Outdoor Power Equipment and Small Engines - Old Kohler beating me up

The patient is an early 70's Jacobsen GT 1200 with a Kohler cast iron line, automatic compression release (ACR), Model K301AQS, spec 47606D, ser. # 8015920.

The symptoms are that if I get it running it pops frequently and will stall if I try to change the throttle setting. Sometimes it will respond ok if I change the throttle very slowly. The popping has existed for at least a year, increasing in frequency with time. Now occurring every couple of seconds. While trying to start it, some drops of either dirty or oil contaminated gas will spit out the carb. Other than the popping, it has started and run fine until the day it wouldn't. The air cleaner housing had enough fluid in it to suggest the carb-spitting may have been present for a while. The spark plug is very fouled with dry carbon deposits. The points were also shot, with a nice sized contact circle appearing evenly pitted on both contacts.

I replaced the plug, points, condenser, fuel and air filters. I had previously adjusted the high and low settings on the carb according to the owner's manual. The new plug begins to foul with carbon deposits immediately.

It is getting spark. I will admit, however, that I am not a good judge of what constitutes "good" spark. I will further admit, that being a "what the heck" kind of guy that I have been using automotive coils for years and that includes the current coil. It is getting better spark that last year when it wouldn't start and there was a weak yellow spark. The current spark is reasonably blue and makes an audible yet subtle ticking sound.

I took off the carb and breather cover and observed the action of the valves to see if I could discern any problems with the intake. I could not. Looking in the intake manifold I could see the deposit line on the stem that doesn't go into the guide and it does not appear, at least based on that observation that the valve is sticking. Although I suppose that it could take a bit of debris smaller than that to perhaps cause a problem.

I did a compression test, for what that's worth with ACR, and it develops about 32 psi.

Before I yank the head and/or buy any more parts, can anyone head me, well, somewhere?

Thanks,
Gary

Are you sure you have the correct plug? Plug properly gapped? (They are seldom right out of the box) Double checked the points gap? Carb been thoroughly cleaned? Compression seems low, but I don't know you used to measure it. Crankcase vent clean?

Plug right, points right, carb not cleaned, vent between crank and air cleaner housing ok. I checked the compression with a screw-in compression tester and cranked the motor until it stopped increasing. But it is low since the motor has compression release. I included the info because someone who is familiar with the engine might be able to tell something.

If you're getting a blue spark and you can hear it, you have plenty of power.. The only other things that can cause an engine to not run or not run well is Air, Fuel and Compression. If the compression release is similar to Briggs' "easy spin starting" you probably will get lower readings because the intake valve opens earlier.. My suggestion is go through that carb. If its popping and/or backfiring its because its lean. I'm sure some of the passages have gunk in them. Perhaps a good soaking in some good carb/parts wash and some new gaskets/o-rings will do the trick..

Tim

I asked the questions before because I've worked a fair amount on these old Kohler "K" series motors. Typically the points are set just a smidge off and affect the timing more than most realize, or the carb is gunked up. Seldom anything else wrong with them, they are great reliable motors.

Thanks you guys. I will check the points again, with your experience in mind. And will do the carb too. With re: carb cleaner, are you talking about the really strong stuff I've used for automotive applications or will some Gunk do?

Use the strong carb cleaner(NAPA 6402 is a good one but expensive) just gon't get any rubber parts in it then spray all holes, cracks and crevases with brake parts cleaner, it doesn't leave a residue. Have a good one. Geo

I got a 1 gallon can that includes a basket that I think is made by Gunk/Solder Seal or whatever. it'll eat rubber and plastic, but it doesnt do much to paper gasket stuff... have a razor blade and a small toothbrush and maybe some compressed air. I'd bet at least half of your problem is fuel related, so cleaning the carb should help significantly.

Thanks much,

Gary