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502 carb gen1V eating pistons question

Old 08-22-2017, 09:08 AM
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Default 502 carb gen1V eating pistons question

I bought a boat with 1 rebuilt motor in it. Shortly after running it. I had 3 pistons with holes in them. Assuming someone didnt set timing correctly. I had motor rebuilt. Since the the motor has been out 3 times with bad pistons. What gives. I have timing set at 8degrees. Seems to run great. The longest it has run is 4 hours. Since rebuild. Anyone else run into this. Im guessing ignition module?
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Old 08-22-2017, 09:36 AM
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when you say eating pistons do you mean detonation that caused holes in the pistons?can you give more information like what exhaust system and any thing that is not stock in the engines.also,have you checked to see what the total ignition timing is set at?have you put a fuel pressure gauge on it to monitor you,r wot fuel pressure?

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Old 08-22-2017, 09:47 AM
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Motor is stock. Looks like from detonation. I have not run fuel pressure test or total ign timing yet.. As soon as i get it back togather. I just wondered if the ign module cauld cause this
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Old 08-23-2017, 08:35 AM
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could be leaning out from fuel side just as well...
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Old 08-23-2017, 08:39 AM
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Carb ? EFI ? What hp rating ?

If carb, you don't by chance and mistakenly (seen many do this) have the mechanical fuel pump vent hose hooked up to a vacuum source do you ?

Edit in:
If carb, which one ?

Has it been the same exact cyl's that get holed each time ?

What spark plugs are you using ? MR43T's ?

Last edited by SB; 08-23-2017 at 08:43 AM.
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Old 08-23-2017, 08:52 AM
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Im running those plugs. I was just talking to engine builder. He says inside pistons on 1 side and outside on other. So it looks like carb problem. Dual plane intake
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Old 08-23-2017, 09:21 AM
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What is the intake ? sounds like a fuel distribution issue
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Old 08-23-2017, 09:24 AM
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Originally Posted by 1badchopper
Im running those plugs. I was just talking to engine builder. He says inside pistons on 1 side and outside on other. So it looks like carb problem. Dual plane intake
Yup !
Pic shows this.
Still make sure fuel psi is good at WOT.


Last edited by SB; 08-23-2017 at 09:28 AM.
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Old 08-23-2017, 10:12 AM
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Originally Posted by 1badchopper
Im running those plugs. I was just talking to engine builder. He says inside pistons on 1 side and outside on other. So it looks like carb problem. Dual plane intake
inside on one, outside on other bank? Like 1-7-4-6 or 2-8-3-5? Bad carb. Primary (front) venturi too lean on 1 side. Other side runs good, and provides enough power to let the bad side roast the pistons. Run a single plane intake and roast all the pistons slower but evenly. Or replace, repair the carb.
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Old 08-23-2017, 10:19 AM
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Yup eating 1-7-4-6 Looks like carb time. Thanks for the help guys
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