Problem Child
Well-known member
I'm a carb guy for life. !!
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The Ginger's New Ride
- Thread starter Gimme Fuel
- Start date
Gimme Fuel
Well-known member
Little update:
Current situation isn't great. Found out the hard way that I had a very weak injector on the starboard motor. She roached #6 piston. This was not a result of the tuning that we did however. Being boat has stock manifolds and no provision for O2 sensors, we did not touch any fueling tables in the programming. We only threw premium fuel at it and changed the lame 29* timing to a still conservative 34*. Also bumped rev limiter 100 rpm and changed how it activates.
This did not occur at WOT. It happened at a 3800 rpm sustained cruise for 20 miles. Decided to take a trip to Caseville with a few other boats. This was the longest period of time these motors have been run by me yet. Typical usage so far has been idle out for 15 minutes then on plane for ten minutes to sand bar and shut down otherwise this would have happened sooner.
I had the notion to pull all the injectors before I ever ran it but it ran well so I just threw some injector cleaner in tank and called it good. Good friend of mine has injector cleaner and flow bench. Will post results of what we find from both motors injectors. Guessing this #6 injector is about 25-30% weaker than the rest. He says he sees every older set of injectors having 1-2 that flow 10-20% less than others and ultrasonic cleaning usually brings them back within 5% unless coil is weak then it needs replacing.
Doesn't look horrible inside, hopefully new piston, rings, bearings on that cylinder since everything else looks good on all the others. Probably new valves on that cylinder and clean up the seats. Do a hone with cordless drill and put back together. They are coming back out as originally planned at the end of season anyways for full refresh still.
Moral of the story:. Anyone with an older MPI motor, take the time to pull your injectors and have them flow checked. You will be surprised. I may do mine yearly especially once things are no longer stock. There is a reason Merc tunes these things pig rich. It is to compensate for injectors over time.
Current situation isn't great. Found out the hard way that I had a very weak injector on the starboard motor. She roached #6 piston. This was not a result of the tuning that we did however. Being boat has stock manifolds and no provision for O2 sensors, we did not touch any fueling tables in the programming. We only threw premium fuel at it and changed the lame 29* timing to a still conservative 34*. Also bumped rev limiter 100 rpm and changed how it activates.
This did not occur at WOT. It happened at a 3800 rpm sustained cruise for 20 miles. Decided to take a trip to Caseville with a few other boats. This was the longest period of time these motors have been run by me yet. Typical usage so far has been idle out for 15 minutes then on plane for ten minutes to sand bar and shut down otherwise this would have happened sooner.
I had the notion to pull all the injectors before I ever ran it but it ran well so I just threw some injector cleaner in tank and called it good. Good friend of mine has injector cleaner and flow bench. Will post results of what we find from both motors injectors. Guessing this #6 injector is about 25-30% weaker than the rest. He says he sees every older set of injectors having 1-2 that flow 10-20% less than others and ultrasonic cleaning usually brings them back within 5% unless coil is weak then it needs replacing.
Doesn't look horrible inside, hopefully new piston, rings, bearings on that cylinder since everything else looks good on all the others. Probably new valves on that cylinder and clean up the seats. Do a hone with cordless drill and put back together. They are coming back out as originally planned at the end of season anyways for full refresh still.
Moral of the story:. Anyone with an older MPI motor, take the time to pull your injectors and have them flow checked. You will be surprised. I may do mine yearly especially once things are no longer stock. There is a reason Merc tunes these things pig rich. It is to compensate for injectors over time.
Problem Child
Well-known member
It's contagious !
Gimme Fuel
Well-known member
Well, hunch was right. #6 injector 24% less and terrible spray pattern. That equates to 2.6 air fuel ratio. So if average tune was set for 12.5 Afr, then that cylinder was running 15.1 Afr which is very lean. No wonder why she went kaboom.
Head looks good, valves and seats in good condition, cylinder not scored. Disassembled the valves last night and will clean up and reassemble. Picked up a used take out factory piston to swap in since they are no longer available. Should be back up and going shortly. Probably not for this holiday weekend, but will be back installed next week sometime.
Can you tell which injector is my #6? Notice poor spray pattern by lack of foaming and decreased volume. Other 3 injectors were a brand new set from merc. Sad thing is right out of box on brand new set of 8 there was a 20% OVERachiever and a 10% UNDERachiever. My injector far right, mean average injector far left.
Head looks good, valves and seats in good condition, cylinder not scored. Disassembled the valves last night and will clean up and reassemble. Picked up a used take out factory piston to swap in since they are no longer available. Should be back up and going shortly. Probably not for this holiday weekend, but will be back installed next week sometime.
Can you tell which injector is my #6? Notice poor spray pattern by lack of foaming and decreased volume. Other 3 injectors were a brand new set from merc. Sad thing is right out of box on brand new set of 8 there was a 20% OVERachiever and a 10% UNDERachiever. My injector far right, mean average injector far left.
Well, hunch was right. #6 injector 24% less and terrible spray pattern. That equates to 2.6 air fuel ratio. So if average tune was set for 12.5 Afr, then that cylinder was running 15.1 Afr which is very lean. No wonder why she went kaboom.
Head looks good, valves and seats in good condition, cylinder not scored. Disassembled the valves last night and will clean up and reassemble. Picked up a used take out factory piston to swap in since they are no longer available. Should be back up and going shortly. Probably not for this holiday weekend, but will be back installed next week sometime.
Can you tell which injector is my #6? Notice poor spray pattern by lack of foaming and decreased volume. Other 3 injectors were a brand new set from merc. Sad thing is right out of box on brand new set of 8 there was a 20% OVERachiever and a 10% UNDERachiever. My injector far right, mean average injector far left.
Where do you send your injectors to have them tested?
Gimme Fuel
Well-known member
Smitty's Engine and Trans, Vassar, MI
Gimme Fuel
Well-known member
Well engine is back in the boat. Was able to get things cleaned up and put back together pretty reasonably. Just waiting on new injectors to arrive next week. Ended up replacing the expensive and issue prone 46 lb/hr Magnetii Marelli injectors with 63 lb/he Siemens-Deka injectors. Drop in refitment but will require some math to be done and converting the ECU fuel tables for the higher flow rate. Getting two flow matched sets from Racetronix. Best price for a GENUINE Marelli injector is about $100 each whereas the Siemens are half that. So instead of wasting money on injectors I was going to toss next year anyways, I decided to do the upgrade for a little more money. Ended up with 4 injectors that were total junk and another 2 that flowed extra. Found one on good motor that wasn't firing at all and stuck. No wonder it lagged a few rpm behind.
mishawakajim
Well-known member
Sorry to hear about your troubles Ron . Best of luck getting her healthy and running again to finish out the rest of the season.
Jim
Jim
Problem Child
Well-known member
Man your hard on equipment hehehe !! 
Last edited:
Gimme Fuel
Well-known member
Many your hard on equipment hehehe !!
Sad part is I wasn't even trying! Ha-ha. Maybe I should have ran it like I stole it!
Problem Child
Well-known member
I hear ya. I was only cruising all day when mine got tore up !
Gimme Fuel
Well-known member
It's that cruising that will get ya every time! Ha-ha.
Gimme Fuel
Well-known member
Well, she is back together and made a good 70 mile fun run on Saturday. Ran great. Had some 30p labbed bravo one props on but was too choppy to get good speed numbers.
Problem Child
Well-known member
How far out to the Charity Islands Ron. I haven't been out there since going out on a perch fishing charter. We always went from out of Tawas though. Glad you were able to enjoy that one !
Gimme Fuel
Well-known member
33 Miles out and 33 miles back! It is a good run for sure. Gorgeous clear water out there too. Little bit rocky but we were all in an area that was mostly sand.