Timing a 1998 force 120.....runs terrible at spec

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
I have a 1998 force 120 that has low hours. I rebuilt the fuel pump, replaced reeds and the plugs. Carbs are set right... 1 1/4 turns and have been thoughoughly cleaned. The motor has 2 settings for timing posted on a sticker. 5 degrees at idle and 28 wot. I set it at idle and it seems to run good but is off considerably at wot. When I set it at 28 wot....it idles fine but sputters as Rpms increase. I know you set it at wot but why would it be off so much between the 2 settings? The compression checked out great. It would seem that 5 degrees idle should be close to 28 wot. I followed the timing procedure but did it in neutral vs in gear ... Not sure if that matters. I'm confident this is a timing issue but am stumped
 
Last edited:

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
When you set it at 5 degree idle, how did you check the WOT? Static? if yes, what was the timing set at? Have you verified at WOT position if the carbs' throttles are at horizontal? Have you verified the carbs' throttles, cam and linkage, idle screws and also the timing tower to be mechanically zero'ed before setting timing?
 

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
At 5 degrees I did not check wot readings. Based on the published procedure, I discarded the 5 degree setting and went right to setting wot at 28. I set the carbs right and at wot the carb plates are horizontal. How would I check the timing tower to be zero'd out?
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
To mechanically zero, it means the carbs throttles are are closed or vertical position; the #1 piston is at TDC, the flywheel zero marking is aligned with the vertical timing indicator, the cam slot marking should be aligned with the eccentric screw slot marking, the control throttle in neutral and the idle screw is not pushing against the block but just barely touching. If you time it in this position, the flywheel should be indicating zero degree with reference to the vertical timing mark.

After attaining the above adjust timing (statically) and set to 28 degrees at wot. After setting this you should set the idle screw for idle rpm of 750 RPM idle in gear in water. This usually translates to 900~1050 rpm in neutral on muffs or tub.

The timing tower is zero'ed out when #1 piston is TDC with the flywheel zero marking aligned with the vertical timing indicator, carb throttles closed, idle screw not pushing against the engine block and finally the cam marking aligned with the eccentric screw slot. If you push the control lever all the way forward, the timing tower should also move at its maximum travel and opening both carb throttles in full horizontal. If they do not fully open adjust the link rod swivels and/or the eccentric screw or the tie bars on the carbs, as appropriate.
 

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
Great summary, thanks Jiggz. I'm confident on all the settings except TDC. Let me get the #1 piston to TDC and make sure the timing mark shows zero. Assuming it doesn't, is there an adjustment to set the timing marks to zero ? I really appreciate the help.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
The zero marking on the flywheel is arbitrary to the #1 piston being TDC and it should be permanent as this is the function of the flywheel shaft key. To verify it is zero'ed you will need to do it with a timing light which will validate if the trigger timing plate is also set to fire at zero degree. If the timing plate is not zeroed at this point, then you can adjust it with the timing rod to make sure everything is zero'ed mechanically and electrically. Then the next move is to set the WOT timing which in your case is 28 BTDC. Thereafter, you should set the idle speed using the idle screw adjustment.

The reason you set the idle screw even before firing is because the engine will not run or if it does it will not idle unless the idle screw is set. When you set the idle screw you will notice three things will be happening, the cam marking will not align with the eccentric screw slot anymore; the carb throttles will slightly open and lastly the timing will also advance.

Personally, I will try 2~3 full turns on the idle screw and try starting the motor. You can always start high and then lower it to around 1000 RPM on muffs. Technically, the manual says 750 RPM idle in gear on water. How that converts to idle rpm in neutral and on muffs depends entirely on the size of the prop. Note most of the time you do not have to zero mechanically but instead just go straight to setting the WOT to 28 degrees BTDC. However, if too many adjustments has been made with the link rod, eccentric screw and even the carb bar tie, mechanically zero'ing is your best bet to get the timing correctly set.
 

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
At zero degrees the piston was TDC...so I know the marks are dead in. I set timing to 28 wot and at idle it's around 5 TDC. The motor fires right up but with any acceleration, it sputters periodically. I tested spark and have spark at all 4 cylinders. The carbs are set right as is the idle. I'm not sue what this could be.
 
Last edited:

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Maybe someone will chime in on why an engine idling perfectly with perfect timing and properly set working carbs will sputter when accelerating. Unless there is a symptom of fuel oil blow back from the carbs. Then the problem could be the reed. But so far you have not mentioned any fuel oil blow back from the carbs.
 

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
I just put brand new reeds on it. The problem existed before the reeds.

New reeds
Carbs cleaned thoughoughly
New starter
New solenoid
Rebuilt fuel pump
New plugs
New water fuel seperator
Adjusted timing
Compression great on all 4
In line spark tester shows spark at all 4

Squeezing the ball while running makes no difference. I sprayed carb cleaner all around the carbs to check for leaks ...makes no difference.

I'm thinking intermittent spark or fuel problem leaning more toward spark. Bad stator?
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
If you are using a built in fuel tank, might try using a portable tank to eliminate a fuel supply issue with the built in tank. Also make sure the fuel vent on the built in tank is open and not plugged. You can open the fuel cap on the built in tank as a temporary test.

It's easy to check the resistance of the stator windings. Disconnect the Green/White and White/Green stator leads from the harness. Measure the resistance between the two leads that go to the stator. You should see 500 to 700 OHMs.

If the stator checks out OK, disconnect the two Yellow leads that run from the stator to the Voltage Regulator/Rectifier and see if that makes any difference. If it does, then the Regulator/Rectifier may be bad.

There is a Black ground wire that runs from the coil mounting plate to the engine block. This is the ground reference for the ignition system. Make sure it is connected and making good contact. I would recommend that you remove the wire and clean both ends.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
If none of the above suggestions makes a difference, maybe a youtube on the motor while idling and when it stutters will help greatly.
 

Derbytime1

Cadet
Joined
Aug 20, 2015
Messages
12
Don't want to appear to be hijacking here, but have a related question. I purchased a replacement flywheel (broken magnet) for our '96 120 Sport Jet from well know used parts dealer, and the timing marks are about 6 degrees off. Will I be able to move the trigger coil that far to compensate for that, or do I need another flywheel? It still ran fine intermittently with the old flywheel, but would not even fire with the new one.
Thanks in advance for any advice!
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Derby can you just start a new thread for you issues? And when you do, post pisc of the old and the new flywheel making sure you highlight what you think is the difference between the two.
 

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
This motor will be the death of me..... Checked the stator. Resistance is 700 on the nose. Disconnected the yellow wires, no difference. Cleaned the ground. Opened the fuel cap. Used an inline spark tester on each cylinder and don't see any noticeable change on any cylinder when it stutters. BUT NOW....I have fuel spitting out the vent on the upper carb. That happened on the lower carb a few months back and I had to clean the needle and seat (which looked very clean to start with). I wonder if this is going to be a fuel issue with the upper carb. I can't thank everyone enough for the help. This is a mystery I'm determined to solve, I also ordered the force manual for this today...good reference for who knows what else this thing will throw at me. Oh yeah....the gas tank and fuel lines are brand new so I don't think it's a tank issue.
 
Last edited:

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
http://youtu.be/Q-VnMs6DiYs

It seems like something new every time. I cleaned the upper carb that was spitting fuel out the vent hole. Made sure the needle and seat were working as it should. When I reinstalled everything, the boat ran but sputtered under load. Came out today and started the motor at 1/2 throttle. You can see in the video the accelerated idle. It stopped cold and wouldn't idle ( which is different than the issue beforehand which it would idle ok np it sputter at speed). This video doesn't really show the sputter it has under idle to mild acceleration but as usual threw a new issue at me. It wouldn't shut off! Never did this before. I pulled the fuel line off tomshut it down. I'm really ready to give up on this.
 

Sdriche

Cadet
Joined
Aug 26, 2015
Messages
16
Sorry about the dark video but this was typical of my issue. This was at 1/4 throttle and it would sputter periodically ( although hard to hear in the video) then shut off abruptly. Fuel issue?

http://youtu.be/s3p1kUT8YgI
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
The video links cannot be viewed because it states it is private. There are two ways to find out if you have fuel delivery issue or carburetion issue. First is with the use of a clear fuel filter between the fuel pump outlet and the carb inlet. Second, is with the use of fuel oil mix spray. With the second, you have to do it with a 2nd person on the boat in the water. With the engine cover off and the carb air covers off, try to slowly raise the control lever to 1/2 throttle while at the same time spraying directly into each carb alternately. If the engine rpm increases it means you have fuel delivery problem. If rpm decreases or worse motor stalls, it means you do not have fuel problem. The same holds true with the clear fuel filter. It should always stay at least 1/2 full with the engine idling or at WOT.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Sir, you definitely have a fuel delivery problem or it could be the fuel air mixture screws are not set accordingly. For troubleshooting purposes, set the fuel air mixture screws (this is the brass screw with a spring on it on top of each carb) to two turns out from lightly seated. As soon as you get the motor to run, you can reset them later. Remember, from lightly seated meaning you will turn each screw all the way in while ensuring you ease in before hitting bottom. Even better unscrew each one all the way out first to check it is not damaged, meaning it is evenly pointed. While out, spray in some carb cleaner in each hole. Then re-screw each all the way in easing just before bottoming out to prevent damaging the points. From there, unscrew each two turns out.

Next, remove the air covers on each carb. Get a spray bottle (even a clean used glass bottle sprayer will do) and fill it half way with fuel oil mixture from your tank. Get another person to do the starting and cranking. Do the test run again, making sure cooling water is provided accordingly. Stand infront of the motor with the spray bottle while directing the other person to do the starting. Make sure he engages the choke (push in the ignition sw and keep pushing while starting) If the motor coughs, like I saw in the video, stop the choking for the next round of starting. Instead, as soon as it starts coughing or running, start spraying fuel oil mix into each carb while listening for changes in engine rpm. You need to find out which carb when you spray into it increases rpm. This will tell you which carb is not getting enough fuel. From there you can start troubleshooting, especially with the float position or even with a sticky needle.

The other thing to check is to make sure the carb's throttles (not the butterflies at the front but instead those way back at the "throat" of the carbs. You will need a flashlight to look into the bore of the carb's to see this). are slightly open in their idle position. If not adjust the idle accordingly. And this is the idle screw at the bottom of the control tower.

At the same time, while you are able to run the motor with a fuel spray, monitor the clear fuel filter. Report your findings on your next post. Goodluck.
 
Last edited:
Top