1991 Force 150 Power Loss at WOT

[shushry]

Been trying to troubleshoot an issue with my 1991 Force 150. On my 19p prop I should see right around 5k RPM at WOT. For most of this season so far though I seem to have a problem with power loss at WOT, and only achieving 4000 - 4200 at best with it.

Symptoms include:

- rough running above 3800 rpm (has a missing or sputtering sound)
- Not much power or RPM difference from about 75% throttle (hits around 4k RPM) and WOT.
- Starts and idles great. Sounds great up to 3500 RPM or so.

The other day I suddenly got a nice surge of power when, at WOT, i suddenly jumped to 4500 RPM, which then made it's way up to around 5k after a few seconds. It was like a missing cylinder suddenly "kicked in", yet all 5 cyls seem to be operational. The phenomenon has happened a few times since then (like bad gas, or something getting "worked out" but I can't seem to get it nailed down), but for the most part runs in the bad condition.

I've also noticed lately that my Voltmeter in the dash varies alot from about 12V to upwards of 15V. Is this normal? I seem to have come across a few posts that indicate this could be a problem with the regulator/rectifier, and statements that this could cause rough running at WOT? Is this correct?

Thinking the issue might be a bad spark plug, or cylinder not firing, I, one at a time, removed the spark plug wire from each cyl and started the engine. Oddly, the engine idled the same irregardless of missing a cyl (from the removed wire) - and sounded the same when ALL 5 cyls were plugged in. Why would that be?

I haven't checked compression, but assuming it's ok, what else might be something to check on?

Thanks all for a great forum -

S

 

[jerryjerry05]

Re: 1991 Force 150 Power Loss at WOT

Never assume!!!! Do a comp/spark test.You say it made no difference when(running) you pulled the plug wires?
What did the plugs look like?All burning good?
You could have low comp.Bad coil.Bad fuel pump diaphrams. Bad stator(doesn't really sound like it but).Water in the fuel.Dirt in the carbs.
You have a fuel/water seperator? If not get one.Check the fuel pumps for dirty filters.Then drop the easiest carb bowl,check for dirt.If dirty the whole system needs to be cleaned.
You really need to do a comp test first.Oh yea fill out the profile,you might be close to someone who can help.J

 

[shushry]

Re: 1991 Force 150 Power Loss at WOT

J - thanks for the great response.

More details on the story:

- Compression is good in all cyls (~140psi) - check
- Fuel lines are clean, and filters are good - check
- Regulator seems fine at least in terms of measurements

Spark on #2 seems to be the issue - here's what we know:

Took an inductive timing light out and could show that all cyls fire up until 3500 rpm. At that point, #2 starts to drop out as you approach 4000rpm. At 4k, #2 is nearly completely dead. Maybe one fire every second or so. Therein is our issue.

At first we thought this could be just the ignition coil for that cyl - replaced it but still an issue. So - this is now leading us back to the ignition switch box (part #817323A1) ("CDI?") - This is a $300 or so part which I'd like to avoid having to replace only to find it's not the issue, or there was something simple to try first -

Any suggestions?

Thanks all!

 

[hsc]

Re: 1991 Force 150 Power Loss at WOT

Hello, I have probably the same problem with my 150 hp Force 1992 (Thunderbold ignition). Rough running above 3800 rpm and a sputtering sound.

I come from Germany an I hope you can understand me
I am not a professional, but I tried to fix the problem with the
++++ Clymer Force Outboard shop manual; 4 - 150 HP (includes L-Drives) 1984 1999 +++++

There is something that I had detected.
If my motor is cold it makes 5500 rpm. But if it is warm (after 15 minutes) the problem begins. First the max rpm ist 4500 then 4200 and 30 minutes later sometimes only 3800. The next day (with a cold motor) it runs again 5500 rpm, but only for 15 minutes etc.
I have also the 15 Volt at the voltmeter and I made a important detection. If I push the tilt switch (the tilt motor then needs much current) the voltmeter goes down to 13,5 Volt and the motor runs 5000 rpm and more. If I stop tilting, the voltmeter shows 15 Volt again and the motor runs only 4000 rpm or less with a sputtering sound. If I tilt the motor again and again it runs always 5000 rpm and more with a good sound and if I stop tilting the problem comes back.

Here my ineffectual trials to find out the problem:
? Compression test
? New gasoline bulb
? New gasoline filters
? New spark splugs
? Spark tester -> a good crisp spark at each spark gap
? New high tesion wires
? Carburator cleaning
? Running without a fuel cap
? Fuel pump output test -> min. 0,65 bar (65 kPa) at each rpm
? Cleaning of all electrical gounds
? Cleaning of all electrical terminals
? Ignition Coil Resistance / Voltage (DVA-meter) at 900 - 4200 rpm
1 -> 1250 Ohm / 200 V
2 -> 1250 Ohm / 200 V
3 -> 1250 Ohm / 200 V
4 -> 1250 Ohm / 200 V
5 -> 800 Ohm / 190 V
? Converter box output -> 300 V (DVA-meter) 900 - 4200 rpm
? Stop circuit -> 300 V (DVA-meter) 900 - 4200 rpm

At the end I have one question. What ist WOT? I don?t now this abreviation.

Thanks
Helmut

 

[foodfisher]

Re: 1991 Force 150 Power Loss at WOT

hsc-You highjacked the post by shushry. Who gets the answers? WOT=wide open throttle

 

[stevetheplumb]

Re: 1991 Force 150 Power Loss at WOT

J - thanks for the great response.

More details on the story:

- Compression is good in all cyls (~140psi) - check
- Fuel lines are clean, and filters are good - check
- Regulator seems fine at least in terms of measurements

Spark on #2 seems to be the issue - here's what we know:

Took an inductive timing light out and could show that all cyls fire up until 3500 rpm. At that point, #2 starts to drop out as you approach 4000rpm. At 4k, #2 is nearly completely dead. Maybe one fire every second or so. Therein is our issue.

At first we thought this could be just the ignition coil for that cyl - replaced it but still an issue. So - this is now leading us back to the ignition switch box (part #817323A1) ("CDI?") - This is a $300 or so part which I'd like to avoid having to replace only to find it's not the issue, or there was something simple to try first -

Any suggestions?

Thanks all!

i would say that its a cdi unit down buy a used one if your cash strapped and if it solves the problem get a new one !

as regarding the coil there either work or they dont so doubt it could be that.

i had a simular problem on johnson v4 turned out to be cdi unit, its not a bad idea to have a couple of spares lying round

 

[jerryjerry05]

Re: 1991 Force 150 Power Loss at WOT

HSC, Sushry stopped posting on this over 2 months ago.You should start your own thread. For some reason this upsets some of these guys.
E-bay sells LOTS of used parts.This time of year is a good time to buy.J