1997 Force 120 will not idle

[Davlabo]

Hi all. Thanks for the help. I'll keep it brief. I just bought this boat a few weeks ago. It basically sat before I bought it. I siphoned out the old gas, and ran it for awhile on a portable 5 gallon tank. It ran great. Began running it on new gas in the main tank. Fuel filter was visibly collecting pieces of varnish from old gas. I put in new filter. No more varnish coming through the filter at this point. It recently has decided not to idle (whether on main tank or on portable tank). It otherwise runs great. I did notice that the upper carb stalls when I put my hand over it, but if I put my hand over the lower carb, the motor speeds up. A related symptom (I assume) is that the idle adjustment screw on the lower carb does nothing, whether turned all the way in, or anywhere in between. The upper carb idle screw works just fine. Also, much stronger suction of air from the lower carb. Is the lower carb not functioning properly? Should I clean it?

Thanks!

 

[Jiggz]

Re: 1997 Force 120 will not idle

Those are not the idle screws, instead they are the idle fuel-air mixture screw adjustments. It adjusts how rich or lean the idle setting is. The idle screw is only one and it's located at the bottom of the tower rod. When you cover the lower carb and the engine races, it's because the lower carb is not working or does not provide fuel. By covering, the lower pistons don't have to compress anything thus the upper pistons have lighter loads. Covering the upper carb stalls the engine because it's the only one working. This could be a faulty float or clogged lines. You cannot properly set idle on a misfiring engine and in your case it's about 50% misfiring. You need to check and clean and probably rebuilt the lower carb. And then set the idle and idle fuel-air mixture settings following the sticky guide on top of the forum list.

 

[Davlabo]

Re: 1997 Force 120 will not idle

I'm thinking the idle jet is clogged, since the boat runs great other than not wanting to idle and has no problem hitting WOT and top speed. Is there an easy way to clean the idle jet without removing the carbs? I dropped both float bowls and cleaned them. The idle jet is supposed to be screwed in at the top, but I don't see any screws.

 

[Jiggz]

Re: 1997 Force 120 will not idle

Well if it works fine at high speed, it's definitely an idle jet problem. The jet itself is covered by another screw. On the attached diagram the jet is item #10 while the covering screw is #11. YOu can check the entire parts listing at boats.net

 

[droach77]

Re: 1997 Force 120 will not idle

There are two different sets of these style carbs without the choke setup on them, i have a set of both one set has idle jet the other does not. Sometime in 97 depending on the serial number they swithed to the carbs without them, my 98 90hp did not have the jets but i had to take them off due to deterioration. I found a set off of a 92 90hp and that was the only difference was the idle jet, and the main jet sizing was a little different, but all other parts were the same. You should check the needles for wear and properly set them, if that does not work you are gonna have to get in the carbs good and clean and inspect them. good luck



dave

 

[Davlabo]

Re: 1997 Force 120 will not idle

Thanks Dave and Jiggz. I pulled off the carbs. I must have the "other" version Dave mentioned because I have no idle jet. The bottom carb had some junk around the bottom of the main nozzle, which runs up through the center of the carb (#15 in the diagram above). The by-pass tube also looked clogged. I am going to soak everything. Two more questions: (1) how do I get the main nozzle out? It looks like it should turn, but I don't want to break the by-pass tube running through the center of it. I think my rebuild kit gave me a new main nozzle but no by-pass tube. Question 2: What the heck does the by-pass tube do? What is its function?

Thanks again for your help!

 

[droach77]

Re: 1997 Force 120 will not idle

DO NOT MESS WITH THE TUBE AND NEEDLE! soak and spray and blow with lots of compressed air but do not mess with that stuff.


dave

 

[jewelsource]

Re: 1997 Force 120 will not idle

I had an identical issue with my (recently purchased) 79 Chrysler. blocking intake and all (except opposite carbs )
Chrysler and Force are almost one in the same.

I went through the carbs (cleaning and all) - only to realize that the fuel pump diaphragms (Part #8 in diagram) were dried out.
Same here.. ran at high rpm, but would not idle.

If your fuel pumps look the same (your carbs do on previous posts), then get a fuel pump rebuild kit (actually 2 kits).
Previous to catching the culprit, mine ran great too. Getting the boat to run after tarnish and old fuel, I too played with the carbs (which I dont regret - because its one less thing to worry about later) I actually got it to run in the water and then failed the next outing. Apparently, with all the toying around: fuel additives and a bit of motion on the fuel pump, the diaphragms simply gave way and cracked on me.

I suspect you will notice the same and be surprised when you open yours up. The reason covering the carbs get no response is because the gas is not getting pumped.

I would take the extra step and take care of this. In any event, it's probably a good piece of mind and you don't want it to give way while you are out.
...or for the piece of mind just dismantle the pump and see if the diaphragms are supple enough to do their jobs.

In reference to diagram: All I replaced were parts 7,8 & 20 ...and it runs like a champ!

 

[Frank Acampora]

Re: 1997 Force 120 will not idle

It is not a bypass tube, but rather a feed tube for the low speed circuit. At low RPM, there is not enough airflow through the carb for the main venturi to deliver fuel through the screw-in dip tube. At these speeds, the thin brass tube feeds the low speed circuit. If fully clogged, you can pass a fine wire up it. I use 1/32 welding wire. If only partially clogged, you can use a pipe cleaner soaked in WD 40 or penetrating oil.

You really need to clean both carbs NOW before running the engine again: A faulty low speed circuit will cause lean running at high speeds and will most likely result in one or more melted pistons.

There is a special tool that looks like a flat bladed screwdriver with a notch in it. It is used to unscrew the main venturi dip tube.