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1996 FORCE 75hp idle issue troubleshooting

re: 1996 FORCE 75hp cuts off when idling or going from F to R

These are the troubleshooting steps I've completed:
1: seafoam - yea, don't laugh!
1a: adjust all carb settings (never do this unless you know what yiou are doing!!!!) lol ~
2: new NGK spark plugs
3: new spark plug wires
4: new water separator
5: new fuel filter
6: clean carb
7: replace all 3 REED BLOCK ASSEMBLIES (yes 2 of the 24 reeds were gapped open a little bit)
since I am a "newby" outboard mechanic I forgot to put LOCTITE on the 6 screws holding
REED BLOCK ASSEMBLIES on the reed adaptor plate! dumbass me!
8: sync ALL settings: throttle arm and cam linkage, WOT, timing, idle mixture, idle speed etc
THIS WORKED, at first! idling GREAT @ dock and after 2 short test runs. BEST EVER!
9: Long "test run" 1 hr @ 5000rpms and return to dock and FORCE dies trying to change gears!
BUMMED!

next on the troubleshooting agenda I have not done yet:

a: pull carb and intake manifold to add the LOCTITE to the 6 reed block assemblies I forgot to do the 1st time!
b: replace the primer bulb fuel line hose going to the fuel pump with BLACK "368 series" fuel hose. I have
grey fuel line (2015) from water separator to fuel pump. FORCE forums say grey fuel hose is a no no!
c: rebuild the fuel pump with new diaphragm kit
d: replace the rest of the fuel line (fuel pump2fuel filter2carb) w/series 368 BLACK fuel hose
e: replace the recirculation one way valves and all recirc tubing
f: replace idle mixture screw and the inlet needle (tip wear??)


Ok, so what am I missing that I should consider to fix this "idle issue"

THANKS!
 
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When I had the engine idling I set the the rpm's in N in water, prop on, at ~950rpms.
When in F the rpms were ~800-850.

It was idling GREAT @ 950-1000rpms @dock and 2 short test runs.
Then the hour long test run @ 5000rpms (ran GREAT) and retiurn to dock cut off when F to R
and will not idle again. I'm sure I had it synced in per specs.


a: I have the "crank timing" timing set at 32B like the manual says.
b: the idle mixture screw is set at about 1 to 1 1/4 turn out. That is what sounded the best. Seemed to smoke more & chug @ 1 1/2+ out.
c: prop on - in the water - idle speed screw adjusted to 950rpms. And I am trying to overcompensate for idle cutting off.
Anything lower sounds like engine is laboring to stay on.
d: yes, cam roller mark is in middle of elliptical roller and just barely touching it.

The weird thing was engine was idling/running GREAT @ dock and on 2 short test runs. The only other thing I can think it might be is that I FORGOT to put LOCTITE on the reed block assembly screws and they vibrated loose ????? in that hour 5000rpm run? ?? I was getting avg 22mph on a 24' pontoon on this 5000rpm test run when all I could muster in the past was about 18mph.
Or maybe the fuel pump diaphragm is acting up. The primer bulb is hit or miss on staying firm at all times. When we had engine dialed in at dock primer bulb stayed firm. After the long test ride now it's hit/miss. Gotta be a reason!
I'm going to get this antique outboard #purringlikeakittenAGAIN! lol ~

Agree on the 3cyl/1carb, but I must have got a diamond.
Been pretty decent since 1996. lol. All I need is 1 more season
it looks like, till the DF140bg arrives.
Who the heck knows when that will be!

THANKS for your advice! Much appreciated!

oh yea, the compression tested last year @ 135 across all 3 cylinders.
Is that ok for a 1996 FORCE 75hp?
 
Comp results: as long as all 3 are within 5# it should be ok.
The gauge is usually the problem when you get low readings on all 3.
Harbor Freight tools suck.
 


Good advice! Thanks!
Ordered the "diaphragm rebuild kit"
Ordered the this series 368 3/8" fuel line:
"Shields Series 368 Low Permeation Marine Fuel Hose 3/8" x 10 FT"
Ordered this 3/8" primer bulb:
attwood Universal High-Output Primer Bulb, EPA and CARB Certified
(I do not like the crimped clamp fittings (prefer the SS worm gear clamps)
This bulb has good reviews, if that counts.

In the meantime I snipped the primer bulb fuel line (GREY - last replaced in 2015 attwood stock pre-made) ends (the tips were deteriorating) and removed the old crimped on clamps from primer bulb barbs and replaced w/ the SS worm screw clamps. This seemed to be a tight fit. Ready to get the GREY off and use the "series 368" fuel hose! And I ordered CLEAR 3/8" fuel hose to replace the black fuel line (not sure how old that is) from the fuel pump 2 the filter 2 the carb. It was suggested CLEAR to look for air bubbles in fuel line from fuel pump to carb.

Found excellent instructions on specs (tower shaft idle speed screw all the way out - measure from stud to actuator + 1/8") to re- install/fine tune the throttle cable, I was off about 7 barrel turns. Since that re-adjusted the "tower shaft" I re-synced the throttle arm/cam making sure butterfly was snapped closed when cam mark in middle+ of carb eccentric roller screw and butterfly perpendicular @ WOT. Re-set the "idle stop screw" and "idle mixture screw" - started at 1 turn out then used my ear in 1/8 turns to find the best setting. It'ss been said this US Marine/OMC/Chrysler FORCE 3 cylinder/1 carb design is not the best BUT it sure makes it EASY to learn and adjust settings. Good uncomplicated way to learn the 2-stroke basics!

YEA! This seemed to get me BACK DIALED IN!
About 2 hours on the water @ 5000+rpms and varied a lot.
Upon return to dock the FORCE held it's idle this time! WHEW!
And this AM started ok, idle was at 800rpms instaed of the 1100rpms where I set it yesterday. ODD! But it still held idle, though chugging. Also, after about an hour the WOT fell back to about 44-4600rpms. Kinda strange but still sound like it was running cleanly. Might have had something to do with my trim adjustments under way.

Also the engine is THROWING LOTS OF WATER up while WOT so I thinking this outboard was mounted TOO LOW? If I get the gumption I might go ahead and put the jack plate on I'm going to use for the DF140bg and toy around w/ the caviatation plate depth.

Still have the reed block screws to do (after return last noght I was seeing some oily gas in the carb throat - from the reed blocks loose???) and replace all the fuel lines and rebuild the fuel pump diaphragm. I sure hope this really gets this 1996 FORCE 75hp dialed in. I feel good about it now but I want to feel GREAT and listen to this antique #purrLikeAKitten!

The boat shop we bought the boat from in 1996 has closed. They did ALL the mechanic work. (old school shop) but KNEW their stuff $$$ ! lol ~ When I went shopping for the Suzuki DF140bg and was told he had NO IDEA when outboard would arrive, that put me in a quandry. I asked him could he fix my "idle issue' and he said he would rather not dig into this old engine. So, guess what? Here I am, bought the specific SERVICE MANUEL, about $1000 in parts and learning way more than I ever thought there was to a 2-stroke (should have done this 20 yrs ago - would have saved a LOT of $$$, less headaches and self-satisfaction ~ it's not rocket science) to save a boating season on the salt waters of Bogue Sound in coastal NC!

#WINNING ...... so far! lol~

Much appreciation for the tips! Helps a LOT!



 
What are the compression values.----Perhaps remove bypass covers to inspect pistons / rings.---Condition of pistons / rings is the major factor in idling.----You need good cylinder compression.-----Good crankcase compression.----And minimum leakage past rings to contaminate the incoming fuel charge.----Water pump impeller is new I hope.
 
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cavitation plate is at the bottom of the pontoon.
That is the suggested height in the ortiginal imstallation manual.
My research shows the cavitation plate should be at the bottom of the transom.
 
The splash: have someone drive(high speed) as you watch the cavitation plate.
Does the plate ride at the same level as the water?
 
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underway. Water splashing up by the motor and up to the top & over the transom
going WOT. I see comments you should see the cavitation plate just under
the water surface at WOT. Is that correct? This caviation plate runs about 8-10"
underneath the water surface at WOT.
24' pontoon - 23" tubes - 20" tansom - 1996 FORCE 75hp
aftermarket prop: (currently installed)
12" dia x 9" pitch Solas SS 3 blade prop
orginal prop:
12 1/4" dia x 9" pitch quicksilver vengeance 3 blade SS
 
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Just at or under (from what I understand).

I'd contact the boat maker and see what motor originally came with the toon? explain the
problem and ask about the mounting??

You have a pick of the motor mounted on the bracket(need to see the bolts) and the length
of the lower unit.

Curious: what rpm's at wot? speed?
 
The pontoon mfg is Brunswick. This 1996 FORCE 75hp is the original outboard installed.
The outboard is hung at the lowest level possible on the transom. Top hole of the outboard bracket.


re:
Water splashing up by the motor and up to the top & over the transom
going WOT. I see comments you should see the cavitation plate just under
the water surface at WOT. Is that correct? This caviation plate runs about 8-10"
underneath the water surface at WOT.
24' pontoon - 23" tubes - 20" tansom - 1996 FORCE 75hp
aftermarket prop: (currently installed)
12" dia x 9" pitch Solas SS 3 blade prop
orginal prop:
12 1/4" dia x 9" pitch quicksilver vengeance 3 blade SS
 

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Looks like it can be raised up a few inches.
Is Brunswick still in the toon business?

Would you try going up 2 bolt holes?
If the outboard is TOO LOW in water would that contribute to WOT only reaching 4500rpms IF
all my other variables are correct?
Thanks!

You peeked my interest in Brunswick. A google search shows their last news flash was an agreement w/ BRP to be
their marine supplier ince BRP discontinued Evinrude mfg'ing. Brunswick has a LONG and interesting "marine" history!
I was leaning towards the E-Tec as my go to repower the last 3 years. Last speing I decide to go for it only to catch the
news of the Evinrude abandonment. Maybe a blessing in disguise? lol ~

Ordered the Suzuki DF140bg in March2021. Dealer says NO idea when it will arrive hence ALL my FORCE inquiries!
Been fun and a GREAT learning experience to keep this antique on the water. Went out 5 hours yesterday and
performed really GREAT. Did cut off at idle once transition F2R when return to dock but much better. Almost there!
I cannot WOT above 4500rpms. I am using the original prop specs and when I got
the pontoon it would WOT up 20 5300rpms. But not now. Trying to figure this WOT issue out now.

https://www.brunswick.com/our-company/our-history

2020

Mercury Marine Announces Supply Chain Agreement with BRP and Frydenbø.

In early summer 2020, Mercury Marine entered into a strategic supply and partnership agreements with BRP and Frydenbø. As BRP announced they would no longer make Evinrude engines, Mercury was selected to be the supplier of choice for BRP owned boat brands Alumacraft, Manitou, Quintrex & Stacer, and the preferred engine partner of Frydenbø’s boat brands Sting and Nordkapp in all global markets.
 
IF?? your getting 4500 then no more?? I'd look into the prop??
The same thing in aluminum might turn up to more.

You'll really like the 140horses.


OMC's been ABSOLUTELY PLAGUED with poor management and BAD decisions for as long as
they made the sterndrives. :(

Volvo came out with the outdrive and Mercury paid the millions for the copyright and then utilized the best
engineers and design people they could find.
OMC the stubborn (older brother) says we can do it with out anyone's help.
WRONG the 800 drive(disaster) the stringer drive (disaster) Cobra drive (disaster until Volvo came along)
But too little too late.
Then the latest debacle with the E-tech, again poor decisions. :(

Oh yea forgot about the OMC VRO screwup. One of the biggest mistakes of I can do it and make it better, NOT

Enjoy the day.
Real glad you didn't get the OMC
 
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