79 Rude Performance Mystery

[BBMerlin5091]

I purchased a boat about 6 months ago with a 79 Evinrude 115 on it that had about 20 hours on a powerhead rebuild. Since then i've done multiple repairs on it (THANK YOU VERY MUCH FOR ALL YOUR HELP GUYS) and it's running better and better. Today was the first day that it actually performed really well in the water, except that it was hard to start and did not want to idle at first. But once i got it going it ran awesome topping out at around 5300 rpm's, ran it around for about 40 mins, and came back to the dock, put it in neutral idled decent but had a bit of a miss, which could have been there when i started, but it runs so rough at first that it would be hard to tell. Anyway we sat there for about 10 seconds just off shore then started to go again, and as soon as i gave it some gas it died. Got it back on the trailer and brought it home and discovered that 2 of the cylinders were not "firing". all 4 cylinders have strong spark, nice and wide, and all will jump a gap of at least 7/16". Compression test revealed that all cylinders had between 115 and 120 lbs. Brand new set of spark plugs(Champions) and it would seem that they were firing to at least some degree because there was no oil buildup or residue on the plugs when i pulled them out. But at idle and up to 3000 rpms under no load ie. out of the water you can pull both of the plug wires off of those plugs and there is absolutely no difference in the way the engine runs.<br /><br /> signed, totally lost

 

[DHPMARINE]

Re: 79 Rude Performance Mystery

I'd start with a sample of the fuel,in a clean jar,let it set,and see what it looks like.Should be clean thru out,no layering of fluids.Take the sample from the line feeding the carbs.<br /><br />DHP

 

[BBMerlin5091]

Re: 79 Rude Performance Mystery

DHP.........i just changed the fuel in that tank yesterday, i siphoned all of the gas that was in it out and replaced with fresh fuel. I also replaced all of the fuel lines, and screw clamps from the quick connect to the carbs as they were leaking slightly. I also put a new primer bulb and fuel line on it. Took the sample, fuel is fine, no layering, no dirt, and as best i can tell no water. When i put this fuel in yesterday, i also dumped a bottle of seafoam in it.

 

[fireman57]

Re: 79 Rude Performance Mystery

If you can pull those plugs and there is no difference in performance you have to suspect no spark to those cylinders.

 

[brehlers69]

Re: 79 Rude Performance Mystery

I'd check your points, your wires and their connections. Your not getting spark at those speeds for some reason. Also check the coils they may be going out on you.

 

[BBMerlin5091]

Re: 79 Rude Performance Mystery

Both of the powerpacks are new, i just replaced them about 2 weeks ago. I also put 2 new coils on it. As i said before there is strong spark at all 4 cylinders. when i pull the plug wires off, the spark will jump from the contact inside of the boot all the way to the plug holding the spark plug wire approx. 1/8" away from the plug. That was my initial thought Fireman, that there was no spark but i can't imagine that with a spark that strong that they are not firing when connect to the spark plug. Is it possible that the engine is setup to only idle on 2 cylinders and for the other two to come online after a certain rpm is reached??

 

[Dhadley]

Re: 79 Rude Performance Mystery

When you talk about the 2 that arent working, which 2 are they? If they are across from each other that would indicate a carb issue. If they are one on top of the other that indicates an ignition problem. I know you have spark but we have to know if its coming at the right time.

 

[fireman57]

Re: 79 Rude Performance Mystery

That spark should jump a lot more than 1/8". Should be almost 7/16". Could be a weak ground. Recheck them. Dhadley is also on the right track. Which two aren't firing is important.

 

[BBMerlin5091]

Re: 79 Rude Performance Mystery

The top cylinder on the starboard side is not firing, and the bottome cylinder on the port side is not firing. Fireman i am sorry for the misunderstanding, it is jumping a 7/16" gap with absolutely no problem, nice wide strong spark.

 

[dolluper]

Re: 79 Rude Performance Mystery

You have spark at wires right now see if the plugs fire sounds like you have 2 dead new champions

 

[BBMerlin5091]

Re: 79 Rude Performance Mystery

The plugs are firing fine, i took them out with the wires still attached, and the spark jumped from the plug to the cylinder head over a distance of almost a inch.

 

[Qld_Kev]

Re: 79 Rude Performance Mystery

Sounds like my engine was running like. I had a blown head gasket (I know you've had a rebuild, but...) Take one of the the plugs out and run the engine on the remaining pots. If it blows water out, the a head gasket is the cause.

 

[BBMerlin5091]

Re: 79 Rude Performance Mystery

Thanks for all the posts guys. I've already had the plugs out with the engine running, did that when i was testing the plugs themselves to see if they were firing, some fuel vapor came out, but no water.

 

[fireman57]

Re: 79 Rude Performance Mystery

I know this sounds stupid and I'm not accusing anyone of anything but is there some way that you could have put the wires on the wrong plugs? Even from the same pack? Have you tried running it on muffs in the dark to look for a plug or electrical wire arcing?

 

[Sherman]

Re: 79 Rude Performance Mystery

I run the same motor and I will put my money on you have dirt in the carbs. Those idle holes are really small. I believe you have tested the spark enough but put on an inductive timing light and check they are firing under compression.

 

[BBMerlin5091]

Re: 79 Rude Performance Mystery

Fireman, i did try running it in the dark, and it i didn't get any sparks, or arcs from anywhere, i thought the same thing too, not that i put the wrong wires on the wrong plugs, but maybe i had a loose ground, or wire that the sheath was gone from around the wire. No such luck.<br /><br />Sherman, i have taken the carbs apart twice now, once when i first got the boat, and again 2 days ago they look like they just came off the shelf of a clean room, no varnish, no buildup, no residue of any kind, i took the needle and seat out, looked new, i blew compressed air through every hole i could find, i didn't even get any particles to come out of it. I have an inductive timing light, and i will check that tomorrow, providing that this rain stops at some point. Thanks for all the tips guys.

 

[BBMerlin5091]

Re: 79 Rude Performance Mystery

finally stopped raining gonna go and check the timing.

 

[levittownnick]

Re: 79 Rude Performance Mystery

You said that the spark jumped about an inch from the plugs when you had the plugs out, but to check the plugs, they need to be grounded and the spark observed jumping the plug gap.<br />One other thought, back a year or two, I learned from this forum that the shifter switch momentarily kills the spark on 2 cyllinders during shifting. If this switch is hanging up instead of the momentary action, this could explain the problem.<br />I would like to give credit to the person who helped me then, but my lame brain dosen't remember who that was.<br />Good luck.

 

[Dhadley]

Re: 79 Rude Performance Mystery

V4 crossflows didnt have interrupter switches. The switch is usually connected to the starboard bank and affects those cylinders only. But a good point, those switches can drive you crazy.<br /><br />I would still suspect the carbs especially if they havent been soaked in cleaner and new OE kits installed. The other thing is that we know we have spark but do we know its firing at the right time?

 

[papasage]

Re: 79 Rude Performance Mystery

try some new plugs and check the firing order to be sure of the right wires on the right plug .some bad plugs want fire under compression . but will fire out in the air . that i dont under stand but seen it on a plug cleaning machine 45 years ago .papasage