1990 Force 120 carb question

[KenOverton]

I'm new here to the board, but I need some assistance if someone can help. I just bought a used boat 2 weeks ago and I have been going over everything prior to taking it out for the first time. The power head appears to have been re-built very recently. Everything has new paint and is very clean to be 20 yrs. old. When I started the motor yesterday it was idled very high, at almost 3000 RPM. Finally got the idle down around 1000 and it was running a little rough. Both carbs mixture screws were backed way out. I am able to adjust the lower carb, but the upper carb will not. Closing all the way or opening all the way makes little difference. I have a Clymer manual on the way by mail.

I am wondering if I need to look at anything else, mainly with the upper cylinders, if they have been run lean?

It is my understanding from reading posts on this sight to start with the mixture screws open from seated position 1 1/2 turns?

Motor starts easy and runs okay.

Any help for a new outboard owner would be appreciated.

Ken

 

[kend301]

Re: 1990 Force 120 carb question

Yes you are correct , Start by closing the adjustment screw and come out 1 1/2 turns and you will be close enough . You must do this on both carbs so if the one is stuck you need to soak it with wd40 to loosen it up !
What I would do is to pull both scews out first and check the ends of the screws for varnish build up . If you have a bunch of sticky gunk on the screws or in the screw holes , time to take the carbs off and clean them or you could try some seafoam to clear them out .

 

[ENSIGN]

Re: 1990 Force 120 carb question

Check the compression spark and fuel(for water)If there ok I would rebuild both carbs,somethings clogged up in the top one.It's also a good time to install a filter/separator between the motor and primer bulb.

 

[KenOverton]

Re: 1990 Force 120 carb question

Thanks, for both replies.

Plugs are clean, slightly "oil wet", look new. No water in cylinders either. I will inspect the upper carb closely and go ahead and do a compression check while I am waiting on my manual. I am hoping it is something simple like gunk. Will post what I find.

Thanks again.
Ken

 

[pnwboat]

Re: 1990 Force 120 carb question

If the plugs are firing, you should show some slight carbon build up on them. If the plug looks like it's brand new, then the most common cause is it's not firing due to weak or lack of spark.

 

[KenOverton]

Re: 1990 Force 120 carb question

All 4 are exactly the same, so I am assuming they are new. Engine starts within 3-4 seconds when cold, just using choke, without advancing the throttle. This was my reasoning. Will post everything I find.

Ken

 

[KenOverton]

Re: 1990 Force 120 carb question

I think I may have found the problem, but if I am off-in-left-field, someone please correct me. When I disassembled the carburetor for cleaning, I found the idle tube extending into the opening of the main nozzle to the point I cannot remove the nozzle without damaging the tube. My manual shows the nozzle in contact with the nozzle wall, just above the slots used to remove the nozzle. I am looking for a kit online now to re-build but if someone knows something I don't, please jump in.

Thanks
Ken

 

[pnwboat]

Re: 1990 Force 120 carb question

The idle tube in all of the carbs that I've taken apart also have the idle tubes sticking down even with the main nozzle. I always thought this was normal, and you needed a special flat blade screw driver with a notch in the middle to remove the nozzle without damaging the idle tube. I now see that in my Clymer's manual, it shows the idle tube up a bit higher so it looks like it's out of the way. Never noticed that before. Regardless, it's probably normal for the idle tube to be in the way of the nozzle since I've seen it so many times. I'm by no means an "expert" in this area, maybe some other folks can chime in on this one.

I generally leave the idle tubes alone except for taking some carburetor cleaner with the small plastic extension and forcing some up the idle tube. Make sure I have good flow of carb cleaner on the outlet side of the tube. Follow up with 100 PSI blast of compressed air.

 

[KenOverton]

Re: 1990 Force 120 carb question

I'll hold off on the kit for now. I did not find any blockage in any of the passages, carb cleaner flowed readily through everything. I'll continue with verifying everything else and keep that in mind if I don't find a fix. Spent last week re-sealing the tilt/trim system and just now getting to the rest. Thanks for the insight.

Ken

 

[KenOverton]

Re: 1990 Force 120 carb question

Ok, finally got around to going over this motor. Compression was 155, 150 155, 150. Checked timing at cranking speed and it is at 28 BTC. I was able to adjust the upper carb mixture after a thorough cleaning. Motor idles a little rough, but runs good. My concern is if I happen to get the mixture too lean, as I am not a pro at carb adjusting, since I haven't had a car or anything with a carb in better than 15 years. What would be the first indication that I have one or both too lean?

Ken

 

[pnwboat]

Re: 1990 Force 120 carb question

Here's one method that I use. Others may have additional tips. Once I get the idle reasonably good in the test tank/muffs, crack the throttle WOT quickly. If it dies, I back the idle mixture screws out 1/8 of a turn to enrich the mixture. Let it idle for a minute or so and try again until it stops dieing. If I do this and it starts to stumble before it dies, the it is too rich, so I turn the idle mixture screw in 1/8 of a turn. Typically 1 to 1 1/2 out from lightly seated is you will end up with the adjustment. Just don't go any leaner that 7/8 out from lightly seated. In addition, you should have a cheap inline filter between the fuel pump and the carbs. This will prevent any crud from getting into the fuel bowls/needle valve and cause a lean condition resulting in a melted piston.

 

[kend301]

Re: 1990 Force 120 carb question

Here's one method that I use. Others may have additional tips. Once I get the idle reasonably good in the test tank/muffs, crack the throttle WOT quickly. If it dies, I back the idle mixture screws out 1/8 of a turn to enrich the mixture. Let it idle for a minute or so and try again until it stops dieing. If I do this and it starts to stumble before it dies, the it is too rich, so I turn the idle mixture screw in 1/8 of a turn. Typically 1 to 1 1/2 out from lightly seated is you will end up with the adjustment. Just don't go any leaner that 7/8 out from lightly seated. In addition, you should have a cheap inline filter between the fuel pump and the carbs. This will prevent any crud from getting into the fuel bowls/needle valve and cause a lean condition resulting in a melted piston.

Excellent advice for those who do not have a good "motor ear" to hear the very slight change when adjusting at idle only. As he stated be sure you are at least 7/8 to 1 turn out , if you are under that or over 2 turns out then you need to find the cause .

 

[KenOverton]

Re: 1990 Force 120 carb question

Thanks for the help. I'll give the WOT test a try next time I have it out of the garage. I went back and double checked how far the mixture screws were "out", and the upper carb was exactly 1 1/2 turns, the lower carb, which I haven't cleaned was 3/4 of a turn out. I opened it another 1/4 turn and will give that a try.

Thanks for the help.
Ken

 

[KenOverton]

Re: 1990 Force 120 carb question

I ended up removing the lower carb for cleaning and it was in bad shape. To make a long story short, I ended up destroying the by-pass tube and main nozzle trying to get them out so I could get all of the green crust out. I am trying to install the by-pass tube but cannot get it all the way in. The wooden dowel I am using just breaks. Attached is a picture showing how far I have it in. Any help would be appreciated. I am a little concerned about using anything much harder than a wooden dowel.

Ken

 

[pnwboat]

Re: 1990 Force 120 carb question

I'd be concerned too about damaging the idle tube too. I looked in my Clymer manual and it says to use a small punch to remove it. Doesn't say what to use to reinstall it, but I would assume a small punch?

 

[KenOverton]

Re: 1990 Force 120 carb question

I finally got it seated even with the bottom of the main nozzle. I made a plastic dowel from a cheap plastic TV technician's adjustment tool. Now, I found I damage the fuel jet somehow, so another online order and wait. Wished I had seen this earlier. Hope to get it on the water next week.

Ken

 

[pnwboat]

Re: 1990 Force 120 carb question

Yeah I feel for you. I normally don't touch the idle tubes. Just clean them out with carb cleaner and compressed air. Take a small wire and run it through them sometimes.

 

[Frank Acampora]

Re: 1990 Force 120 carb question

This is why I NEVER recommend rebuilding carbs; they very rarely need it , usually a good cleaning will do, and the potential for damage is great.

 

[KenOverton]

Re: 1990 Force 120 carb question

This is why I NEVER recommend rebuilding carbs; they very rarely need it , usually a good cleaning will do, and the potential for damage is great.

My thoughts also.

 

[kend301]

Re: 1990 Force 120 carb question

Agree x3 here , clean the bowl , make sure the vent is clear , carb cleaner through everything else and let 'em run ! I just did new idle tubes on mine , What a pain but I took the cheap way out , hobby shop for tubing stock and made mine . I will never pull them out again !!