1998 digital ignition 5.7 carbureted taking flat when at 165F

[tomconnolly]

My 1998 chaparral 240 runs great until it reaches about 165F on the temperature gauge. Then when I hit wot it runs at about 4000 rpm and then bogs down then tries to pick up again and bogs until it drops to 2000 rpm. If I idle then start over it did same thing. Runs great until it reaches this 165F opposing temperature. Seems like a digital spark issue to me since it only happens when the motor is hot. Please advise diagnosis steps. Just bought the boat and I'm not familiar with the details of these motors but pretty mechanically inclined and able to diagnose with help.

New plugs and compression is all good. Full tank of fuel could be older fuel. I smelled fuel rich exhaust fumes when this occurred.

 

[alldodge]

Need a serial number?

I smelled fuel rich exhaust fumes when this occurred.

Might just need a carb rebuild

What do the plugs look like?

 

[tomconnolly]

Need a serial number?



Might just need a carb rebuild

What do the plugs look like?

Have not pulled plugs. I expect they will look normal since it runs fine most of the time. I put new plugs in today. Don't have serial number yet. I'll work on that tomorrow. Thx

 

[tomconnolly]

Need a serial number?



Might just need a carb rebuild

What do the plugs look like?

Engine serial number photo attached

 

[tomconnolly]

Photos of old plugs attached

 

[alldodge]

0L058689 comes back as TBI so no carb
Yes, your running rich

The ECM controls fuel flow by info from the MAP and TPS. Need to start by checking fuel pressure. There is a plug (item 3) that can be removed to attach a gauge
https://www.mercruiserparts.com/bam/subassembly/31844/2704/110

 

[tomconnolly]

I cleaned to crusty distributor terminals and cap in case spark was intermittent and put fuel additive in the tank because the fuel was evidently a year old over winter. It ran flawlessly all day today. I'll get a cap and rotor on order today.
Where does everyone recommend ordering mercruiser parts online? I also need an oil change kit. Is it best/ok to just buy quicksilver oil and crossover wix or other good brand oil filter at local auto parts store?

 

[alldodge]

I buy parts from who ever has the best price. Start with the part number then search

So far as motor oil and filter, pick any good oil. Many use 15W40 diesel oil, but 10W40 or straight 40W is good. Same goes for filters, I use WIX

Drive lube I do use Mercruiser