Compression 110/105/90?

[Anchor Marine Repair LLC]

Re: Compression 110/105/90?

Ok, took it out. No power. Used to run 38mph, now runs 21mph. Buddy told me, it's because my gas is a month old? Is fuel really that bad? It idled smooth, just no power. I didn't get jets in the wrong place, did I? Smallest jet goes in the bottom of the carb, and larger one goes behind, where normally would be a mixture screw. Correct? Just a thought?

Month old gas lol Was he joking or serious? Either way it's funny.

If gas that was a month old would cause running problems, the planet would be out of fossil fuels. Because everyone would be dumping good fuel to refill with more good fuel.

Think about it. The little old lady who takes her car out of the garage maybe twice a week, how old is that gas getting?

Your description of putting the smallest jet in the bottom, then the larger where a mixture screw is exactly opposite. The main jet is the biggest orifice, and the main sits in the carb bowl. So maybe you are mistaken.

I guess I've never seen them reinstalled backwards. But experience tells me it couldn't run 21 MPH or idle smooth.
But if it is truly opposite, then you might get a better result if installed correctly.

Here's a pic of the exact piston that's in your motor. That's how bad they look with 110 lbs compression. I'm not saying it won't run, but it greatly complicates your running trying to run right.

 

[huntxtrm]

Re: Compression 110/105/90?

Month old gas lol Was he joking or serious? Either way it's funny.

If gas that was a month old would cause running problems, the planet would be out of fossil fuels. Because everyone would be dumping good fuel to refill with more good fuel.

Think about it. The little old lady who takes her car out of the garage maybe twice a week, how old is that gas getting?

Your description of putting the smallest jet in the bottom, then the larger where a mixture screw is exactly opposite. The main jet is the biggest orifice, and the main sits in the carb bowl. So maybe you are mistaken.

I guess I've never seen them reinstalled backwards. But experience tells me it couldn't run 21 MPH or idle smooth.
But if it is truly opposite, then you might get a better result if installed correctly.

Here's a pic of the exact piston that's in your motor. That's how bad they look with 110 lbs compression. I'm not saying it won't run, but it greatly complicates your running trying to run right.

Oh, I fear they are in backwards. That piston looks bad. I am not wanting to put any money into this motor, unless worthwhile. And, from what I've seen, rebuild parts will run around 500.00. dont' know if I want to spend that much on a 40 year old motor. If I can't get this sorted out cheaply, I'm looking for a newer one. Ive already spent money on coils, for this thing. Don't want to get in to much deeper.

 

[Bosunsmate]

Re: Compression 110/105/90?

Check those jets are not reversed and try again and replace your shift seal.
that water outflow looks normal
90psi might indicate broken or seized in rings but it wouldnt in my experience drop you from 38 to 21mph

 

[huntxtrm]

Re: Compression 110/105/90?

Ok, just to make sure I'm not still crossed up. Here are some pics. Small jet goes here under the screw, where normally would be a mixture screw? Larger jet goes here facing down, through the bowl gasket? Correct?

 

[Bosunsmate]

Re: Compression 110/105/90?

yep thats it.
Bottom one is the main jet, not sure which way it faces

 

[huntxtrm]

Re: Compression 110/105/90?

No change! Still runs the same! I'll fool with it tomorrow, I'm tired.

 

[huntxtrm]

Re: Compression 110/105/90?

Ok, today. I have checked the spark. It is getting spark, consistently to all cylinders. I pulled the spark plugs and the top two had evidence of running. The bottom one looks brand new! Like it has not been firing off any fuel? It does spark, I grounded it and turned the motor over and I am getting a spark jumping the gap on the plug. I, unfortunately, do not have access to a cylinder leak down tester to check the cylinders for that. Even if leak down is bad, shouldn't that plug at least be fouled, or something? Besides, looking new? The jets deal has me boggled. I swapped them, and it ran the same. Jets are definitely different size. but not a change when I swapped them. Im thinking, I have a dead cylinder, not getting fuel? What are your thoughts. By the way, this motor was running good, until it set for a month. Last month I had it at the lake, it ran 39. put it on the trailer, now it runs 20 tops. Is there a way to check and see if that bottom cylinder is starving for fuel? Thanks for all of your help so far. I found a nice "Reconditioned" motor just like this one for 1500.00 might be the way I go, if I can scrape up the funds? and I cant get this one going again.

 

[glenn property of pam]

Re: Compression 110/105/90?

premix a little gas/oil in a spray bottle and spray In the carb with the clean plug and see if the engine picks up rpm. If it does you need to check that carb to see what the problem is. I would not bet against a outboard motor unless I knew that I did the compression test correctly and the compression tester was checked to make sure it is with in range. The reason people are asked for the compression numbers are to see the difference not the number as most cheap compression tester will give a number that may be wrong but you can look at the 3 wrong numbers and spot the difference. If you can get the carbs working correctly then de-carb with sea-foam and check compression again.

 

[huntxtrm]

Re: Compression 110/105/90?

premix a little gas/oil in a spray bottle and spray In the carb with the clean plug and see if the engine picks up rpm. If it does you need to check that carb to see what the problem is. I would not bet against a outboard motor unless I knew that I did the compression test correctly and the compression tester was checked to make sure it is with in range. The reason people are asked for the compression numbers are to see the difference not the number as most cheap compression tester will give a number that may be wrong but you can look at the 3 wrong numbers and spot the difference. If you can get the carbs working correctly then de-carb with sea-foam and check compression again.

My compression tester is a sunpro. It's good. I checked it twice. Numbers all came out the same. I tried the spray bottle trick. Top cylinder no change, middle cylinder bogged it down, bottom cylinder no change. Does that mean, I'm not getting the right fuel to top and bottom cylinders? Could I safely pull my drain plugs while the motor is running to see if I'm getting fuel pressure at those two carbs?

 

[huntxtrm]

Re: Compression 110/105/90?

Sorry it's a "Sun". Brand. Thread in compression tester. But now checking it warmed up. Top to bottom. 85/80/75! Is this motor going down hill?

 

[huntxtrm]

Re: Compression 110/105/90?

Well, found the little round gasket, was missing on the tube going down into the bowl, on the top carb! Probably what was wrong with it. But still haven't figured out the bottom carb.

 

[jbjennings]

Re: Compression 110/105/90?

Well, found the little round gasket, was missing on the tube going down into the bowl, on the top carb! Probably what was wrong with it. But still haven't figured out the bottom carb.

If you're spraying fuel into the carb and it doesn't change, most likely they are running lean. I personally think the engine is not in great shape internally to have that big of a range in compression, but I still suspect a carb problem or spark problem if it was running good one day, then badly the next and you didn't notice a change on your last run of the motor. I think you would have noticed a change while it was running if a bad internal problem took place. Cylinders should be at least within 10% of each other---yours are 18% apart with 110/105/90 psi. That's pretty bad IMO.
Anyways, the carbs should bog when you spray fuel in them pretty much at any speed or they're lean. So I'd check carburetion. THe carbs are synched, right? Are all 3 throttle plates level at WOT? How about closed at idle? Until you get the carburetion right, you won't know how well it can run---and they can run pretty nicely even with compression as you describe as far as I know.
Lastly, I wouldn't get another used motor until you solve the issues on this one. Pretty much all used motors more than a few years old are going to need some work. The one you have may have a lot of hours left on it. Sometimes you can even find a good used block/whole used engine with good compression that you could swap out if you look hard.
JMO,
JBJ

 

[jbjennings]

Re: Compression 110/105/90?

Is that bad? It's a 74 Johnson 70hp. Piston tops look clean, by flashlight?

Like steam cleaned???? If so, water intrusion........ ANy milky stuff on the plugs? Plug ends steam cleaned? The piston tops should look black.

 

[glenn property of pam]

Re: Compression 110/105/90?

does the 74 have a tell tale as I didn't see one in the video. Clean plugs and clean piston crown and compression dropping when warm does sound like a head gasket which is why im asking about the tell-tale.

 

[huntxtrm]

Re: Compression 110/105/90?

does the 74 have a tell tale as I didn't see one in the video. Clean plugs and clean piston crown and compression dropping when warm does sound like a head gasket which is why im asking about the tell-tale.

This one has a "tell tale" I installed it. With the help of the very good direction of you folks! It works great, and squirts water good. Ive never had it hot enough, that I couldn't hold my hand under the tell-tale.

 

[huntxtrm]

Re: Compression 110/105/90?

Like steam cleaned???? If so, water intrusion........ ANy milky stuff on the plugs? Plug ends steam cleaned? The piston tops should look black.

No the pistons are black, just not a bunch of crude on them. Like carbon, is what I meant.

 

[huntxtrm]

Re: Compression 110/105/90?

If you're spraying fuel into the carb and it doesn't change, most likely they are running lean. I personally think the engine is not in great shape internally to have that big of a range in compression, but I still suspect a carb problem or spark problem if it was running good one day, then badly the next and you didn't notice a change on your last run of the motor. I think you would have noticed a change while it was running if a bad internal problem took place. Cylinders should be at least within 10% of each other---yours are 18% apart with 110/105/90 psi. That's pretty bad IMO.
Anyways, the carbs should bog when you spray fuel in them pretty much at any speed or they're lean. So I'd check carburetion. THe carbs are synched, right? Are all 3 throttle plates level at WOT? How about closed at idle? Until you get the carburetion right, you won't know how well it can run---and they can run pretty nicely even with compression as you describe as far as I know.
Lastly, I wouldn't get another used motor until you solve the issues on this one. Pretty much all used motors more than a few years old are going to need some work. The one you have may have a lot of hours left on it. Sometimes you can even find a good used block/whole used engine with good compression that you could swap out if you look hard.
JMO,
JBJ

I believe you are right. After further hair pullin, I found this wad of JB weld on the crank case.. I don't know much about these motors, so this might be hair brained but here goes. 2 strokes pull the fuel oil throught the case, correct? So, if this JB Weld gave way? Wouldn't it make the cylinder it is associated with lose vacuum to the carbs? and possibly pull air at the case crack, instead of pulling fuel/air through the carb? That stuff is on the Cylinder in question. Is the crank case on these motors segregated from each other, and idependant to each cylinder? That seems the only way a multicylinder 2 stroke would run? Like I say, I've never messed with a 2 stroke bigger than a dirt bike or a chainsaw. So, I'm just Theorizing. Looks like trash to me?

 

[torbjorn]

Re: Compression 110/105/90?

The 70 should pull 120-125 psi if the rings and cylinders are good. On all 49.7 c.i. OMC 3 cyl. loopers 1968-1988
the inner exhaust plate warps with heating over the long haul. Water is pulled past the gasket into the combustion chamber and
washes the oil off the pistons. If you run it long enough like that, water gets into the crankcase and destroys the rod journals and
bearings. Even if the cause is other than this, always pill the exhaust plates and resurface or replace the inner one. I wrote
about this in the July 2012 Antique Outboarder.

Joe
AOMC Johnson classic tech expert

Month old gas lol Was he joking or serious? Either way it's funny.

If gas that was a month old would cause running problems, the planet would be out of fossil fuels. Because everyone would be dumping good fuel to refill with more good fuel.

Think about it. The little old lady who takes her car out of the garage maybe twice a week, how old is that gas getting?

Your description of putting the smallest jet in the bottom, then the larger where a mixture screw is exactly opposite. The main jet is the biggest orifice, and the main sits in the carb bowl. So maybe you are mistaken.

I guess I've never seen them reinstalled backwards. But experience tells me it couldn't run 21 MPH or idle smooth.
But if it is truly opposite, then you might get a better result if installed correctly.

Here's a pic of the exact piston that's in your motor. That's how bad they look with 110 lbs compression. I'm not saying it won't run, but it greatly complicates your running trying to run right.