Home › Forum › Ask A Member › 1961 Merc 500 Idle Issues
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crosbyman.
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May 23, 2025 at 10:06 pm #296707
Hey y’all, I’ve got my ‘61 Merc 500 about ready to go onto my Feathercraft Vagabond, but I’m having issues with it idling.
I can’t get it to idle down below about 1400 rpm. This obviously makes shifting very rough and I don’t want to put that much wear on the lower unit.
I feel like this is a timing issue, because my mind says if it was an air leak, I could completely close the throttle plate and it would still idle high. In my case, if I gradually close the throttle plate, the motor will just shut off below about 1350-1400rpm.
I’ve read the timing procedure in the manual, but I don’t have any of the tools referenced. Is there another way to set timing, maybe with an inductive timing light?
May 25, 2025 at 10:01 am #296761Welcome propav8r,
Need background on engine first what do you mean by ” about ready to go”? What status is engine currently in. Once that is understood I will get some good feedback and suggestions. Do you have a Master Service Manual & parts list, if so excellent if not i would suggest you get both. For your fishing engine application to time the flywheel and distributor pulley you will need to line up the timing mark on flywheel which is a straight line with the timing mark arrow on the distributor assembly. All is shown section IV-Ignition of manual. Once good there you will need to set max spark advance, adjust carburetor throttle pick up & carb adjustments on yours only low speed high has fixed jets. There is a complete process for all in book. On a side note we do have a members only section on this website with loads of information and videos for all makes and models.
Travis
Travis
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May 25, 2025 at 4:39 pm #296764My gut says it is a low speed fuel mixture issue. Have you adjusted the mixture screws on the carbs? Do they make any difference? If not they are probably gummed up.
May 25, 2025 at 5:54 pm #296765Install new crankshaft seals then go from there. It might idle just fine after that.
May 26, 2025 at 8:43 pm #296791I don’t know about your motor but on a 1956 Mark55 the idle is set by adjusting the remote control stop. Maybe yours is like that?
dale
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May 27, 2025 at 7:26 am #296792Thanks for this image! Helps a lot!
May 27, 2025 at 8:21 am #296797https://www.youtube.com/watch?v=MfTpU6HS4cA
see around 11:00 idle passage
https://www.youtube.com/watch?v=MfTpU6HS4cA
no expert on Merc carbs but when I had a problem idling a small 4hp Merc a few years ago it was suggested I properly clean the idle passage (small tube) and that instantly fixed my idling problem !
you indicated the engine dies at low rpms below 1200-1400 indicating a likely fuel supply problem ( timing issues aside if nobody messed with timing and idle stop adjustment etc…)
your initial post (top) does not say you fully took care of cleaning ALL carb passages and as per M.Anfossi’s suggestion… that may be your easiest option.
easy stuff first ! btw my boating life years ago included a Merc 500 and a Classic 50 (45hp) 4 cyl. and both were superb idlers…all day long. I have since moved to ETEC technology 75hp 🙂
btw please post exact mdl and ser# !!!
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June 3, 2025 at 7:57 am #296988I’ll pull the carbs and clean them again. I did already do that once, but who knows, maybe I missed some gunk.
Thanks for the input y’all! I’ll start by checking the basics again and go from there.
@Crosbyman, my serial number is 1423438. I believe the motor is a Merc 500M that was converted to electric start, but has no charging circuit. I’m not sure though, it could just as easily be a 500E with the charging gear removed.June 3, 2025 at 8:04 am #296989Welcome propav8r,
Need background on engine first what do you mean by ” about ready to go”? What status is engine currently in. Once that is understood I will get some good feedback and suggestions. Do you have a Master Service Manual & parts list, if so excellent if not i would suggest you get both. For your fishing engine application to time the flywheel and distributor pulley you will need to line up the timing mark on flywheel which is a straight line with the timing mark arrow on the distributor assembly. All is shown section IV-Ignition of manual. Once good there you will need to set max spark advance, adjust carburetor throttle pick up & carb adjustments on yours only low speed high has fixed jets. There is a complete process for all in book. On a side note we do have a members only section on this website with loads of information and videos for all makes and models.
Travis
Thanks, just getting back to this post. I’ll check out the members section. I do have both the factory service manual and a parts list. By “ready to go” I mean I’ve done the basic tune up (new plugs, new magneto belt, cleaned points, new rotor, new wires, rebuilt harness, etc)
I did not crack the cases open, but it may have been done at some point.
June 3, 2025 at 10:10 am #296995john’s old mercury site is also a place where Merc folks hang out 🙂
JohnsOldMercurySite – Index page
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