1995 Force 120 will no longer idle

[beepx2]

Last year I had great use of my Trophy 1802 with the 1995 Force 120. I had replaced plugs, fuel pump, filter, fuel line, I run from an external tank with non-ethanol fuel. I was able to adjust the idle perfectly last year, properly fitting the idle screws at 1-1/4 turns. and adjusting the idle stop to get about 800rpm warm idle in the water. Last fall, I was running as normal, and suddenly it would not idle. When I slowed down to idle in gear it would slowly drop revs in gear and sputter out after 5 secs or so. To start it I would need to set the throttle high, but then when I reduce it to engage gear it would stall. It still performs fine at full speed, revs to 5000 or more, and provides full power. Compression was even at 120 last time I measured 2 years ago. I think the engine has relatively low hours.

I removed and disassembled the carbs, and noticed two things: The floats were set lower than spec by about 10 degrees or so, such that the fuel level in bowls would be lower than spec. I also noticed that in one of the carbs, the main nozzle was completely unscrewed and just fell out when I unscrewed the float bowl bolt. So I screwed in back in.

I've reassemble the carbs and reinstalled. Engine starts if I set it for high throttle, but when I slow it down to idle it will still sputter out. I also noticed that at low rpm as it is sputtering and before it stalls, it is pulsing sprays of fuel out the top carburetor, which accumulates and is dribbling out of the carb throat. (this does not seem normal)

My theories:
1) somehow the needle valve on that carb isn't closing, and the fuel pump is pushing fuel up the main nozzle into the air flowing through the carb throat. Maybe I messed up by adjusting the float angle. Theneedles and seats looked fine when disassembled.
2) There may be something wrong with the reed valves such that I'm getting airflow back through the upper carb. (I've never worked with those before)
3) when messing with the carbs I may have damaged the idle tube(s), bending them around while tightening the main nozzles.

Any ideas what to try next? I'm stuck. I installed a new starter today, which spins and starts the motor quickly. The motor is on a boat in my backyard, near my workshop where it is easy to get to.

Thanks!

 

[jerryjerry05]

Fuel out the front of the carb: could be the fuel pump is bad? the float stuck?
It sounds like the motors sucking air from somewhere.
You had the carb apart. Reset the float: carb upside down- the float should be even with the carb body.
Inspect the needle: solid tip?=the bowl inlet where the needle sets, there's a rubber o-ring that could be missing?
Needle with rubber tip: tip should be smooth and no grooves.

Starting fluid test. Get motor running, spray starting fluid around the intake side of the motor: this includes under the carb and around the packs/coils and by the 4 port covers and anywhere the air might get in. The gasket under the port covers are thin and get sucked out of position and allows air to be sucked in making for poor idle.
One tiny backfire, cough or stutter can blow the port cover gaskets.

 

[beepx2]

Well I pulled the reed valve blocks and I see that one valve is missing, many are cracked or chipped, and they all hang open a bit leaving an air gap. I'm surprised it ran at all like that. I imagine I was getting little compression in the top two cylinders at idle. I think I'll replace them first and try running it again. I know for sure floats weren't stuck and fuel pump is working, and the needles are rubber tip in pristine condition. Any suggestions on reed valves? Original were stainless, I don't know how long they lasted. The valve blocks and mating surfaces are all OK. Thanks for your input, Jerry.

 

[Mc Tool]

A not very good tuners trick is to bend the reed stoppers so to allow the reeds to open further . There should be a spec to set the stoppers . It is possible that a po has bent the stoppers ,this wont help longevity of the reeds so maybe look into this before replacing reeds.
Just found these boys . Fibre reeds are said to be more responsive and they dont destroy the motor if one gets loose.
Make sure the broken remains are not stuck inside the motor ......they like to hide in a transfer port and jump out after you have rebuilt the motor .

 

[Nordin]

Replace the reed valves with new stainless steel valve paddles.
They will last for a very long time.
In mid 90.es they replaced the stainless steel ones with plastic typs ones, but in my experience they do not last as good as the stainless typs.
You might find used ones at Ebay or buy new ones.

 

[jerryjerry05]

Good find!! The reeds can actually be opened a tiny bit and not affect performance.
But missing that's not good.

 

[beepx2]

I saw that carbon set on ebay, but something is wrong as the picture shows sets of 5, and my motor has sets of 4. I couldn't find any stainless ones, only full valve block assemblies. I ordered a set of fiber ones from CCMS, which look correct in the photos (Link below). How might I find the right spec for the spacing of the stoppers? It's not in my Force service manual. A mystery to me is how long the reeds have been broken. I recently put on a new prop which lets the engine rev to redline at WOT, so maybe that did it. I will look for the broken bits in the motor before reassembly. I plan to use a bore scope through the plug holes, and in through the gap where the valve blocks go. Is that the transfer port?

Many thanks for the help guys!. I will post some pics of the broken valves, and let you know what happens with the new ones.

BTW the starter had been turning slowly and heating up the cables. last time a bit of smoke came out of it after a lot of hard cranking. I bought a new starter and put it on, and the difference is like night and day. I should have done that a long time ago. Piece by piece I'm refreshing this motor, hoping that eventually it will be reliable: Plugs, fuel pump, filter fuel line, rectifier, impeller, prop, rebuilt the tilt drive motor. I like how simple and easy to work on it is, and how cheap the parts are.

CCMS Force Sport Reed Valves 100-140hp 1993 & Up PN.544S - Chris Carson Marine Service and Supply

This is a complete set of CCMS composite Sport reed leafs for your Force 100-140hp 1993 & Up PN.544S Our Sport Reeds are good to 6500 rpm at Wide Open [...]Read More... from CCMS Force Sport Reed Valves 100-140hp 1993 & Up PN.544S

chriscarsonmarine.com

 

[Mc Tool]

Sometimes ebay just has a generic pic of an item ,usually small print says "actual item may differ from pic " but yeah , sorta puts a bit of strain on the confidence ( I have a set of rings for the "other " 4hp Yamaha )

 

[beepx2]

Update: News reeds are installed. Kind of an easy job, my first time doing it. 9 of the 24 old reeds were chipped or cracked. One was half gone.

Reattached the carbs, and she fired right up. No gas leaks. Idles fine at 900-1000 on the muffs, but when I go lower it idles rough or dies, although the motor was cold at that point. I tweaked the idle screws to no effect. In the past it idled nicely at 800 rpm in the lake. Next I will check the timing to see if it's out of spec. The new starter really spins that motor like crazy, what an improvement - I should have bought that first thing.

 

[jerryjerry05]

Update: News reeds are installed. Kind of an easy job, my first time doing it. 9 of the 24 old reeds were chipped or cracked. One was half gone.

Reattached the carbs, and she fired right up. No gas leaks. Idles fine at 900-1000 on the muffs, but when I go lower it idles rough or dies, although the motor was cold at that point. I tweaked the idle screws to no effect. In the past it idled nicely at 800 rpm in the lake. Next I will check the timing to see if it's out of spec. The new starter really spins that motor like crazy, what an improvement - I should have bought that first thing.

NOT IDLE screws. while they will affect the idle thats not what they're for. They're for air/fuel mix at low rpms. The idle screw is on the towershaft. Set the air screws at 1 and 1/8th turn out. Then adjust from there. Once you get it running, do the starting fluid test. Start the motor, spray SF around the intake side of the motor. Around the base of the carbs and base of the coils and packs and around the 4 port covers. If spraying makes it run different??? then it's sucking air somewhere???