1991 force 120 decelerates after hitting top speed

[pnwboat]

Re: 1991 force 120 decelerates after hitting top speed

One other thing just crossed my mind. Check the wires from the trigger and stator. Sometimes the insulation on the wires gets rubbed through to the bare wire. When you move the throttle, it moves the trigger assy. which in turn pulls on the wires and causes the bad spot to short out to the block. There should be enough free play in the wires for the trigger assy. so that they don't get stretched too much. With the engine turned off, have a helper move the throttle back and forth and look at the trigger and stator wires.

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

i have a solenoid actuated choke butterfly....BLUEFISH...i can bypass them but my thinking is if the filters put too much restriction then it wouldnt have run great the 6 times i have had it out...just my thinking though...and my filter between fuel pump and carb stays full at all time and thats why i havent looked at the filters in the lines because if my thinking is correct then if there is a blockage before the pump then that filter would run dry...but like i said i may be thinking about it wrong...will be glad to bypass if it may help thanks...ok will look at the wires prolly tomorrow since a buddy is coming over to help me...i am gonna check the timing on it just to rule it out with his help there so we will check the wires while we r in it

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

i checked the diaphragm in the fuel pump and it is in great shap....also checked the wires on the trigger and stator and had plenty of length on them and no bare spots that i could see....the trigger wires were still wrapped in plastic cable shield....will be checking timing on it hopefully tonight...if u have any other areas just let me know....i do plan on bypassing the filters on my next test run to see if it makes a difference if I dont find anything else wrong...

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

is it better to use timing light with the spark plugs out or can you perform the test with motor running....i watched the two vids on the sticky but they kinda confused me a litttle....one guy says it should be at 30 when cranked but 28 on starting...he also said that the test can be performed with the motor running but what degrees should I be looking for with it at idle.....i would rather do the test with motor running to minimize the chance of damaging the cd modules due to spark plug not getting properly grounded....sorry for my questions I am kinda ignorant when it comes to the timing test....What degree should I see at wot....thanks for your time

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

Timing test for today at motor running at idle speed....timing does advance as I throttle up it goes close to 28 degrees....

.....any ideas

 

[pnwboat]

Re: 1991 force 120 decelerates after hitting top speed

When you try to play your video, a message pops up and says "This video is private" and it will not play. Anyways, the timing for the Prestolite ignition system is 30? BTDC while actually running at WOT, or 28? static, which is using the starter to crank the motor over with the throttle WOT and plugs grounded.

NOTE: Running the motor in neutral at WOT without a load can cause damage.

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

i never run at wot out of water ...I fixed the video hopefully ....try it again....it is idling below 28 degrees ...half way between 28 and 0...but climbs towards as I advance the throttle

 

[pnwboat]

Re: 1991 force 120 decelerates after hitting top speed

Without the motor at WOT, it's kind of hard to tell the exact timing. Usually at idle the timing is somewhere around 5? BTDC.

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

ok...plan on doing a true timing test tomorrow just to rule that out...I am also going to open the carbs up tomorrow just to verify everything is still how it was set before...thanks for all your help....i did rev it up to about half throttle just long enough to look at the timing and it was probably about 15-20 degrees rough estimate...

 

[Jiggz]

Re: 1991 force 120 decelerates after hitting top speed

As mentioned, if you think your timing is correct, the simplest way to verify if it moved or not is to validate TDC. If TDC is correct (#1 piston TDC with flywheel mark aligned with stationary marking), then it is well assumed the timing did not move. However, if TDC is off, then timing moved and needs to be reset. Of course, it is always better to verify timing with a timing light.

 

[jerryjerry05]

Re: 1991 force 120 decelerates after hitting top speed

You said you put in 2 filters and a watersep filter?? Too much restriction?? Did you run it on a remote tank?

All fuel hoses were replaced 2 months ago and 2 fuel filters were put in them as well as a new water seperator....i run non ethonal fuel through them....my carbs were set at the same time with the carb upside down it was set to 11/32 which is paralell to the base and the float was set to almost touching the nozzle ....new main nozzles were put in carbs as well as carb kits with new gaskets....i will checkk the fuel pump to verify that the new diaphram has not torn...all plugs are firing and coil packs work and ohm within specs when tested...i have a previous thread on this motor that I started when I was working on it....You can read it if you would like to see everything that I have done and checked....http://forums.iboats.com/force-chrysler-outboards/force-120-1-cylinder-not-firing-626239.html thatis the web address of it...I have no manual so i have had to find the documentation on the motor from the web....I have sparyed carb cleaner around all gaskets and cannot locate any intake leaks...thats why this baffles me...like i said though i will check the fuel pump again to verify since i know they can rip easily....I know it happened when I hit the patch of floating mill-foil....I am open to any ideas and i appreciate all of u guys knowledge and help....I will check these things this evening wheni get home

 

[BlueFishCrisis]

Re: 1991 force 120 decelerates after hitting top speed

You said you put in 2 filters and a watersep filter?? Too much restriction?? Did you run it on a remote tank?

I still think these should be bypassed and ruled out. I disagree that the filters/bowls would be sucked dry if you had too much restriction. If all of your lines are tight, there would be a good seal and the result of to much restriction would be a lack of fuel into the intake, although it will be full in the lines and components all the way up to the carb throats. Perhaps the filters also picked up debris the last few times out running and have added enough resistance to restrict fuel flow. Just rule them out. My 2 pennies.....

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

fair enough blue fish....i can understand that and makes sense to me....just like to understand why I am doing something first before I act....figure the more knowledge I can get about this the more it will help me in the long run and on future problems...I have bought the fittings to remove all filters from the fuel line excepte the water seperator since it was on there from the get go....I did notice last night while I was tinkering with it that after I primed the bulb there was excess fuel coming out of bottom carb which had not done that since I had set the floats and when I checked the spark plugs on 3 and 4 there was what appeared on them unburned fuel....maybe something in the carb not allowing float to close completely and is flooding my 2 lower cylinders....top cylinders 1 and 2 where dry....so tonight I am gonna bypass fuel filters...check top dead center just for piece of mind and open up bottom carb to make sure everything is set correctly.....it is hard to run portable tank since it is in a bayliner cobra and no where to really put it.....will let yall know my findings this evening....big thanks to everyone

 

[jerryjerry05]

Re: 1991 force 120 decelerates after hitting top speed

The pump is a low volume pump with a 2-4# of pressure(if that).
The more you have in the system? The harder it will have to work.
Get a remote tank and hook it direct to the fuel pump.
The 91 came with 2 different pumps,the old has a guitar shaped diaphragm(my opinion a better one).
The new is the later Mercury square one.
The valves in the later one are tiny circles of hard plastic.
If they are bent at all that can be part of the problem.
Either pump, can go bad with just one revolution or backfire.
Just put the tank on the floor and hook it direct to the pump after you remove the cover.

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

took boat out today for a test....took all filters out of the fuel line....i did replace the water seperator and put a brand new filter with less restrictive flow in line from pump to carbs...when I pulled old filters out there was trash in the filters....let boat warm up and took off it ran on plane for longer this time but did the exact same ...but this time it would help when we squeezed the primer which it never did before....we then removed the hood and took off again and when it slowed again we hit each carb with a shot of carb cleaner...the top one would bog tghe motor down but the lower carb would speed the boat back to WOT...so led us to think problem was in the lower carb...pulled carb off at the house and opened it up to find the needle stuck again in the seat sleeve...we cleaned the crud off the sides of the seat and got the needle to where it would slide in and out freely....does it sound like we are on the right track....also checked TDC and it was right on the money...the fuel pump on this motor is the guitar shaped one and looks great inside it with no blemishes

 

[pnwboat]

Re: 1991 force 120 decelerates after hitting top speed

Well certainly sounds like your on the right track.

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

Question.....when priming the pump bulb should you be able to see fuel run out of the carbs

 

[pnwboat]

Re: 1991 force 120 decelerates after hitting top speed

If the motor is sitting in it's normal running position, you should not see any fuel running out of the carbs when squeezing the primer bulb. If it does, then usually it's the needle valve not shutting off the flow of fuel into the carburetor fuel bowl. Normally the primer bulb should get pretty firm after squeezing it 4 or 5 times.

 

[jerryjerry05]

Re: 1991 force 120 decelerates after hitting top speed


Gas leaking from the carb is usually the needle and seat or the float level.
If the float drop isin't enough you'll run out of gas.
In the carb.There is a long skinny tube is it still in place or did it come loose?
You have a manual for setting the float?
The pics are close to what you need.

 

[leej]

Re: 1991 force 120 decelerates after hitting top speed

Took the boat out for another test after thoroughly cleaning needle and seat on lower carb ...... boat got on plane as always and ran really great then bogged. Down to 30 mph for a short bit then climbed right back up and ran like a top....never missing a lick...thanks to everyone for your help and knowledge.... I left the fuel filter out of the line between the tank and seperator...