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GCV 160
by NormK - 07/11/25 03:53 PM
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Joined: Jan 2010
Posts: 234
Apprentice level 3
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heheh, agree totally grumpy! thats why i was saying that there's no way im going anywhere near the blades. I think i can see the 'visible rotating part' just under the starter mechanism for the honda (its the old one with the all metal chassis so there are gaps under the starter), ill give it a shot and see how i go.
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Joined: Jan 2009
Posts: 6,926 Likes: 10
Pushrod Honda preferrer
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I don't know how much experience you have with stroboscopes John, but the only trap involved is that you can get what looks like a valid reading at a harmonic of the actual speed, depending on what the moving part looks like. The standard way to deal with it is to put a chalk mark, bit of sticky tape, or whatever somewhere on the moving part, then raise the instrument's speed setting until you get two images of that mark, exactly opposite each other. Read the speed, divide by two, set the instrument for that, and if you've got a clear image, you can rely on that being the right speed. When you can only see part of the rotating bit, you may not be able to follow this procedure and you can easily get a wrong answer.
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Joined: Jan 2010
Posts: 234
Apprentice level 3
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yeah, i have had a bit of a readup on it and i had a go, though the problem is (it seems) that the idle speed varies buy a fraction every now and then since i can set the stroboscope and then it changes and reverts back to the original setting again(im guessing the engine is surging very slightly..) time to look for air leaks 
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Joined: Jan 2009
Posts: 6,926 Likes: 10
Pushrod Honda preferrer
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If the speed excursions happen at 2,000 rpm, you should try to cure them by adjusting your idle mixture. They don't matter anyway, but since you have an idle mixture adjustment, this sounds like a good time to try to get some benefit from it.
Honda's idle specification is 2,000 rpm plus or minus 150 rpm, so if the speed it is running at is within that range (ignoring the odd stumble) that is satisfactory - but the speed may vary a bit when you adjust the idle. Remember, the instructions say start with the screw at three turns, and see if you can make the idle speed increase by adjusting the mixture. If you can, then back off the idle speed screw to get back to 2,000 then try the mixture screw again to try to get it to run a bit faster. Repeat the process until you've found the mixture that gives the fastest idle, and the speed screw adjustment that gives 2,000 rpm with that mixture setting.
If it makes you feel any better, classic Briggs engines do those occasional speed changes too - and they don't have an idle mixture adjustment that might cure it. Each time it does a speed twitch though, the crankshaft position (frozen by the stroboscope) seems to only move a fraction of a turn. You just keep telling yourself "OK, this isn't a car engine. You can't expect much." (And having said that, before Port Fuel Injection, car engines didn't idle all that well either.)
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