420 CC question

hrdman2luv

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My first MTD engine (that I know of). It's one a Craftsman 247.203724

Per customer: Smokes on start up. Sometimes a lot. Sometime barely any. Runs good for about 10 minutes then starts to lose power. Has to clean off the spark plug regularly.

When we unloaded it, it smoked like the dickens backing off the trailer. Then cleared up (not all the way) once it was level. (Note: Wasn't much of an incline) Smoked a little more once it was throttled up.
150lbs of compression. No smoke coming out of the oil filler tube (after the engine is turned off). But some coming out of the carb, after it's turned off.

Anyone have any idea's? I'm gonna clean the plug and mower with it for a little bit. Should have more details then.
 

dfbroxy

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If the oil is over-full and smells like gas, check the carb fuel shut-off silinoid. I have this same engine and would like to be updated on what you find wrong with it. So far other than haveing to keep the valve lash adjusted it has given me no problems.

The only ways i Know for oit to get into combustion chamber is rings, head gasket, or valve seats. I am not a mechanic and dont know alot so let some of the other pro s on this site chime in.
 

hrdman2luv

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If the oil is over-full and smells like gas, check the carb fuel shut-off silinoid. I have this same engine and would like to be updated on what you find wrong with it. So far other than haveing to keep the valve lash adjusted it has given me no problems.

The only ways i Know for oit to get into combustion chamber is rings, head gasket, or valve seats. I am not a mechanic and dont know alot so let some of the other pro s on this site chime in.

No solution yet. But the oil was a little over filled. Maybe a 1/4" over full. When I removed enough to put right on the full mark, I let it run again. No difference. Although it runs rough. This afternoon, I'm going to adjust the valves, and see if that makes a difference. The fact that it turns over great, makes me think the valves aren't out of adjustment.

The smoke had a bluish tint to it. I drained he carb bowl. There was a little trash in it. Changed the fuel filter and shot some seafoam spray into the carb while it was running. Several squirts until it tried to die. Stop, then squirt more. Repeated about 5 times. No change in the way it ran. And the smoke.

The smoke comes and goes.

I ran it until it started running bad. Checked the spark plug (which I cleaned before I cranked it again), and it was still about as clean as it was when I cleaned it. A little more dirty. But nothing major.
 

hrdman2luv

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It looks like the solution was a valve adjustment. They were way out of whack.
BTW, adjusting these were a little tricky. Get'M set, tighten them down, and the gap gets way too small.
10mm int. .15mm exh.
 

hrdman2luv

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It runs better for about 10 minutes. Then sounds like it's bogging down while mowing. Release the mower, and she picks up a lot. But not all the way.
 

hrdman2luv

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Lots of oil in the carb after mowing with it. A couple of times, in some taller grass, it would've died if I hadn't released the mower deck.
 
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It's an MTD 4P90HUB

Nope MTD does not make engines either..

It is gonna be a Briggs or a Kohler If it's a Tecumseh then it's an older model.

If it's a Briggs OHV the model type and code is on the Valve cover. You might have to clean it to see the #'s
 

dfbroxy

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Sounds like a head gasket. Start motor and warm up a few minutes, pull dipstick and check for blowback with motor running, if there is any its prob gasket.
 
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