless marine pipes .... there are no leaks that I know of ..
