98 Evinrude 115 crossflow V4 Idling question

[GatorMike]

I spent a week at Marco Island and did a lot of boating. My boat ran OK but just seemed a little off. It seemed to take a little longer to get on plane, top speed was maybe 5 mph lower than normal and she didn't idle as well as normal.

Now that I am home I am starting to check things out. I have a question, just wondering if this is normal or if it might point to a possible problem. When I start the motor she idles fine, after she runs 4 or 5 minutes the idle drops about 400-500 rpms. Is it normal for rpms to drop after warm up or would this tend to point to an ignition coil or spark plug breaking down as it gets hot?

 

[racerone]

Compression the first thing to look at on these crossflow motors.----They have a history of breaking piston rings.

 

[GatorMike]

Did a compression test as soon as I got home. 120 on 2 cylinders 130 on the other 2. I suspect my compression gauge reads a little high but those actual numbers don't really matter they are in tolerance.

 

[V153]

Yeah if it only does it after warm up it could be dropping a cylinder due to a bad coil, etc. Just have to try and isolate it.

When it starts acting up I'd pull the plug wires one at a time and see if you can trace it to a specific cylinder. Then test the coil.

 

[interalian]

I dropped one coil on mine last year and it lost a lot more than 5mph - more like 15. And it ran like a bag of rocks. But yeah, cylinder drop test when it's acting up, and check your head temperatures.

 

[GatorMike]

I am going to update my original post. After further fooling around with it I was a little off on my original description. When I was down in Marco Island she would start and idle at about 900 rpm in the water. After running a while the rpms would drop and she would eventually stall. Now that I have it out of the water running on muffs she starts at about 1800 rpms she will run a while then drop to about 1400 rpms letting her run a while the rpms drop to about 900 where she will run a while then jump back up to 1400 or 1800 rpms then after a while drop back to 900. I'm having a problem figuring this out.

 

[V153]

Per the manual: Should idle at 650 plus or minus 50 rpm.

 

[Joe Reeves]

Your idle is set quite high.

On a flushette, a 20" shaft engine should idle at 1000 rpm... a 25" shaft engine should idl;e at 1200 rpm. The idle would drop to normal when in the water.

 

[GatorMike]

Thanks Joe,
I had turned up the idle while in Marco to keep it from stalling when the rpms dropped. I just adjusted it back. On the flushette she now idles at 1200 rpms for a few seconds when first started then drops back to about 800 rpms for a while, then back and forth from 800 to 1200. The drop and gain in rpms is always about 400 rpms. She seems to run steady at each rpm for anywhere from a few seconds to a couple of minutes. I'm just trying to figure out what is causing this jump.

 

[jakedaawg]

Do you experience this with the hood both on and off? Or only when the hood is on.

 

[GatorMike]

Both hood off and hood on.

Although I suspect it is a spark or timing issue I did replace the fuel filter and take the carburetors off tonight and will clean them and put them back on in the morning. To see if that helps.

 

[Joe Reeves]

A sharp instantaneous back & forth loss of power would indicate ignition... a gradual change would be fuel. Carefully, after a bit of running in this condition, inspect the spark plugs to see if just one spark plug stands out in appearance as compared to the other three. If one does... and if the jumping back and forth is a sharp immediate change... suspect the coil in which case, replace it and/or inspect all connections carefully (plugs/pins, and wires attached to them).

 

[GatorMike]

Thanks Joe,
Yes it is an instant drop in rpms. I have plenty of spare parts for this motor I replaced the J115tslecm that came on the boat with a used E115tslecm a few years back and saved all the electrical parts so I will swap out some of those parts tomorrow after I get those carburetors back on. Gee I wish I had read your post before I removed those carbs. LOL

 

[V153]

I got a buddy up in Nokomis. Replaced each and every imaginable ignition part on his 115, still wouldn't run worth a chit. Turned out to be a plug wire ...

 

[GatorMike]

OK Joe I have the problem isolated now, I know exactly what is going on I just need to figure out the fix.

This morning I put the carbs back on and put in new spark plugs. I knew from your post yesterday this was not the problem but it did straighten things out a little (made the problem more consistent) Now the rpms don't jump back and forth as much. She starts, runs for a few seconds then drops.

I put a spark tester on each cylinder one at a time and discovered it is the upper right cylinder, that would be #1 I believe. Anyway upon startup the #1 spark plug fires for a few seconds then quits firing all together. If I rev the engine it starts firing again but when I throttle back she drops again. I have some spare ignition coils off my old engine so I swapped that coil out...it ran the same on 3 different coils. I also have some old spark plug wires and swapped them out with the same results.

My guess at this time would be either the power pack or timer base but I'm not a mechanic so that would be a guess. Have you ever seen this in an outboard and do you have any ideas?

 

[interalian]

Try swapping power packs and see if the problem tracks to the other bank.

Edit: not a dual pack motor. Carry on. Pay no attention to the man behind the curtain.

 

[Joe Reeves]

I put a spark tester on each cylinder one at a time and discovered it is the upper right cylinder, that would be #1 I believe. Anyway upon startup the #1 spark plug fires for a few seconds then quits firing all together. If I rev the engine it starts firing again but when I throttle back she drops again. I have some spare ignition coils off my old engine so I swapped that coil out...it ran the same on 3 different coils. I also have some old spark plug wires and swapped them out with the same results.

My guess at this time would be either the power pack or timer base but I'm not a mechanic so that would be a guess. Have you ever seen this in an outboard and do you have any ideas?[/SIZE][/FONT][/COLOR]

Before you throw a pack or timer base at it... closely, carefully check all connections, especially the round rubber plug connections if they exist. I've encountered cases whereas unplugging and plugging those thing would cause the pin or socket to back out slightly, resulting in a break and make connection, and also the wire that attaches to those pins/sockets. The wire would break away from the pin/socket and rather than be soldered to it would be barely touching the metal... BUT... the wire would appear to be securely attached due to the tightness of the rubber socket gripping the wire insulation.