520 runs rough after back fire. Lets take bets on what broke

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rowdy1
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520 runs rough after back fire. Lets take bets on what broke

Post by rowdy1 » Fri Dec 09, 2016 9:37 pm

I took the airboat out today for a little fishing at Cedar Key. very little water, even at high tide. I did slay the redfish, found a hole and parked, caught over 50 reds. On the last move of the day, I tried to start the motor and it back fired, its never done that before. It did eventually start but its running rough. Oil pressure is good, oil temp is good. The motor sounds "hollow". Any guesses? valve seat, bent pushrod. It is a fresh rebuild, less than 10 hours. Come on boys, place your bets and tell me whats wrong with it.

barhopper
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by barhopper » Fri Dec 09, 2016 9:42 pm

I don't know what your motor problem is but I'd like to know what time you were fishing.

rowdy1
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by rowdy1 » Fri Dec 09, 2016 9:54 pm

The bite started about 2:30pm, I sat in 1 spot and killed them. lots of 12 - 17 inchers, 5 or more in the 20 - 27 range. One monster, 30'' long and had shoulders about 6'' wide. Two of us caught a fish nearly ever cast for 2 hours. dead low tide was about 4:30. Best day in a long time until the motor started acting up. Come by the house and pick me up, Ill take you right to them!

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jopete
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by jopete » Sat Dec 10, 2016 8:29 am

maybe running on one mag?

helicsher
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by helicsher » Sat Dec 10, 2016 9:39 am

One of your intake hoses just barely popped off ?

$$$
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John Fenner
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by John Fenner » Sat Dec 10, 2016 9:39 am

Broken valve spring.
I never finish anyth,,,.

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John Fenner
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by John Fenner » Sat Dec 10, 2016 9:40 am

helicsher wrote:One of your intake hoses just barely popped off ?

$$$
Good call.
I never finish anyth,,,.

GMAC 76
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by GMAC 76 » Sat Dec 10, 2016 10:00 am

might have broke and impulse coupling spring?

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John Fenner
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by John Fenner » Sat Dec 10, 2016 10:08 am

GMAC 76 wrote:might have broke and impulse coupling spring?
Thing is, he never mentioned anything about mag drop, I would've gone for this or cracked distributor block.
I never finish anyth,,,.

rowdy1
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by rowdy1 » Sat Dec 10, 2016 10:37 am

Ding, Ding, Ding, we have a winner! Broken spring on the impulse mag. I took it to my engine builder this morning. He tried to start it, listen to what it was doing and made the call.

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Re: 520 runs rough after back fire. Lets take bets on what b

Post by gpu rick » Sun Dec 11, 2016 1:00 am

I my guess would be carbon tracking on your terminal block in one of your magneto's.

GMAC 76
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by GMAC 76 » Sun Dec 11, 2016 10:47 am

the "back fire" and then rough running gave it away.....happens a lot especially when ya try to start on both mags

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Re: 520 runs rough after back fire. Lets take bets on what b

Post by flcracker9 » Sun Dec 11, 2016 4:13 pm

Greg (GMAC 76) just rebuilt my mags a couple months ago, now I start the motor on the impulse mag only, and hit the other mag once she cranks
12' Open Palm Beach, IO-0470-L 260hp, 72" NGQ

rowdy1
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Re: 520 runs rough after back fire. Lets take bets on what b

Post by rowdy1 » Tue Dec 13, 2016 8:55 pm

Back up and running!

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