After rebuild woes
 

After a rebuild, my K301 ran fine for the 15 minute break-in run. Ran it at various throttle positions and it ran great. I then let it cool down over night, re-torqued the head bolts and tried to start it. Would hardly start. Got it started at idle throttle and some choke. At idle, it runs OK. Any position of the throttle above idle and it barely runs. Quite a bit of snorting, coughing and a missing. It will die fairly quickly if I don't get it back down to idle

I thought(more like hoping) it might be the high speed mixture port so swapped out with a known good carb and same symptoms

At idle, as I mentioned, it runs pretty much OK. But if I hold my hand in front of the carb, it is apparent the intake valve is not closing all the way (or in time) as my hand feels a backdraft of air and fairly quickly gets coated in gas.

I've had this happen in my life twice, and once was broken valve spring and one time an engine dropped a keeper. So I pulled the breather and the springs, keepers and valve clearance are all OK.

I have limited with small engines and none with compression release. So I am humbly coming here with hat in hand hoping for a little help, guidance and direction as to how to proceed. I am at a loss.

Many thanks in advance!

1966 123 with a Kohler K301

So the springs and keepers are OK but did you rotate the engine and watch the valve movement??
I thinks a sticky valve could cause the symptoms you describe. :TwoCents:

Thanks - good question. I did turn by hand and watch and seemed fine. Using a block of wood as a fulcrum I operated them with a screw driver as well. Felt fine too.

My first thought was something in your timing was off, like at the
points or you were off a tooth when you lined up your cam.
The fact that you got 15 good minutes out of it kinda messes with
that thought though.
When you did the rebuild did you use new valves and new valve guides?
How were the head bolts when you did the re-torque? I would expect them
to be looser but not loose loose.

Feel free to put your hat back on. There is not an Honest person on the
forum that has not had battles after big projects like you are on.

Ken

Thanks, some good thoughts. Re-torquing went as expected. Maybe a few degrees of turn on 2 or 3 and the others clicked the wrench without any movement.

New valves, springs and keepers. The guides were reused as they were good according to the machine shop.

The backdraft from the carb and associated gas mist on my hand (dangerous now that I think of it. A carb backfire would lite my hand on fire!) has to be a clue.

It is beginning to feel like a timing issue as suggested. I have a small HF bore scope. Could i remove the cam gear cover as a way to sneak a peak at timing? Don’t want to mess that gasket up if someone knows the answer off the top of their head.

Not sure how I would mess up timing. I don’t remember thinking “Geez, these marks are hard to see”. The marks were clear and obvious if I remember right

I'd start off on an easier road by checking everything going on with the points.
I'd suggest static timing by lining up the "S" mark in the sight hole.
Attach a test light to the points (-) terminal on the coil.
Adjust the points to where the light almost wants to flicker between on and off.

I'm still in the stuck valve corner, and I'd probably remove the head for a looksee
just to remove all doubt.

I've seen situations it would idle fairly well but not rev up.
turned out to be the condenser.
Its worth a try if you have a known good one, to try swapping it.:bigthink:

Life happened
 

Sorry for the delay - Life happened and it prevented me from spending time in the shop. Plus had to order the breather gaskets and wait on them.

Had not considered the condenser since it was new when I did the rebuild but have gotten bad ignition parts brand new out of the box before so I’ll test it

Likening the sticking valve a little more too. Will thermal cycle the engine several times by running it at idle 15 mins at a time and letting it completely cool overnight. Will do that several nights to see if the valve unsticks itself

So will test condensor
Re-time the engine.
Reassemble breather
Thermal cycle

If none of the works in probably out of options and will have to pull the engine and drop the pan and check timing.

So condenser is fine, but I think the ground was bad. Ohms fluctuated sitting still. I’ll bet ohms were really dancing when throttling up. Will button up the breather and jumper the body to a better ground.

Why is the ground bad you ask?

The coil was bad at the start of the rebuild so I used a known good one and it’s been running on that. However, its diameter is marginally bigger and the clamp won’t collapse enough to to get both bolts through the coil bracket. Between new paint on the engine, sketchy bracket mount it’s just not getting consistent ground I think.

Which brings me to this. I’d like to keep this coil as backup and buy a new one for this tractor. How do I make sure to get one that works with my bracket?

Thanks in advance

NCDiesel
1966 Cub Cadet 123