compression terror

[royboy321]

Purchased a 1994 Merc 15 hp at a good price. The engine was in nice condition from my limited knowledge. Though a little weathered on the outside, rubber parts seemed fresh, lots of grease around the parts. The engine looks pretty new. Seller said it had been sitting for over eight years but low hours. He also started it and it ran for a few seconds. I took it to the river and had some difficulty starting it but finally got it to idle and I expected this on an old engine. After about two minutes I put into gear and the engine died every time I applied throttle. Again, I expect a little difficulty with an old engine so I gave up for the day. To me, I do not hear anything horrible. It has a telltale water spout, etc. Engine purrs in idle (no clanking or missing). The Old Man mentioned - "hope the compression isn't bad." Now I am terrified!!! I put the engine in a bucket and started it up. It spit a few clouds of smoke and idled up and down a bit, but after a while it started to smooth out.

So...question is...are these symptoms of poor compression or hopefully just gunk and in bad need of cleaning? Maybe sparkplugs? Please let it not be the compression.

Thanks

 

[jerryjerry05]

Re: compression terror

If it starts and idles it probably has good compression.The fuel system sounds like it needs a good cleaning.Jerry

 

[Yachtzee]

Re: compression terror

I do not have the credentials that some on this forum have and am no expert.
But For my 2 cents, if you are concerned about compression buy or borrow a compression gauge And service manual if you can find one. Do not know the spec without the book but something around 120+ and pretty close to equal on both cyl should be ok.
If the thing sat around for years, it will be full of gunk. Especially if someone let the carbs sit full of old fuel till it dried out.
Failure to rev up smoothly under load can be carb or ignition related.

And even though you are peeing a full stream you need a new water pump impeller. If you run an impeller that old it way work at first but it may well be dry rotted and will at least have a "set" to the vanes. It is very likely to fail very soon and bits of it can end up clogging the water passages in the block. You know to not even start it without having it in a barrel of water or on "mickey mouse ears" and a hose right?

The guys on this forum would probably tell you to pull the carb(s) and clean and rebuild. and that would be a good start. But if you are not that mechanical, you could try the "deep creep" and "seafoam" treatment. You can search the forums for the details. Seafoam gets mixed into the premix in the tank and MAY help clean gummy carbs a bit.You spray deep creep into the carb intake with the engine running. Makes a ton of smoke. I have brought back from the dead 5 old merc outboards a 9.8 a model 402 40 HP and 3 merc 650s and this treatment though no panacea, improved the performance of each one. If your compression is low it may not mean a disaster, I have seen the deep creep treatment improve compression significantly twice, I assume by freeing stuck rings and removing carbon. If you run an old motor with stuck rings or carbon behind the rings you risk damage form a ring catching and breaking as they slide past the exhaust and intake ports in the cylinder wall. (disaster)
Also give a close look to the lube in the lower unit to make sure it is not milky or mixed with water. I'd change it and look at again after the motor has run in the water for a few hours to make sure there are no failed seals in the lower unit. If you put it away for the winter in freezing temps with water in there it can freeze and crack the casting.
Hope this helps a bit

 

[royboy321]

Re: compression terror

Thanks for the good advice. I knew there would be maintenance and cleaning. Thanks for the heads up on the impeller as well. I am happy to change oil and clean carbs, just not into tearing an engine apart and starting over. I have renewed confidence.

Just to know, what would happen if say a new engine somehow had a manufacturers defect and it did have poor compression. What would the motor do? (smoke? missfire? noise?)

 

[hkeiner]

Re: compression terror

Just to know, what would happen if say a new engine somehow had a manufacturers defect and it did have poor compression. What would the motor do? (smoke? missfire? noise?)

It is probably not worth thinking about the typical symptoms of poor compression and then trying to judge if an engine has poor compression based upon symptoms. It is much better to just go ahead and perform a compression test using a gauge. If the readings are bad, then there are some things you can do to deal with it before tearing the motor apart. Just my thoughts.

 

[Yachtzee]

Re: compression terror

I'd agree with hkeiner. Motor is not THAT old, anyway. use a gauge to test compression or worry about compression last on the list after degunking and possibly cleaning/ rebuilding carb via your perferred method, then looking at ignition (you need a manual for timing and sync) etc for performance issues.

My guess is gooey carbs after sitting 8 years.

Of course it could be squirrels. I had a 40 hp that sat in a barn for a decade. Squirrels had nested and died in it. We cranked it over without taking the cover off for a look see first and sucked bones and fur up against the intake screen.We cleaned it out and it ran pretty good!

 

[royboy321]

Re: compression terror

Well i sprayed the carbs with cleaner and added some fuel additive. Fuel filter also looks clean. I made progress in that the motor starts much easier and sounds better. Still dies when I throttle the engine.

Well a picture is worth...

http://tinypic.com/player.php?v=sdfi1g&s=4

The video shows engine in idle and dying when put in forward and throttle. It also shows the engine reving when pulling the choke. The last bit shows that there is some power with the choke pulled and in gear.

What do you think?

 

[steelespike]

Re: compression terror

You have classic symtoms of a gunked up fuel system.Any motor that has sat for 8 years is going to need the fuel system , from tank to carb, checked,cleaned and repaired as required.

 

[James R]

Re: compression terror

A compression test is the very first thing to be done. If the compressions are not good then you are wasting your time and money going any further. I agree with all the stuff about cleaning carbs. If you run a two stroke with a dirty carb you risk blowing the motor. The spray carb cleaner is a waste of time and can damage carb parts. The carb must be removed and dissassembled and soaked in the cleaner for the job, to remove the muck. Advance Auto carry the carb cleaner kit by the manufacturers of Gunk Products.This is what I use and with 100% success.
Having a manual for your motor is most important if you want to work on your motor successfully

 

[royboy321]

Re: compression terror

Gentlemen, All comments greatly appreciated. I was at the store and ready to purchase a compression tester, but they were out. So now I could be back into compression issues? I do know that a manual is essential. Cleaning is essential. Reading the instructions...essential. I've tinkered with the idle screws and carb adjustments but maybe I am missing something. But back to my original question - I already have too many tools and am trying to cut back - I just would like to know what would poor compression sound like in an engine? If it has a hint of poor compression then it goes back - I do not wish to spend another dime on it. No manual, no tester, no more goo. If someone who is familiar with this engine and willing to take a listen and offer advice and thinks it can be saved, please let me know.

Thanks

 

[hamit59]

Re: compression terror

Our auto zone has a compression tester for loan ( you make a deposit and get it back when you bring it back ) you can check and see what they have for loan. As for the book if compression is good then, I would look for one on line or check with your library to see if they have the book you need. I have found a lot of my books used online some were library books at the start.Now I have over 30 books the ones I like the best are merc books and seloc .I even have a book by hayes for i/o's and it pretty good too. so you can start on the cheep but the book is worth a mint

Oh by the way you can never have too many tools !!!!!

Just my 2 cents worth

Hamit
BT1 USN ret

 

[jerryjerry05]

Re: compression terror

Bad compression would be a dead miss at all RPM. Hard starting no acceleration,motor cutting out.
Someone mentioned a carb soak.They work great.Just remember to put NOTHING in them but metal!!!!!!!!!!!!!!!!!!!!! They will ruin paint,plastic,rubber seals etc.Years ago I soaked a Force carb and didn't get the needle valve rubber seat out and it swelled up and I (didn't know it was even in there)Had a heck of a time trying to figure out why it wasn't getting fuel.
At a lot of automotive stores is a product that is from Chevron.Black bottle looks like a long skinny funnel.It says it Chevron with Techron.It says mix with 8-20 gal I mix it 1 bottle with 2 gal of gas add oil for 2 gal then run a while and let set after it gets into the system.This stuff helps. I use it in all my autos,motorcycles my boats(have 4) Jerry

 

[j_martin]

Re: compression terror

RoyBoy,
Read and heed all the help you're getting.

1. Poor compression and good idle are not compatible. Stop worrying about it.

2. Your motor is showing the symptoms of clogged jets in the carbs. Deal with it. (take the carb(s) off, disassemble them, and clean and adjust them properly. If you can't do it, ask the teenager fixing the lawnmower next door, he can do it.

3. If you continue to run this 2 cycle engine with the malfunctioning fuel system, the most likely outcome will be your first worry. (burned piston, no compression)

4. It's been sitting for years. Change the water pump before you start it again. The impeller, even if it looks good, is likely to break apart and clog up the whole engine cooling system. The first indication would be your first worry again. (burned up)

If you are going to tinker with it, the one tool you need the most is the service manual.

hope it helps,
John

 

[j_martin]

Re: compression terror

PS, it's well past the magique fuel system cleaner in a bottle stage. Take the carbs off and clean them properly.

If you use the canned fix, and it almost gets it cleaned out, it'll run like a cat with it's tail on fire, right up until it burns down because one cylinder was a little lean. (durned first worry again)

John

 

[hkeiner]

Re: compression terror

I do not wish to spend another dime on it. No manual, no tester, no more goo.

This is not an optimal strategy when taking on the role of getting and keeping an outboard motor running well yourself. Compared to the cost of having a shop mechanic do this all for you, the cost of manuals, testers, etc., is minor. In addition to the excellent advice you already got on how to fix your motor, I thought I might add some advice on changing your strategy.

 

[royboy321]

Re: compression terror

Checked out the manual today. I do plan to clean carbs and change the impeller - spark plugs too. I just wanted some confidence that it wasn't the compression before I dove into it. Bad experience with this. As for my strategy, I am barely patient enough to go fishing, much less become a mechanic. A fault, I know. Maybe, this is why I purchased the boat. The motor will be set aside and properly taken care of. I thank everyone for the advice (very appreciative). I will post the results of the cleaning, but it may be a while as I have to get in gear for it (so to speak).

 

[James R]

Re: compression terror

Ok guys lets not get neurotic about carb cleaning. There is nothing to it. The carbs must be removed and dissassembled per the manual. The makers of Gunk products make a Carb Cleaning kit. Just consists of their solvent in a gallon can and a basket. follow the directions and all will be well. I have never seen a problem with plastic parts but rubber parts may be affected. Remove rubber seals as a precaution. This cleaner will remove all the gas gunj from the jets and carb drillings. Advance Auto here carry this product. Whatever you do do not use the so called spray type carb cleaner. This will destroy parts and finish.

 

[j_martin]

Re: compression terror

If you dismantle the carbs, getting out the rubber and plastic parts you plan to reuse, in this case probably the float and needle valve. (viton tip), then the cheap spray can carb cleaner can be used to remove the varnish and goop you'll find.

Where the spray can stuff is useless is trying to clean a carb while on the engine. Outside doesn't make any difference, and carb cleaner in a 2 cycle engine can do major damage, both by washing the oil off moving parts, and causing preignition at start up. No carb parts that need cleaning can be reached without disassembling the carb.

Use it outside, It's both a fire and a health hazard when used inside.

I like the aqua-shield ultra solvent cleaning systems, too. It's just not worth the hazard and expense for this shade tree mechanic.

hope it helps
John

 

[royboy321]

Re: compression terror

Hey - anybody still monitoring this thread?

As suggested, I cleaned out the carb. I found quite a bit of dirt in the high speed jet. I took it to the river and it now seems to idle and rev well. I also broke down and purchased a compression gage and both cylinders seem ok.

So now, engine seems to rev well and no longer dies when applying throttle. Haven't yet measured with tach but sounds good. Still not getting enough power to get out of the hole (runs like a 5 hp). At first I thought the pitch on the prop was too low. It has the number 9 stamped on it (apparently by someone who worked on it) but a prop shop said it was indeed an 11 (manual says 10.5).

So question is...what is robbing my power? The next thing I will do is replace lower gear case oil. Can old oil in the gear case cause a 10hp (engine is supposed to be 15hp) loss?

Thanks

 

[JB]

Re: compression terror

Sounds like you have the carb working after a fashion, Roy, but maybe not 100%. I see no evidence that you have done anything about the timing.

You need to do a linkage and synchronization procedure, by the book. Attempting to troubleshoot that engine, even with the good advice you get here, without a Service Manual is folly. You have already cost yourself many hours and several bux to little avail.