Rhojo's '88 Johnson 70's J707TLCCA, updated... reed fix

[Rhojo]

I wanted to go ahead and start this thread even though I don't have everything ready for posting. I'll be adding info, pics and hopefully some video after this weekend.

Brief history:

These are VRO motors but it is disabled, I mix my own gas and I'm a bit anal about my mix, I use one of the seachoice measuring botles and I make sure I'm looking at the 1:50 marks.
These are '88 models as mentioned however I have had a professional do a motor and powerhead swap on the port side motor. So the port side is an '86 midsection and lower unit with my good '88 powerhead swaped onto it. It runs the very best of the two. Just prior to the engine swap I had the same pro rebuild all six carbs. I installed new air cleaner gaskets. The corks ones on the air handlers, both the ones that seal up the air cleaner cover and the ones that go between the carbs and the back of the cleaners. I have new in-line fuel filters under the cowls as well as a clean water/fuel seperator every season. No water in my tank at the moment. All of this has been done over the last two seasons. I never run ethanol without running Startron fuel treatment, never. I've only had non-ethanol gas in the boat once and that was 35 gals of 93 octane in Southport this past weekend. The ran perfectly with this one exception, the starboard motor. It has always been a little sluggish compared to the port side.

I can run them one at a time on the muffs and all seems well. Good throttle response even from the starboard, although I don't rev it much at all. Just take it through the motions prior to launching at the lake. As soon as we get in the water, under load, the starboard engine likes to stall between gears and when I'm getting out of the hole the rpm's are much slower on starboard side to come up.

If I run the starboard engine on the muffs and get under the cowl and take the air cleaner off at idle I have fuel mist coming out the front of the middle carb, a very fine fuel mist. It will even collect in the air cleaner and over the course of a day running the motor will get black carbon on the exterior built up. I do have good and new plugs. I check them and my filters regularly. My fuel lines are in good condition.

I'm going to get some video of the engines on the muffs in the driveway and some video of us in a hole shot on the lake.

I'm looking forward to what all of you guys have to say...

[fitz73222]

Me, Georgie, and Debur are on the starting line... I already have 3 possible causes in mind. But I should let my OMC brethren have two seconds out of the tree!

[gran398]

Jon, quick question. How does the idle speed compare between engines? On the starboard engine that dies when shifting...may be something as simple as knocking the idle up 100 rpm's.

My little Mercs, Farley set up to idle @ 850 RPM. After putting around 60 hours on them, the starboard engine had backed off to 600 at idle. Some of it may have had to do with the throttle linkage slipping at the helm. It would sometimes cut off going into forward from neutral. Got a little more pronounced in that 37 degree weather Saturday morning.

Bumped it back up to 850 Sunday night...she's running like a champ again.

Edit: Double post, sorry about that. But mine didn't count...once you run black you'll never go back.

[dburr]

Jon when the carbs were done was the reed block checked? Does the mist look like it is pulsing?  Just odd that vapor is coming out and not being drawn in...

[Rhojo]

Jon, quick question. How does the idle speed compare between engines? On the starboard engine that dies when shifting...may be something as simple as knocking the idle up 100 rpm's.

My little Mercs, Farley set up to idle @ 850 RPM. After putting around 60 hours on them, the starboard engine had backed off to 600 at idle. Some of it may have had to do with the throttle linkage slipping at the helm. It would sometimes cut off going into forward from neutral. Got a little more pronounced in that 37 degree weather Saturday morning.

Bumped it back up to 850 Sunday night...she's running like a champ again.

Edit: Double post, sorry about that. But mine didn't count...once you run black you'll never go back.

Both idle about the same, less than 1000 rpm but more than 800, I'll check it.

[Rhojo]

Jon when the carbs were done was the reed block checked? Does the mist look like it is pulsing?  Just odd that vapor is coming out and not being drawn in...

No mention of the reed block from the previous mechanic so I don't think he did anything there. Although he did say he did a thorough check on the whole engine. The mist doesn't seem to pulse, just a steady fog machine type mist but not that heavy.

[fitz73222]

Jon when the carbs were done was the reed block checked? Does the mist look like it is pulsing?  Just odd that vapor is coming out and not being drawn in...

I was thinking the same thing but if she isn't coughing back through the carb it's probably not a chipped or stuck reed valve. I was thinking that the float level is set too high in that carb and fuel is percolating up the high speed nozzle at idle and loading up in the venturi causing the mist condition. This could also cause the engine to bog on take off because it's loaded up in that cylinder and runs OK once she is cleared out. I found more often than not that the engine needs to be "set up" correctly before you can really start to understand whats going on. That means base idle timing, throttle pick-up position and max timing including a compression test done correctly.

A more sinister issue inherent with this engine design exclusively was worn lambert (spelling) seals in the block. These were machined grooves in the block between each crank journal that was designed to keep cylinder pulses isolated from one another during intake and compression rotation of the crank. When these seals get worn the pulses start to invade each other during the vacuum and pressure cycles and the engine will not idle smoothly, will stall and bog on take off. There is no repair for the condition. If the engine idles reasonably well on the muffs out of water but runs poorly in the water with back pressure this can be a sign. Lets hear the video and see if it gives us any clues.

[Rhojo]

Jon when the carbs were done was the reed block checked? Does the mist look like it is pulsing?  Just odd that vapor is coming out and not being drawn in...

I was thinking the same thing but if she isn't coughing back through the carb it's probably not a chipped or stuck reed valve. I was thinking that the float level is set too high in that carb and fuel is percolating up the high speed nozzle at idle and loading up in the venturi causing the mist condition. This could also cause the engine to bog on take off because it's loaded up in that cylinder and runs OK once she is cleared out. I found more often than not that the engine needs to be "set up" correctly before you can really start to understand whats going on. That means base idle timing, throttle pick-up position and max timing including a compression test done correctly.

A more sinister issue inherent with this engine design exclusively was worn lambert (spelling) seals in the block. These were machined grooves in the block between each crank journal that was designed to keep cylinder pulses isolated from one another during intake and compression rotation of the crank. When these seals get worn the pulses start to invade each other during the vacuum and pressure cycles and the engine will not idle smoothly, will stall and bog on take off. There is no repair for the condition. If the engine idles reasonably well on the muffs out of water but runs poorly in the water with back pressure this can be a sign. Lets hear the video and see if it gives us any clues.

good stuff right there, ok I'll get the vid, both in the muffs and in the water.

[Rhojo]

Here is the video:

starboard on the muffs
http://www.youtube.com/watch?v=5D53yWu6e6M&feature=youtu.be

from idle
https://www.youtube.com/watch?v=Pg6CDXOLtCE

from a dead start
http://www.youtube.com/watch?v=I18hKGgIgh4&feature=youtu.be

 :)

[Georgie]

Hey Jon,

Sorry for the delay.  Been on vacation in Key West since Wednesday...

That first link is an EXCELLENT video and shows quite a bit of pulsing backpressure pushing a signficant amount of fuel back through the middle carb throat.  She's certainly not going to run well with that happening and stalling at idle or while shifting would be a very typical symptom.  That amount of reverse air movement simply shouldn't happen if the reed box is functioning properly.  I imagine once the engine gets up and going, the increased volume of air being pulled through the carb at higher RPM's diminishes the degree of fault in the cylinder's combustion by a significant percentage, so it probably runs much closer to normal at cruising speed and above.  Fitz is right that it will help to narrow down the possibilities if you can at least verify that some basic tuning elements like timing and jets are all consistent between engines and carbs respectively. I could be wrong since I'm unfamiliar with the Lambert seal condition he mentioned, but any exchange of vapors between combustion chambers would probably cause BOTH affected cylinders to run poorly.  The video you posted seems to show the problem is very much isolated to the middle cylinder.  There's a chance you may be able to see an improperly seated reed or an obstruction by taking the carbs off, but if it's not obvious you'll most likely need to take off the intake manifold too in order to properly inspect.  Not sure if that'll require powerhead removal on your 3-cyl OMC's b/c I've never worked any of 'em.

Hope this helps and keep us posted as you work through your diagnostics.  Curious what the others will say after seeing the videos.

[fitz73222]

Well there is no question that crankcase pressure is migrating back through the reeds. Can't say I ever saw one that bad that wasn't coughing like crazy. At full throttle does that engine turn the same RPM's as the other? Do a compression test next and see if any of the cylinders are low. It may have swallowed a piece of reed valve. This could also be as simple as a piece of gasket material from the carb rebuild has lodged in one of the reeds and is holding it open. Either way, if a compression test does not show and issue you are going to have to pull the reed cages and have a look. You have the newer style lost foam block after '85 so you may be able to pull the reeds without removing the powerhead. I will check and let you know.

[fitz73222]

Well there is no question that crankcase pressure is migrating back through the reeds. Can't say I ever saw one that bad that wasn't coughing like crazy. At full throttle does that engine turn the same RPM's as the other? Do a compression test next and see if any of the cylinders are low. It may have swallowed a piece of reed valve. This could also be as simple as a piece of gasket material from the carb rebuild has lodged in one of the reeds and is holding it open. Either way, if a compression test does not show and issue you are going to have to pull the reed cages and have a look. You have the newer style lost foam block after '85 so you may be able to pull the reeds without removing the powerhead. I will check and let you know.

I looked at the powerhead schematic and it looks good to try to do this without pulling the powerhead.

[Rhojo]

Thanks fellas, I'll check my compression and report back.  

[Rhojo]

Compression test results:

Cyclinder #1 (Top)-105
Cyclinder #2 (middle)-100
Cyclinder #3 (bottom)-105

[Georgie]

Right on!  At this point I gotta believe the problem has something to do with the reeds, although reed problems aren't the most common problem in the outboard world.  Just can't think of another reason for THAT much fuel to be spitting back out of the carb.  

Either way, if a compression test does not show and issue you are going to have to pull the reed cages and have a look.

 Time to break out the tools.   :twisted:

I looked at the powerhead schematic and it looks good to try to do this without pulling the powerhead.

 Assuming Farley's right, this makes the job quite a bit easier.  Do you have a service manual?...or at least a good parts schematic to follow?