Honda 2 hp outboard kicks back violently at pull start.

[MarkD]

Hi all!
I apparently have had this problem occasionally for years but never really paid attention to it.However, this autumn the problem became very serious. Last time I had a very hard time starting the motor, badly injured my hand, etc.
I looked over the internet and found out that indeed it is a quite common problem with 2 hp Honda. Most people say it is either a problem with decompression valve or exhaust intake valve timing.
Ok, probably.
But I still cannot get it. To jerk the rope with the handle out of your hand the motor should start rotating in the opposite direction. Is it ever possible? And is it possible due to a problem with the decompression valve or timing?
Thanks for all suggestions!

[TroutSlayer]

Sounds like pre-ingnition. A timing issue is my guess.

[dean.f]

I have a Yamaha generator that does the same thing, pretty much guaranteed to hurt your hand on the second pull if you don't roll the engine past the compression stroke with the rope before you yank it hard.

[MarkD]

Sounds like pre-ingnition. A timing issue is my guess.

Sorry, do you mean ignition timing?
Because, if I understood it correctly, pre-ignition usually means “diselimg”,”when the air/fuel mixture in the cylinder ignites before the spark plug fires”. https://en.wikipedia.org/wiki/Pre-ignition

[MarkD]

I have a Yamaha generator that does the same thing, pretty much guaranteed to hurt your hand on the second pull if you don't roll the engine past the compression stroke with the rope before you yank it hard.

Well, I’m not sure if I understood you correctly, but I’ve read a few times on the other forums the suggestion that you need to bring the crankshaft to the compression point (when you feel the resistance) and only then you should pull hard.
Is it opposite to what you are suggesting?
Thanks!

[TroutSlayer]

Sorry, do you mean ignition timing?
Because, if I understood it correctly, pre-ignition usually means “diselimg”,”when the air/fuel mixture in the cylinder ignites before the spark plug fires”. https://en.wikipedia.org/wiki/Pre-ignition

It sounds like you are getting ignition (spark) before top dead centre for whatever reason. By timing, I mean you are getting spark too soon. I'm just guessing though.

[canthitathing]

Check that the spark plug gap isn't too small or carboned up. Check the woodruff key isn't sheared putting the flywheel out of timing. Put piston at TDC and check the timing alignment mark lines up correctly. Could put a timing light on to see what it shows if you get it firing too.

[MarkD]

Thanks! Some of your suggestions are already done, some others will do.
Appreciated!

[dean.f]

Well, I’m not sure if I understood you correctly, but I’ve read a few times on the other forums the suggestion that you need to bring the crankshaft to the compression point (when you feel the resistance) and only then you should pull hard.
Is it opposite to what you are suggesting?
Thanks!

This is what I meant. I pull it until I feel the resistance from compression then let the rope back in and pull to start it.

[MarkD]

Oohh.. I thought I already replied to that… But apparently I didn’t submit it…

I was actually doing this intuitively before and it seemed to work previously but not anymore.
I now took a look inside the combustion chamber and it’s full of the black deposits.
I would certainly prefer to find a solution without disassembling the engine, at least to try it first. I hope a new plug and cleaning the chamber will help.
What is the best way to clean the chamber though? There are at least a couple products, like Intake Valve & Combustion Chamber Cleaner and Sea Foam. But they all seem to be designed for bigger engines.
Is it Ok just to spray this stuff into the engine through the air intake of the running engine?