1998 Force 120 Compression Test

[kamboat64]

Bought my first boat and it has a 1998 Force 120 on it. Wanting to do compression test on it, but want to know if I need to disable the fuel pump first? If so, what is best method for this? Thanks for any assistance.

 

[jerryjerry05]

No the pump is fine.
It will operate and the needle/seat won't let too much fuel past.

Comp: your motor might read a little different??
Some later models had different readings on the #1/4 compared to #2/3
It can be 10-15# different.
Do the test and post the results.
Remove all the plugs,
Jump at the solenoid.

Does it start and run ok?

 

[kamboat64]

It starts OK. Runs OK after it warms up for a bit. It does stall out when I put it in gear unless I'm really quick to get it there. It seems everything I see on forums says, "do a compression test". So I figured I'd start with that and see where it takes me.

I'm new to this working on outboards, so excuse the newbie in me, but you say "jump at the solenoid". I was not aware I had to do any jumping. Everything I see just shows to connect the tester at each plug (after removing all plugs) and turn it over 4 or 5 times. Am I missing something?

BTW, thanks for any and all input and assistance.

 

[Nordin]

Spark and compression test is simple and give you a quick information where to start troubleshooting.

"Jump the starter" is a way to avoid to damage the CDI boxes when performing the compression test.
If you run the starter from the key switch you have to ground the plugs, if not you can damage the CDI boxes.
The CDI boxes has to dump the charged voltage in the capacitors.
If you have a lanyard, pull it and then you can run the starter from the key switch.

The key is to run the starter when performing the compression test with the ignition OFF or grounding the plugs.

 

[jerryjerry05]

Even pulling the lanyard isn't safe for the packs.
I did it that way when I was a newbie, my boss chewed me out saying it could still hurt the packs.
My boss knew EVERYTHING about Chryslers and Forces

Using the key you need to ground the plug wires.

Turn it over until the gauge stops going up, 4-8 times, maybe more? Probably less.
Depends on the gauge.

 

[jerryjerry05]

If it runs but stalls then I'd say the comp isn't the trouble.
Real low comp on 1 or more cyl. the motor would be hard to start.

What's the rpm's in gear at idle? 775-800 is what they should be.
To adjust, the bottom of the towershaft has a screw/nut that controls the idle.
In the drive on the hose, about 1100-1200 rpm's

 

[kamboat64]

Started with the idle screw. Attempted to do in driveway, but tach was jumping around. Was able to adjust some. Put the boat in the water today and it actually
went in gear first attempt without stalling. Tach read much better in water. RPM 's in neutral idling about 700. In gear around 600 or so. Will adjust again next weekend in water with the goal being around 800 in neutral at idle. Thanks for the input.
Now to figure out why the tach jumps around so much on hose. Thoughts?

 

[Nordin]

I have not had that thoughts about the RPMs in water and at hose cause I most of the time set the idle in water.
But I think two strokers need a bit of back pressure for the exhaust to run better.
They run calmer in water then at hose and that is because of the back pressure from the water.

 

[jerryjerry05]

The tach jumping: could be it's reading/or not reading the signal when it misses at idle?
Old parts?
Take the plug off the back f the tach and spray WD on the contacts,

 

[kamboat64]

Got my compression tester and spark tester. Spark on all four...yay! Ran motor about 5 minutes, kill switch to off, throttle. wide open, pulled plugs. Result:
#1: 170
#2: 175
#3: 175
#4: 175

Seem high but could be tester. At least they are within 10%.
Going to borrow another tester and check again.

 

[Jiggz]

Those numbers are good and no need to test again. Make sure the carbs are at least 1 1/8~1 1/4 turn out from seated. And then set the idle rpm, in water, at idle, in gear to 750~800 RPM. If you are still having stall problem when going into gear, try running the motor without the top cover and see if that makes a difference.

If it does, you could have exhaust leak somewhere succumbing the motor.

 

[jerryjerry05]

Like Jiggz said, in the water, in gear, and moving not tied to the dock or on the trailer.
The comp results, good.

 

[kamboat64]

Finally got the boat out again this weekend. Set carbs at 1-1/4 out. Boat started right up. Idle was really rough at around 700 rpm. Put in gear at idle. Adjusted idle screw to get around 800, but still rough. Went back to carb adjustment screws and noticed that it didn't make a difference on top carb how far out or in I adjusted, it didn't change the idle. Removed the cover and noticed that I have fuel (not much, but some) spitting out the front of the top carb. Not so with the bottom carb. But at least it continually went into gear without stalling. Motor was a little slow getting up to around 20 mph but after that, it ran great. Topped out at about 43 mph (by GPS) at around 4900 rpm. My question... what do I need to do to that top carb to get it idling correctly and not spitting fuel out the front? Is it trying to flood itself out at idle?

As always, any and all assistance is appreciated.

 

[Nordin]

Check the float level and reset it if wrong at top carb.
The float should be parallel with casting edge for bowl when turned upside down.

Also check the reeds which is behinde the carb and intake manifold.
They should rest and no gap, maybe 0.005 in gap will work.

When a carb spitt back there is usually problem with the reeds.
Later Force had problems with braking reed pedals, Chrysler did not have problem with this (they used Swedish stainless steel from Sandvik, my opinion because I work at Sandvik).

 

[Jiggz]

With fuel blowing out of the top carb, you most likely have broken reeds. It's now a question if it's on #1 or #2. Doing a simple cylinder drop test will confirm which one is not firing (due to not enough fuel oil mix getting into the cylinder).

 

[kamboat64]

Jiggz, if you would, maybe a quick rundown on what a cylinder drop test entails.

 

[Jiggz]

Cylinder drop test is the term used to test a misfire by pulling the spark plug wire. Pulling the spark plug wire causes the said cylinder to be dropped or not to fire, hence the term cylinder drop test. MAKE SURE YOU DO THE PULLING OF THE WIRE QUICK AND REPLACE AS SOON AS YOU DETERMINE IF IT'S FIRING OR NOT. THIS IS TO PREVENT DAMAGING THE CD MODULES. If you are uncomfortable doing this, the only other way to find out which reed block is broken is by using a tiny endoscope (about $20) inserted through the top carb with the throttles in WOT position. Just make sure you remove the carb's air cover.

1. Start and idle engine, make sure the top cowl is off and cooling water on muffs is provided
2. Using a piece of rag or some form of insulation, pull the spark plug wire one at a time on each cylinder.
3. Listen to change in engine rpm. If there is no change, it indicates that the cylinder you pulled the spark plug wire from is not firing. If there's a change in engine rpm or engine stops, then it means that cylinder is firing and contributing to engine rpm.
4. Continue to test the rest of the cylinders just to make sure it's all firing.
5. Note, sometimes due to the engine already misfiring pulling a plug wire can cause the engine to die or stop. This means the cylinder is actually firing or maybe the only one firing. To continue testing, restart engine and move to the next cylinder.

 

[jerryjerry05]

I bought a new bore camera $10 eBay.
Just make sure you order for your camera.
I have Android and the first one they sent was wrong.
The camera comes with 2 different leads, one is a firm lead and good for our applications.
The soft lead is good for ????

A misfire cam also be a broken trigger lead.
The shrinkwrap can hide a broken wire, pull on the leads.

 

[kamboat64]

Bought a bore camera. Is this pic showing me
I have a broken off petal? That’s my thinking
right now. What do you guys think? Not the
best pic, but my first attempt with this.

 

[Jiggz]

Unable to tell but if you can make a comparison with #3 and #4 reed, you should be able to tell if the reed is missing petals. Since both #1 and #2 are served by common carb, i.e. upper carb, why don't you just remove the carb and take a look on both reed blocks? Eventually, you will need to replace one or the other assuming you have broken reeds. The only reason for the bore scope is to find out if you need one or two sets of reeds.