Good Compression=Fixable?

[EMC 1810SS]

I have a 1996 Mariner 3 cylinder 2 stroke 75 Horse outboard. It was running rough land backfired a few times from being lean so I rebuilt the carbs and fuel pump. After that I found a bad reed on #2 cylinder. I replaced all of the reeds with Chris Carson Fiberglass units. I did notice that they were punched slightly off. Well, long of short, #2 ran for about 60 seconds and quit running again.

The good:
All three holes have 120 psi compression
Carbs have been cleaned, new needles etc.
New diaphragms in the fuel pump (I cant believe it ran on the old ones)
Good spark on all three holes.

When I pull the plug from #2 and #3, the engine will actually start and run on #1. It will also start and run on # 3 only. #2 will pop but not run.

Also, visually from the bottom the piston's look good, the bores have no markings note do the ports from the bottom. The piston tops all look decent from the plug hole also.

My question, with good compression, I would imagine that whatever the issue, it IS fixable if I find it Correct?

This weekend I am going to go back through the carbs, and the reeds. Maybe something is off?

Any other suggestions? I really want to give this chunk of aluminum a new lease on life but it isn't being to agreeable......

 

[Maxz695]

Re: Good Compression=Fixable?

I would start by checking the coil grounds and the trigger leads esspecially to the terminals for #2 on the switchbox and the coil for #2. I would also try swaping the plug from #1 to #2 and retest it.

 

[EMC 1810SS]

Re: Good Compression=Fixable?

I swaped the plugs and even the coils (switched the trigger wires). I dont think it is a spark issue. All three coils are firing a good 1/2" spark that will knock you on your A** if your not carful with the plyers testing it. I even tried putting the old spark plugs in.

Can it have GREAT compression but still some sort of mechanical failure that would make it not run? Is there still a chance this block is trash? It doesnt knock either.....

 

[Faztbullet]

Re: Good Compression=Fixable?

Index the flywhell and check timing, you likely going to find the timing off on #2 due to a bad switchbox(bias) or trigger.

 

[EMC 1810SS]

Re: Good Compression=Fixable?

Index the flywhell and check timing, you likely going to find the timing off on #2 due to a bad switchbox(bias) or trigger.

Interesting. How would I do this? Find top dead center of #2 and mark the flywhweel? Definetly something to test. Being off could cause the backfire that ate the first set of reeds also?

 

[JB]

Re: Good Compression=Fixable?

If it will start and run on only #1 or #3 your trouble is unique to #2. Could be carb, reeds, trigger or switchbox. Don't mess with anything that also affects #1 or #3.

 

[Maxz695]

Re: Good Compression=Fixable?

With good compression, I highly doubt it is the engine cylinders. With good spark, I highly doubt it is electrical. This is appearently a 3 cylinder according to your post, and the problem lies in the cylinder #2. Three cylinder engines have 2 reed blocks.The upper reed block takes care of # 1 and #2 cylinder, and the lower reed block takes care of #2 and #3 cylinders. My opinion is the outter reeds of #1 or the inner reeds of #2 reed block has a bent reed. This is just my opinion. The reeds must be flush with the block period. Although a slight space may be compensated by the back pressure of the compression stroke, over reaching reeds (Spaced wide) will not seal on the compression stroke losing precious fuel nessecary to start the engine.

 

[ENSIGN]

Re: Good Compression=Fixable?

You may also want to check the seam between the two engine block haves.With the engine running spray some carb cleaner along both sides and listen for a change in the idle speed.If you're having any spit back of fuel out of the carbs the reeds are not sealing properly.

 

[Faztbullet]

Re: Good Compression=Fixable?

Three cylinder engines have 2 reed blocks.The upper reed block takes care of # 1 and #2 cylinder, and the lower reed block takes care of #2 and #3 cylinders.

Max this is a 3 cylinder looper and it has a reed assy behind each carb, it is not a crossflow DC like you have.

Interesting. How would I do this? Find top dead center of #2 and mark the flywheel?

Remove plugs and insert a dial indicator or wooded pencil in cylinder #2 and slowly rotate engine till piston reaches TDC, repeat with #3 cylinder. Take a timing light and check timings at idle, 1500rpm and 3000 rpm. You should see the timing advance on each cylinder the same amount of distance as RPM increases. If you see #2 stutter in flashing ,slow to advance or off the scale the switchbox or trigger has a problem. I have only seen a stator do this once on a V-6 as it was supplying overvoltage to the switchboxes thru the bias circuit....

 

[Maxz695]

Re: Good Compression=Fixable?

I see there removable without disassembly of the case . Cool

 

[EMC 1810SS]

Re: Good Compression=Fixable?

Thnak you for all of the sugestions. I will be checking all of these ideas this weekend. I will let you know what I find.

 

[quicktach]

Re: Good Compression=Fixable?

If you get under the flywheel, check stator and trigger coils. You could have a bad CDI too ...they get real weird when they act up and you can only diagnose a CDI as bad if all other electrical checks out OK.....usually. Timing and synchronizing check is needed.