1brent1

Engine seems to idle fine, revs above 3000 rpms with no load. Only experiencing an issue out on the water under load. It’s a mefi3 and same Cam (cam was the only thing not touched during rebuild and stock as far as I know). It was originally a 2014 remanufactured quicksilver 502.
I set the Base timing to 8 degrees btdc, in base timing mode. I even tried advancing/retarding both ways 4 or 5 degrees, made no differences still cuts out the same like seen in this video-

During the rebuild I replace, plugs, wires (847701Q17 blue not sure if correct?), quicksilver cap, rotor.
Bravo 3 outdrive is newer with 15 hours. New hill marine 24pitch 4by4 props
I checked the following so far.
Fuel pressure remains 41 psi.
Gas vent cleared
Fresh non-ethanol gas
CodeMate MEFI Code Reader doesn’t pickup any trouble codes before, during or after experiencing the issue.

Note: I did find a broken spark plug (porcelain split in half) in cylinder number 3. It did get a little less noticeable after replacing all the spark plugs. Maybe the plug wire went bad?
I double checked all connections, used deoxit on some of them.

Really appreciate your time and knowledge.

Helmwurst

What spark plugs are you running?

1brent1

I last replaced them with NGK BR6FS (.035 gap)
Maybe I should go with ACDelco RapidFire 1? My local napa store has them in stock.
I'm going to check my spark plug wire resistance/ohms today. The wires were new with rebuild (Quicksilver 847701Q17 Blue).

Thank you for your help.

Ryanw10

Side note: Was the bravo 3 common behind a 502?

Did you do anything with the injectors during engine rebuild? Have you pulled plugs to get a reading on them? Is the new bravo 3 the same ratio as the old bravo 3?

1brent1

>Side note: Was the bravo 3 common behind a 502?
Yes, my model boat (1999-2001 Mariah z302) came with both 454mag mpi & 502 mag mpi with bravo 3's, with all 3 different gear ratios 1.81, 2.00, 2.20

>Is the new bravo 3 the same ratio as the old bravo 3?
Yes 2.00

>Did you do anything with the injectors during engine rebuild?
I sent the injectors off to be cleaned and flow tested, all good there unless I damaged one during install.

>Have you pulled plugs to get a reading on them?
I will check them today. I only have less than 1 hour with the new BR6FS plugs. It had MR43T but I found one of them was broken so I replaced them all with what I had already BR6FS

Helmwurst

I am not certain on the MPI 502's, but all other 502's use extended tip plugs. Ex: AC Delco R43TS or MR43TS.

1brent1

Valve covers show AC MR43T
I will try putting in rapidfire’s #1

I pulled all the plugs and took these photos. Any thoughts?
I was hoping the tops of the Pistons would have looked better.
I was also surprised to see the cap looking like that with only two hours. Maybe from when it was running with the broken spark plug.

BR6FSNumber 6 spark plug, all others look the same

BR6FS Number 6 spark plug, all others look the same

This was a new cap with 2 hours.

Pistons all look similar, 2 hours of run time.

Pistons all look similar, 2 hours of run time.

This was a new rotor with 2 hours.

Griff

No reason to run the Rapid Fires in a stock 502mpi. You are running the correct NGK BR6FS plugs for a 502mpi.
That dist cap is horrible. Mine look better after 3 years. What brand cap and rotor?? Use OEM merc/quicksilver or the Sierra marine ones

1brent1

Not sure if it matters on the plugs but it’s a 509 mpi after rebuild. Bored .30 with JE pistons.

The cap and rotor I used was Quicksilver 808483Q1. Not sure how it could have got so bad.

One thing that I'm noticing, my tach jumps around a bit more noticeably at startup and lower rpms which didn't happen before rebuild. I will try doing "wybmabiity" Cure for fluctuating tach problem, post #12 link-
Tach and Oil Pressure Flucuates 500 efi.

I did paint my block as well as the base of my distributer. I have a feeling the paint might be creating problems. See in this photo-

F-2 Speedy

Not sure of the noise but sounds like the valve train needs adjusted