Power loss

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Jacobswahn
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Power loss

Postby Jacobswahn » Wed Aug 08, 2018 1:33 pm

I run an 0-540 on my boat, lately I have had a problem with it cutting out. I have changed plugs and wires fuel hoses and cleaned carb. It runs great at idle and I had no problem for about twenty thirty min run time stopping in between for a little while. But after that it just starts cutting out like it's missing . My mags both drop rpm the same when I shut them off any ideas would be great thank you.

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keebo
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Re: Power loss

Postby keebo » Wed Aug 08, 2018 1:55 pm

Could be condenser going bad
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GMAC 76
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Re: Power loss

Postby GMAC 76 » Wed Aug 08, 2018 6:40 pm

what rpm are you checking the mag drop......might have a coil going south ...the longer it runs the hotter it gets the worse it sparks...let it cool its ok till it gets hot again

Jacobswahn
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Re: Power loss

Postby Jacobswahn » Thu Aug 09, 2018 11:30 am

That's pretty much is what's happening. I usually check the mags at 17 or 18 they both drop about two two and a half at that rpm.

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John Fenner
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Re: Power loss

Postby John Fenner » Thu Aug 09, 2018 12:04 pm

If both mags are still dropping the same rpm when it is acting up then I doubt it is coils, most likely point gap is too tight, not breaking open at E-gap and once hot capacitor is not getting saturated.

Also, what fuel are you running? If you are running 100ll then disregard next statement.

If you are running 93 car gas then you need to back timing down to 20-22° as it is detonating, also if it has 10:1 pistons and with 100ll you need to run same degree.
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Jacobswahn
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Re: Power loss

Postby Jacobswahn » Fri Aug 10, 2018 10:18 am

Been running 91 or 93 but I always add some octane boost to it . I'm not sure what Pistons I'm running. I will pass all this on to my mechanic thank you all for your ideas. Very helpful will post when I find something out. Thanks again.

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John Fenner
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Re: Power loss

Postby John Fenner » Fri Aug 10, 2018 11:01 am

Put some av gas in it and see if it still does it.
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Re: Power loss

Postby GMAC 76 » Fri Aug 10, 2018 11:11 am

250RPM is a big mag drop....sounds like its time for a little tlc

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Slidin Gator
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Re: Power loss

Postby Slidin Gator » Fri Aug 10, 2018 10:13 pm

John Fenner wrote:Put some av gas in it and see if it still does it.

GMAC 76 wrote:250RPM is a big mag drop....sounds like its time for a little tlc


X2 on both of these posts, it is the middle of a hot summer where detonation and mag issues show up. Per the O-540 manual, RPM drop should not be more than 175 RPM on either mag, and the difference between drops should not be more than 50 RPM. It is also (a more remote possibility) that the mixture is too lean.

Start with the Fuel, 5 gallons of AV gas is an easy check, just to understand if detonation is at least part of the problem to guide the rest of the decisions. Then its time for mag rebuilds and re-timing the mags. Pick 25 deg advance for 100 LL and retard (as in it's retarded to do) to 20-22 for 93 pump gas with lead substitute. Don't cheap out on the 91!

Do a compression test if you don't know the pistons and post the results.
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Jacobswahn
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Re: Power loss

Postby Jacobswahn » Sat Aug 11, 2018 9:12 pm

It may be a big drop for the mags however I have owned this boat and motor for 26 years it has always dropped the same . Maybe your right I will check the other things you guys suggested and post back with results thank you guys

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Slidin Gator
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Re: Power loss

Postby Slidin Gator » Sat Aug 11, 2018 10:57 pm

After I posted, I went back and re-read the thread and caught this:
Jacobswahn wrote:That's pretty much is what's happening. I usually check the mags at 17 or 18 they both drop about two two and a half at that rpm.

The spec for the 175 RPM mag drop is at 2100-2200 rpm vs the 17-18 mentioned.
Image

250 rpm drop at 17-18 means even more drop at 22. Both mags didn't go out at the same time, you may have been running a bad mag for some time. These motors are made to keep running and they will run reasonably smooth on one mag, just not as much power if your not dialed in to what is going on. Now summer comes, it get's hot and mag #2 starts to act up, then it runs like crap.

That, or you got extra crappy fuel, either way it is time for a tune up, sounds like it has needed one for a while.
I grew up thinking that I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540. A Bob Stossel original, still running strong.


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