Force 70 HP - Full throttle in reverse but underpowered in forward

[itzjohnny]

I have a 70 hp Force outboard that is having trouble getting WOT in forward gear. From what my tach says, its getting to about 3000rpm in forward gear. When shifting to reverse i can get full throttle of about 5000rpm. I've done adjustments from both engine side and remote side with no luck. Any help is appreciated.

-Side note, I got it to seemingly run close to WOT at home in forward gear but when i'm out on the lake, under load, the issue arrises.

 

[topgun3690]

Running it up to WOT at home......on the muffs....in gear? Or using a test wheel in a test tank?

 

[racerone]

Sounds like the motor is running on 2 of 3 cylinders.------Sounds great on a hose to the untrained ear.-----Will rev up running on 2 of 3 cylinders.-----Step #1 is compression test.---Post the numbers.-----Then check for strong spark on the 3 leads.----Must jump a gap of 5/16" or more.-----Revs up in reverse because exhaust bubbles reduce load on the prop !!

 

[itzjohnny]

Running it up to WOT at home......on the muffs....in gear? Or using a test wheel in a test tank?

Yes WOT on muffs and in a 55 gallon drum at home. I've checked for compression and spark and i have both on all 3 cylinders.

 

[itzjohnny]

Sounds like the motor is running on 2 of 3 cylinders.------Sounds great on a hose to the untrained ear.-----Will rev up running on 2 of 3 cylinders.-----Step #1 is compression test.---Post the numbers.-----Then check for strong spark on the 3 leads.----Must jump a gap of 5/16" or more.-----Revs up in reverse because exhaust bubbles reduce load on the prop !!

Ive checked spark and compression, but don't remember the numbers. i will do another test though! The spark plug isn't a traditional style, it use a NGK BUHW.

 

[racerone]

But the spark test does not involve the sparkplug.----It is a MAXIMUM OUTPUT test of the ignition system.----A good ignition can jump a gap of 3/8" or more!----Check the reed valves as well.

 

[itzjohnny]

I will do them tests today. I recorded this clip to show what exact problem i am having. The file is too big to be posted on the forum.

 

[racerone]

Did you read post #3 ??----I say your motor is running on only 2 of 3 cylinders.----It it easy to test and find out why.----If you keep running it with a plugged carburetor you may destroy the motor beyond economical repair.

 

[flyingscott]

Your motor is running on less than 3 cylinders. Your reverse test proves absolutely nothing.

 

[itzjohnny]

Compression test from top to bottom
100
105
105
Spark test gapped to 3/8 then 5/16
All have good spark
The photo attached is the spark plugs pulled. Left plug pulled is top cylinder. Right plug is bottom cylinder

 

[flyingscott]

Your top cylinder has an issue. I would expect your spark to jump 7/16" gap. Is that a single carb motor?

 

[itzjohnny]

Your top cylinder has an issue. I would expect your spark to jump 7/16" gap. Is that a single carb motor?

Yes we’ve tried up to 1/2” gap on all. We got spark all the way through. Yes, it is a single carb motor.

 

[racerone]

You are running on 2 of 3 cylinders.----#1 has an issue.-----No spark.----Or no fuel.----Or too much fuel.-----Or no crankcase compression..----Should be easy to figure out.-----Might be a broken reed valve or some seagull feather holding a reed valve open.----Could be a hole in the block too.

 

[itzjohnny]

Okay so I removed the reed valves out and they look fine. I’ll post a picture of them on both sides. While take the bottom reed assembly off there was a puddle of fuel in the bottom of what I would assume is the intake on the bottom cylinder. Crank case compression is good as well.

 

[racerone]

Bad sparkplug ?

 

[itzjohnny]

Bad sparkplug ?

I replaced all 3 about 3 days ago. I’m thinking it maybe be something with the carburetor, maybe dumping too much fuel. But still not understand why I’m not getting to WOT in forward. I’m kinda at a loss with this thing.

 

[racerone]

Year and model # of motor ?----Just 1 carburetor or 3?------What boat and what pitch is the prop.-----Is the boat waterlogged ?----Fuel pump diaphragm ruptured ?

 

[roscoe]

gasket leak on cylinder 1 ?
That plug is too clean.

 

[itzjohnny]

Year and model # of motor ?----Just 1 carburetor or 3?------What boat and what pitch is the prop.-----Is the boat waterlogged ?----Fuel pump diaphragm ruptured ?

1991 Force 70hp Model 708F91B
1 carburetor
I believe the prop is a 10 1/4 x14
Boat was not waterlogged when I took it out this weekend. Only had maybe a cup full of water come out at the boat inspection.
Fuel pump diaphragm looks good. Checked fuel filter as well. The screen was clean. Fuel lines look in decent shape.
I had the boat running perfect about a year ago let it set for a while then all the problems started arising.

 

[itzjohnny]

gasket leak on cylinder 1 ?
That plug is too clean.

I thought so as well but didn’t go too deep to check the gasket but we put it on muffs today and the top plug looked like the others today.