Motor will not idle unless timing is advanced

[NashForce125]

I picked up a 1985 Force 125 and have been working on getting it water ready.

When I purchased it, the ignition was not firing all cylinders. Compression on cylinders was around 140psi, so I figured I would roll the dice and try to get it going.

I got the ignition sorted out pretty easily and got it on the lake. Motor ran fair, but would stall going into gear at idle. Also found that carb butterfly was not hitting WOT. Thus ends test run #1.

I watched some YouTube videos about how to set all the linkages for throttle and timing. During this setup, I found that a previous owner had rigged up the timing linkage with a bolt tail and a spring. This greatly advanced the timing idle and allow the plastic block to slide when the timing could hit the mechanical stop. See picture in thread from me.

i ordered the correct timing linkage parts and got it set up with a timing gun. I left carb throat covers off since I had been tweeking throttle settings. Engine would not start, and I could see an occasional drop of gas coming out of throats. I found that if I advanced the timing the engine would start.

I figured the carb needles were not sealing, which they were not. So I cleaned the carbs out, got new needles and seats thinking the engine was flooding and the extra idle speed was burning the extra gas, but the issue persists. It will only idle with the timing advanced a lot. To the point that with stock linkage the timing tower cannot go the WOT due to mechanical stops on timing coil. This I would explain the modified timing linkage.

i have looked at the reeds and they are all there and feel like they are pulling air (hard to tell with carb adapters on). I have not removed them to check for light leaks.

I checked my vacuum/recirculating lines and they all seem to hold lung pressure.

What am I missing? Any tips or troubleshooting ideas would be appreciated.

 

[NashForce125]

[No message]

 

[The Force power]

Welcome to IBoats:welcome:

You should still remove the dog-bone shape cover to inspect/clean the screen to have the re circulation system working properly.

Then follow these instructions below ( written by the late Frank A.)


1. Disconnect the ball link to the carb cam at the timing tower. Disconnecting at the cam risks bending the cam. Move the cam away from the carb roller.
2. Loosen the screw(s) on the aluminum tie bar and let all carbs close completely, then tighten again.
3. Set the cam so that the scribed line is pointing directly at the black roller on the carb lever. If the cam has two closely spaced lines, set the black roller directly between them.
4. The black roller is held with an offset screw and nut. Loosen the nut and turn the screw until the black roller JUST touches the cam. Tighten the nut and re-attach the ball link maintaining the scribed line at the roller.
5. Adjust the ball link so that at full throttle the bottom carb butterfly opens substantially horizontally. Adjust the aluminum tie bar so all carb butterflies open equally at full throttle. They need not be perfect but should be rather close to horizontal for best performance.
6. Adjust timing to 28 degrees before top dead center at full throttle.
7. Adjust idle speed to 700-750 RPM in the water in forward gear. Do this with the screw on the bottom of the timing tower. Loosen the locknut and adjust. Screwing in increases idle speed. Do this in small increments and let the engine rev and adjust itself before the next adjustment. A little goes a long way here. When correct, tighten the nut. Note that the scribed line on the roller will now be (usually) below the black roller a bit.
8. NOW we adjust the mixture on the carbs. Set all low speed needles to about 1 1/4 turns out from lightly seated. Do not force as this will damage either the needles or the seats.
8A. With the engine idling in neutral, turn each the needles in equally about 1/8 turn at a time. Give the engine a couple of seconds between each adjustment to stabilize. Adjust until the engine either "sags" or stalls. Note this setting.
8B. Now go the opposite direction. Adjust until the engine runs rough, burbles, or stalls. Note this setting.
8C. Set all needles to the average between the two settings: That is, for example, if it stalled at 3/4 turn out and burbled at 1 1/4 out then set all needles to 1 turn out.
8D. Readjust idle speed to 700-750 RPM.
9. Take the boat out on the water and do a "hole shot"--Full throttle acceleration from a stop. If the engine "sags" then recovers and picks-up it is too lean. Open the needles about 1/16 turn at a time until the engine accelerates with no hesitation.
If the engine sputters or coughs or burbles, then clears itself and accelerates, it is too rich. Close the needles about 1/16 turn at a time until the engine accelerates smoothly.


10. I can NOT stress this enough! NEVER set the low speed needles less that 1 turns out no matter how poor the idle or acceleration. To do so will run the engine too lean and detonation and melted pistons at or near full throttle operation will result.

 

[Redbarron%%]

Does the engine set up the throttle and timing at WOT and idle.
That is if you set the WOT at 30* can you get the 9* for idle or is it lower? This and the idle gap and the WOT for the throttle opening?
I have found that if the bias circuit is bad the RPM increase will advance the timing too much as the speed increases and the timing will be too low at low RPM.
This may possibly be your problem.
Remember 9* idle to 30* WOT (engine running and in the water) at the same time from throttle plated closed and thaT slight gap at the cam to WOT (throttle plates 90*).
If the bias circuit is bad the spread between the idle timing and WOT will be more so the WOT is backed down and that puts the idle timing off low.

 

[NashForce125]

I know which covers you are talking about. I was not aware that there were screens in there. I will pull those covers and clean them out.

I had had seen Franks instructions on here. They were extremely helpful to get me to where I am after finding the rigged timing linkage.

i will let you know what I find.

 

[The Force power]

Does the engine set up the throttle and timing at WOT and idle.
That is if you set the WOT at 30* can you get the 9* for idle or is it lower? This and the idle gap and the WOT for the throttle opening?
I have found that if the bias circuit is bad the RPM increase will advance the timing too much as the speed increases and the timing will be too low at low RPM.
This may possibly be your problem.
Remember 9* idle to 30* WOT (engine running and in the water) at the same time from throttle plated closed and thaT slight gap at the cam to WOT (throttle plates 90*).
If the bias circuit is bad the spread between the idle timing and WOT will be more so the WOT is backed down and that puts the idle timing off low.

Sorry, I should of mentioned set to 28 degrees at cranking-speed

 

[NashForce125]

I had the timing set to 28 BTDC at WOT cranking. I could not get it to idle. Advancing the timing gets it to start. But at that point, the throttle control will hit timing coil stop before WOT. I should hit it with my timing gun when I can get it to idle and see where I am BTDC.

I think this is why a previous owner rigged the linkage to slide.

 

[jerryjerry05]

The last service bulletin for the 85hp. said:
The air screws should be set at 1 turn out and
left there.
BUT!! some older 85's won't run at that setting.
One of my customers needed to have his set at 3
turns out??????

The way to set the difficult:
Get the motor running at what ever setting you can.
Then turn the air screw in 1/8th turn wait 10 seconds
Then turn another 1/8th turn wait 10 seconds.
Do this until the motor stalls, bucks, stutters then
turn the screw out 1/2 turn.
Then do the other carbs, same way.
Do this twice. maybe 3 times.
The 10 seconds burns the fuel at the old setting.

You also need to set the carbs in the water, running and in gear.
Your idle should be 800 in F

Do the starting fluid test.
Start the motor, spray SF around the intake side of the
motor, that's the area under the coils and packs and the base of
the carbs, this shows if there might be an air leak somewhere??
One tiny backfire, stutter can blow the port cover gaskets and
the motor will NEVER idle right.

 

[NashForce125]

I have had a few backfires during my testing, trials and troubleshooting. I will check out the intake port gaskets as suggested if those are prone to blow on backfire.

 

[NashForce125]

“I have found that if the bias circuit is bad the RPM increase will advance the timing too much as the speed increases and the timing will be too low at low RPM.
This may possibly be your problem.
Remember 9* idle to 30* WOT (engine running and in the water) at the same time from throttle plated closed and thaT slight gap at the cam to WOT (throttle plates 90*).
If the bias circuit is bad the spread between the idle timing and WOT will be more so the WOT is backed down and that puts the idle timing off low.”

what is the bias bias circuit that is being referred to? Is this an electronic component?

If it’s part of the CD modules, I replaced them with new during my ignition work.

 

[Redbarron%%]

It is part of the CDI box if it has the CDI system and a part of the trigger Assembly in CDM ignitions. Still the spread of the timing over the idle to WOT is important and even a new box could conceivably be bad.
Remember 9* to 30*. If you need more advance at idle this could still be a cause.
I adjust the 30* first and then set the idle at 9* after that I adjust the cam gap and WOT for the carbs.
Of course there are many other possible causes, but you mentioned timing so I mentioned the bias.
The bias circuit corrects for the spark advance due to the voltage of the leading edge of the pulse from the trigger getting to that .6 volts + where the ignition fires the plugs. The bias generates a negative voltage to offset that positive shift as the RPM increases. If the bias is not working the timing shifts more advanced as the engine speeds up creating the greater spread from idle speed to WOT.

 

[NashForce125]

I broke down and bought the service manual. I ran the gauntlet on troubleshooting this. My initial thought that the engine was flooding was correct. Turned out to be the carb float setting. This particular carb wants to have a 13/32" gap between the float and carb body. The engine now idles great on muffs. I still need to do a water test, but I think it's ready to go now.