1988 Force 85hp Top end rpm loss troubleshooting help.

[DunbarLtd]

I'm pretty sure you are over propped. You said this is a new prop. What was the old one and what RPM did it do. For comparison, my 16 ft bayliner with a 75hp runs a 10 inch diameter 12p 4 blade and hits 5100 RPM. I tried a 14P and could only get 4200 RPM. 13 inch diameter and 17P sounds like way too much prop.

I dont know how you gained almost 1k rpms from 2 degrees of pitch but thats amazing. Typically its at most 200rpm per degree of pitch.

But to answer your question, the new prop and old prop are exact same. 13.25" x 17P

Didnt have a tach with the old prop but had gps speedo and they both do the exact same mph. Im sure a 15P would give me maybe 400rpms which would be good for getting closer to the recommended operating range.

But if theres another cause as far as motor issues then id like to rule all of them out first before i blame the prop. Im nearing the end of ruling things out with the motor. Just a few other things id like to check before i go blaming the prop.

 

[DunbarLtd]

Just out of curiosity, where is the timing set at?

Okay so we did the timing today. Im no marine mechanic but it looks like its on 28 degrees. 1st mark on the right at cranking. I did it 5 times to make sure.

 

[Jiggz]

Looks like timing is perfect. And I presume you are already using NGK BHUW spark plugs. And has verified the control handle at WOT position places all three carbs' throttles (butterflies) at full horizontal (no more, no less) with reference to the carbs' bodies. And that the choke butterflies are also at horizontal when not engaged.

The air screw or air-mixture screw on each carb is at least at 1 1/8- ! 1/4 turn out from seated. And if you have a clear fuel filter between the carbs' fuel inlet and fuel pump outlet that it stays at least half full with 50:1 fuel-oil mix at WOT.

If this is all true then the only thing left to do is to try a smaller prop and see if it'll take you to at least 5K rpm. Or at least check the reeds to make sure they are not missing petals or are closing all the way. You can easily do this with a mini-endoscope which you can buy online for less than $20 without removing the carbs.

 

[DunbarLtd]

Looks like timing is perfect. And I presume you are already using NGK BHUW spark plugs. And has verified the control handle at WOT position places all three carbs' throttles (butterflies) at full horizontal (no more, no less) with reference to the carbs' bodies. And that the choke butterflies are also at horizontal when not engaged.

The air screw or air-mixture screw on each carb is at least at 1 1/8- ! 1/4 turn out from seated. And if you have a clear fuel filter between the carbs' fuel inlet and fuel pump outlet that it stays at least half full with 50:1 fuel-oil mix at WOT.

If this is all true then the only thing left to do is to try a smaller prop and see if it'll take you to at least 5K rpm. Or at least check the reeds to make sure they are not missing petals or are closing all the way. You can easily do this with a mini-endoscope which you can buy online for less than $20 without removing the carbs.

Champion UL-18V is what is listed for this motor. I wouldnt mind trying the NGK's but I called Mercury and they looked up some reference i dont know how but they said the proper plug was UL-18V. The guy i bought it off had Champion UL-76 in it. Didnt notice a difference honestly and Im actually curious why they were running those plugs as I never got to ask him why he was running them.

Carbys set up and about 1 1/8 i believe. Ive confirmed the fuel filter stays full as seen through the clear plastic window. One thing i noticed tonight was the filter was near empty. But ive raised the motor all the way up and its likely the needle in the float bowls let go when tilted and the fuel leaked out. I suppose i could leak test from the gas tank to the fule pump but @ WOT i am pretty sure the filter stays full and i never have a hard time restarting after warm. Itll cough here and there but thats rare.

Ive removed all 3 reed blocks because i changed the intake gaskets there. I saw a few of the petals that had the slightest amount of light shining through them but none with obvious warpage. Visually they all looked pristine and looked like they were flat and sealing.

dont know the tolerance other than the specs for the amount they should bend until they hit the stop. I know they need not be tightened too much or they will warp so i made sure of that. After inspecting the reeds and replacing the intake gaskets there was no noticeable difference in running performance.


I guess at this point i may try a new prop and see what happens. Theyll buy my new one back and sell me a 15P. Worst case I gain some rpm but no increase in speed. I dont see a down side to a new prop. Thanks for the help.

 

[jerryjerry05]

The reeds can have a little light shine through.
Not a lot.
I've found no difference in the Champion or the NGK plugs.(somebody's gonna disagree)
The UL76 Is it a plug with an electrode?
Some don't like the surface gap plugs??? I love em!! Just wipe off and they're clean.

 

[DunbarLtd]

The reeds can have a little light shine through.
Not a lot.
I've found no difference in the Champion or the NGK plugs.(somebody's gonna disagree)
The UL76 Is it a plug with an electrode?
Some don't like the surface gap plugs??? I love em!! Just wipe off and they're clean.

Sorry it was a L76V

U means it has an auxillary gap inside.
L means 14mm x 13/16"hex head and 1/2" reach
76 is heat range
V means Surface gap.

So It looks like it to me they were using a plug with a MUCH hotter heat range according to champion plug charts. The higher the number the hotter the heat range.

How much hotter the 76 is i have no idea. When I had the head off i did not see any signs of scoring in the cylinders. Maybe they did a lot of trolling? idk.....

Also found a comment from Frank A "BUH is the NGK equivalent to L20V. I think BUHW is the equivalent to UL18V which is just slightly colder and was specified for the Chrysler 140 and a couple of other models. It would also give satisfactory performance. I also think that BUHX is the equivalent to Mercury L76V, which I think Merc used in the later Force engines so, BUHX should also give satisfactory performance.

Any of these plugs run cold enough not to harm the engine. The main concern is that a bent electrode plug is much hotter than the surface gap plugs and could cause holes to be melted in the piston crown."

Ive been doing a little reading as well and so Im wondering if the internal "auxiliary gap" in the UL18V has an effect on my CDI system. Im wondering if the cdi system is worn out and not firing as good as it supposed to, that it may not always make the jump inside the plug.

If I go to the L76V it does not have an internal gap and may possibly fire better?

 

[Jiggz]

I used to have the UL18V for my 125 which I find cold starting to be hard and also at WOT seems to have infrequent misfires. Switching to BUHX alleviated this. Maybe it's just personal preference but at less than $3 each I went on to try it. And was very glad I did. Both of these plugs, BUHX and BUHW are surface gapped.

 

[DunbarLtd]

The X and the W indicate whether or not they have internal "auxiliary gaps" or "booster gaps".

I believe the BUHX has a booster gap and the BUHW does not.

So the argument is whether or not the internal gap affects overall spark in tired or worn out CDI ignitions.

I am pretty sure I have all original electrical components on this engine by the looks of them. I cant confirm if the stator or trigger is by the looks because i havent removed the flywheel yet but the packs and coils all look like original oem.

Therefore, It is possible this system is not producing the ideal amount of voltage at WOT. And if it is not I am not sure if one would actually be able to perceive any loss of power simply be ear, unless you have a very trained ear. Perhaps by rpms you might though.



I found this:

"Some plugs use an internal gap in their design so that the breakdown voltage of the capacitive discharge burst is fixed by this auxiliary gap and not by the firing gap within the engine. This is quite common in plugs for two stroke engines (such as outboards) to prevent cold fouling."

The UL18V has a booster gap. It seems to me that cold fouling should be eliminated but in your case it sounds like it made it worse, which is interesting. Assuming the electrical system is producing full voltage.

Also since the BUHX has a booster gap, I question whether the UL18V actually is any worse of a plug. Its the same technology and design although the NGK used Tungsten threads instead of Nickel.

Other than that they are the same plugs and should theoretically perform the same.

If you dont mind me asking, how did you confirm the WOT misfire?

I have nothing against trying a different brand plug, but im just curious how you confirmed it had a miss at high speed.

Reason is I cant tell just by sound if the UL18V im using is causing a miss and the rpm dont indicate a miss because they dont jump around. It runs steady @ 4100-4200 rpm.

 

[DunbarLtd]

Does anyone know how to tell what ignition system my motor has.

Model # is 856X8A 1988 Force 85hp

It has black coils and 2 black CD packs. I read some comments on here that the Prestolites were the blue coils. I always thought I had Prestolite but if I have the Thunderbolt ignition system then I think the UL18V is the wrong plug.

How do i find out what ignition system i have???

 

[Jiggz]

The T-bolt system uses a Switch box which incorporates the CD modules and its associated power supplies. This system gets its ignition power straight from the battery unlike the Prestolite which gets it from the stator.

Prestolite system can come either in Blue (old style) or the newer black CD mods.

 

[Jiggz]

The X and the W indicate whether or not they have internal "auxiliary gaps" or "booster gaps".

I believe the BUHX has a booster gap and the BUHW does not.

So the argument is whether or not the internal gap affects overall spark in tired or worn out CDI ignitions.

I am pretty sure I have all original electrical components on this engine by the looks of them. I cant confirm if the stator or trigger is by the looks because i havent removed the flywheel yet but the packs and coils all look like original oem.

Therefore, It is possible this system is not producing the ideal amount of voltage at WOT. And if it is not I am not sure if one would actually be able to perceive any loss of power simply be ear, unless you have a very trained ear. Perhaps by rpms you might though.



I found this:

"Some plugs use an internal gap in their design so that the breakdown voltage of the capacitive discharge burst is fixed by this auxiliary gap and not by the firing gap within the engine. This is quite common in plugs for two stroke engines (such as outboards) to prevent cold fouling."

The UL18V has a booster gap. It seems to me that cold fouling should be eliminated but in your case it sounds like it made it worse, which is interesting. Assuming the electrical system is producing full voltage.

Also since the BUHX has a booster gap, I question whether the UL18V actually is any worse of a plug. Its the same technology and design although the NGK used Tungsten threads instead of Nickel.

Other than that they are the same plugs and should theoretically perform the same.

If you dont mind me asking, how did you confirm the WOT misfire?

I have nothing against trying a different brand plug, but im just curious how you confirmed it had a miss at high speed.

Reason is I cant tell just by sound if the UL18V im using is causing a miss and the rpm dont indicate a miss because they dont jump around. It runs steady @ 4100-4200 rpm.

Surely, with the above explanation you only have on choice left to find out what's exactly is causing your motor not to reach above 4K rpm and that is trying a smaller size prop. Misfires at WOT are very hard to determine except with personal experience with the motor and that your max rpm is lower than when you try other plugs or stuff. For newbies, even with 2 cylinder motor only firing with one cylinder, are unable to tell the difference. Except they cannot get the thing to plane at WOT.

 

[DunbarLtd]

Surely, with the above explanation you only have on choice left to find out what's exactly is causing your motor not to reach above 4K rpm and that is trying a smaller size prop. Misfires at WOT are very hard to determine except with personal experience with the motor and that your max rpm is lower than when you try other plugs or stuff. For newbies, even with 2 cylinder motor only firing with one cylinder, are unable to tell the difference. Except they cannot get the thing to plane at WOT.

Thanks Jiggz. Motor planes fine. Im trying to cover all the bases before i just accept it and move on. But everyone here has been very helpful and i appreciate all of you to take the time and help me with my engine issues. I know I can get a bit wordy but I am just trying to understand as much as i can about these outboards.

I will see about a new prop and if no improvement then it is what it is and ill just go fish and stop worrying.....Thanks again.

 

[Nordin]

Jiggz just want to ask you about the black and blue CD modules and coils for the Prestolite system.
From my experience I think the black modules and coils are the older and the blue the newer but I am not sure when you says the opposite.

From pics I have seen and engines I own and have own it seems like the black are the old ones.
I have a had a 60Hp twin carb Chrysler which hade the retro fit kit from factory and it was the Prestolite system. These engines was equiped from factory with the Mag II system in the begining.
This engine had a black module and black coils.

My youngest boy has an 1988 85Hp Force on his boat and it has black modules and coils.
Have an 120Hp Force 1991 myself and it has blue modules and coils.

Restored a 90Hp 1990 Force a couple of years ago and it had blue modules and coils too.

Can someone confirm which stuff is old and new.
jerryjerry or jiggz who have a lot more experience than me and who are in the US where these engines are much more common then here in Sweden where I am.

 

[jerryjerry05]

The blue is the older.
The black is supposed to be an upgrade???
That's why they have the connectors backwards compared to the blue, so
you won't use them together(unless you cut off the ends) (I do)

A miss at high speed? You'd be able to tell.


It really sounds like the props wrong or the timing's off.

One of my customers came to me for an oil change and tune up.
9.9 Mercury.
Got to looking and saw one plug wire laying in the bottom of the cowl.
I fixed the motor and didn't tell the owner about the plug.

He comes back a week later and said" WOW " the motor runs better than it ever has!!!
Seems it ran like this for over 2 years.
Said it ran twice as fast.
Some 2 cyl. Force run almost as good with one plug as they do with 2.
I did tell him then.

The 88 85 (had 4) if one cyl. misfires or has low comp. it ain't gonna get 4400rpms.

 

[DunbarLtd]

The blue is the older.
The black is supposed to be an upgrade???
That's why they have the connectors backwards compared to the blue, so
you won't use them together(unless you cut off the ends) (I do)

A miss at high speed? You'd be able to tell.


It really sounds like the props wrong or the timing's off.

One of my customers came to me for an oil change and tune up.
9.9 Mercury.
Got to looking and saw one plug wire laying in the bottom of the cowl.
I fixed the motor and didn't tell the owner about the plug.

He comes back a week later and said" WOW " the motor runs better than it ever has!!!
Seems it ran like this for over 2 years.
Said it ran twice as fast.
Some 2 cyl. Force run almost as good with one plug as they do with 2.
I did tell him then.

The 88 85 (had 4) if one cyl. misfires or has low comp. it ain't gonna get 4400rpms.

I picked up a DVA adapter. Gonna do some voltage tests for the heck of it. Im assuming everything will check out but its worth a shot as they are easy tests to do. And Ill learn something in the process.

Looks like typical voltages are about 210v when cranking.

Now only question i have is when cranking whats the easiest way to crank it without it starting but not kill the voltage outputs?

Just remove the coil wires and ground them???

Service manual simply says crank engine. Thats it. So I assume they dont want the motor starting when doing the test. Looks like they want you to disconnect the stator wires off the terminal strip when testing. So i dont think i can do the test if the motor is running.

 

[Nordin]

I do not have the factory service manual infront of me right now but to check the output from stator to CD modules you pull the plugs out and ground them all three (HT wires connected at the plugs).
This just for sure not to damange the modules, if there are some voltage stored in the modules it has to dump it somewhere.
Disconnect the stator wires from terminal strip and measure the output voltage while running the starter from keyswitch.
If good it should put out 210VDC DVA or more.

If I am not wrong the DVA voltage from CD module to coil should be 210VDC or more too.
You can check that too.

 

[DunbarLtd]

I do not have the factory service manual infront of me right now but to check the output from stator to CD modules you pull the plugs out and ground them all three (HT wires connected at the plugs).
This just for sure not to damange the modules, if there are some voltage stored in the modules it has to dump it somewhere.
Disconnect the stator wires from terminal strip and measure the output voltage while running the starter from keyswitch.
If good it should put out 210VDC DVA or more.

If I am not wrong the DVA voltage from CD module to coil should be 210VDC or more too.
You can check that too.

OK perfect. Thanks for the help.

 

[jerryjerry05]

outboardignitiondotcom has the test procedures for your motor.

 

[DunbarLtd]

outboardignitiondotcom has the test procedures for your motor.

Out on the lake today. I tested the stator and trigger outputs according to service manual (DVA adapter) and both were in spec.

Hooked up the spark tester with 7/16" gap and #1 fired just fine while the motor was running and in idle.

As soon as i hooked it up to #2 and #3 i noticed the spark wouldnt jump the gap sometimes and when it wouldnt the motor stumbled, which makes sense if it isnt firing. I tried a smaller gap and it didnt miss as much but it still missed.

But like I said when Im @ WOT I dont notice the motor stumbling or anything. Not sure what to make of my finding so far.

Im assuming i might have issues with the cd packs or the coils starting to go but i dont know. Any ideas??

 

[jerryjerry05]

Stator test good? but can still be bad
The trigger leads, make sure nothing is grounding out??
The grounds on the panel holding the packs/coils.
Remove and clean the area's grounding the packs/coils.
The tach can cause spark drop. Try unhooking and see if that helps?
The flywheel magnets, I say magnets because there are 2-3 in the older Prestolite.
One around the perimeter and 1-2 on the center.
Make sure they are all glued in place.

The only real test for a coil is to swap it with a known good one.
The packs also really don't have a good test other than switching it

The plug wires. Run after dark and see if the wires are shorting out?