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1942 K Motor plugs rapidly fouling

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kmkemper
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1942 K Motor plugs rapidly fouling

Post by kmkemper » Tue Aug 04, 2015 11:37 am

The last two times I have taken the boat out this summer, the time on the lake has been cut short by the engine running badly. Here's the scenario. A couple of days ago, we had the boat out on Donner Lake (~6,000 elevation) and the boat ran fine for several hours, then gradually started running worse and would not rev past 1,500 RPM. I surmised that the plugs may be fouling on account of the elevation, the thin air causing the engine to run rich. When I pulled the plugs (Champions) at home, at low elevation, they were quite fouled. Replaced the plugs with slightly hotter Autolites, and the boat ran great in the driveway for 10 minutes. Yesterday, had the boat out at another lake at 2,000 elevation and after less than an hour on the water, the same symptoms arose. New plugs are fouled as bad as before.

Engine was recently restored and rebuilt by the former owner and does not have a lot of years or hours on it. Does this sound like a simple fuel mix issue or something more. Distributor has a Pertonix installed, and the cap looks perfect. I am not familiar with this engine yet (though I am mechanical) so if carb adjustment is the place to start, some tips are welcome. Could this be a gasoline (ethanol) issue? The fuel in the tank on both trips came from the same place.

Thanks in advance for all advice given

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Bilge Rat
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Re: 1942 K Motor plugs rapidly fouling

Post by Bilge Rat » Tue Aug 04, 2015 12:45 pm

What does the plug fouling look like?

Black and sooty?

Shiny and oily?
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1953 Chris Craft Sportsman 22 foot "Summerwind"

kmkemper
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Re: 1942 K Motor plugs rapidly fouling

Post by kmkemper » Tue Aug 04, 2015 1:22 pm

I am glad that you asked, and I should have been more specific - plugs are black and sooty, dry rather than wet or oily.

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Re: 1942 K Motor plugs rapidly fouling

Post by Bilge Rat » Tue Aug 04, 2015 3:12 pm

The immediate thought would be the altitude: Higher altitude = less air = less fuel needed. You know that the carbon fouling is too rich a mixture but what is causing this is the question. You didn't go into detail on how the engine performs otherwise; hard starting, misfire, sputtering when opening the throttle, backfire through the carb. Are you certain that the choke plate is fully open when warmed up?
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

kmkemper
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Re: 1942 K Motor plugs rapidly fouling

Post by kmkemper » Tue Aug 04, 2015 4:25 pm

I had assumed that the fouling at Donner Lake was the result of the altitude, but after I changed the plugs out and ran the boat the next day at low altitude, the fouling still occurred. Previously, and generally, the engine has ran well, and generally starts with little effort unless it has been a long time since the engine was started. When the plugs are fouled, it sputters when you give throttle, but when I ran the boat in the driveway with new plugs it took the throttle without hesitation. I haven't noticed any misfiring, and certainly not a backfire through the carbs. One possible thought is that the coil may not be producing enough spark, I only say that because the engine was not fouling plugs before and I haven't messed with the carb at all. I will check the choke though. Generally, when I start the boat I apply the choke, crank it, and it won't start. Push in the choke, crank it again, and it starts up, though I usually have to open the throttle lever at start up before I crank it, then back it down once the entire fires.

I appreciate your assistance in helping me troubleshoot this

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Re: 1942 K Motor plugs rapidly fouling

Post by farupp » Tue Aug 04, 2015 5:15 pm

Check the float valve, making sure it is not stuck open or partially open with a speck of rust or something. Then check the float level for the correct setting. If those are not the problem, check the fuel pump to be sure the check valves are working. That is assuming you still have a mechanical pump. If not, check the fuel pump outlet pressure. Too high may flood the engine causing the plugs to foul.

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davidvn
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Re: 1942 K Motor plugs rapidly fouling

Post by davidvn » Tue Aug 04, 2015 7:22 pm

There are several possibilities that I would take a look at. First make sure that your choke is wide-open don't rely on the position of the knob on the dash. Take the flame arrester off and look at the position of the butterfly. The early model K had an adjustable high-speed jet. I If you have one I would screw it in gently until it stops and back it out no more than three turns and then go through the process of adjusting the high-speed needle valve. Another possibility is that fuel is spilling out of the float bowl because the needle and seat are not working properly and fuel is filling the throat of the carburetor causing the engine to run Rich There are other possibilities but these are the most common
good luck

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mfine
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Re: 1942 K Motor plugs rapidly fouling

Post by mfine » Wed Aug 05, 2015 6:41 am

I would add weak spark/coil to the list of things to check.

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Re: 1942 K Motor plugs rapidly fouling

Post by martinfeletto » Wed Aug 05, 2015 9:54 am

Kevin - its Marty. I would confirm the choke first but would swap out the coil and perhaps coil wire before getting into fuel.

kmkemper
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Re: 1942 K Motor plugs rapidly fouling

Post by kmkemper » Wed Aug 05, 2015 11:27 am

Thanks, and good to hear from you Marty!

I will inspect the choke, but I have a feeling that the coil may be involved, since the problem seems new in origin and I haven't messed with the fuel system at all. Easy to drop in a new coil to replace the one I have, to see if that makes any difference

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