I have a Craftsman lawn tractor with an 18.5 HP Intek Engine (97700 series).

It starts fine; but, after a minute or so, it begins blowing white smoke, then stalls. The smoke is not real thick, but enough to make a haze around the mower. When the mower first begin stalling, gas seemed to be getting in the oil.

I've replaced the head gasket, changed the oil, cleaned the carburetor, replaced the air filter, and checked the valve clearances. Is there anything else I should check before taking it to the repair shop?

3 Answers 3


If the smoke is coloured blueish white you are burning bit of oil. it could be many things. overfilling the crankcase with oil, Malfunctioning crankcase breather or air leak in the crankcase are the usual things to check. if the head gasket is sound and you are not operating the machine over 15 degrees tilt all the time that leaves only few other possibilities. simple ones like wrong oil type or water in the gas. You mentioned you check the carb and imo water in the gas is very high unlikely too. Worse case scenario is worn cylinder or rings if ignored can cause big problems. You probably done this already but if it was mine i would drop the oil fully and fill it with exact amount it says on the manual and give her few rounds around the yard with full power without the blades and than engage the blades and start cutting

  • You are right, I've gone through your entire checklist. Is there a relatively easy way to rule in/out bad rings? The good news is that after checking the valve clearances, there is much less smoke. I wonder if I had sealed the valve cover poorly (1) allowing some oil to drip on the muffler, and (2) getting some loose gasket sealant into the system. The bad news is that my nose tells me there might be some gas in the oil (although not as much as before).
    – Zack
    Apr 17, 2017 at 11:22
  • Worn rings will cause oil traces on the spark plugs other signs would be loss of compression and not enough resistance on the flywheel when you start the engine. If you can get your hands on a compression tester 100 psi is the number you are looking for. Anything below this would indicate worn rings or leaking valves. Did you check the valve clearence for both inlet and exaust? Should be around 0.2 to 0.25 mm Apr 17, 2017 at 12:30
  • This weekend, I tested the gap between the rods and the rocker arms. They were around .005 as specified in the manual. I checked the valves themselves when I replaced the head gasket. I didn't measure; but, they seemed to open and close fine. (A friend last tested the compression about a year ago, and said it was find. I'll have him teach me how to check it myself this time.)
    – Zack
    Apr 17, 2017 at 16:19

Well the one thing I look at is the Air filter , you might also want to check your A/F mixture level.

This really sounds like your mixture ratio is off, it can also be a sign of BAD rings.

A manual - look at 97700 series http://faculty.missouri.edu/~schumacherl/276781SingleCylinderOHV.pdf

  • your carburetor may not have been rebuilt correctly - so please have a read of the manual... From Chapter 4 page 67-68 of the manual:

These carburetors have a fixed high-speed main jet and a non-adjustable idle mixture (except on early production models), and are available in manual/remote choke or Choke-a-Matic® versions.

Many early carburetors had adjustable needle valves to compensate for high altitude conditions. Later carburetors use replaceable main jets to compensate for various high altitude ranges. See the appropriate Illustrated Parts List for replacement needle valves or jets.

  • I did get a new AF (forgot to mention that). According to what I've read, the most likely cause is a bad A/F mixture, how do I adjust it? Is there an easy way to verify whether any of the rings are bad?
    – Zack
    Apr 17, 2017 at 11:18
  • @Zack how would a nice manual help you ... faculty.missouri.edu/~schumacherl/276781SingleCylinderOHV.pdf
    – Ken
    Apr 17, 2017 at 16:19

I had a neighbor who let hers sit for a long while and the gas went bad. Probably gummed the carburetor up. So I bought some pre-stabilized 4 cycle gas from the local big box and worked it with that. The premix stuff is cleaner and helped work the varnish mess out. We finally got it working after a long while of cranking fun.

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