'79 115 runs rough

mikesjohnson · Jan 19, 2007

just got my 115 running after sitting for quite some time. its running like crap though. what i dont understand is why. the three things an engine needs to run is air, fuel and spark. well, i have all three. i can pull number 3 spark plug off with no change, any other plug and it dies. i also have too keep the revs up to keep it running. when i had the carbs off for the rebuild, i had a look at the reeds, and all looked good. someone give me some inside info.

Joe Reeves · Jan 19, 2007

Re: '79 115 runs rough

If you have compression and spark.... that is spark that will jump a 7/16" gap with a strong blue lightning like snap..... that would indicate a problem within the fuel system.

Sounds like the carburetors are fouled, gummed, clogged. If you've already cleaned them, double check the high speed jets located in the bottom center of the float chambers and manually lean them with a piece of single strand wire.

mikesjohnson · Jan 19, 2007

Re: '79 115 runs rough

i just did a carb o/h. i let them soak in MEK (extreamly strong!!!!) then replaced all gaskets and o-rings. is it possible that the powerpack is firing both cyls. at the same time. i havent yet hit the water with the boat. like i siad, all three elements are there, air/feul/spark. and i have a great spark. boy does it let out a loud bright snap (it hurts too).

Silvertip · Jan 19, 2007

Re: '79 115 runs rough

All three elements are not there if you can pull #3 plug wire and nothing happens. No change indicates that cylinder is dead because there is 1) no compression, 2) no fuel, 3) no/weak spark or 4) any combination of the previous three. A compression check is in order. Use a squirt bottle with a little fuel/oil mix in it. Squirt some fuel into the #3 carb throat. If the engine picks up, you found the problem (no fuel = bad carb rebuild). If the carbs have idle mixture screws, do you have those adjusted correctly? Are float levels set correctly. Are fuel inlet needle and seat functioning properly to allow fuel into the carb?

emdsapmgr · Jan 20, 2007

Re: '79 115 runs rough

If you do what Silvertip suggest and still have the problem, could be an ignition problem. Try swapping the coil on #3 with another coil. If the problem moves, it is the coil. If it is still misfiring on #3, swap the power packs. If the dead cylinder moves to the other side, it is the pack.

mikesjohnson · Jan 20, 2007

Re: '79 115 runs rough

i've tried swapping the power packs, condition does not move. tried swapping coils, no change. compression is 131, 131, 127, 129. there are no idle mixture screws, just jets. it still missis on the top end too. tried using starting fluid in that cyl while running and still no change. i have 10 years of mech. exp with Dodge, i am a little more than mechanically inclined. i have fuel in both float bowls, which are not adjustable. i've even gone so far as to test the coils, trigger and stator, no tools to test power packs, but i have verified that they are both god by swapping from bank to bank.

72SideWinderSS · Jan 20, 2007

Re: '79 115 runs rough

Did you try cleaning the ground wire terminals for the coils?

Regards,
jimmy

emdsapmgr · Jan 21, 2007

Re: '79 115 runs rough

Compression is excellent. If you pull the plugs and compare them, does the #3 plug look the same as the rest? With the engine running, put a timing light on the plug wires and see what flashes you get on #3 compared to the rest.

Joe Reeves · Jan 21, 2007

Re: '79 115 runs rough

It possible for a pack to fire both cylinders on the opposite bank due to an internal diode failure, BUT since you've changed/switched the packs and the problem did not follow the pack..... that eliminates any powerpack problem.

I'm assuming that you have a strong blue spark on all cylinders that will jump a 7/16" gap at cranking speed "With The Spark Plugs Removed"? The 7/16" gap anf the strong blue snap of a spark is important. If you haven't made this test, do so.

You states the compresion as 131, 131, 127, 129 but you don't say which reading pertains to which cylinder. If the problem cylinder is one of the lower readings, it's possible that a slight head gasket failure exists which may allow a fine water mist enter the cylinder.

Standing in back of the engine, the cylinders would be numbered as follows. Which cylinder is not firing, and which cylinders have those compression readings?

2......1

4......3

mikesjohnson · Jan 28, 2007

Re: '79 115 runs rough

well, i found the problem. no wonder it dosent run right. i removed the cyl head and found a freakin hole in the exhaust port.:'( the corosion has eatin its way through the water jacket that surrounds the center exhaust port on #3 (thanks previous owner for not flushing the salt out!!!). the power head is junk. does anyone know where i can get a used powerhead for a resonable price in FL?

ezeke · Jan 28, 2007

Re: '79 115 runs rough

Joe Reeves knows just about everyone in Florida. His email is ReevesJ32@aol.com

Joe Reeves · Jan 28, 2007

Re: '79 115 runs rough

I appreciate the vote of confidence Ezeke but I don't have any of those powerheads left, nor do I know anyone who has one at the moment.

However, if "iboats" doesn't have one available, I'd suggest that Mike checks around with the various dealerships and other outboard repair shops for a replacement powerhead. It might just be that one of them has a engine with a blown lower unit and electrical/ignition problems BUT with a good powerhead.

The alternative, if that hole is small, would be to try to patch it with "Marine-Tex" (great stuff). Use the Gray mixture, not the White as the Gray mixture seems to be the strongest of the two.

mikesjohnson · Jan 28, 2007

Re: '79 115 runs rough

will the "marine-tex" stand up to the exh gas heat. i also think that cyl. will need to be bored over, the water left rust in the cyl and drug it through the rings, and the cyl wall is now scored preaty bad.

Joe Reeves · Jan 28, 2007

Re: '79 115 runs rough

Mike..... That red hot exhaust blast would take its toll. It would be better to go the powerhead route.

'79 115 runs rough

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