Troybilt tractor, Briggs 31C707-1346B2...Nikki carb...

[dart451]

Hello,
I have been working on this Troybilt tractor...had a guy bring in the tractor, he said it was blowing smoke terribly while running. I figured it was the Nikki carburetor leaking into the crankcase and when he brought it in, the crankcase was full of gas. Drained the oil/gas, filled with fresh gas after taking the Nikki carb off and replacing the O-ring. Thought I had it whipped...but the engine wouldn't run, it will start if starter fluid is introduced but once it's burned off, it won't run. I figured I screwed up the o-ring/carb so I ordered a new carb, installed it...it will only run at full choke, once you release choke it dies. I imagine if I put on the old carb, it would do the same. I took off the gas line, it's flowing gas very well, it's not plugged at all. Is it possible the motor is fubared due to running it with the oil/gas mix? I cannot figure this thing out!

[SUKI]

Have you done a leak down test with the rocker cover off? These engines are bad about blowing the head gasket between the cylinder and push rod galley.

[dart451]

No, I have not tried the leak down test. Would it run that good on full choke though? Doesn't sputter, miss, runs smooth!

[bgsengine]

Sure they can seem to run pretty good, but your symptoms seem to indicate lean, so blown head gasket, valve clearance problems, intake elbow leak , cracked intake port in head can by themselves or in combination with each other cause your problems.

[38racing]

There's usually blowing smoke when the head gasket goes. My neighbour's would start and run but as soon as the blades were engaged it belched the smoke, stopping mostly if blades were disengaged. I was able to baby it down the road to replace the head gasket.

[dart451]

Thanks guys, how little I know! I'll give it a leak down test tomorrow...thank you for you help!

[dart451]

Did the leak down test today...also took off the valve cover. I tell you...this engine is very, very quiet and doesn't appear to leak any air! So, I did not detect any leaks at all so I'm at square one again...I think I'll throw the old carb back on and try again. You're right! It's got to be lean as hell...just can seem to figure out why!

[38racing]

Did the leak down test today...also took off the valve cover. I tell you...this engine is very, very quiet and doesn't appear to leak any air! So, I did not detect any leaks at all so I'm at square one again...I think I'll throw the old carb back on and try again. You're right! It's got to be lean as hell...just can seem to figure out why!

A cold leak down may not work for the blown head gasket. Maybe fails when hot.

[bgsengine]

Stupid question: does the new carb have a solenoid on it? Is it getting energized, if so?

[dart451]

So, checking cold won't pinpoint a gasket leak...but it runs only on full choke when it's cold too...no changes when it warms up. Also, yes, there is a solenoid in the bowl of the carburetor...I did check it, it's getting fuel...or I assume it wouldn't run at all...