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Results 1 to 17 of 17
  1. #1
    Join Date
    Jan 2007
    Location
    Myrtle Beach, SC, US
    Posts
    7

    Default "First, my apologies for posti

    "First, my apologies for posting this issue here. Couldn't find another related forum.

    I have a 1988 Onan 6.5 H-series Marine Gas Generator. Low hours. 2-cylinder opposed with aviation plugs and braided/shielded ignition wires from coil. Engine starts and runs well at idle with little or no governor hunting; also runs well with full load, including 2 AC systems, refrigerator, etc., that push it to 20 amps. Carb clean; points clean and gapped properly; fuel lines clean; new fuel-water separator; idle and heavy load mixture set to factory defaults; engine temp good; closed-system coolant clean; sea water pump working well.

    Problem: When stepping up from idle to 15 amps load, Genset works great. When adding load greater than 15 amps, genset backfires, coughs, governor hunts erratically, but eventually achieves desired load and holds steady voltage/amperage.

    Then, still at full load, genset will eventually die as if it is out of gas (tank full).

    Any help is appreciated. Need to resolve backfiring, governor issues, and reasons for engine quitting under load. I have ordered new plugs, but the old ones are clean and gapped properly. Trying to find new choke assembly, but it starts fine and idles smoothly, so that doesn't seem essential to these issues."

  2. #2
    Join Date
    Nov 2002
    Location
    Mullica Hill, New Jersey, United States
    Posts
    1,810

    Default "Gordon, The problem seems to

    "Gordon, The problem seems to be only when you are requiring the most fuel and air. How is the air cleaner? Is everything tight? These guys vibrate alot. Make sure carb and intake bolts are all tight. Also, try adding an outboard primer bulb in-line between the tank and the genset. It is possible the fuel pump is weak and it you are actually running out of fuel. When the engine starts to act up, squeeze the primer, this will suppliment the fuel pump and may well give you your answer,

    Good luck
    Rick"

  3. #3
    Join Date
    May 2006
    Location
    Florida, USA
    Posts
    103

    Default If what Rick said does not wor

    If what Rick said does not work go through the carb again. Small ports can be plugged off and effect performance. Use high pressure air to clear them. If that does not work get a new carb.

  4. #4
    Join Date
    Oct 2007
    Location
    orlando, fl, usa
    Posts
    91

    Default "was this problem resolved. I

    "was this problem resolved. I know of a few things that could also cause this problem.

    Most likely carburator and or fuel pump related. These little fuel pumps get tired and need to be replaced. also suction tube can not be bigger than .25" . If larger than this a pump with a few years on it cant suck the fuel. What is easier sucking water through a straw or a 1"pipe.

    also these carburators have very small passages in them. carb needs to be dismantled and soaked in car cleaning bucket. I just did this for the first time with my spare carb and installed it. took care of all problems.

    My question is on carb float setting on the Nikki . all manuals show the Welbro carb but not the Nikki. very similar design but the float is completely different. Float setting with float just under the top of the bowl has the gas just above the needle valve body on the welbro but the float at same level on Nikki has gas lower than this. I set mine to be above the proper level, there is gap in the upper half but am concerned that the float may be hitting the top and not allowing needle to close. think carb is high enough to not allow gas to syphon, of course with full tanks this may be an issue.

    anyone have nikki carb experience?"

  5. #5
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "Hi Gordon: I was hunting thr

    "Hi Gordon: I was hunting through the archives for some unrelated info. and I came across your post. I have spent a fair amount of time fiddling with a 1984 Onan 6.5 KW MCCK genset and have finally got mine running well.

    In your post there are several symptoms that may be unrelated, i.e. rough running and hunting when a load is first applied and a hard stall after running for a while at full load.

    First and foremost the raw water pumps are very finicky on these units and the slightest vacuum leak will reduce and or completely eliminate flow and cause one of the two high temp. limits to trip, killing the ignition. I know you mentioned “good raw water flow” but in my experience the pumps are prone to poor performance. The raw water intake hose should be continuous with no tees or connections and have the most positive connection to the pump intake as possible, preferably with some sealent for good measure. Replacing the pump impeller is also recommended. I have seen these pumps “pump well” one day and not draw a drop the next day, or hours later the same day for that matter, and on more than one boat. The exhaust high temp. switch is located at the exhaust elbow; there is another engine coolant high temp. switch on the block. Check these for continuity after a hard stall.

    Another common failure that is often intermittent in nature is the low oil pressure sensor switch on the block. Yours is most probably a 30 year old pressure switch that has already outlived its useful life. I replaced mine at NAPA (4 psi 1/8 npt thread) for about $20. It solved my remaining intermittent failures. Be careful while the engine is running; I believe 120 V A/C is routed through the switch to an ignition relay that keeps the ignition circuit live so long as A/C is being produced.

    20 amps is not that high of a load for a genset that is capable of producing in excess of 50 amps. It is quite possible that one cylinder may not be firing as these horizontally opposed two cylinders will run very smooth on one cylinder. Check for heat at both cylinder heads immediately after start up. Change or swap plugs if no ignition on one side. Also check breaker points for wear and set gap to 0.020”. Replace if worn. These ignition systems are not the stoutest and small defects can interfere with proper operation. There is no distributor as both sides fire at the same time (one is a waste spark on the exhaust stroke). Replacement coils and automotive plugs can be found and used from the RV version of this genset (Onan RCCK) for much less money than the aircraft style shielded plugs and coils that were OEM (and that will cost you many hundreds of dollars to replace). The new coils are potted in epoxy and are watertight. From the RCCK:
    Onan plug cable 23" #167-1602, Onan ignition coil #166-0772, Onan spark plug # 167-0237, Onan condenser # 312-0027.

    This engine design is susceptible to carbon build up in the valve area and pistons, etc. and usually benefits from a little seafoam poured slowly down the carb. throat. Also make sure the carbs. have been cleaned and rebuilt. Finally, here is a good small engine technical forum visited by experts in generator repair. http://www.perr.com/forum/viewforum....2e45e1f1d2375d

    Best wishes,"

  6. #6
    Join Date
    Jun 2008
    Location
    Newport Beach, Ca, USA
    Posts
    10

    Default "I also have a 6.5KW MCCK same

    "I also have a 6.5KW MCCK same vintage and had same problems. Had major tune up and new carb, fixed it all. One thing I was also told was to check exhaust elbow. They many times fill up with carbon deposits triggering the exhuast temp. sensor that will shut down engine. Points are also very critical, and slightest amount of moisture, condensation or dirt will lead to same symptoms."

  7. #7
    Join Date
    Jan 2009
    Location
    seattle, wa
    Posts
    90

    Default "I too was searching for other

    "I too was searching for other material when I came across this Onan discussion. My Onan worked great one day and the next, it would not take a load and wanted to die with or without load. It runs rough. I then changed fuel filter-no result. I checked plugs and they are moist. I believe I can smell fuel in crankcase oil. When it's running, I manipulate linkage (manual choke) and it does not help. Also when running, it smells as if it's trying to flood itself out with fuel. Exhaust is not excessive and no 'rainbow' from exhaust water. Carb dismantle time?"

  8. #8
    Join Date
    May 2008
    Location
    Tampa, Fl, USA
    Posts
    17

    Default Check the temperature and make

    Check the temperature and make sure it is not overheating and causing the heat sensor to shut down the generator. If this is happening it acts the same as if it is running out of gas. You may need to go thru your cooling system.

  9. #9
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "You have an overly rich condi

    "You have an overly rich condition, perhaps from crud in the needle value seat, sticky needle valve, defective float, etc. A carb inspection and rebuild could be in your future. You should be able to determine if gas is in the oil by smelling the oil; further, the oil will be thin and overfilled. I sent my carb out for cleaning and inspection last spring and it came back with a tiny piece of gasket material in the valve seat. I was fully expecting the genset to roar to life and run strong the rest of the summer; instead, it flooded immediately and it was weeks before I discovered gas in the oil...

    If the genset runs rough with reduced power AND the exhaust smells rich, it could well be running on one cylinder. I have had this happen from a fouled plug. Check the temperature of both cylinder heads at start up; these engines are horizontally opposed twin cylinder designs and you’d be amazed how smooth they run with one dead cylinder.

    It is also possible that the electric choke is defective. To verify, run the engine for 10 minutes, remove the flame arrester, and see if the choke is opening up; if not, hold it open with a screw driver and see if the situation improves.

    If all else fails post a message on the small engine technical forum at perr.com (www.perr.com/phpBB3/). There are several generator experts that monitor the site including the moderator. Be sure to state your generator type and model; the Onan MCCK is a cousin of the RV RCCK genset and many thousands of these units were produced over the last several decades."

  10. #10
    Join Date
    Oct 2007
    Location
    orlando, fl, usa
    Posts
    91

    Default "If you find both cyl firing ,

    "If you find both cyl firing , timing and points are good then fuel is most likely the problem.

    The carburator is very simple, not much in there. I make my own gaskets and did my own work. Floats can be problem as they are composite. Can soak up gas and are less buoyant.

    Guessing you have the Nikki or Welbro. Please confirm that yours has an aftermarket manual choke or does it have the OEM electric choke."

  11. #11
    Join Date
    Oct 2007
    Location
    Germantown, TN, USA
    Posts
    227

    Default "Last year I had a lot of work

    "Last year I had a lot of work done on my Kohler 7.5 KW generator. It included carb, magneto, fuel pump, pulled heads and removed carbon build up, spark plugs etc. When we reassembled it, it would only produce about 20 amps. Problem turned out to be the timing was not set correctly. A simple fix."

  12. #12
    Join Date
    Feb 2006
    Location
    Arlington, VA, USA
    Posts
    952

    Default "The stall does sound like you

    "The stall does sound like you are tripping a safety limit switch somewhere. Oil pressure, exhaust temp..."

  13. #13
    Join Date
    Sep 2002
    Location
    Posts
    118

    Default "i had the same problem with m

    "i had the same problem with my onan ,solved the problem by jumpering all the cut outs then it ran fine put each one on line one at a time problem was oil pressure switch now all is well."

  14. #14
    Join Date
    Apr 2009
    Location
    baltimore(middle river), md, usa
    Posts
    2

    Default "i have an onan 6.5kw mcck spe

    "i have an onan 6.5kw mcck spec d control-o-matic on my 1976 trojan f-32. my problem is this. the genset always 'hunted' when a load was applied so this season i turned up the rpms but did not adjust the governor (didnt know how to do that). that seemed to mitigate the hunting a little, but the volt meters read between 145 and 150 volts when the idle was sped up. last week i turned on the genset and when i switched to 'gen' on the electrical panel, i did not get any ac power from the genset. i did a continuity test on several boards and diodes in the controller and discovered that the load sensor amplifier .25amp fuse did not register anything when the tester prongs were touched to it. could it be something as simple as a fuse that causes current to not flow to the panel? i was wondering that when i boosted the rpms,(remember, the governor was not adjusted accordingly to the higher rpms) that boosted the voltage and after i shut her down a power surge caused the sensor to blow. any advice would be appreciated. thanks.
    aaron in baltimore,md
    tovyah@aol.com"

  15. #15
    Join Date
    Oct 2007
    Location
    orlando, fl, usa
    Posts
    91

    Default "If boat sells in next couple

    "If boat sells in next couple of weeks I will be selling my Onan spare parts kit separately. Price of boat too low to provide any spare parts.

    Kit will have rebuilt Nikki Carburetor that has been engine tested, Spare spark coil, Pump impellor and seal and shaft, Several gaskets, seals and some electric choke parts, a couple of relay switches and several other parts."

  16. #16
    Join Date
    Mar 2009
    Location
    Port Huron , Michigan, United States
    Posts
    7

    Default "I have the same Genny, and ha

    "I have the same Genny, and have experienced the same symptoms. The fix for me has always been points and condencer. I keep a spare set of plugs that have been blasted clean by a plug blaster. For my MCCK (85 vintage 400 hrs. ) this is an every 100 hr task. Clean fuel and fresh oil and make sure the overtemp sensor located on your exhaust is tight."

  17. #17
    Join Date
    May 2008
    Location
    Tampa, Fl, USA
    Posts
    17

    Default "High RPM causes to much volta

    "High RPM causes to much voltage and can blow fuses and relays. Weak throttle spring is usual culprit for "hunting".

    WWW.smokstak.com all the info you will ever want about ONAN generators."

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