1990 Force 120 HP L-drive motor troubles

[CumminsChris]

Hi guys, I just recently bought a 1990 Bayliner with the 120HP Force L-drive and was wondering if you all could me with some issues. The boat runs decent on the muffs, idles fine, revs fine, but will occasionally die at idle if you run it long enough. However when you get it in the water it dies frequently at idle, getting into gear and moving is hard. If you manage to get it in gear and above idle without killing it you are golden, it will run all day at any RPM but idle. It is a real pain to launch and load because it will just die on you and drift around while you are trying in vain to get it restarted.

Restarting is no walk in the park, because it also has a weird quirk where after it dies, it often won't crank over fast enough to start, it's like all of a sudden the battery is really weak, or the compression of the motor tripled. If you mess with it long enough, you can get it to crank over and try restart it, but by then then it's usually flooded. Starter and all wiring from battery to starter is brand new.

Normally I would attribute the idle issue to tuning and the not wanting to crank as a weird quirk, but then I pulled the spark plugs as part of my troubleshooting and found the top 3 were slightly carbon coated with black soot, nothing major, but the bottom one was clean enough to eat off, didn't have the fuel/oil sheen of the other plugs, and had water droplets beaded on the threads. Now there is no way the engine isn't firing on all cylinders when cruising, it runs great, sounds smooth and has plenty of power. It just HAS to be firing, but after finding the plug clean like that and evidence of water, I am very suspicious of how that might relate to my other problems. Could you more experienced fellows shine any light on this for me before I go do drastic things like pull the motor? I'll put a pic of the plugs below, thanks for any help!

 

[SkiDad]

your idle rpm is probably low - set it for approx 750 in forward gear in the water - this will be at least 1000 rpm in neutral in the water but I think it's more important that you are around 750 in gear - mine will stall if it is lower than 700. If the rough idle persists you probably need to look at your 2 fuel mixture screws - they should be set around 1 turn out from lightly seated. There is a FAQ at the top of this Force forum that will explain some of this stuff.

 

[Jiggz]

Chris good troubleshooting and providing pics makes it really easy to provide accurate response. This is what I will do in your case.
1. Check the idle rpm and also the air fuel mixture settings as mentioned by SkiDad
2. Make sure you are using BUHX NGK's or UL16V Champions, I prefer the NGK's for some personal reasons
3. The battery cabling maybe be new but is the ground cable clean and tight to the engine block? I always used split lock washers on this connection and in addition use dielectric grease to keep it clean and tight.
4. Do a compression test of the motor especially on #2 cylinder. The clean as a whistle plug tip tells me it is being "steam cleaned" meaning it still fires especially at above idling throttle position (due to increase in fuel into the cylinder) but there is also an indication of minor water leak into the cylinder. Post your compression numbers.
5. When starting make sure you follow standard starting procedures, i.e. prime, fast idle, choke and start. You crank no more than 10 seconds at a time, usually 3~5 secs is good enough or until the engine "coughs" or starts. Thereafter, reset the start key and re-start again without the choke. If it doesn't cough or start on the first 10 secs, reset and try again until it re-starts or coughs. Thereafter, if it still would not start, re-start again but without the choke or you will flood it. In short, the choke should not be used every time to avoid flooding. In fact, I only recommended choking it for the first try only.

 

[CumminsChris]

Thanks for the responses guys. Let me go point by point.

1. I believe the idle is about 1000-1100 out of water, but my tach is very jittery at low RPMs. I am working on getting better idle numbers to share with you guys. We have checked and rechecked the mixture screws, they should be good.

2. The plugs are NGK's all but one look brand new, the one looks slightly worn, but fine.

3. The cables and everything related to them are clean, new and solid.

4. I just got the compression tester I've been waiting on from our shop, and will be doing a check when I have time, and will share those results.

5. Yup, that describes my starting experiences except for the part where it gets really hard to crank and won't turn fast enough to even think of firing.

So unfortunately I don't have much new info yet, but I will be getting it soon. The main reason I didn't just wait to post this is that I have another question with this engine that isn't directly related to the issues above. The rectifier/regulator gave up the ghost quite suddenly, and I have been trying to fix it. I got a rectifier on there, but there is too much overcharge, so I bought what was SUPPOSED to be the factory replacement from Caltric, and what I got was a 3 phase rectifier/regulator. The wiring is totally different, and I have no idea if it will work. I contacted the seller, but who knows when they will get back to me or if they will be any help. Some other stuff I found on the web indicated that I could indeed use it, just wire it in for single phase and leave one yellow wire loose. That still leaves me unsure of the wiring configuration.

Well I tried to include a pic so I didn't have to type this all out, but this site isn't letting me upload one right now. The one I had originally had 2 yellow input wires, a grey for tach, and a red for DC output. It was case grounded. The one I ordered was the same, but with a dedicated ground wire. What I actually GOT has 3 yellow wires, a green one, and one that could be called red or brown.

I don't know if this is something you guys will be able to help me figure out or not, but I figure it's worth a shot!

Thanks again for your help!

After I typed all that out, I got the upload to take, sigh, oh well here's the pic.

 

[Jiggz]

I supposed you can use the 3-phase as a single phase rect/reg. However, unlike the unit pictured on the screen, the unit you are holding doesn't seem to have a dedicated connection for the tach input signal. Also is the green wire the ground wire? You can obviously test the unit just make sure there is a load (battery connected to the unit while the motor is running so as not damage it) And then do some voltage input and output readings.

As for slow cranking, after checking all of the above and compression numbers are good, then it is time to check the starter and load test the battery.

 

[CumminsChris]

OK, here's my new info.

The idle is set at about 1000-1100 in neutral on the muffs, and it runs great for the first couple minutes, after a while it just starts to bog down and then dies. Then it's a bear to get restarted, keeps kicking the starter out and doesn't want to fire once you get it cranking. Once you do get it restarted it's the same deal, it'll idle great, then bog down and die again if you don't give it some throttle when it starts to die.

I did a compression test and got:
1 - 145
2 - 145
3 - 110
4 - 120 (This is the one that had water, which I saw more of while setting the timing with the plugs out)

I checked the timing, it was way advanced, I backed it down to 28 degrees static advance at WOT, that didn't make a lick of difference in how it runs.

Thanks for the input guys! I swear I will get this boat running reliably some day! No matter what it takes.

 

[Jiggz]

Too much difference on the compression numbers. Time to open and inspect by removing the head not to mention the water intrusion on #4. You can try saving the head gasket if possible for post analysis or reuse if not damaged.