1979 25 hp runs rough at idle, please help

spacemonkey77

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Nov 16, 2015
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Ok thanks for the info. It may be a few days before I can get too it again!

yes only one carb! It’s been totally rebuilt!
 
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oldboat1

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What? You have other things to do?! :)

Probably should also think about additional carb work. Cleaning/rebuilding isn't hard, but requires some technique. Spraying without disassembly won't do the job, but may find that a proper cleaning will do the trick -- issue might be a dirty high speed jet, but would probably want to do the full job.
 

spacemonkey77

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Nov 16, 2015
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Haha yeah tell me about it. Work calls. Lol

Yes I actually fully rebuilt the carb about a year ago. I recently pulled it and completely disasembled the carb and recleaned it too.
 

oldboat1

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Yeah, sounds like you weren't shy about getting into it. I soak tops and bottoms in lacquer thinner after disassembly, then poke every opening with soft wire and finish with carb spray. Sounds like you have mid-range issues, but wouldn't hurt to do the idle passages up at the top (remove and replace the domed fitting). If the idle needle isn't sensitive to adjustment, might need some cleaning up there.
 

spacemonkey77

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I pulled both plugs. They both were a bit wet but one (the bottom cylinder) is a little more gummed up than the other.
here is a pic. The one at right is the top and left is bottom!
 

racerone

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Dec 28, 2013
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There may be an issue with the lower crankshaft seal.----Or a reed valve.
 

spacemonkey77

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Nov 16, 2015
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Ok I’ll have to research those as I have no idea where they are and how laborious it is to fix.

I did however fire it up this morning on a cold morning and it actually started up really well and did not bump like it has been . I did clean the needle valve seat and I Richened up the needle adjustment a bit. I’m wondering if part of my issue with it running to lean in the cold weather.

I also let it warm up and felt both cylinders and they both felt warm. The water coming out of the PEe hole was warm as well!

here are vids!
 

racerone

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?----Reed valves are behind the carburetor and powerhead must be removed to inspect the crank seal.----I believe the lower seal has been superceded to an improved item !!
 

racerone

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You say that the lower cylinder does not appear to be pulling it's weight.-----So it is up to you to do the trouble shooting and the work.
 

spacemonkey77

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Oh no I’ll def do it. Just gotta figure out how. I’m no mechanic. Just learning as I go. I’ve never torn that far into an engine before! I’m not afraid to try at all. I’ve just never done it! I appreciate all the help and advice!
 

Bosunsmate

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Yep definitely start on the reeds, but hey if its running alright now then id wait and see, sometimes engines can fix themselves, i get it on my car a lot luckily.
Sometimes something gets sucked into the carb manifold and can hold a reed open, youd normally expect to hear a back fire on that but not always
 

oldboat1

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Could spray some WD-40 or carb cleaner around the bottom of the pan at the crank to see if there is any change in rpms (crankshaft seal). I'm more inclined to think it's use issues rather than mechanicals (cold water running) -- also think it would probably run worse if reed valves were the issue, particularly at idle. But that's a guess.


You are getting some nastiness at the plugs, and I think that kind of fouling is likely due to cold water use. If you run in fresh water, it's not too bad to pull off the cylinder head cover to inspect the condition for fouling -- will guess you probably have a good amount of goop or carbon build-up in the cover. You might be able to clean some of that up. If you replaced the t.stat, you can probably reuse gaskets. (If you go back in, I would replace the pressure release spring just in case. Also, check the t.stat seal -- if the slotted kind, the flange is inserted in the slot.) You could try a decarb. I don't run the stuff in my tank, as I think ongoing use creates issues, but that's an opinion.

Your plugs don't look like L78Vs, based on the length of the side electrodes -- believe the L78s were used(?). A fresh set of plugs might help (.030 gap).
 
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