Sorry missed the model number by 1 digit. The model number is: 31C707 0230 E1.

Intake .003" - .005" Exhaust .005" - .007". I have detailed instructions including some tips that will save you money in the long run IF you would like them. Address below, put in proper format and remind me, model number, what you want.

Walt Conner
wconner5 at frontier dot com

Always wider has been my experience on OHV engines.

Walt Conner

OK. This weekend I intended to take a close look at the valve clearance since my tractor has been a little difficult to start this season. Since my grass was pretty long when I got to my cottage, I figured I would cut the grass first.

Again, the machine was sluggish to get started but once started it worked well for about 15 minutes. Then it seemed to start missing and complaining, usually when I was going through the long grass or up a little hill. It seems to me it was either starving for air or fuel. I looked at the air filter. It seemed fine. Started it up again and it seemed OK for about 5 minutes and then started missing, complaining and stalling. I changed the fuel filter and again, good for about 5 minutes and then complaining and of course stalling.

Then the last time I had it running, just before it stalled on me, I opened the gas cap to see if it might be a vent problem, and it revived well. I left the cap on but not very tight and cut the rest of my grass. The next day I decided to see if it would be hard starting without the gas cap on and it started up perfectly. So I poked the little hole in the cap, soaked it in seafoam and then blew it out with compressed air. I suspect it is free of crud now.

My question then is. Would an unvented gas tank make the motor hard to start? I can see it eventually stalling but I would think that with a full carb bowl of gas that it should have started fine but perhap starve for gas a little while later. My problem originated with being hard to start. The stalling happened just this last weekend.

"My question then is. Would an unvented gas tank make the motor hard to start? I can see it eventually stalling but I would think that with a full carb bowl of gas that it should have started fine but perhap starve for gas a little while later. My problem originated with being hard to start. The stalling happened just this last weekend."

You are correct assuming by hard to start you mean the engine doesn't want to turn over, stalls at compression.

Walt Conner

Yes. It would not seem to want to catch when cranking. Not sure how well it was turning over. All I know is it took a lot longer to catch and run when starting.

I have an outboard motor on my fishing boat with a seperate fuel tank and hose. I have occasionally forgot to open the vent on the tank. I would prime the primer bulb as one is supposed to. The outboard in this condition would start up fine and run well out of the gate, but about 50 yards from the dock it gags for gas and dies (unless I am quick enough to give the primer bulb another squeeze).

The lawn tractor seemed to be the opposite. It was difficult to start but for quite a few times this season, worked quite well after it started.

"My question then is. Would an unvented gas tank make the motor hard to start? I can see it eventually stalling but I would think that with a full carb bowl of gas that it should have started fine but perhap starve for gas a little while later."

The time for the engine to stall out with a plugged fuel tank cap vent can vary with how full of gas the tank is. A full tank will stall more quickly due to the reduced air/vapor space inside the tank (gaseous expands/contracts some; liquid does not). but, a more typical time for such a stall is 10-15 minutes with a tank 1/4-3/4 full, IMHO.
In your case, I agree with Walt about excessive compression being the primary cause for your hard engine starting. The plugged fuel cap prob was just an unfortunate coincidence..glad you found/fixed it.

What exactly is stalling at compression? Would an unvented tank have anything to do with it?

"Stalling at compression" refers to the cylinder/piston being in the last portion of the Compression Stroke where the piston is compressing the air/fuel charge in preparation for the ignition spark which will then send the piston downward under its own power.
It requires a lot of effort by the starter to compress the air/fuel charge when the engine is cranking (but not yet running on its own power).
For this reason many engine makers have designed compression release mechanisms (aka decompressors) to make it easier for the starter to get the engine spinning fast enough for it to get going under its own power, at which point the starter is no longer needed.
Sometimes things like valve adjustment can have a defeating effect on the compression release causing it not to work well enough to get the engine to crank past the compression pressure of the cylinder. When that happens it would rightly be called "stalling at compression".
Other factors regarding the health of an engine can also lead to stalling at compression, such as a buildup of carbon on the surfaces of the combustion chamber. These buildups of carbon cause compression pressures to increase because they take up space (volume) in the combustion chamber and with a much smaller space to compress into.......the compression pressure becomes greater.......and harder for the starter to overcome.

Thanks mownie for that explaination. I did check my valve clearances at the end of last season and they were bang on. It is possible they have moved out of alignment since then.

It seems like quite a coincidence that once I vented my gas tank the motor seemed to start up much better. I gave it an entire day to sit (it usually started up OK when warm but when it sat for 7 days was more sluggish).

It doesn't seem to make sense to me that an unvented tank would cause start up problems but in my manual's troubleshooting, it indicated that for "hard starting" motors, one cause could be a dirty fuel filter. I suspect if a fuel filters restriction can cause hardstarting an unvented tank might work in the same way. I just don't even understand how a dirty fuel filter could cause hard starting unless it was not letting any gas by and then it would be a non-starting motor as opposed to a hard starting motor.

I will probably know more next week when I need to run it again.

The only way I can even imagine that a clogged vent might cause any kind of stalling when attempting to start an engine would be if the tank was refilled with fuel PRIOR to parking/storing the machine. A clogged vent in this case might possibly cause fuel to be forced past the carb needle valve and on into the engine to cause hydrostatic lock (liquid slug).
I suppose if the carb needle was a bit leaky it would lend to that scenario, but I can't remember ever hearing of that as being someone's "cause and effect" story.
I will only say that expanding fuel and vapor pressure (if hot enough ambient) could probably unseat even a good carb needle enough to overflow the bowl.
I guess we will stay tuned to see if indeed you starting is better after cleaning the vent.

OK, you guys were right. I did have two seperate problems. When I went to cut my grass on Thursday, the motor was "hard starting" again. During the initial crank it did stop turning, which I suspect was that "stop on compression" you guys mentioned. It eventually started and I cut my grass and confirmed that my previous gas tank venting problem has been resolved.

Later, I checked my valve gaps and they were not too far out but I am not sure what constitutes far out. First, I did Walt's test and confirmed that the intake valve seems to do a small movement after it closes that I believe is the compression release. I checked this before and after I adjusted the valves.

When I first checked my intake valve clearance, at first I couldn't seem to even push a 0.005" feeler through the gap. Then when I played with the rocker arm it went though no problem. An 0.008" was very snug. So I took that as out of spec. for the 0.003"-0.005" it should be. Now, even with me playing with the rocker arm a 0.004" will go through but the 0.005" will not.

On the exhaust side, when playing with the rocker arm, a 0.006" will snuggly go through but an 0.008" will not (I don't have a 0.007"). So I took that as OK for the 0.005" to 0.007" spec. and never changed it.

When I was done the motor started up very well but I had that happen last week when the motor only sat one day, so next week I will be able to test for sure. It seemed to be more hardstarting when it sat for more then 5 days.

Since I like to understand these things, I have a few questions that maybe someone could help me with:

1) Since the intake valve seems to control the compression release, how important is the exhaust valve clearance?
2) Does this compression release keep happening when the motor is running or just during start up? Seems that you would like it during start up and hate it during running.
3) If the valve gaps were to wide why would my motor seem to only have hard starting issues during initial start up but when warm it seem to start up just fine?

Thanks for your help.

1) Since the intake valve seems to control the compression release, how important is the exhaust valve clearance?

Too tight and you can burn a valve. Too loose and you start loosing "performance" to some degree because you aren't "exhausting" as much of the burned combustion gasses, allowing more room for the new "unburned" air fuel mix to enter the combustion chamber. It's akin to giving the engine some degree of emphysema-

2) Does this compression release keep happening when the motor is running or just during start up? Seems that you would like it during start up and hate it during running.

When running, it happens so fast that one simply doesn't worry about it. It IS WHAT IT IS!

3) If the valve gaps were to wide why would my motor seem to only have hard starting issues during initial start up but when warm it seem to start up just fine?

Cold oil vs warm, "warm" battery has higher capacity, battery being "topped off" from running etc.

If you put a battery charger on it for awhile before your first cold start, it'd probably crank slightly better.