Johnson 150 Ocean Pro - rough idle

[deviljohn]

I have a 1995 Johnson Ocean pro, V6-loop charged, carb'd, VRO disabled (pre-mix), fresh power head & rebuild.

Have just rigged my boat, new moller gas tank, lines, fuel/water sep, primer bulb etc.....

Engine idles rough w/ sneezes and in the 800-2000 rpm range runs rough as if a cylinder may not be firing correctly...when I get on the throttle and get the rpms up, it runs smooth and like a scalded cat.

yesterday I disassembled carbs and cleaned all the bowls, floats, needles etc..did not appear to resolve anything (idled w/ flusher, have not water tested yet) Didn't find any suspect looking debris in the carbs...I suspected a sticking float. also cleaned out the in-line filter at the intake...minimal debris there.

Have shorted the quick start out w/ engine running, doesn't seem to effect the sputtering at idle.

Plugs look fine and are new. Fuel pump appears to be pulling fine (finger test of vacum on line pulled from fuel/water sep...next step is to put remote tank in and skip the onboard fuel tank, see if I can isolate any potential air leaks..

Short of a fuel issue, is there possibility of ignition circuit not firing right at lower rpm range?? Also, getting what I deem to be very poor fuel economy...about 1-1.5 mpg (pushing 1985 18ft. Mckee Craft CC 1500# hull wt.)

any help appreciated.

 

[tashasdaddy]

Re: Johnson 150 Ocean Pro - rough idle

did you uses new kits on the carbs, clean the high & low speed jets. http://forums.iboats.com/showthread.php?t=244013
do you have spark on all cylinders? does your motor have the shift cutout switch, that kills 1/2 the cylinders, when shifting?

 

[deviljohn]

Re: Johnson 150 Ocean Pro - rough idle

Here's the scenario thus far:

Rebuilt all 6 carbs w/ new OMC kits (some old gaskets were showing minimal signs of dryrot cracking, but no noticeable gunk) very meticulous about cleaning and blowing out all orifices, jets and holes w/ compressor. discovered pinched spagetti seal between throttle body and manifold on cyl#1 side, replaced both sides w/ new spagetti seals..yes, used slight amount of grease to hold in place in the groove and very meticulous install and alignment...throttle body plates synched..

no change after carb job...

Outboard mechanic diagnosed...fuel pump errant, as well as fuel supply issue..thus:

rebuilt both sides of fuel pump (motor and diaphragm) w/ OMC parts, did away w/ backflow preventer check valve at (new) tank and installed std. open barb, installed OMC primer and not the after market junk...discovered pinched o-ring on the fuel inlet beneath the vapor float, replaced. checked all hoses and re-tie wrapped fittings...

motor runs 80% better, however, still have a slight intermittent cough at idle and motor will still periodically cut-out at idle....although not nearly as bad...perhaps I may have an ignition issue at lower rpms (motor still seems to run rough until up on plane) or still a nit picking air-leak in the lines somewhere...Timing timing timing?? I realize setting this is not easily done by shade tree mechanic, thus i will not monkey w/ it.

next will begin to diagnose a) spark wires (they are black, not the grey CDI type i see recommended for the optical ign. system) thinking to run engine in dark and see if I may be getting some intermittent spark to gnd off a nicked wire, will also check resistance of wires w/ meter. b) timing plates sticking?? perhaps, will check as well...I guess my general question is if I am on the right track to trouble shooting this dog?? Tips, ideas appreciated.

 

[boatmonkey82]

Re: Johnson 150 Ocean Pro - rough idle

you say new power head ? check that your bleed tubes are all hooked up and routed properly , sounds like a lean cough or sneeze , i have seen some newer mercs blow off or burn up a bleed tube and start coughing like that. also check that all of your low speed screws are timed with each other and to th

 

[boatmonkey82]

Re: Johnson 150 Ocean Pro - rough idle

you say new power head ? check that your bleed tubes are all hooked up and routed properly , sounds like a lean cough or sneeze , i have seen some newer mercs blow off or burn up a bleed tube and start coughing like that. also check that all of your low speed screws are timed with each other and to the correct setting

 

[boatmonkey82]

Re: Johnson 150 Ocean Pro - rough idle

im sorry that motor may not have screws for the low speed it may have low speed jets

 

[deviljohn]

Re: Johnson 150 Ocean Pro - rough idle

Roger that, the carbs do not have adj. low speed jet, it's orifice type.... I wrote down the orifice sizes (intermmediate/low) when I did the carb job here they are:

Facing carbs,
left side (cyl#1 up top): 28/34**, 28/43, 33/43
right side: 28/43, 28/43, 28/43

**note: I took the motor to the seller/rebuilder before i did the carb job, he installed a smaller dia. orifice (.034") in the low speed (bottom) hole to tweak that carb to run richer (that's what he determined in his brief diag. w/ dog-ears on (no barrel, ie. no-exhaust pressure...motor idled well then, but still ran like ca-ca when afloat after his "pro" diagnosis)

I also noticed the bottom right carb (cyl#5) has a larger intermediate orifice at .033"...dunno why, seems to me like the should all be equal as on the right side. Perhaps his mag. glass failed him when re-assembling the motor..

I tie-wrapped all the recirc hoses on, as prior to the fuel pump rebuild, hose was popping off at cyl#1 due to backfire...also tested the check valves on the manifold side of each hose and they appeared to be OK

I'm studying up on various ignition tests, but I still can't rule out fuel...Item I did not monkey w/ was the vapor separator, perhaps a sticking float in there??

Realize that it's damn near impossible to diagnose an engine via writing, so really appreciate the help. I do have the factory OMC manual on this engine...It's first time around on a larger 6 cyl OMC fer me, so I tread lightly when it comes to tweaking...

I'll double check the recirc hose routing as well, only big PITA is that the right side is covered up by the starter

 

[deviljohn]

Re: Johnson 150 Ocean Pro - rough idle

OK, more diagnostics...same issue. Now that I have replaced the two diaphrams w/in the fuel pump I am noticing that the irregular "click" the pump makes has not been solved..note that I did not notice any visual indications on the xisting diaphrams when I took it apart. so now, new shaft, washers etc in the pump.

The irregular clicking disapates when the primer bulb is squeezed...ie. it goes to a more regular once per 8 secs or so....but w/ motor idleing the click begins to get irregular and more rapid again....squeeze the bulb and it goes away temporarily...this tells me air is getting in the fuel system and now I am suspecting a worn shaft hole w/in the intermediate housing of the fuel pump...note that when I first dissassembled the fuel pump, the one item i noticed was some wear and tear on the pump shaft...unusual that the pump housing was not designed w/ a replaceable bushing...

Also, in the clear tube at the fuel inlet on the motor cowling, I am seeing bubbles w/ engine running (after the clickyty click gets erratic). when I removed this assy. and disconnected the fuel line from the in-line filter, I tested, priming the line w/ thumb over the end as well as discharging into a separate tank....no bubbles evident. Is it possible that a worn intermediate housing on the pump motor would allow air to get back into the line as far back as the cowling tube??

so now I suspect the intermediate fuel pump housing...I would swap it w/ another VRO fuel/pump assy I have off an old V4, but the fuel out fitting is barbed and not like the V6 w/ a double o-ring push-in fitting (to the vapor sep. bowl)...does not appear I can interchanged the two as I gently attempted to remove the fitting from the V4 VRO by turning cc, but it seems to be solvent welded or just part of the housing and not interchangeable...

So, experts and tinkerers, do I sound on track. I know there's lot's o variables here, but I and suspecting that crank side air is bleeding thru the pump housing into the fuel side...makes sense, as I said before, once engine gets up on rpms, the rough idle/cough disappears...any tips/help appreciated in advance.

Also plan on two courses of action, call my outboard dude and see if that *%^&*% intermediate housing is purchaseable as one part or does one have to buy the whole VRO assy...

 

[doug1234]

Re: Johnson 150 Ocean Pro - rough idle

Did you found out what the problem was?

Thanks doug