2000 mercury 125hp fuel delivery/rpm issue?

[mebe007]

OK guys I have a 2000 125hp mercury. I purchasedon't it on the back of a 20ft center console. I know this boat beckons for more hp but I figured I could repower down the road.I didn't have much history on the boat and engine, So I started off by pulling the lower unit and replacing the water pump impeller, wear plate, housing, and a new base since it was corroded pretty badly reinstalled and filled with new gear oil. Next I replaced the the 2 fuel filters (small one for accelerator pump, and the large one for the main fuel pump) and I also replaced the racor water separator filter. The is put in new plugs gapped to .040" per the manual. Took her out and ran her. Slow to plane and only saw 4700rpm and 26mph. Figured it was over propped with the 16p vengeance stainless prop that was on it so ordered a 15p hustler aluminum just to try. Saw about 4800 rpm and between 27 and 28mph but still not where I feel it needs to be. So for the hell of it tried a 13p. It was no faster out of the hole than the 15p and definitely slower at 23mph top end but the rpm went to 5200 which is about max. So I pulled it back offoff after than one run figuring there's a fuel or timing issue. So I decided to do a full link and sync. All that is correct, timing is correct, accelerator pump properly adjusted. Went back out with no change at all. Did a full DeCarb twice with power tune and keep Seafoam in the fuel, no change except at idle. Engine idles smooth as silk for a 2+2 engine. And runs smooth on the top end but just not pulling enough rpm. So figuring that holeshot sucks with all 3 props I'm thinking there is a lack in the fuel delivery. Take it back out with the little plugs pulled from the attenuator plate and open it up. Just a little blast ofrom carb cleaner in each carb. Results below

Top carb: no change in engine speed, stand smooth
2nd down: engine stumbles
3rd down : engine stumbles
Bottom carb: engine stumbles

In my thinking lack of fuel the rpm would increase with the carb cleaner so I'm confused on the stumble part. Anyways headed to ramp and loaded boat up and headed for the house. So at this point I'm hoping for some insight.

Thanks in advance,
Mark

 

[Silvertip]

Changing props is not going to make an engine that is too small perform like an engine with the required power for the boat. What is the boat rated for.??

 

[flyingscott]

I would check the top cylinder. What is the compression have you done a spark test? Stop spraying carb cleaner in it

 

[mebe007]

Compression is 125 psi +/- 2on all cylinders. Boat is rated to 185hp. Like I said, I understand the boat is under powered. But I would have expected a difference in hole shot between a 13p and 15p prop. Also please understand I didn't douse it in carb cleaner just a small squirt. Sorry just trying to understand this a little betteric. I'm well versed in inboard outboards not outboards

Thanks so much guys

 

[mebe007]

As far as spark, I have a cdi 8cyl spark gap tool and while checking timing I had spark across all 4 cyl

 

[flyingscott]

I would look into that top cylinder because it should have stumbled like the other 3. You know that's a 2+2 motor right.

 

[mebe007]

Correct 2+2 only idles on the top 2 cylinders as they have full idle circuits in carbs vs the lower 2. Where should I start with the top cylinder? I know it's running on it at idles as is responds to idle circuit adjustment. Just seems like a top end thing, so I'm not sure where to start

 

[mebe007]

Should I swap the coil to a different cylinder and see if the problem follows, if so then replace the coil?

 

[mebe007]

Just as an update. Had the boat in my shop at work yesterday to replace the swivel pin and pull the exhayst/ cooling jacket plate to replace the gaskets and bolts. Did another compression check and had a solid 125psI on all cylinders.I opened my spark gap tool up to a 1/2" all cylinders had spark. However 2,3,and 4 had a nice straight bright spark. #1 was not as bright and tended to not jump straight across and sort of wandered across the gap. Haven't had the boat in the water to try swaping the could around.

 

[mebe007]

OK took the boat out today. Swapped cdm 1 with cdm 2. Usedo an inductive tach and #1 still non responsive. Shut her down and disconnected harness from cdm 3 and did a run. Cylinder 1 was alive and well. Shut it down reconnected cdm 3 and disconnected cdm 4. Cylinder 1 again alive and well. Does this mean both 3&4 cdm modules are bad?

 

[mebe007]

Was just going through the manual doing some cdm tests. #3 would not pass coil secondary impedance test. I removed the plug wire and it passed. The end of the wire looked burnt and degraded. Cut it back a half inch and it looked good. Reinstalled the wire on the cdm and it passed the test. Could that be the culprit or is it deeper? This cylinder had spark at all time. This is driving me absolutely nuts. Please does anyone have input?

 

[flyingscott]

Could be a bad connection clean every connection you can find. Look over all wires.

 

[mebe007]

Thanks I will look it over tomorrow after work.

 

[mebe007]

OK, cleaned all connections with no change. Talked with cdi and they said to replace all cdm modules. So 4 cdI cdm modules later and it was a different boat. 5000rpm and it jumped out of the hole and picked up 6mph........for 2 trips. Yesterday with the wife it was slow out of the hole and back to slow in general. 4700rpm max. Online spark tester appeared to show fire on all 4 at wot. However at one point I pulled back on throttle ever so slightly and it tried to pick up bUT did not. This is driving me nuts trying to get this right before vacation

As a side note on my gps charge side of stator output, battery voltage at wot is 13.7volts. Is that where it should be?

 

[mebe007]

Verified yet again, no spark no 1 cylinder. This is with new coil packs on all cylinders. Unplug 3, no change, Unplug 4, no change. Swap 1 and 2 no change. Could this be a bad trigger? I've went over all connections again. One thing I notice. On The wires coming out of the trigger behind the oil tank, the insulation is all swollen and can be moved around on the wire itself. Probing the wire 3/4 of the way up and the connector for #1 cdm show continuity. I'm so frustrated at this point. 2 trips and she ran like a scalded dog now........back to square 1

 

[mebe007]

Just an update, verified again no spark on #1. Do pulled the flywheel and stator to today and replaced the trigger with a new cdi module. Then when reinstalling the flywheel I noticed that I was missing 2 3/8" out of one of my magnets. Could this be the root cause of everything? My stator looks like new.

 

[flyingscott]

It could be broken magnets are not good. Put up a pic but I would bet you need to replace the flywheel.

 

[mebe007]

I will when I get a chance. Ordered another flywheel and a new cdi stator to be on the safe side. My stator looked fine, however on the exposed metal pickups some ate matte black and others have Shiney spots on them as if the nagnet had rubbed. Ohm testing across the white/ green and green/ white wires the stator tested 20ohms above spec. I'm really hoping I can get this thing fixed, as the wife wants to enjoy it over family vacation next week. Between a new trigger, new stator, new cdm units, and a replacement flywheel that's pretty much the entire ignition system to my knowledge.

One thing I noticed as well if I would pull the throttle back slightly from wot you could feel #1 try to kick for a second then lose itself. Back down to idle and fire again exists.

 

[mebe007]

OK so time for an update. Replaced to flywheel and she ran great for about 20minutes then started to act like it hadid a slight miss. Again in #1 like before. I pulled all the plugs and #1 was clean and burnt looking. Led me to believe there was a blockage in carb causing a severe lean condition. Rebuilt the carb since kits are cheap enough. Finally got back into the water today. Out the hole great 5000 rpm then 20min in drops to 4800 and acts like it has the miss. Pull the plugs and #1 again looks the same.

Now looking in the cylinder the piston appeared to be wet but not like the others. It's appeared clean and wet. Swabbed with a quip and no residue on the quip and no smell of fuel. Did the other cylinders and got the expected fuel smell and slight Carbon color on quip. This has me thinking water is possibly getting into the cylinder.

Now as for that right after I seemed to have resolved the no spark on #1 earlier with coil replacement I replaced the exhaust plate and cover gaskets and bolts as the bolts were rusted to hell. I prepped the surfaces really well and put in the new green quicksilver gaskets and torqued per the manual. Upon inspection this evening I can see salt residue at the joints. So could these gaskets be leaking and allowing water into #1. I did not use sealant on the surfaces because the gasket felt like an odd material, not like the black ones with sealant line that came off of it.

I'm really losing my mind at this point.

 

[mebe007]

Here is #1









Also I rechecked compression and all cylinders are still 125psi thankfully. And the other 3 plugs look perfect, nice and tan.