1990 Force 120HP carbs mix adjustment help

[Nordin]

Hard to say when not have the engine to look at.
But I think you problem are in the LU.
The pinion gear have to have right play/back lash.
Too tight the pinion gear will press at the forward and reverse gear.
But as it idles in neutral at 800 RPM and the press are at the F and R gear even in neutral, I would guess you have a too tight end play in the prop shaft.
The nut holding the bearing cage assembly for the prop shaft should be tighten so it will bottom the cage.
I interprets it as you have to loosen it a bit to be able to turn the prop shaft.

 

[Nordin]

Have not looked at the wideo cause I can not and will not login to drop box.
Pulling the plugs and put the drives in forward gear and then compare how hard it is to turn the flywheels may give you some clue.
But you are turning the impeller too and depending how flexible the impellers are it might give you some wrong feeling about how hard to turn.

 

[gica]

Have not looked at the wideo cause I can not and will not login to drop box.
Pulling the plugs and put the drives in forward gear and then compare how hard it is to turn the flywheels may give you some clue.
But you are turning the impeller too and depending how flexible the impellers are it might give you some wrong feeling about how hard to turn.

Thanks for the reply. You should be able to see the video without login in right?
I opened the drive and by the clutch dog there were 2 spacer washers. I took out the thinner one put it all back and now the drive is moving just like the other one same play same turning without the plugs in in gear as you said.
I went to the lake yesterday and unfortunately it still dies at idle when in gear. If I run the good motor and start the other one while moving I am able to get it going and after running it a bit it does stay in gear even at idle. It is an improvement. But right out the door it doesn't.
Another issue I noticed I cannot start the engine up after it has sat for a while. Even in the parking on the hose if I try to start it I have to use starting fluid it does not start even with the choke activated by pressing the key in.
Once I start it with the fluid it does restart right away. And I swapped the carbs from the other drive at the lake it made no difference, it was not the carbs. I suspect the fuel pump?! Even though I already rebuilt it, or who know what else it could be. The moto was fully rebuilt.
Otherwise, it goes to 4k rpm and in tandem with the other one it gets the boat to 35mph. I even ran it by itself, but it does sometimes act like it is starved of fuel when accelerating.
Your help is highly appreciated. Keep it coming please.
Here is the link to the video again, try it.

20240424_161648.mp4

Shared with Dropbox

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[Nordin]

Hard to start then I advice you to check the reed valves.
I do not know when they started to change the reed valves from stainless steel to plastic valves but the plastic ones had tendency to break.
I my opinion the stainless steel reed valve are much better.
Is it hard to start after sitting for a while even if you use the choke?
How are the choke butterflies adjusted? Are both closing fully?
From my experience these engines are bloody hard to start cold without using the choke.
BTW I looked at the video and it sounds like the LU is to tight at the prop shaft assembly.

 

[gica]

Yeah if it sits for awhile then I have to spray fuel at the top carb and it starts. Might take 2 tries but it does. Then it restarts no problem. The choke butterflies are fine remember I swapped the 2 carbs with the other motor and they work fine there. It was starying fine until a few weeks ago. Don't know what happened.
My issue was the running and dying then.
Now it is this not starting with thebchoke which is electric push key type.
As far as the prop being too tight, I just removed the prop shaft and main shaft and as I mentioned above I removed one of the spacers that go between the cluch and the front gear. There were two there. The shaft was hard to turn when I tightened the retainer but after removing one of the spacers it was exactly the same as the shaft on the other engine.
I am including a picture of the diagram,
the spacer is number 44.

 

[gica]

I took out the reeds and they are not the plastic ones. No light going through don't see cracks.
I also remived the fuel pump and the membrane shows a little tear. I ordered new gaskets and membrane for everything.

 

[gica]

The elbow connector for tye cylinder drain cover was loose could turn it by hand. So I will have to remove it and tighten it.
I will change the hoses and add clamps. There are no clamps there, don't know if that makes a difference.

 

[gica]

Hard to start then I advice you to check the reed valves.
I do not know when they started to change the reed valves from stainless steel to plastic valves but the plastic ones had tendency to break.
I my opinion the stainless steel reed valve are much better.
Is it hard to start after sitting for a while even if you use the choke?
How are the choke butterflies adjusted? Are both closing fully?
From my experience these engines are bloody hard to start cold without using the choke.
BTW I looked at the video and it sounds like the LU is to tight at the prop shaft assembly.

So as you can see above the reeds are stainless not plastic. They look new. I am waiting for the gaskets to put it all back. As I said the membrane on the fuel pump had a little scratch looking mark along the circular line. It was showing only on one side of the membrane not the back. So, I ordered another one since I don't think there should be any marks. I am also waiting for that. I sure hope I find the reason I get this dying in gear issue, but it has to be a fuel supply problem?! The lower drive is not tight anymore.
I also replaced all of the hoses to and from the fuel pump with 5/16 ones and there are a few short ones and even one that is 1/4 inch. I also clamped everything. I assume having a loose hose is not that good for the suction.
Let me know if you have any more advice. Thanks

 

[gica]

I got all the gaskets and the fuel pump membrane and gasket. In the pump I took out the screen and there was some sediment in there, sand and black stuff.
Cleaned it put it together, changed and clamped all the holes, new fuel filter, put the reeds and gaskets plus carbs back on. The motor now starts without spraying starting fluid so that's a plus. I am almost afraid to put it in water to see if it still dies in gear. So that is where I am.

 

[gica]

Put it back on the lake and I had to adjust the idle screw all the way up. It held idle at 1150 and 800 something in gear. It sometimes died but a lot of times it was ok. I still think there is an issue because I had to turn the idle screw all the way in.
I must be missing something. The propeller is a 13x19. It goes to 4400 ROM at WOOT I think a 13.5x17 or 15 would be a better one allowing higher RPM and better fruising at low speed. What do you think?

 

[Nordin]

I think the recommended RPM at WOT for best performance is 4800-5200 RPM.
Try to go down 2 in in pitch, 1 in down will rise the RPM about 200.
A 17 in prop would end up with about 4800 RPM at WOT.
If it sometimes will die when put in gear at 800 RPM in gear, try to rich the air/fuel mixture at the carbs with about 1/8 turn.
1 1/4-1 1/2 turn out from seated is a general setting BUT the setting can be from 1 turn to about 2 turn.
You have to try and tune to the best setting for your engine.

 

[gica]

I think the recommended RPM at WOT for best performance is 4800-5200 RPM.
Try to go down 2 in in pitch, 1 in down will rise the RPM about 200.
A 17 in prop would end up with about 4800 RPM at WOT.
If it sometimes will die when put in gear at 800 RPM in gear, try to rich the air/fuel mixture at the carbs with about 1/8 turn.
1 1/4-1 1/2 turn out from seated is a general setting BUT the setting can be from 1 turn to about 2 turn.
You have to try and tune to the best setting for your engine.

Thanks man I don't know why the guy I got it from used 13x19 to replace the old propellers that have a 21 marked on them. I think everywhere I looked for the 120s they recommended 13.5 x17 or 15.
Anyways so to keep the motor running în gear I had to have the engine idle at 1100 RPM when I put it in gear it showed 450-500 and that's why it died.
I have pretty much exhausted all I can think of to fix this issue. The only thing left is the recirculation system being plugged up, but I just rebuilt the engine and I am sure I cleaned the screens, or maybe the valves in the plates are bad?!
And there could be too much 2 stroke oil in the old gas and even though it works fine on the old engine next to it, it could be more sensitive in the new and rebuilt one. This is a shitty problem non the less.
Should I go down to 15 pitch or is 17" fine?
Thanks again

 

[racerone]

It is not TOO MUCH oil in the gas.------Do some trouble shooting.-----The motor may be running on 3 of 4 cylinders.-----Do not drop pitch on the props to gain RPM without knowing the reason.-----Have the motor run on a dyno to determine actual power output of the motor !!!

 

[gica]

It is not TOO MUCH oil in the gas.------Do some trouble shooting.-----The motor may be running on 3 of 4 cylinders.-----Do not drop pitch on the props to gain RPM without knowing the reason.-----Have the motor run on a dyno to determine actual power output of the motor !!!

Thanks man so I have been trouble shooting for ever. I wrote about it throughout the thread. I don't know when this started since I haven't put it in water before the rebuild. So I do have spark on all the coils. CDI stator and trigger are good measure good. Fuel pump and hose all new. No air leaks tested with starting fluid spray. It gets 4200RPM at WOT and runs great at higher speed when used with the other motor. By itself it runs ok with the adjustments reaches 3k RPM just like the other motor.
I had to remove a spacer from the lower drive, it had 2between the clutch and the forward gear, because it was too tight when tightening the prop shaft after rebuild and it now acts the same as the other one as far as turning it by hand, play etc.
As far as running on 3 out of 4, I will pull the wires one by one and see, good idea.
Both motor are getting sub par RPM at WOT. The rebuilt one is at 4200 and the other at 4400 or so. Boat goes 38MPH at WOT with both running.
It's a struggle to adjust it to stay at idle in gear. I have the stop screw all the way in.
I cannot put it at 900 in the water it will die in gear. On the water hose it runs great.
I am trying to find out what the dyno deal is. But please keep responding and giving
advise guys. Really appreciate it.
By the way I am in LA and I called 10 different places and nobody works o these anymore. I am on my own with this.
You guys are it for help
The volts on the rebuilt show 16V at WOT with a 5 wire rectifier. I think it is too much. I read about it and being a 7Amp system they say it is not a big deal. I did buy the original black rectifier and I will use it i stead of thw 5 or 6 wire
one. The other motor has a 6 wore and it shows 12v at idle and a little more at WOT.

 

[gica]

Ok so on both engines when I take off number 1 and 2 plug wires there is little change in running but there is spark. On 3 and 4 especually 4 the engine dies. But both are the same at idle.
I just sprayed 1 can of starting fluid at the intake recirc area and nothing. If I spray the carbs at the mix screws engine dies it hapens on both motors.
Ok I just sprayed the exhaust side and one area caused the motor to bog down and even died once. Can that cause bad idle?

 

[gica]

So when I rebuilt the engine I changed the gaskets. Here are pics of some of the bolts from the exhaust cover. One in particular is rusted all the way in. I am sure I cleaned it when I put it in. I did not use any sealant on the bolts though.

 

[gica]

Here is a picture of the spark plugs after usage. The problem engine plugs are pretty clean with a drop of black fuel/oil mix. I don't even know if that drop is oil or water. The other engine plugs look different.

 

[gica]

I just sprayed carb cleaner on the 2nd engine exhaust cover and it also dies. Must be normal. Still the plugs are too clean on the problem engine.
I did compression again and 1 and 4 are 140 2 and 3 135.

 

[Nordin]

Clean plugs maybe is a sign of water intrusion.
Check the head gasket, looks like it is okey from the compression numbers but there are also a chance it will have water intrusion from the exhaust side.
Leakage at the gaskets at the exhaust cover can also cause water intrusion to the cylinders.

 

[gica]

I just took a picture of the #2, 3 and #4 cylinders with an endoscope cam. #2 and #3 look dry #4 looks wet that is not normal right? Even thoigh it's the bottom and everything reponds to gavity.
I am taking off the exhaust cover. Should I take the head off also. I did get good compression at 140 and 135?