Help with a 10 hp Kohler

chzuck · Post by **chzuck** » Mon Oct 20, 2014 6:36 pm

I overhauled a 10 hp Kohler and put it in my Cub 70 recently. I have a problem with the engine that I cannot seem to remedy. It has, for lack of a better word, what I call a blubber when it idles, half throttle, or full throttle. I have gone through the carb settings twice and checked the timing with a timing light. I did not notice the problem when under load mowing, just in a no load condition. I made a short video of it running at about half throttle so you can hear what I am talking about. Right at the beginning there is one "blubber", then about half way through until the end there are several more. Hopefully someone will be able to give me some pointers to solve this.
http://www.zucksrototillers.com/Cub100.wmv

BigMike · Post by **BigMike** » Tue Oct 21, 2014 7:20 am

Charlie, how loose is the throttle shaft in the carb bore? It may have a vacuum leak.

chzuck · Post by **chzuck** » Tue Oct 21, 2014 11:55 am

BigMike wrote:Charlie, how loose is the throttle shaft in the carb bore? It may have a vacuum leak.

It is a newly rebuilt carb with the brass bushing installed to take care of a worn carb throttle shaft bore.

chzuck · Post by **chzuck** » Sat Oct 25, 2014 5:59 pm

Below are listed the things I have done to this point and no change.
adjust carb
new points & condenser
changed out coil with know good one
checked valve clearance
checked governor setting
I need to get a new plug yet, but I am about out of options, other than an engine dis-assembly, which I don't plan on doing unless the problem gets a lot worse.

Klapatta · Post by **Klapatta** » Mon Oct 27, 2014 9:38 am

Do you have your spring mounted in their correct hole locations ?

: DSCN4933.JPG (401.4 KiB) Viewed 5385 times

ksanders · Post by **ksanders** » Mon Oct 27, 2014 6:05 pm

If you have one available trying a different carb might save a lot of trouble. Not certain that's the issue but it does sound fuel related and every once in a great while you run across one that no amount of disassembly, soaking, or adjusting fixes. I've had one or two in probably over 100 messing with. Might be worth ruling out if you have one available.

Mayor · Post by **Mayor** » Tue Oct 28, 2014 8:12 pm

Re-adjust the point.....start at .020 but leave the screw just a little loose....now then with the engine running, adjust the point by ear until the blubber goes away and you hear the engine smooth out!. Get it as good as you can and tighten the screw without moving anything!. Now run the engine wide open throttle and adjust the main jet screw on top the carb. Find the sweet spot that the engine runs it best!. Now idle the engine down....it may die!.....but keep it running until you adjust the idle screw and find the sweet spot!. This is the way I adjust all my kohlers and it always works. If it dont....then I go on to look for dirty points, bad plugs, stopped up emulsion tubes, bad gas, wrong float heights, bad head gaskets, bad carb gaskets, loose throttle shafts, etc.

A lot of old kohlers have warped heads and bad head gaskets.....its a very easy fix with a new head gasket and a flat file!.

Hope something here helps!

chzuck · Post by **chzuck** » Tue Oct 28, 2014 9:23 pm

Klapatta wrote:Do you have your spring mounted in their correct hole locations ?
DSCN4933.JPG

Yes, I have the spring in the 3rd hole on the governor arm, but in the top hole of the throttle lever. Didn't think that would change nothing.

chzuck · Post by **chzuck** » Tue Oct 28, 2014 9:27 pm

Mayor,
A lot of those things you mentioned I have done. Carb was well cleaned, made sure all the tiny holes were clear, throttle bushing installed, and new parts installed.
Presently, I have the timing set with a timing light right in the center of the timing hole. When I was timing it, I noticed if the mark was on one side of the hole or the other, rpm dropped noticeable.

Klapatta · Post by **Klapatta** » Wed Oct 29, 2014 11:12 pm

Not sure that I understand the statement, if the timing mark is bouncing around while the engine running I'd suspect a worn points push rod. Was it replaced ?

chzuck · Post by **chzuck** » Thu Oct 30, 2014 1:19 pm

Klapatta wrote:Not sure that I understand the statement, if the timing mark is bouncing around while the engine running I'd suspect a worn points push rod. Was it replaced ?

The timing mark was responding to my changing the point gap. The Mayor is good at setting up his cubs without a timing light. I basically ended up with the same result. When the timing mark is centered in the hole, the engine appears to run its best. One fellow I ask to look at the video said popping out the exhaust is an indication of a worn valve guide. His explanation made sense to me, but at this point I am going to run it as is.

JMech · Post by **JMech** » Mon Nov 17, 2014 9:56 pm

When you say adjusted the carb, do you mean you set it to the starting point the book says and left it? Or did you tune it to run? (By turning the screws one way then the other, to find the best running point.)

Sounds to me like a fuel issue. But, you don't give much detail to your rebuild. Did you replace the valves? If you installed new, did you grind the new ones and the seats?

Could also be a bad ground on the condenser. Or even a bad condenser.

My money is on carb setting. I'd say its just a little rich. What plug are you running?

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Help with a 10 hp Kohler

Help with a 10 hp Kohler

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