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  1. #1
    Join Date
    Apr 2011
    Location
    hendersonville, tn
    Posts
    15

    Default engine idling high

    ok sorry for the long story here but I want to give all the details.
    2001 Mobius ls
    Engine is indmar 5.7l carb with electronic distributor.
    Last fall I had the head gasket replaced on the left side of the engine (I believe 1,3,5,7). Head gasket was blown between 3 and 5 cylinders. A mechanic friend of mine replaced the head gasket for me and we took the boat out and it ran perfect. we ran it for about 3 hours, running it wide open, cruising, idling and shutting it off a couple of times. On the way back to the boat ramp boat was running fine, and then I took the boat out of gear to slow down and I noticed that the engine was idling around 1100 rpm and there was some whitish blue smoke coming from the right exhaust. the following is what I have checked so far to
    1. I adjusted the idle set screw all the way down and the rpms never fell. I could adjust it up but
    not below 1100 rpms
    2. I disconnected the throttle linkage to see if it was sticking open but it was all the way down
    3. I replaced the pcv valve and conditions did not improve.
    4. I checked the vacuum by using a vacuum gauge and was getting 20 lbs/in. I also checked for leaks around the vacuum hoses, base of the carb, and intake manifold by spraying starter fluid around those areas.
    5. I checked timing and it was 6 BTDC.

    As of now I am out of ideas and looking for some help

  2. #2
    Join Date
    Oct 2013
    Location
    Ft. Collins, CO
    Posts
    221

    Default

    Blue smoke = burning oil

    Normally, the best-case-scenario is a faulty PCV system. Worst-case is blow-by through the cylinder rings/pistons or valves which means an engine rebuild/valve job. Since you just had service done, there could be residue oil burning out but that would normally burn out in 15 minutes or so. Burning a little bit of oil isn't the end of the world. You could probably run for years like that, just keep an eye on your oil level. The only bad thing that could happen would be to run low on oil. I wouldn't expect this is something you can fix by tuning the carb or otherwise.

    It always seems like when you fix/rebuild the head gasket, lower block/cylinders, or valves you just expose the weakness in the other pieces. How many hours are on your motor?
    2007 Mobius LSV
    1989 Sanger Skier DX - sold

  3. #3
    Join Date
    Apr 2011
    Location
    hendersonville, tn
    Posts
    15

    Default

    Quote Originally Posted by gregski View Post
    Blue smoke = burning oil

    Normally, the best-case-scenario is a faulty PCV system. Worst-case is blow-by through the cylinder rings/pistons or valves which means an engine rebuild/valve job. Since you just had service done, there could be residue oil burning out but that would normally burn out in 15 minutes or so. Burning a little bit of oil isn't the end of the world. You could probably run for years like that, just keep an eye on your oil level. The only bad thing that could happen would be to run low on oil. I wouldn't expect this is something you can fix by tuning the carb or otherwise.

    It always seems like when you fix/rebuild the head gasket, lower block/cylinders, or valves you just expose the weakness in the other pieces. How many hours are on your motor?
    About 800 hours

  4. #4
    Join Date
    Apr 2011
    Location
    hendersonville, tn
    Posts
    15

    Default

    I will do a compression test this afternoon. but what could explain the high idle.

  5. #5
    Join Date
    Aug 2011
    Posts
    1,120

    Default Re: engine idling high

    Did you have the head checked by a machine shop before re using it?

    Sent from my Nexus 5 using Tapatalk
    2002 Moomba Mobius LSV - Sold
    2006 Moomba Mobius LSV

  6. #6
    Join Date
    Apr 2011
    Location
    hendersonville, tn
    Posts
    15

    Default

    Quote Originally Posted by parrothd View Post
    Did you have the head checked by a machine shop before re using it?

    Sent from my Nexus 5 using Tapatalk
    Yes the head was sent to a machine shop and everything was good

  7. #7
    Join Date
    Aug 2011
    Posts
    1,120

    Default Re: engine idling high

    Is the choke working?

    Sent from my Nexus 5 using Tapatalk
    2002 Moomba Mobius LSV - Sold
    2006 Moomba Mobius LSV

  8. #8
    Join Date
    Apr 2011
    Location
    hendersonville, tn
    Posts
    15

    Default

    it is an electric choke and it is disconnected because I could never keep it working. but the butterfly plate is open and not shut.

  9. #9
    Join Date
    May 2013
    Posts
    182

    Default

    Being that the carb was removed. I would suspect gunk got stuck in it causing a rich issue. When it's running look down the throats of it and see if there is equal amount of fuel coming out of each venturi. The only thing that causes high idle is more, gas, less vacuum or timing. Vacuum and timing can be usually effected with resetting the idle though.

    What do the plugs lo like after your run?

  10. #10
    Join Date
    Apr 2011
    Location
    hendersonville, tn
    Posts
    15

    Default

    sorry for just now posting back. I have been busy this week and just had some time to look at it again today. I check compression on all cylinders and while they were low they werent showing any abnormally low cylinders. 150 on all cylinders starboard side and the port was as follows - 1- 150 / 3- 140 / 5- 135 / 7- 140. I checked again for vacuum leaks and found none. I spoke to the dealership and they think it is a carburetor issue and that it is running to rich. at this point I am tired of waisting my time when the weather is nice. I am going to take the boat in on Tuesday and be done with it.

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