I now have compression and it still won't run:(

[martynkim]

The WD40 trick was true some time ago. Then after some time, they changed the formula and it is no longer combustible.

Lighter and a new can of WD-40 begs to differ!

[TiffanySpree]

Ok, well, that's what I've read. Sorry if it's wrong info. If it's flammable, is it combustible? Now, I'm curious. I'll try it tomorrow.

[Bear45-70]

The WD40 trick was true some time ago. Then after some time, they changed the formula and it is no longer combustible.

Interesting, it is beings used as a tire inflator last winter, spray and light. Besides, if they change the formula as WD-40 stands for Water Displacement- experiment #40 and if they change it it isn't WD-40 anymore.

[PimpinSpree]

Ya. Wouldn't it be wd-41

[PimpinSpree]

Crank on the motor for a little while. Then pull the spark plug. It will most likely be all wet. But might be bone dry.


Dry means lack of fuel. Rebuild the carbon

Wet means its getting fuel but not burning it. First thing to check is spark. Grab the spark plug tip with one hand and tough some bare metal with the other and crank the motor over. Actually a better check is to out the tip of the spark plug on some bare metal and crank it over. You should be able to see a little blue spark.

Other possible problems.
Low compression
Over oiled air filter
Timing off from flywheel being installed wrong.
Exhaust partially plugged
Crappy old gas




First you should check for spark and compression though

[tom waite]

Low compression. 90psi dry, and cold. The books says I need 170psi with the motor warm. Rings are new, piston is new and the cylinder measured within spec. No clue where my compression is going.

[TiffanySpree]

Do a leakdown test. Easy to make. Just need something to pressurize the cylinder with air, maybe a small tank with a gauge. The air leak will be obvious. (crankcase = rings or ?, around head = gasket, etc). Not sure if the reed valve plays a part in compression.

[Bear45-70]

Low compression. 90psi dry, and cold. The books says I need 170psi with the motor warm. Rings are new, piston is new and the cylinder measured within spec. No clue where my compression is going.

Did you do the compression with the throttle at WOT?

[tom waite]

Yes. Compression was done with carb off. Reeds double checked and fine. Double checked bore. Perfect. When I remove the head though, I notice the jug, head gasket, and head are wet with gas/oil. Shouldn't it be bone dry if it is sealing? Would there be a little bit of oil?

[Bear45-70]

If you mean the outside of the jug and head, then yes it should be dry.

[tom waite]

No. Let me give you a walk through. I wipe mating surfaces of head and jug before install. I install the headgasket and head. I run a series of compression tests. I pull the head off and the mating surfaces, and headgasket are wet. Nothing on the actual fins of the jug.

[Bear45-70]

You need to check to make sure the head and top of the jug actually flat.

[tom waite]

sob. Probably something a machine shop will have to do for me?

[Bear45-70]

sob. Probably something a machine shop will have to do for me?

I have a steel "T" square that I use. You just need something flat to lay across the head and put a light behind it. If you see light it it is not flat, except in the combustion chamber of course.

[bakaracer]

are you reusing and old head gasket? did you torque the head bolts to spec?