Burnt spark plug tips ! 4.3 mecruiser

[Heywire77]

I have a 1994 Crownline with a 4.3 mercruiser with thunderbolt ignition ,I purchased the boat unfinished with a reman motor in it that wasn't all the way hooked up , so I finished wiring it and everything took it out to find the exhaust flappers were letting water in the cylinder when I would stop the boat so I put new ones in and I noticed it was a hard to start so I rebuilt the carb and it would start first hit of the key and I timed the motor according to speaks then all next day coil was acring out the side shorting out so I went to parts store autozone and they matched up one said it should be same so it ran like new again then another time out it started running rough and I checked the brand new plugs less than a couple weeks old and found one with the tip burnt off I thought it was problaly from when the flappers let water by and it ruined it maybe so I put new plug in and it ran great . We'll I let a buddy borrow it and he called me and said it backfire a couple times I said it never done it was problaly the old gas but he ran it for 4 hours like that ! Got the boat back and it has 4 burnt plugs the tips were completey burnt off ! It had new fuel filters in it and new water separator in it and new motor and rebuilt carb . I put some more new plugs in it and now it sounds like it is missing on 3 cylinders and I have a ton of money in his boat I can believe how much trouble it has been , I have had boats all my life but never problems like this , so now I don't know if it has ruin the pistons or maybe burnt the valves . Sorry but what could have been causing this problem because I don't want to fix say maybe burnt valves and it happen all over again , also the riser gaskets were just replaced when we put in the flappers but we had to cut them out from gasket material because we couldn't get them local , I know if it had a vacuum leak then it would not have idled so sweet like it did and it ran like new across the water also ! Any help would be great .

 

[bruceb58]

I would be checking compression at this point to see if you have holes in your pistons. Sounds like it ran lean but it could also be your timing was way off. Did you set it with a timing light?

What plugs are you running and what gap are you using? If you have arcing form the coil, you either have bad spark plug wires, bad rotor/cap or your spark plugs are gapped too wide.

 

[Heywire77]

The acring from the coil was the old coil and yes had the correct a/c delco plugs in it and cap and rotor looked like new , and yes I set the timing with the timing light I looked up the specs for timing and set it I can't remember now but I think it was a round 8 degrees before top dead center.and yes I know that next thing is compression test and then leak down test to see if it has burnt valve of hole in piston , sorry been a drivability tech on auto's over 20 years at dealership but boats I just started fooling with about 6 years ago . I'm hoping it isn't internal damage actually praying ! If anything I would rather a burnt valve then wholes in pistons . But if the exhaust risers gaskets weren't sealing all the way would it burn the plugs ?

 

[bruceb58]

But if the exhaust risers gaskets weren't sealing all the way would it burn the plugs ?

No.

What is the part number of the AC plug you are using?

 

[achris]

Even if the exhaust shutters are faulty/missing unless you pulled the throttle back suddenly, no water should have got in the engine. You should check the height of the top of the elbow and the 'at rest' water level on the boat. If the exhaust is too low, then water in the engine will be continuous, and you should be installing elbow risers.

As for the burnt tips, check you have the coil wired up correctly, purple should be to the '+' terminal.

Chris.

 

[Heywire77]

The plugs I put in it were ac delco R45LTS6 , and about the water coming in thru the exhaust yes the flappers were completely gone and I was flying across the water and stop all of a sudden and the water rushed up into the cylinders that fixed that problem when I replaced the flappers .and yes I had the coil wired correctly .

 

[MikDee]

Those plugs sound like "long reach" plugs? Is that what it calls for?

 

[achris]

They are WAY the wrong plug.... Should be NGK BR6FS or AC MR43T. The plugs you have are for the Vortec engines (1996+).. Yours' (1994) should not be a vortec....

 

[Heywire77]

The motor cam with Bosch plugs and they were the same length , but now I double checked on a parts site and it is saying it takes a r42lts , it has been awhile but I know I didn't cross reference the Bosch number with ac delco I looked them up on a marine parts site then wrote them down and went to the local parts store and bought them but I'm going to see if I can find a place to look them up and make sure it is right and see what number it shows like said the motor is a 4.3 mercruiser with the thunderbolt ignition and it was in a 1994 Crownline 182 ski boat . Maybe I did screw the pooch !

 

[achris]

Forget the year of the boat, what year is the engine? Or better still, the engine serial number... (and No, the year of the engine and boat are not always the same, they can and do vary)

 

[Heywire77]

Yeah I understand that about the year and yes I see know I had plugs for vortec and yes I know mine is the pre vortec motor , dam it I must have looked it up wrong I was in a hurry . I know the motor that was ordered and put in the boat was a 1994 motor I can get to it right now to look at numbers but yeah I'm sure it isn't a vortec engine like said I been a mechanic for over 20 years but I screwed up on this trying to hurry , I should have double checked . And I'm sure that is a lot hotter plug I had in it we'll I will be doing compression test and cylinder leak down test when the weather clears up it may be the weekend hopefully I didn't burn a piston I would rather a burnt valve if anything because I have an extra set of good heads .

 

[MikDee]

They are WAY the wrong plug.... Should be NGK BR6FS or AC MR43T. The plugs you have are for the Vortec engines (1996+).. Yours' (1994) should not be a vortec....

Thanks achris, I kinda thought they were the wrong plugs.

 

[Heywire77]

Will update when I get everything checked out .

 

[Heywire77]

I finally got a chance to pull the motor down last night and thank The Lord that the cylinders and pistons still look like new even the heads looked like brand new the motor was a remanufactored motor with less than 20 hours on it , I looked at the valves and at first I couldn't see any difference till I looked closer and I found the cylinders that had no compression the valves were not flat anymore they looked like a bowl and the good ones were completey flat . Lucky it is the none vortec heads so I have a good pair of extra heads so I will throw them own it and save these and replace the valves later and keep them for extra . I have seen burnt valves before but usually they will have a piece missing or burnt off these you could see they didn't have long before They would have came apart . My piston tops looked great and the cylinder walls still look great also . So hopefully this will get it taken care of !