Merc 350 bolt v 2 barrel carb fluctuating RPMS

wryork25 said:

Update: spark appears to be consistent to all cylinders. It is hard to tell but I am seeing the same hesitation on all cylinders with the light. I am in the process of going through all the wiring again to make sure I do not have a bad ground or connection. After that I am at a loss. I am not really sure how to check an ICM for something like this. I have gone through he troubleshooting chart but it does not really fit this scenario. I really don't want to replace the module until I am sure, and if I do replace it should I try and find a thunderbolt V or just replace the whole ignition system with a delco EST? I am canvasing people I know in the boating community to see if I can find a module to swap out for testing but no luck so far. Any thoughts or advice would be greatly appreciated.

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Scott06 said:

Easiest plug and play is to find a used module and try it. Delco est is also a very good / oem quality system but you will have to do some minor rewiring.

have you verified there is no play in the distributor shaft and rotor? And when you say timing is even it is no longer jumping around ?
check for vacuum leaks around the manifold to head and carb to manifold spray starter fluid if it picks up rpm mean there is a leak

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nola mike said:

Also a tb4 module should work fine.

Edit: rereading this, did you replace the ignition sensor before or after you started having problems?

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