Mercury 800 TB 80HP problems

[jlams73]

Hello,

I have a Mercury 800 Thunderbolt ignition and I believe the engine is 1970's era. The control box has 2 levers. I think the small lever is to control the throttle..correct?

Well, I took it out yesterday to test the boat and it will not go into reverse. I do not feel the reverse gear engage instead it revs up and the further I pull back on the shift level the higher the rpm.

The forward gear works but can go only max speed of 5mph or fast idle. The motor doesn't rev up to speed. If the shift linkage is out of adjustment, can it also affect the lack of power? There is old gas in the tank though.

I would like to go ahead and replace the spark plugs too. What is the recommended gap size and can I just get the spark plugs from an auto parts store?

thanks!

 

[jerryjerry05]

Re: Mercury 800 TB 80HP problems

THe small lever is for reving up in neutral.
Sounds like the prop hub is spun.
Spark plugs:any good auto parts store will have a book listing plugs for everthing.Tell them what year and size and they can tell you what they need and the gap.
Shift linkage will not affect power.J

 

[jlams73]

Re: Mercury 800 TB 80HP problems

Thanks for your response Jerry.

I thought the small lever is the throttle lever and the large lever is to shift into gear? I do not feel the reverse shift into gear and engine revs high. The forward gear is opposite. I can feel it shift into gear but does not rev that high and max speed is at most 5mph with small lever at full throttle. Could this be a shift/throttle linkage adjustment AND fuel issue?

 

[jlams73]

Re: Mercury 800 TB 80HP problems

And I'm not ruling out possible spun prop hub. Can it be spunned in one direction only like my reverse issue?

 

[usskydvr]

Re: Mercury 800 TB 80HP problems

Does your control look like the pic I attached? As previously stated the small lever is basically a fast idle lever. Used mostly for starting. It must be down
for the Large handle to move properly. The large handle controls BOTH the gear and throttle cables. Straight up is Neutral. Moving forward about 45 degrees will put the motor into forward. Moving from 45 degrees to 90+ degrees moves the throttle from idle to max. The same for reverse only in the other direction (back). You can check you gear engagement (when not hooked to the control unit) by disconnecting the gear cable at the engine.
You can then manually move the gear selector. It should have a detent in the Neutral position. and move both forward and backwards for Forward and Reverse. The gear cable should provide the same action. With the gear cable removed put the control in Neutral and the motor gear shift lever in neutral.
Now reinstall the control gearshift cable. You may have to adjust the barrel screw so the locking pin aligns with the mounting hole.

Picture link
http://www.google.com/imgres?imgurl...v=/images?q=mercontrol&hl=en&gbv=2&tbs=isch:1

 

[jlams73]

Re: Mercury 800 TB 80HP problems

usskydvr,

Thanks for your response and educating how to work the control box. I've been doing it wrong the whole time it seems.

I think the pic is the same as mine. I can't really tell, so I've attached a pic of my control box. The small lever is all the way down in "rest" position. The mess in the pic has been cleaned up since getting rid of the bird's nest under the console.

I will check it out today and report back what I find. If it's more extensive than that, I may just take it to a mechanic instead. It needs new seals in the LU and plus a good carb cleaning will do it some good too.

thx again for the valuable info!

 

[usskydvr]

Re: Mercury 800 TB 80HP problems

Yup, same one.

 

[jlams73]

Re: Mercury 800 TB 80HP problems

I had time to put the muffs on the motor and test the gears/throttle with the new operating method. It operates much better...thx again usskydvr! The props moved forward and reverse with no problem. The reverse seems slower to spin. Is this normal?

Also hand checked the the props while in gear. The motor was off! When in forward gear, the prop locks and ratchets the other way. In neutral spins freely both ways. And reverse, locks up too. All normal with gears..correct?

I will check the shifting mechanism on the engine tomorrow. One thing I did noticed when I moved the boat is that there is a little puddle of motor oil. This indicates the motor is 4 stroke since there was no fuel mixed in? I would like to change the oil and the spark plugs soon.

 

[wcsd106]

Re: Mercury 800 TB 80HP problems

One thing I did noticed when I moved the boat is that there is a little puddle of motor oil. This indicates the motor is 4 stroke since there was no fuel mixed in? I would like to change the oil and the spark plugs soon.

If this is a 1970's era outboard I don't believe they were making 4 strokes at that time. I would try to find the location of the oil leak though.

 

[Moody Blue]

Re: Mercury 800 TB 80HP problems

Certainly not a 4 strk. Describe the oil you found and where it was.

Was it black and smelled like gas or light in color and smells like gear oil (pungent) ?

AS for the gears, did the prop lock both directions in reverse? Why do you need to check the shift mechanism on the motor? Didn't you just do that?

Back to the 2 vs 4 strk issue. I'm assuming this is a new motor to you and you have been using premixed fuel that came with the motor? If you have not been mixing oil with the gas then you are asking for huge problems.

 

[jlams73]

Re: Mercury 800 TB 80HP problems

thanks for the response wcsd106 and Moody Blue.

The oil was black and the puddle was on the ground under left side of prop. It is probably gear oil since there is a bad seal around the prop. I wasn't expecting black oil because it used to be kinda milky. This is another item to fix!

As for the gears, I checked with using the control levers. I haven't unhooked the cables yet and will do that tomorrow to check for stretched linkage. When the control level is in reverse, the prop lock CW and ratchets the opposite direction. All good?

I am first time boat owner since couple weeks ago. And yes, I have been using what is in the fuel tank.

Thanks for all the help, it makes for a more enjoyable boat owner even though I haven't had the chance to play or fish on the water yet!

 

[Moody Blue]

Re: Mercury 800 TB 80HP problems

thanks for the response wcsd106 and Moody Blue.

The oil was black and the puddle was on the ground under left side of prop. It is probably gear oil since there is a bad seal around the prop. I wasn't expecting black oil because it used to be kinda milky. This is another item to fix!

More than likely its just unburnt combustion product, a mix of gas and oil that isn't fully burnt. Will accumulate in the exhaust tube and drip out of the exhaust around the prop

As for the gears, I checked with using the control levers. I haven't unhooked the cables yet and will do that tomorrow to check for stretched linkage. When the control level is in reverse, the prop lock CW and ratchets the opposite direction. All good?

Neutral = prop will spin free both directions
FWD= prop will lock in one direction and ratchet in the opposite direction
REV = prop will lock in BOTH directions (approx 1/4 turn then lock)

I am first time boat owner since couple weeks ago. And yes, I have been using what is in the fuel tank.

Thanks for all the help, it makes for a more enjoyable boat owner even though I haven't had the chance to play or fish on the water yet!

I'm still learning about my boat and motor every day and with the help of the members on this forum I have learned much along the way. Doing it yourself has its rewards and its heartaches

 

[jlams73]

Re: Mercury 800 TB 80HP problems

REV = prop will lock in BOTH directions (approx 1/4 turn then lock)

The REV does not lock in both direction. It will spin freely oned direction. For the other direction, there is some resistant but with some pressure, you can spin it. What does this mean?

 

[jlams73]

Re: Mercury 800 TB 80HP problems

I've never adjusted throttle/shift links before. Is the big vertical metal bar what changes gear?

 

[Moody Blue]

Re: Mercury 800 TB 80HP problems

Negative, that is the throttle arm.

Shift linkage is directly below that arm. Just follow the other cable to see where it terminates.

 

[jlams73]

Re: Mercury 800 TB 80HP problems

I had time to disconnect the shift linkage today and shift gears manually. This is what I found.

FWD = locks CCW and ratchets CW
NEUTRAL = free spins both ways. However, it will make ratchet noise CCW and click noise CW
REV = it will lock up but with some pressure (15-20 lbs) I can spin the prop. slipping gear?

Does this sound like a gearcase problem?

Also, how do you adjust the barrel nut? I tried every way and cannot figure it out...

thanks!

 

[jlams73]

Re: Mercury 800 TB 80HP problems

Nevermind on the NEUTRAL and REV. I found the sweet spot for both and works like it should.

Now I'm trying to put it back together and cannot figure out the adjusting the linkage. Do you hold the barrel nut with a wrench and adjust the cable pipe with a plier?

Please help someone?

 

[jlams73]

Re: Mercury 800 TB 80HP problems

I was able to figure out how to adjust the cable. There is a slight problem though, when in neutral position on the engine, the cable end does reach far enough to connect. I assume there is a cable adjustment in the control box too?