8.1 power issue

S

sarbog

Member
Aug 22, 2008
135
Emerald Isle NC
Boat Info
'05 340 Sundancer
Garmin 7610xsv
1951 Penn Yan 9' Aerodinghy/2018 AB 9vl w/ 15 hp Evinrude 2-strk
Engines
Twin 8.1 Horizons v-drives
I'm having an issue on my port engine ('05 8.1 Horizons). Last week I noticed significant throttle "lag" on the port engine. I cruise around 3400 rpm and to get the port engine up to 3400 to match the starboard requires significantly more throttle. Temps, pressures, etc., all OK and runs smooth with no alarms. It just won't turn up. Had the fuel filters changed and it was fine. Next day the same problem. Could it be the Cool Fuel module issue? Before I spend a lot of bucks and loose a lot of water time, if not the rest of the summer, having a mechanic tear into it I thought I'd seek opinions.
 
When was last time bottom cleaned, we had a fouled prop over the weekend. Could not turn up. Bottom was cleaned 4 weeks ago. Our water is really warm right now.
 
CHeck plug wires/change plugs. Mine did this to my port 3-4 weeks ago. Was not sure what was going on but have had 496 mags before and they like to make dirty plugs.. they will also run a Jug down and still be smooth. Got all new plugs and went to change them, and the first wire i got to was off the plug....... still swapped new plugs in and then checked all wires a 2 time. boats back to even thorttle and correct RPM/throttle input.
 
Those 8.1's will run like that when the plugs need to be replaced. They might last about 150hrs, after that plugs can start to fail but the engine is sophisticated enough to compensate by adding fuel to the cylinders still firing. If it's only 1 cylinder not firing you really can't tell other than that engine needing more throttle or seeing a WOT RPM difference of about 200RPMs. You probably have a couple of cylinders not firing consistently to be that noticeable.
 
Anyone know off hand what the plug size is for the 8.1's? Also the conversion for the serpentine belt it you wanted to get it at Auto Zone, etc?
 
searay495 said:
Anyone know off hand what the plug size is for the 8.1's? Also the conversion for the serpentine belt it you wanted to get it at Auto Zone, etc?
Click to expand...

Go to the maintenance section.

Go to page 3.

Look for the title "question about belts"

There is a long list of belt sizes and interchange info there.

Sorry, haven't figured out how to paste the thread link here yet.
 
plugs are Merc 33-863622001 which are ac Delco 41-983, equivalent NGK pztr5a-15 (7862) or NGK TR55IX (7164) gap .060

Just replaced my belt with Dayco 5060990, fit was perfect.

Start with plugs. If that doesn't help, have the injectors serviced.
 
I lost rpm once during a trip - it was a chaffed plug wire arcing out against the ex manifold and dropped that cylinder. As others have said check plugs and or wires.
 
Last edited:
Good timing. I just ordered mine 5 minutes before I saw this thread. If you live in a state that has Pep Boys auto parts stores, you can get 8 of them for $42 not including your state's sales tax by using code MMJ30 before 8/31.

Sarbon - did your lagging engine's exhaust smell "rich"? I've had my boat for 10 years. As soon as my exhaust starts to smell a little rich, it's time for plugs. I let it go for a couple of extra weeks this time, and it seems to be getting worse faster by the day.
 
Last edited:
Never thought about plugs! I'll try that this weekend. Bottom was cleaned about 2 weeks ago and I was out on the hook this past weekend and put the mask on to check and everything clean.
 
skibum said:
Good timing. I just ordered mine 5 minutes before I saw this thread. If you live in a state that has Pep Boys auto parts stores, you can get 8 of them for $42 not including your state's sales tax by using code MMJ30 before 8/31.
Click to expand...

I'm on Pep Boys site now. Even with discount code they come up as $24.49/each. You got 8 for $42. Amazing.
 
spent 100 ish on 16 plugs, then mailed in rebate.
 
I'm still seeing $5.24 each. Be sure to add them to your cart, and put the code in.

Regular price is only &7.49

PepBoys.jpg
 
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Rock Auto and Advance were much better prices.
 
AC delco has a 2017 plug rebate on all plugs, so 2 bucks rebate on Delco 41-983
 
Hey paulswagelock, thanks for the info on the serpentine belt. But I have a question, Dayco 5060990 is a 90 inch belt, and mercruiser tells me Mercruiser part number 865635-002, which is on my boat now is a 83 inch belt.
 
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