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Johnson 175 mystery running problem. (retired omc tech even puzzled)

D

Daveparm

Member
A friend of mine purchased a 2000 Johnson 175 60 degree looper (carbed) that we just can't seem to get running. It will run if we force it to by giving quite a bit of throttle, but won't idle. One of the main things to note is that the motor pushes air out of rather than sucking air in the top two cylinders. Both top cylinders run hot compared to the rest of the block. I would guess this is either a vacuum leak or reeds . However, seems odd that the top reeds on different banks would go at the same time (backfire???) Also, the retired omc mechanic that did the first carb rebuild said he had the starboard throttle body off and said the reeds looked good (not sure if he actually removed them though)

Things that I have checked so far. Compression good, aprox 95psi per cylinder, cleand carbs (took off) & throttle body left on, but did confirm idle circuit was clear on all starboard cylinders, cleaned float bowls resurfaced to remove warp, Lync and sunc set as per manual & timing set on specs of idle at 6 atdc, and hs 20 btdc, all colis/cylinders spark, isolated out rectifier, isolated out quick start, and a few other things which I am sure I forgot. I adopted this and did what is listed in this paragraph as the mechanic "gave up on it".

Please help!!

Thanks
 
Not sure if google drive links work on this forum, but here is a vid of how it sounds. it does sound rough - kind of hard to explain.

[video]https://drive.google.com/file/d/17kg6x5-GoxTiCmRdWe10PS2GP9zaJQ6q/view?usp=sharing[/video]
 
Pushing air out the two top carburetors?..... Remove the intake manifold and inspect it..... either the leaf valves are shot or the gasket is deteriorating so bad it is practically non-existent.

The high speed jets, located horizontally in the bottom center portion of the float chambers, way in back of the drain screw.... clean them with the blunt (not pointed) end of a piece of single strand steel wire as solvent just doesn't do that job properly. Fuel must flow thru those jets freely before it has access to any other fuel passageway.

On that engine, compression of 95 psi starboard bank, and 90 psi port bank would be ideal.
 
Hey joe,

Thanks, kind of was thinking the same thing with the manifolds. We did spray carb cleaner around there while running and no change in throttle. As both banks were doing the same thing, kind of thought it as odd they would both leak. Will pull the intakes and clear the mains with a wire. I always though that was the holey(pun) sin! but trust you thoroughly!!
 
I did do a visual inspection of the visible areas of the joint when looking it over. And did spray around that area to see if I could detect bas seal Let's just hope it's not that. Haven't had a chance to get with my friend to look it over again. Will keep posted
 
??----Post # 5 mentions " seal rings "------These are rings fitted on the crankshaft to separate the 6 crankcases in this V-6 engine.
 
There could be a case of every crankshaft seal ring being broken on that engine... BUT... none of that would cause air being blown out the top carburetor throats!
 
Hey guys, sorry for the delay in my reply. Coordinating my schedule with my friend that owns the motor has been tough with both our schedules and being out of town.
Checked the Jets again used wire as joe suggested, they are def clean. Ruled out the intake manifold gaskets. Then sprayed carb cleaner down into the crevice between each carb set and block and got a change when doing this on both sides. When you mentioned crankcase seal ring, I was thinking fazbulet was referring the the seal between both crankcase halves, nott the seal between each cylinders section. Either way by looking at it, it appears that I could split the crankcase while the powerhead is still mounted the the leg (mid section) on this motor. Is that true? If so, and this could be done without powerhead removal, what is the recommended sealant to use for the case and seals? Thanks
 
Oh one other thing, if I remove the carbs and spray soapy water around this joint while turning motor over, will that help me pinpoint a leak area?
 
Just thought I would try to bump this to the top. Would really like to get this done in the next night or two. Do I need to pull the powerhead to split the case on this motor??

Thanks
 
Thanks flyingscott. Looked like none of the bolts that held the bottom case were screwed into the leg, so I was wishful thinking. Oh well.
 
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