Engine Missing Causes.
 

I have a 79 Formula with a Merc 260. Went through the whole boat this past winter. The motor ran well last summer so I left that alone. It has 600 hrs on it and is in very good health. It has an edelbrock carb on it. I took it out for the first time today since the resto. I noticed going through the harbor, the idle missed a tiny bit. I just assumed from sitting. I warmed up then hit the gas. It ran well. Did 54mph on GPS @5000rpm with full fuel and a passenger. we then settled into a 3000-3500 rpm cruise. The boat developed a bad miss. Struggled to get on plane. It was also missing when idling in gear. Out of gear it seemed ok. I have brand new plugs in it. Also I swapped out the cap and no change. It ran great all last year. Any ideas?

Btw the points have been converted to petronix I think. There is no points.

How about the plug wires? Sure they aren't arcing out? A good test is in the dark, get a spray bottle filled with water. Spray the wires with mist of water, and look for sparks coming from the wires.

Any popping from the carb and or exhaust?

New plugs, wires, cap and rotor are a great idea to do all at once. After you have done that then I'd start trouble shooting bigger things.

Changed the cap an rotor. The plugs are also brand new. The wires are relatively new. It was also surging a bit idling back to the marina. I have heard that its a fuel delivery issue.

I had a miss in the mid range went thru my whole electrical. Thought for sure it was some kind of electrical causing it, bad plug, cap, rotor, wire, Ect. Nope it was the dam carb. Bought new carb(wanted a little bigger anyways) and was fine then two years later it did the same and was carb again, rebuilt and was fine. Ethanol gas sucks .

I am leaning toward the carb. I screwed up and topped it off with regular. I was even at a 100% gas pump. I hit the wrong button on the pump.

Regular 87 octane wont cause whats going on with your merc 260. If its fuel related, you probably have a gummed up carb or filter.

There are a couple threads on here about those carbs. Something about epoxying something in the bottom of them. The guy that I rent a shop from did this last year and cleared up all of his loading up and missing.

I went thru this a few times with Q-Jets. The ethanol anymore ruins rubber parts in Carbs...just know this and run either pure gasoline or learn how to go thru your carbs periodically. I am in the process of securing a new pair of Quick Fuel Double Pumpers which will help alot.

That $hit plays hell on everything rubber thats not designed for it. My 79 Formula is getting all new hoses in the fuel system because of it.

Last season when i was out, boat was running great. Parked for awhile to swim, started her back up and everytime i moved the sticks the port motor kept dying. WTF??? Got home pulled carb apart, and the rubber dougnut on the accel pump was laying in the bottom of the well. Kinda hard to get that big shot o gas like that. Freaking corn liquor is not good... For boats at least

Sounds like it could be fuel, but I'd always do the wires and any fuel filters before tearing the carb down. Make sure to dump out the fuel into a glass jar to check for crap and separation too. If that doesn't find your trouble go get Cliff Ruggles book on the Quadrajet. It's got everything you can need to know. Plus he hosts a q&a web site. It's cliffshighperformance.com. Or spend the money to get a replacement carb now and rebuild the original one at your convenience, you will need it sometime. It's more money out, but boat season is here!

Found the Miss! I started pulling plugs. 2 plugs on each side were closed. I then looked inside the cylinders. It seems that a split washer fell down the carb and hit all 4 cylinders fed by the drivers side plenum. Really sucks as I have never had the spark arrestor off. So now here I am $7500 in a 79 Formula F18 and now it needs a motor. I tore down the motor. One cracked cylinder, bad heads, and 4 broken pistons. It is all at the machine shop getting prepped to be a 355. I have also purchased a new set of 906 vortec heads. The motor will now be .030 over, speed pro pistons, moly rings, stock crank, stock rods, xtreme marine 262 cam, vortec heads, Air gap intake, Edelbrock 1409 carb. Think my little boat will hit 65 or so?

Btw my machinist is sleeving the block for $90, then another $220 for boring all 8 cylinders.

If I were you I'd find a diff block. I've had bad luck with sleeved blocks in a boat, although I do hear of others that work out fine. Also I would start with a fuel tank of 100% fresh fuel before running the new engine. Your description up till the split washer thing sounded like detonation due to last falls fuel took out a few pistons.

by the sound of your damage,it was caused by detonation,id check the fuel system before the new engine goes in the boat,you don,t want a repeat after spending all that money rebuilding your engine.

I would have to say its a washer because there were several pieces embedded in the pistons. The pieces were all hardened steel. There is no missing pieces of ring missing or any other engine components for that matter. Its really odd.

Is there any way I can test the fuel? I dont know what to do with 38 gallons. Its full to the brim. I am not worried about the $150 to refill the tank.

Its probably a valve seat or piece of ring you see in the piston.

FYI I burned the rankest oldest gas out of a boat I bought a few years ago (over 200 gallons) in my daily drivers with no issues. I added about 5 gallons of bad gas at each fillup and put in 93 octane of fresh where I would normally run 87oct.

None of the rings were missing any pieces. The valves were not missing any pieces either. I will take apart the heads and look at the valve seats. I think I will burn the gas in my girlfriends Taurus.