Motor cutting out at high rpm

« **on:** May 08, 2016, 10:49:54 AM »

This weekend boat ran fine on Friday at AVI , but Saturday it was different story. Any thing past 4500 rpm it would sputter and cut out .
Checked fuel filter was clean
Jets in carb were clean
Fuel pressure good
Any input ?

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« **Reply #1 on:** May 08, 2016, 11:06:20 AM »

Wet ignition, failing ignition coil, sticking valve, bad wire, loose connection electrically, valve/rocker/pushrod problem.

How I would handle finding the problem with the limited information.

Compression check.

Spark plug analysis.

Fuel jar check (looking for water/debris).

Timing check.

Pull distributor cap and check for oil/water.

After that, it gets tougher.

« **Reply #2 on:** May 09, 2016, 05:53:05 AM »

Cool Gt I'll start there ..

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« **Reply #3 on:** May 09, 2016, 07:01:57 AM »

If it runs fine below 4500 rpm I would still think it's something to do with fuel. Especially since it was running fine the day before. I'm not discounting anything GT says, I would follow similar direction after going over the fuel system again. I've had fuel filters cause this that looked fine, replaced and problem went away.

« **Reply #4 on:** May 09, 2016, 09:00:19 AM »

What ignition box? Does it have a Rev limiter? What's it set at? They're common to fail or be off quite a bit of rpm.

« **Reply #5 on:** May 09, 2016, 10:23:55 AM »

Quote from: Onthenos on May 09, 2016, 09:00:19 AM

What ignition box? Does it have a Rev limiter? What's it set at? They're common to fail or be off quite a bit of rpm.

MSD box
Rev limiter set 6k

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« **Reply #6 on:** May 09, 2016, 10:38:48 AM »

Quote from: 69kona on May 09, 2016, 10:23:55 AM

MSD box
Rev limiter set 6k

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. I heard it Saturday morning not sounding so good. I know Dennis had a pill go bad before. Not sure you may have the dial type. If not pull the pill and it will clean up if that's the problem.

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« **Reply #7 on:** May 09, 2016, 11:37:35 AM »

Yuuuuuppp. I bet you a 12 pack that's the problem. If it's a dip switch aka dial type, max it out and see if it goes away. :-)

« **Reply #8 on:** May 09, 2016, 12:58:13 PM »

Quote from: jimpen on May 09, 2016, 10:38:48 AM

. I heard it Saturday morning not sounding so good. I know Dennis had a pill go bad before. Not sure you may have the dial type. If not pull the pill and it will clean up if that's the problem.

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Good idea 👍
I took carb apart everything looked ok

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« **Reply #9 on:** May 09, 2016, 03:06:07 PM »

If removing the pill doesn't fix it, it might be the box itself. I've had two go bad on me, with similar symptoms to what you describe: Engine miss-fired terribly above a certain RPM. Good luck.

« **Reply #10 on:** May 10, 2016, 12:56:27 PM »

Would av gas be a problem to run ? My buddy said he thinks it's my be the problem...

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« **Reply #11 on:** May 10, 2016, 01:48:12 PM »

Quote from: 69kona on May 10, 2016, 12:56:27 PM

Would av gas be a problem to run ? My buddy said he thinks it's my be the problem...

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That's possible too, really depends on where you got it. I get mine from the airport in Temecula and it works great, but I've used the AV gas from parker Oil in Parker and it ran like shit.

« **Reply #12 on:** May 10, 2016, 03:57:16 PM »

Quote from: 69kona on May 10, 2016, 12:56:27 PM

Would av gas be a problem to run ? My buddy said he thinks it's my be the problem...

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. If the AV gas is clean and know water it is fine to run. Have you checked your valves?

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« **Reply #13 on:** May 10, 2016, 08:33:25 PM »

Quote from: jimpen on May 10, 2016, 03:57:16 PM

. If the AV gas is clean and know water it is fine to run. Have you checked your valves?

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as a.
Nope not yet. That's my next step. I put my buddy's vacuum gauge on and it was normal. If it there was a big problem would it show on gauge?

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« **Reply #14 on:** May 11, 2016, 10:17:28 AM »

Depends on what the problem is.

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« **Reply #15 on:** May 11, 2016, 10:52:57 AM »

69kona, did you change the Rev limiter and put the boat back in the water and test it yet ??

« **Reply #16 on:** May 11, 2016, 11:15:36 AM »

Quote from: Onthenos on May 11, 2016, 10:52:57 AM

69kona, did you change the Rev limiter and put the boat back in the water and test it yet ??

Not yet.... Gonna finish up new motor just incase

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« **Reply #17 on:** May 11, 2016, 11:28:34 AM »

I'm betting that it will take care of the problem. It happens often.

« **Reply #18 on:** May 11, 2016, 12:31:18 PM »

Going on 6 years on this motor that's in the boat now freshened up 2 summers ago should be something easy to fix.
If not
New motor has
Bbc rods
ICON Forged Pistons 10.5 to 1
Oil mods
And still a ticking time bomb lol
But I'm a dye hard olds lover screwy

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« **Reply #19 on:** May 11, 2016, 01:35:20 PM »

i run the same AV fuel you do from the same airport... Not the issue. Speaking of which, did you add marvel to it? How much?

Im betting its ignition somewhere

« **Reply #20 on:** May 12, 2016, 04:16:25 PM »

Pulled MSD rev pill out made it run alittle better still lacking rpms
Pulled plugs and they look little lean
Did compression test and have 155 psi in 7 cylinders and one at 145

Why lean?

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« **Reply #21 on:** May 12, 2016, 04:18:35 PM »

Motor used to be on rich side !!!!!screwy

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« **Reply #22 on:** May 12, 2016, 04:31:55 PM »

Maybe a fuel line collapsing do you have a fuel pressure gage to check it at rpm

« **Reply #23 on:** May 12, 2016, 05:46:53 PM »

Did timing somehow change ?

« **Reply #24 on:** May 12, 2016, 08:44:06 PM »

I checked timing..... Frustrating! good compression , vacuum was steady
Went through carb was all good
The only thing I found was rev limiter pill was bad....but still only revs to 4500
Motor usually spins 5100

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