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8Ercob jumps around above idle

ba_50

Regular Contributor
Motor knocks worse as more power is applied. Sometimes it will smooth out , go fast, then quit. I took the lower unit off and spun the flywheel with a drill and there wasn't any knocking. There weren't any metal filings in the lower unit and the prop turns smoothly.
I am positive it wasn't water in the gas.
If electrical, what would be most likely? Thanks
 
Unlikely that an ignition problem would result in a knock "unless" there was play in the wrist pin or rod to c/shaft areas. That can be checked as follows:

(Piston Play Check)
(J. Reeves)

This procedure will tell you if there is any wear or play in the Wrist Pin, Wrist Pin Bearing, or Connecting Rod to Crankshaft area.

Remove the spark plugs. Insert a screwdriver, dowel, punch, or some object of your choice through the s/plug hole and into the cylinder/piston area. Hold the tool lightly against the top of the piston. Turn the flywheel by hand, bringing the piston up to top dead center, then continue turning the flywheel to pull the piston down about a inch..... all the while holding the tool lightly against the piston top.

Now, at the point whereas the piston has been dropped down about a inch, grab the flywheel and hold it firmly. Now, push that tool solidly and firmly against the piston top.

If the piston moves without moving the flywheel, there is a problem (wear, play, clearance, etc) somewhere with the items mention in the first sentence. Be sure to check all of the pistons/cylinders.
********************

You describe the problem as a "knock" above idle. How far above idle... the higher rpm range?

Could this knock perhaps be a sensation that the engine is hitting a submerged object time and time again, resulting in a jumping action at the transom?
 
Joe
It was difficult togo in on an angle and feel what was happening. A few times it felt like the top cpiston had a little play, but after about 50 tries they both seem ok.
The plug was gapped .028 and the other .034. Should have been .040.

I could take the back cober off if a new wire doen't help.

Would any plug wire work?
Thank you.
 
130 & 135#. It has never been run without oil. A plug wire prong must have lost contact.
I started it and it bucked for a couple of minutes then ran normal for 20 miminutesIt did knock about 3x when the throttle was brought down abruptly but not slowly. I shut it off and tried starting it cold. No luck. Dirt in carb bowl. Drained fuel line and put a better filter on it. Fresh fuel and clean tank.
Still won't start.
If the piston rod was loose wouldn't it knock all the time?
It is in a barrel right now.
It is back firing through the exhaust again. Opened mixture 2 turns instead of 1 1/2. Didn't help.
 
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Once it starts it jumps around for 4 to 5 minutes then runs great for 20 minutes. After shutting it off, cooling down, same thing.happens again.
I checked the key before and it wasn' t the problem.
 
Have you checked engine sync? There is no timing adjustment the throttle butterfly should just begin to open as the follower roller is center on the line on the throttle cam. Did you tighten the flywheel nut to correct torque?
 
You can get the sync exact with with a alligator clip with a straight wire crimped to it. Clip it onto the throttle shaft in the carb then watch the wire as you open the throttle. The wire should just begin to move as the line on the cam passes center of the follower cam roller.
 
I can only get 30# torque on flywheel key by holding on to flywheel. Does the torque affect the timing?
It must be timing since the pull cord snaps back.
The line on the cam is 1/4" behind the roller when the throttle starts to open. Can't remember how to change it.
 
Pull the flywheel and turn the key upside down. I use a old belt and loosely wrap it on the flywheel then put in a bar and twist it tight. I don’t have access to the torque specs but get close to possible to spec. If the flywheel key has a bad crease in it just get a new one. The screw on the follower adjusts the position of the roller sounds like your loading the cylinders with too much fuel per spark advance get the sync as close as possible and then you can properly adjust the slow needle.
 
The torque is 40 to 50 ft lbs.
I got the line and roller centered so far
Tried to get the key out with a screw drive and vice grips. Messed up key and still in shaft
 
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If the magneto plate wiggles up and down that could also throw the timing off you would need to correct that before you torque the flywheel.
 
I would recommend tightening the plate up you can get a new support plate and bearing here for around$35 plus shipping and use a high quality marine lithium grease. That being over 30 years old a new head gasket may be in order.
bearing #0322435
suppprt #0332063
that should be a one pull start engine.
 
I tried hitting both ends of the key with a punch but could't get it to move.
I replaced the head gasket a gfew yrars ago.
Might have toyhake it to a mechanic because of the key.
 
It can be stuck in there pretty good if you Ching up the taper I just wraps strip of rag soaked in oil around the shaft to catch any shavings from the seal an use a small fine file to knock off any burrs. If you have a old dull wood chizzle put it flat with the taper and try and push the key out that way it will eventually come out of your persistent.
 
Thr key came out and there wasn"t any crease.
If the roller is 1/4" off the line will that cause back firing by itself?
Would a bad spark plug connection cause the knocking?
How much more trouble can it be?
 
"Knocking" is a broad term. Without a clearer description of exactly what you describe as a "knock", it's hard to accurately recommend what action is needed and very often this leads to the unnecessary removal or replacement of parts which are not related to the problem. Is the knock a loud metallic noise, is it from a cylinder firing intermittently, does it come from the power head or from the lower unit???? Accurate descriptions of a problem are essential to an accurate diagnosis.
 
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