I have a real head scratcher. I've been following advice on this forum. Can't get mower to start. It was running rough and popping out carburetor. I've changed spark plug, carburetor, engine coil. I pulled flywheel and key is ok. I'm getting spark at plug. Out of desperation, i sprayed a little starting fluid into air filter housing/ carb intake, pulled cord and popped out of carburetor and had a flame to smoother. I've set valve on intake side to .152mm and exhaust valve to .203mm. After all this, still doing the same thing. I also have good compression. I don't have gauge but rope hard to pull with plug in and easy with it out. Could this be a valve issues?

 

It could be a valve issue. Are your rocker arms moving the same amount when you turn the engine? It would be good to know how much compression you have. Fire coming out the intake can be ignition problems, flywheel timing, or valve problems or valve timing. What did it do prior to this? Was it sitting up or did it hit something or was it taken apart? Is the timing belt loose? You might have to retime the valves.

 

It was running fine before, my son in law was using. I don't believe he hit anything. When he brought over to my house it would run, but popping whole time. air filter was real dirty. Timing belt is tight, and rockers seem to be moving same amount. I've replaced coil, but old one and new one spark. When i had carb off i could see build up in port that carb bolts to. I'll see if can get compression gauge to check compression.

 

I'd check the valve timing with the timing belt. I'm betting it jumped time.

 

Will do. Thanks so much! Didn't think of that

 

Hey Cheese, finally got back to looking at mower. bought compression gauge. first pull on rope registers 30 psi. If i pull 7 or 8 times goes up to 75 psi and holds there. I took a screwdriver and marked top dead center on piston through spark plug opening. The notch on gear that has belt on it is in center between Valves. The vavles seem to be opening and closing the same amount. I'm going back to double check vavle gap/ lashing. Any clue whats going on here. I put spark checker on coil to spark plug, good spark. I already replaced carb

 

Ok, i went back and checked valve lashing, intake .152mm and .203 mm exhaust. I measured the travel of rocker arms, they are the same. I did notice exhaust rocker arm had a little more play in it than the intake, when piston at top of travel..I replaced flywheel key even though old one looked ok

 

When i did compression test i screwed into spark plug hole and pulled rope. each time i pulled rope setting was locked on gauge. I didn't release pressure each time i pulled rope. 30 psi on first pull. I have a snow blower more hp than mower it was 50 psi one pull of rope. I also check flywheel for magnetism

 

Is the compression release mechanism still attached to the cam? Does it move freely?

 

Yes compression release on cam moving freely. Its wierd, I went back and checked vavle lashing. I watched video on how to set vavles. I have spark at spark plug. I took original carb apart, took out jet. Sprayed carb. Watched video on how gasket sequence goes. After all this same issue. I spray starting fluid in carb it pops and have a flame i have to smother. My son in law was using. He didn't try working on it, he brought to me.

 

Rotate the engine to TDC again and then rotate 360 degrees to put the piston at TDC on the wrong stroke. At this point, rotate the engine a little back and forth so that the piston goes up to TDC and past, then back to TDC and past. This is where the valves should "rock". As the piston goes past tdc one way, one valve should begin to open and as it goes past tdc the other way, the other valve should begin to open. The exact point where the piston hits the top is the exact moment where both valves should be closed. This checks your valve timing, regardless of timing marks. Check that and report what you find.

 

You would have to pull the engine over a few times to get a good compression check. The starting position of the piston in the stroke will affect the reading. Spin it over two or three times, then check it. The high end of the reading is what you're after.

 

Ok , used mechanics mirror and can see timing marks on bottom side of cam. Rotate flywheel till on combustion stroke. Marks line up. Magnetic part of flywheel lines up with coil. The lobe on cam is facing straight out away from engine. Now I'm wondering about lack of compression

 

It has a compression release...
What kind of plug did you put in it? NGK? If so, get a champion or autolite and try it. I've had this kind of problem with NGKs.

 

Well , I did compression leak down test and air escaping through crankcase where cam belt goes in. Just for the heck of it i took apart. Cylinder wall grooved up pretty bad. Rings didn't look good.