85hp force engine sputters at wot

[Forcepower]

Hi all new to the site recently purchased a 88 17’ Bayliner Capri With a 85hp for engine. First boat in great shape just trying to get the engine to run like a top. When I inspected the boat I did a compression test and all three cyl were at 130psi. I got the boat ready for the lake put new plugs in the engine which are ngk buhx. I added a see thru fuel filter before the fuel pump checked the fuel pump inlet screen which had alittle bit of debris in it but not a lot. Filled the tank with 50:1 premix using Lucas marine 2stroke oil.
Once Out to lake boat starts right up idles great,runs good from idle to about 2k rpms. Once I put to wot the engine rpms starts to climb Then Boggs down and the engine sputters. Tried doing hole shots to see if I could figure out what’s going on. The motor sounds good throughout until about 2500-3000 then starts sputtering. Tried hitting the electric choke and the motor wanted to die but didn’t. Trying to squeeze the primer build didn’t change anything.
I had the wife drive the boat while I was farting around with the engine. While she had it at wot and the engine is sputtering I manually shut the choke blades and the engine woke up and started to sing. Tells me the carbs are starving for fuel. I tried the primer bulb and it didn’t seem to do anything.
I tried looking through the basics on the ignition side. I noticed when replacing the plugs that the metal clip inside the spark boot for #1 cyl was rusty. Other two cylinder the clip looked new no rust. I tried cleaning and put dielectric on all the plug ends.
So after finding the problem with the choke making the engine run better I thought for sure the carbs were gummed up. I didn’t know what the PO had done so I pulled the carbs. I looks at the reed plates and they looked to be in good shape. I purchased new Boyesen reeds just haven’t replaced yet till I get the motor running right stock then I’ll change the reeds out. Pulling the carbs apart was disappointing because they were clean as a whistle. Not one spec of debris, float are level, plungers look new. The only thing I found that doesn’t seem right is the top carb has a #58 main jet and the other two have a #74 main jet. From my research they should all have a #74 am I right on this. Why would the top carb have a smaller jet than the rest?? And at such a big variance almost 20 sizes lower??
i haven’t dug into the fuel pump to see condition but I’m gonna order a new diaphragm and valves. I already order new float plungers and gaskets but looking at mine their very new looking.
I am new to the outboard world but am a mechanic by trade and am very competent on repairs just haven’t figured out what could be my problem yet. Manually closing the choke and the engine running better tells me there’s something going on with fuel delivery does that sound correct? Anyone know what main jets should be in tillson carbs for a 85hp force? Any info or tips would be greatly appreciated thanks.

 

[The Force power]

Welcome to IBoats

Inspect/replace the fuel-pump inner parts, check/replace your fuel-lines, check the tank-vent.
Do a compression test & post the numbers
Do a spark test & see if it jump at least 3/8"

as far as the jets goes;

There were a couple dozen different carbs used on those motor.

Find carb part number, like
tc119a
tc107a
tc138a

MAIN Jet sizes for a 3 cylinder motor with 3 carbs are .070, .074, etc.

MAIN Jets for a 4 cylinder with two carbs are larger, .092, .094, etc.

Id the carb, then verify the correct jet installed for your altitude.

you can sort through all the carbs, and the corresponding jets per altitude, on
the mercruiser parts dot com web site.

Note, the top/middle/bottom carbs are not necessarily the same, and the jets aren't either.

Keep us posted

 

[jerryjerry05]

Parts list says main jet 74 at seal level.
The other jet is 58
It's on the side of the carb.
Maybe someone switched them when cleaning????
Look up a parts diagram for your motor.
iboatsdotcom has parts diagrams listed under Mercury.

Do the starting fluid test, start motor, spray SF around
the intake side of the motor, under the coils and packs
and the base of the carbs. If this changes anything?
Then the motors sucking air, probably from one of the
port covers.
One tiny backfire can blow a port cover gasket.

 

[Forcepower]

Thanks for the responses guys. I had just did a compression test and all three cylinders were 130. When I pulled the carbs I checked the numbers and they are we18-1a. 631061-2 for the top then the other two are we18-2b. 632061-3. From my understanding all three carbs are the same except the top one has a jet for a air vent screw for bowls and the bottom two have different fuel inlet pipes. I wouldn’t think the main jet would be almost 20 sizes smaller . Refresh the top carb has a .058 main jet and the bottom two have .074 main jet. To me that’s a pretty big swing in numbers.
my problem is the boat is 120miles away from me at the moment it’s kept at the cabin. My plan was to clean out the carbs and get them dialed in. Rebuild the fuel pump because unknown what the PO did. Replace the primer bulb and check for plugged or broken pickup and vent. I have inline spark checks so I will install and see how’s the spark. I do not have a spark gap checker which I’ll look into getting. I haven’t checked timing but will be on my list of things to check.
I’m just really baffled as to why the top carb has a 58 main jet and the other two carbs have a .74. I know .74 is stock but why the hell would they go down 16 sizes on the top. Wouldn’t you try more fuel to get performance not lean it out. I’m gonna either drill out the jet to a 74 or try and source one depends how hard that will be. Any more advice is appreciated thanks.

 

[Forcepower]

Is their a way to do the spark Gap test without the special tool. I’m confused how they say plug has to be grounded for drop testing coils. When you pull the plug are you not loosing your ground on the coils?? Why is their not a chance of frying packs when doing that?? For the spark gap test can I take a plug connected to the coil wire I’m gonna test and just Space it from the head bolt or something and have someone crank the engine?? See how far I can get it to spark from the head?? Or should I use the specific spark gap tool? Thanks again for the input.

 

[Nordin]

My answer about the cylinder drop down test is that you pull the HT wire boot for just one or a few seconds.
The chance to break down the CD module is really low.

You can check how far the spark can jump without a gap tester.
Do as you describe in #5 post but be careful if you are going to hold the HT wire with your hand and space to ground.
You might get an electrical shock if you do not wear rubber gloves or use insulated pliers.
The voltage of the spark is 30-40000 volts.

 

[jerryjerry05]

Plug tool is $7
The factory says to ground the plug wire or
possible pack failure will result.
When I first started working on these my boss
who is possibly the greatest Force/Chrysler tech
showed me how and he didn't ground the leads
when he was testing.
Myself I'm not a gambling type.
I use the homemade octopus I fabricated.
3-4 18"pieces of #10 wire connected with a cable
connector.

To do the drop test.
Start the motor raise the rpm's to about 900
Then with care pull one plug wire at a time.
If this makes it run any different then that shows
something is wrong with that cylinder.

You can swap the packs and see if the problem
follows the swap???

You do the starting fluid test??

 

[Forcepower]

Thanks for the responses guys. I found out about the mystery jet problem. Jerry Jerry had mentioned of the top carb with the air jet. Later that day after work I was looking at the carbs again and what do ya know there is a 74 jet in the air jet spot. I instantly knew what the problem was. Whoever PO mixed up the carb jets on the top carb. It explains kind of why the motor would run better when I manually shut the carb blades.
Luckily the new float needles and carb gaskets came in. I’m gonna reassemble the carbs with new seats and gaskets. Then this coming weekend we will be going up to the lake and I’ll be able to test her out and hopefully that’s all that was wrong with her. Thanks for all the input on these engines. That’s half the battle with vintage stuff.

 

[jerryjerry05]

Glad to help.
Just send the check to