Need a second opinion or third or fourth-Update

[gonefishie]

I am working on a 97 Force motor, model# 120ELPT, Serial # OE276926. Recently noticed a weak pee stream at idle spped. I decided to replace the impeller since it hasn't been done in a long time. Surprisingly, it's in great shape but I replaced it anyway. While testing my new impeller installation this afternoon, I noticed the motor didn't seemed to run right. I pulled the plug wire on the first cylinder and it appeared that this cylinder wasn't doing anything at all. I pulled the plug wire on other cylinders and the motor did stutter so it seemed they're fine. Checked for spark and got spark on all 4 plugs. Checked compression, got 150-155 on the top 3 cylinder but only 140 on the fourth one. I replaced the fuel filter and pumped the bulb, got a bowl full of gas to check for water and didn't see any. Took the carb cover off and noticed some water condensation at the front of the top carb's throat and some milky stuff which indicates the present of water. There is no water in my gas, already verified that earlier, doesn't means there really isn't though. Took the carb off and cleaned out everything with carb cleaner, blowed dry with compressed air. Did the same cleaning with the bottom carb. Installed carbs, adjusted mixture screws, fired up the motor with it trimmed up so the carb are tilted forward. I noticed some gas/oil mixture dripping out of the carb but it was a milky mixture. That indicates water is getting into one of the top two cylinders right? if not both. Most likely just the top since it didn't seemed to do anything right? I have a blown head gasket right? but how does it have a 150 psi compression with a blown head gasket? I was just on the water Thursday running WOT at 5200 rpm and normal top speed. How was this possible if I was only running on 3 cylinders? If the top cylinder is having problem then why does it have a higher compression then the fourth one? I am really confused, what the hell could be my real problem? If I can't figure it out, I will have to go after the head gasket which I don't really want to do. What do you Force gurus think?

 

[roscoe]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

first thing
i would do is a spark test on all 4 plugs.
if no spark, it could totally flood the top cylinder

would address the possible water issue after I checked for spark

 

[gonefishie]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

first thing
i would do is a spark test on all 4 plugs.
if no spark, it could totally flood the top cylinder

would address the possible water issue after I checked for spark

Did checked for spark, they were good.

 

[pnwboat]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

It's not unusual to get some water condensation in the throat of the carburetors. As the fuel air mixture flows through the throat of the carburetor, the velocity of the mixture is accelerated due to the "venturi" effect. This creates both a pressure and temperature differential and may result in some condensation. Depends on atmospheric conditions as to the amount of water condensation. Maybe that's what you're seeing?

If your head gasket was leaking water it would be very unlikely that you would see any water anywhere around the carburetors. The carbs and intake manifold areas of the motor are always operating under a vacuum. The airflow in this area of the motor is always sucking into the motor. Having said that, there is one possible scenario where you may get "outflow". If one of your reeds was broken or leaking. The reeds are essentially "one way valves" for the fuel/air mixture.

Check your spark plugs for water. If there is no evidence of water on your plugs, and it appears that you have good compression, it's safe to say your head gasket is probably OK.

You mentioned that the motor didn't seem to run right after you changed the impeller, and that when you pulled #1 plug wire, it didn't affect the motor. Here's what you can try if it really bothers you.

1. Check all of your connectors, especially the grounds. Make sure they are touching bare metal and no corrosion. Pull the connectors off of each of the 4 CDM modules and reseat them. Visually inspect the male pins on each connector to make sure you don't have any bent or pushed back pins. Check all of the bullet connectors from the stator to the wiring harness. The bullet connectors on the yellow wires supply the AC voltage to the regulator and may be somewhat discolored. This is normal. Not sure if this is good though, but I see this discoloration all the time. Looks like it's from heat so I suspect that there is a significant amount of current that goes through these wires. Once you do this, perform your spark plug wire test. If no change go to step 2.

2. Switch the CDM module between the 1st and 2nd cylinders. The CDM module is the ignition coil and capacitive ignition components all in one. Very easy to swap on the 1997 models. After swapping, do your spark plug wire test again. If your problem moves to #2 cylinder, then I would suspect that that CDM is weak or bad. If no change, go to step 3.

3. Inspect your reed valves. To do this you must remove the carburetors and intake manifolds. Not hard to do, just a lot of bolts to take off. The reed valve assy. sits directly under carb/intake manifolds. The later model Force engines with the Mercury design reed valves are more prone to breaking than the earlier pre-Mercury design. Remember that when you put the intake and carbs back on, you should do a Link and Sync.

It's really up to you if you want to go through the trouble to go through the 3 steps outlined above. The old saying "If it aint broke, don't fix it" really holds true here. Steps 1 and 2 are pretty simple and easy to do and don't require any parts. Step 3 may require new gaskets. If the motor is turning 5200 RPM's at WOT, it can't be too bad.

 

[gonefishie]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

There were water on #1 plug. Also, lot of moisture in the air yesterday which could add to the moisture in the carb throat but it only occurred on the top carb. I didn't take the intake manifold off but did looked at the reed valves through it with a flash light and they appeared to be ok. Will do step 1&2. Thanks fellas.

 

[pnwboat]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

Water on the plug is not a good sign. My guess is that doing steps 1 and 2 will not change anything if you have water on the plug. Since your compression is good and you are turning 5200 RPM's, I would suspect a water leak on the exhaust cover side. Either the stainless steel exhaust plate under the cover has a crack, or the gaskets (there are two) themselves on the exhaust cover and or exhaust plate is leaking. Relatively easy and cheap fix.

See items 32 and 33 in diagram below.

http://www.boats.net/parts/search/Merc2/Force/120%20H.P.%20%281997%29/0E203000%20THRU%200E287999/Cylinder%20Block%20Assembly%28Serial%20%23%200E138600%20Thru%200E173427%29/parts.html

 

[gonefishie]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

Thanks pnwboat. Do you know what's the torque specs for the bolts on both the cylinder head cover and the exhaust cover?

 

[moparman]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

Pnwboat has more than likely hit the nail on the head, as these motors have a tendency to crack the exhaust cover,and sometimes you have to really look hard to fine the crack as they can be real fine.At one time someone offered an after market cover to replace the crack prone stock unit, but I can't find the site now [that's normal,when your goofing off looking at things ,you find all types of neat stuff, but the minute you need it you can't find it, it's like the lost sock syndrome in the washing machine......]. Keep looking and keep us posted on your results. The cylinder head bolts go to 120 in lbs plus 90 degrees, the cover bolts go to 70 in lbs ,the exhaust cover goes to 115 in lbs, hope this helps, MOPARMAN

 

[gonefishie]

Re: Need a second opinion or third or fourth-UPDATE

Re: Need a second opinion or third or fourth-UPDATE

Well, the head gasket was blown, replaced it, top cylinder still wasn't running right. Took off intake manifolds to have a full view of the reed valves. One was broken which is why the top cylinder wasn't firing cause it aint' getting any gas. One was partially open, the other two are in bad shape too but were working. I got 4 reed block assembly on order, should be here tomorrow. Man, I started with a simple, inexpensive impeller replacement and ending up doing a damn near engine rebuild. I got about $500 in parts on this job. Ain't Murphy nice?

 

[pnwboat]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

I'm surprised that the compression was that good with a blown head gasket. But then again, I've seen stranger things. It just shows you how well these motors will run with some pretty significant problems. Not sure that's a good thing though....LOL.

 

[john from md]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

The easiest way to damage reeds is by having the engine backfire. Some folks don't use the choke and or the fast idle position and thus get backfires which leads to bent and broken reeds.

John

 

[gonefishie]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

The easiest way to damage reeds is by having the engine backfire. Some folks don't use the choke and or the fast idle position and thus get backfires which leads to bent and broken reeds.

John

Whoa! fast idle causes backfires? I fast idle a lot. It takes too long to get to where I really want to fish If I'm doing true idle speed.

 

[john from md]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

I didn't say that. I said that people who fail to use fast idle and enough choke usually get backfiring engines during start. This eventually damages the reeds and can damage the fuel pump diaphram also.

John

 

[gonefishie]

Re: Need a second opinion or third or fourth

Re: Need a second opinion or third or fourth

I got ya! I bet that how my reeds got damage because a lot of the times I have to give it a little bit of gas to start. The fellow that started a thread asking about doing a tune up has the same symptoms as my motor.

 

[gonefishie]

Re: Need a second opinion or third or fourth-Update

Got the motor all back together, tested drove it last night in a weak hurricane like wind. She purred like new, idle so much smoother, started much easier. It's unbelievable how much better she running now.

 

[john from md]

Re: Need a second opinion or third or fourth-Update

Glad that it all worked out for you.

John