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1995 Johnson 20hp "missfire"

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1995 Johnson 20HP "missfire". Cleaned up the carburetors / rebuild kit, new plugs and plug wires. Swapped out the power pack. Swapped out the fuel connectors on the tank.

To be honest previous owner told me he sprayed out the carb with carb clearner. It looked clean before I rebuilt using the carb kit.00 Do these symptoms seem to be carb related?

What's next?

 
racerone said:
Running too lean or throttle plate is NOT closed at idle.---
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I showed this video to another friend and he thinks it's an ignition issue perhaps timing. His claim is that observing the exhaust in the video is giving him that indicator. I'm going to try cleaning the carburetor out tomorrow. But I did do the carb rebuild, with the exception that the previous owner cleaned it. So perhaps he didn't do that well.

Regarding the throttle plate at idle. I purchased this engine on a boat. The previous owner took the control box apart. I have not yet figured out how to put the controls back together. Then I am not really running it at idle. I start it up and rotate the (throttle plate?) to give it fuel through the carburetor. Then I am not really testing it's idle. I should probably figure out how to get those controls back together also. Maybe I will try that first thing tomorrow.

It's clear that I don't have a ton of mechanical experience, but trying to learn as I go along.
 
I took the carbeurator top screw almost all the way out. Behavior didn't change. Wondering if controls might effect idle if not hooked up properly, leading to the issue.

But tried to ignore that by advancing the throttle plate. Next assumption is that I need to clean the carb .
 
Raceroni is correct (as usual). That bad boy is running lean at idle (Aka lean sneeze). As fazbullet has said, you really should have it in a barrel or in lake as the lean sneeze may vanish altogether with some back pressure. If it doesn’t, I’d start by thoroughly cleaning the idle jet passages of carb (YouTube should give you some good guidance there). This may mean popping off the lead plug on top of carb to access the 3-4 tiny holes that provide fuel flow to carb throat at idle. Or you can use some fine wire and poke at them from inside carb throat. If that doesn’t do it I’m afraid you are go into “chasing an air leak“ mode. Could be a gasket or bad lower crank seal.
 
Throttle plate open at idle means that the idle circuit runs lean.----So simple if you understand how these motors work !!
 
bigtime_mcalpine said:
Raceroni is correct (as usual). That bad boy is running lean at idle (Aka lean sneeze). As fazbullet has said, you really should have it in a barrel or in lake as the lean sneeze may vanish altogether with some back pressure. If it doesn’t, I’d start by thoroughly cleaning the idle jet passages of carb (YouTube should give you some good guidance there). This may mean popping off the lead plug on top of carb to access the 3-4 tiny holes that provide fuel flow to carb throat at idle. Or you can use some fine wire and poke at them from inside carb throat. If that doesn’t do it I’m afraid you are go into “chasing an air leak“ mode. Could be a gasket or bad lower crank seal.
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I put it in a wastebin full of water and it "coughed" in the tank and splashed the water around. Going to take the carb apart and clean it and hope that helps.
 
I took apart the carburetor. It appeared very clean. It looked like there was a small fracture on the white plastic part that connects in the middle of the float. I don't know if that will cause an issue, I would assume not but can replace it if it's recommended. I hit the orifices with a can of compressed air, but will ask a friend to use their air compressor tomorrow. However I shined light across every orifice where I thought it would allow light travel. I didn't see any blockages. https://www.flickr.com/photos/198910795@N04/
 
how is the small pin holes right at the back of the butterfly thats where the fuel comes in at idle they may be easy to miss to the untrained eye they are small it will be routed to the idle air mix screw\orifice you may have to remove a welch plug to blow thru all the channels. the only other thing it could be is a vacuum leak like a crank seal or intake seal of some sort i would think
 
now that i read that a little closer have you verified by looking down the carb when the throttle is in idle position that the butterfly/throttle plate inside the bore of the carb is closed thats what racer is trying to tell you the mag plate has to advance quite a ways before the carb butterfly starts to open there should be a mark on the cam that opens the butterfly it is number 40 in the fiche below. the cam follower should start to open the butterfly just as the cam gets to that point. if the butterfly opens before you get to this point you will get the same exact symptoms that you have now it will kick and buck and refuse to run at idle49918.gifs-l1200.jpg
 
OzarkMike said:
how is the small pin holes right at the back of the butterfly thats where the fuel comes in at idle they may be easy to miss to the untrained eye they are small it will be routed to the idle air mix screw\orifice you may have to remove a welch plug to blow thru all the channels. the only other thing it could be is a vacuum leak like a crank seal or intake seal of some sort i would think
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I think you are referring to the three tiny pin holes
https://flic.kr/p/2oVppXd
that are in the recessed pill shaped groove. Shining light through them and I see beams of light traveling through the orifices into the carburetor, which give the impression they are very clean.
 
OzarkMike said:
now that i read that a little closer have you verified by looking down the carb when the throttle is in idle position that the butterfly/throttle plate inside the bore of the carb is closed thats what racer is trying to tell you the mag plate has to advance quite a ways before the carb butterfly starts to open there should be a mark on the cam that opens the butterfly it is number 40 in the fiche below. the cam follower should start to open the butterfly just as the cam gets to that point. if the butterfly opens before you get to this point you will get the same exact symptoms that you have now it will kick and buck and refuse to run at idleView attachment 30999View attachment 31000
Click to expand...
I think I identified this component and I believe it is rotated by the throttle, and connects perhaps to the throttle plate and I think I saw an adjustment screw. I believe I can and did rotate that plastic piece all the way in both directions when trying to start the boat. If I understand correctly I should look for a mark to set a location between that plastic plate and the carb butterfly.

I think I mentioned above that the controls are disconnected. It turns out the guy who sold me the boat conned me a little. He told me he took the controls apart and everything was working beforehand. But it appears the throttle cable attached to the motor doesn't match the control box. This is all an aside but I am trying to make it clear I am trying to test the engine without controls connected.


I will try to understand the claims above and ensure operation of this component.

I do have another friend with some mechanical experience. His claim is that this doesn't look like a lean sneeze. He thinks it's an electrical miss. He claims that the video or sounds are more abrupt than a lean sneeze.

Well I will try to follow along the lean sneeze claims first and try to resolve or eliminate that as the cause.
 
the remote control has nothing to do with how it idles. bear with me it would only take me a second to show you how to do this if i was there its harder for me to explain than actually do the job. the armature plate has a cam and on that cam is a mark the roller should not touch that cam untill it gets to those marks or maybe a little past em. if i was a betting man id say remove the linkage from the carb to the roller and it will idle fine but you wont be able to acheve full throttle cus you lose the ability to control the carb with the armature plate but it will tell you if thats the problem. if the butterflys open before you get the required advance it will kick back and sneeze just like its doing in your video also make sure all return springs are in place the butterfly cant not be open at all untill the cam follower gets to those marks on the picture below there is 2 marks close together this is what the cam roller has to line up with before it can be allowed to touch the cams-l1200.jpg
 
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