changed most electricals, still misses

[flcruiser]

Bought a used 89 3 cyl merc 60 two years ago and I have slowly replaced most of the ignition system. New Trigger, stator, rectifier, plugs, wires. Now after lastly replacing the wires I have a hard miss at low speed. Sometimes the miss brings the RPM down to 800 for a few seconds then back up. Normally I have isle set at 1200 RPM. Seems to miss after enrichment turns off. Doesnt seem to have hi speed miss.<br /><br />Also when I put the new wires on the charging voltage dropped from 16 V to 13.8 volts.. Any connection?<br /><br />Ideas would be appreciated. I don't think its the fuel system. New fuel pump innards, new connectors, fuel line and bulb. Could it be the carbs getting air elsewhere into the fuel. Did have an issue with air leak which would raise the idle RPM to 2000.

 

[KCLOST]

Re: changed most electricals, still misses

Check the intensity and consistency of the spark on each cylinder at idle.... I like to use a spark gap tester $10.....<br /><br />If you have a miss in one of the cylinders, you could have a faulty switchbox or coil..<br /><br />Let us know...

 

[dolluper]

Re: changed most electricals, still misses

Also check connections on recitifer ,make sure they are clean and tight also all grounds switch box,coils,allwires areclean and tight

 

[flcruiser]

Re: changed most electricals, still misses

Thanks,<br /><br />I'll check this over next weekend.

 

[KCLOST]

Re: changed most electricals, still misses

Let us know...

 

[flcruiser]

Re: changed most electricals, still misses

Well, I had a chance to check the three wires. I bought a spark gap tester at Autozone and checked each wire one at a time. The tester grounded the wire and the plug obviously did not fire for each wire. Keep the throttle position the same for all three plugs. Heres the results.<br /><br />Plug #1 Bypassed with gap tool -Engine ran basically at 2000 RPM with some drop in RPM to 1800, similar to hard miss I experienced in the first place. <br /><br />Plug #2 Engine ran smoothly (as best it can on two cyl) at 1200 RPM Also the electrically firing snap from the gap tool was about the same for #1 and #2<br /><br />Plug #3 Could not keep engine running under any throttle position. Cranked enough to hear good firing sanp, but the engine would not continously run.<br /><br />As far as the plugs, I had NKG nonfouling plugs BUHW in there and I changed to regular tipped Champions. I repeated the test and got the same results.<br /><br />The NKG's are new. I had run the boat with the NKG's for about two hours before this problem surfaced. <br /><br />Also I checked the plug condition when I switched to the Champions. #3 was the cleanest, with no deposits, virtually no wetness. #2 and #1 were both wet, but no hard deposits.<br /><br />I think its #2 coil or continuity since isolating out the #2 plug gave me a smooth ( again relative) idle , but I don't understand why isolating #3 would cause the engine to not run.<br /><br />What do you all think and what's the next step?

 

[Chris1956]

Re: changed most electricals, still misses

Let's see, the engine ran best with number 1 plug wire disconnected. That makes number 1 cylinder the weakest. Engine ran not as good with number 2 plug wire disconnected. That makes number 2 second weakest cylinder. Engine would not run with number 3 plug wire disconnected. Number 3 cylinder is the strongest.<br />I would check for low compression on numbers 1 and 2. If the compression is good, put a timing light on the spark plug wites to assure they ann fire all the time(during miss). If so then start troubleshooting carbs of number 1 and 2.

 

[flcruiser]

Re: changed most electricals, still misses

I agree that #3 is the strongest. However with #2 grounded, there is no miss, with #1 grounded there is a miss although the RPM are higher.I will check with timing light when it dries out down here.

 

[Yepblaze]

Re: changed most electricals, still misses

If this is the three cylinder model that shares two carbs, it may never run as you would like it to.<br /><br />From what I have garnered from my time on the web they don't idle down all that smoothly. Even in their best state of tune.

 

[flcruiser]

Re: changed most electricals, still misses

Agreed, always has run rough compared to other engines. And I also agree that the two carbs are something to be desired and maybe #1 and #2 may be effected by the top carb, but I do have a hard miss (the engine shakes like it had a sneeze) that leads me to electrical. Besides, I didn't have the miss a few days ago.

 

[Yepblaze]

Re: changed most electricals, still misses

I might suggest you add a post over at the old merc outboard site http://www.pfs-ware.com/kwast/mercboard/index.htm <br />There's a guy there named George Garland that apparently knows them well.<br /><br />When you say sneeze though, that immediately makes me consider a lean condition.

 

[fishhead24]

Re: changed most electricals, still misses

You might try switching the #3 coil with the # 2 coil and see if the problem moves with the coil.If it does the coil is bad.

 

[NathanY]

Re: changed most electricals, still misses

Have you checked compression?

 

[flcruiser]

Re: changed most electricals, still misses

Well the rain stopped and it got a little warmer so I tested each plug wire with a strobe timing light. Curriously all three wires showed erratic blinking. A bright blink, then constant blinking then blank then bright again. <br /><br />is this the switchbox? it cant be one coil. Also is the switch box on top of the three coils?

 

[KCLOST]

Re: changed most electricals, still misses

Could be the switchbox, but I don't think it is... If the box was bad, you "normally" wouldn't have any spark. This could be trigger problem, but thats uncommon also...<br /><br />The switchbox in on the starboard side of the engine.. It a rectangular shape about 3"x5" in size (3/4" thick) with all kinds of wires connected to it. <br /><br />Are you sure the switchbox is grounded properly?

 

[Nos4r2]

Re: changed most electricals, still misses

I'd go over all the new wires with an ohm-meter-and pay particular attention to the trigger wires. Try GENTLY wiggling the wires while you're doing this to simulate vibration as though the engine's running and see if the reading changes.