1987 Rinker with OMC Cobra 4.3

[Trackertrucker]

Hey all, I bought a new to me boat a couple of weeks back from the original owner, it has been meticulously maintained by the local marina and I have all of the receipts for all the work ever done to it. Took it out on the water and it ran and drove great! Bought it and on the way home filled it with rec90 and mid week it started idling rough and stumbling around 1800Rpm, when I talked to the po he said he always ran 89 octane from the gas station. So wondering if the timing is off and needs to be set different for the Rec 90? Thanks in advance

 

[Swimforshore]

Increasing the octane that much will not cause an issue. higher octane resistes spark knock and will allow you to run more spark advance. You have something else causing your running issues that need fixed before adjusting timing. Possibly bad gas or maybe a little water in the gas. Do you use ethanol free gas? Otherwise I would look ignition still points ignitions? Moisture in distributor Cap?

 

[Trackertrucker]

Still has points,they were replaced in the fall along with cap,rotor,plugs and wires. Think I will check the fuel water seperater next weekend as I keep it at the lake and I'm not there this weekend

 

[Swimforshore]

A small amount of water in your gas tank will make the ethanol separate from the gas and could cause that or just plain bad gas. An ethanol fuel treatment will help everything stay mixed up. If I use regular pump gas I use an ethanol treatment

 

[Trackertrucker]

What ethenol treatment do you run? I've heard of one called like startron I think? I'd really like just run the Rec fuel bit now I'm scared of buying it since it may have water in it

 

[Swimforshore]

I was just at the lake today I have an 88 OMC cobra 4.3 says 90 octane or 87 if the timing is adjusted according to service manual. I usually run pump gas with marine formula stabil or BG ethanol treatment but I get the BG stuff as free samples when I can from work

 

[Trackertrucker]

Well my thought is I'll check water seperater when I get back north this weekend,pump fuel out and start over