93 Evinrude 115 V4 Crossflow

[chopperguy]

Need help again with this old crossflow outboard. I am getting an occasional pop from the exhaust only below 1500 rpm with a puff of smoke. Runs great at WOT never skips a beat. The pop only started after I got the O/B back from a powerhead repair. Here's what has been done so far.

New piston rings, replaced one piston due to broken ring. Compression all above 120psi
Carbs cleaned and carb repair kits installed (no idle mixture adj. on these carbs)
New stator, power pack and reg/rect.
New fuel pump, VRO removed
All new fuel line and primer bulb
Checked idle timing 4 deg. TDC
Checked linkage and made sure butterfly valves are closed at idle. linkage timing is set correctly.

The spark plugs are slightly wet but not fouling. I have not checked the primer solenoid for leaks yet. Any ideas on what else to check? Thanks.

 

[emdsapmgr]

Couple of things to check: Carbs: if the idle passages in the upper carb body get restricted at all, the engine will have a "lean sneeze" This is an occasional misfire at idle only. When the carbs are running on the idle jets only. Once you throttle up just a little, other jets take over and the sneeze should disappear. This is usually a mild misfire event. Ignition: If the coils were reconnected incorrectly after overhaul, you can get a backfire. This is a more violent event. This could be from two coils directing fire to the wrong spark plugs. Check the color code on the power pack wires. Sync and Link: If the timer base is not adjusted correctly with the spark advance lever, your timing could be off somewhat. Check to be sure the link arm is connected between the timer base and Spark advance lever. This can cause rough running and could backfire if it's off enough.

 

[chopperguy]

Thanks, I've gone through the carbs diligently. Every passage blew high pressure air through. I did connections to coils and power pack to coil. I check timing in accordance with manual excerpt I found online. 4 degree TDC at idle.
Oddly, when I asked the mechanic that did the work and has worked on these v4s for 38 years he said, oh you will never get rid of that popping.

 

[racerone]

Is it popping in the water or just on the hose and muffs?--------You could look into installing smaller idle air bleeds to richen up the mixture.-----Likely it is not an ignition miss !!----What happens is a lean mixture will not ignite in the cylinder.---But it does ignite when the exhaust ports open that mixture to flaming exhaust from other cylinders !!!!

 

[ondarvr]

None of my crossflows ever popped unless there was an issue.

Take the carb cover off and put your hand over each carb, when it stops popping you've found the suspect cylinder, start checking there.

My last one started to pop like that, I cleaned the carbs four or fives times with no change, doing the hand over the carb test I found which cylinder it was, checked compression and it was 40PSI, the rest were at 120. The locating pin for one of the rings backed out, which eventually broke the ring, which then broke the piston edge.

It actually ran well at higher RPM's, no popping, no loss of speed, just a pop at idle.

 

[emdsapmgr]

The idle timing need not be set to exactly 4 degrees. That's a starting point. You set the idle by rpm, not by timing. Set the idle when the boat is floating normally in the lake. And in forward gear. Set the rpm's at 650-700 rpm's. Can't set it on the trailer and setting my timing may not get to your target rpm's when it's in gear in the lake.

 

[chopperguy]

None of my crossflows ever popped unless there was an issue.

Take the carb cover off and put your hand over each carb, when it stops popping you've found the suspect cylinder, start checking there.

My last one started to pop like that, I cleaned the carbs four or fives times with no change, doing the hand over the carb test I found which cylinder it was, checked compression and it was 40PSI, the rest were at 120. The locating pin for one of the rings backed out, which eventually broke the ring, which then broke the piston edge.

It actually ran well at higher RPM's, no popping, no loss of speed, just a pop at idle.

I hope this isn't the issue. I just had a bad Piston replaced. All rings were replaced due to carbon. Mechanic had 38 years experience. I checked compression myself. They are good.

 

[emdsapmgr]

Blowing air thru the passages of the carb body may not be enough. If there is dried fuel residue left over in a passage, air won't touch it. You need some product which will dissolve dried fuel-Like an aerosol Gumout type product. That will get the job done. You need to do a spray/flow comparison between all the passages.

 

[chopperguy]

Ok I will pull carbs for the third time this weekend.
One thing that leads me to believe this not a fuel issue is because the exhaust pop is not consistent. I am seeing a pattern. Sometimes it doesn't do it at all at idle . It never does it above 2000rpm. It does it the worst when I start the engine to flush it. This is when the engine is its hottest. Some extra heat seems to be a factor which would lead me to believe a coil is breaking down due to heat. That's the only ignition part I haven't changed.

 

[1983 ercoa 21']

If it's a steady miss find out which cylinder it is with a cylinder drop test once you know which cylinder it is swap that coil with one of the other cylinders if the mis follows the coil then replace it. This will either confirm your theory or disprove it.

 

[rothfm]

I re-read this post and had a thought...I have this exact motor and got bit by a weird issue some others have experienced. Can happen on lots of versions of this motor.

A Plug wire was grounding out on a cover latch, intermittently but fast. It also sort of popped, and small puffs of blue smoke as the cylinder actually fired up. Sometimes it would actually run good at high speed. Just depends on the RPM setting up a vibraton that would make it short out due to a bad plug wire.

Just thinking out loud.

 

[chopperguy]

Thanks for all the comments. No resolution yet. When you first start the boat and get underway it doesn't do it. Seems to be it's worst after the boat is pulled from the water and i'm flushing the engine. Something to do with increased engine temp I think.

 

[emdsapmgr]

Weak ignition components tend to fail, once the engine heats up to normal operating temps. May run fine when cold, then have running problems when warmed up. So, when testing, make sure you run it long enough to really warm it up.

 

[emdsapmgr]

Also, double check to make sure the timer base is moving freely-that it returns to the normal idle position. If the grease under the timer base dries out (with age) it can cause the timer base to stick and that can cause timing problems at idle.

 

[ondarvr]

Did you ever test to see which cylinder is doing this, by either pulling a plug wire or putting your hand over each carb?