This thing is not starting- it has compression, fuel, spark, but will backfire like ignition timing is not correct at times. Is there anything that could cause the ignition to have wrong timing & backfire? Or should I look elsewhere. It does have compression, so I would think that the valve timing & valves should be good enough to start.

 

Extremely unlikely to be ignition timing out, but I have known it. You can usually see the piston through the plug hole if you shine a light on it. Find TDC this way, then check if the timing mark on the flywheel agrees (within reason). If it doesn't, the flywheel has sheared it's key and spun round on the crankshaft. If it does, check that the timing mark on the cam agrees too.

 

Is it backfiring threw the carb or exhaust? If its exhaust check the valve lash. If its carb you might have an air leak. also I have had this problem and the carb float is sticking and there is too much gas

 

Here we go again with more info- Compression test shows 150 ... Has good spark.. squirting gas through the carburetor doesn't make it pop or anything, I even shot some ether in the carb and nothing happened- It doesn't backfire or anything. It almost has to be an ignition timing issue? Any way to check that timing system? I am sure there is a magnet on the flywheel that triggers a pickup that then signals a module which pulses the ignition coil to spark.

 

You don't adjust timing on these there is no adjustment. Have you checked your valve lash yet? Do you have your air box hooked up and sealed when your trying to run it? Have you messed with the air fuel mixture screw on the carb? all of the things I have stated can cause these issues. Only other thing I can think of is your woodroof key might be sheared but that and your cdi box is a last resort.

 

pull your spark plug. Pull the plug on left side above flywheel turn the motor over counterclockwise with the wrench until the T lines up with the mark on the case. Pull the time gear cover off the head and see if those timing marks line up if the T is lined up in the right spot and your mark on the gear up top is lined up with its mark your good on timing. than check and set your valve lash and see what happens. let us know whats up after you do that Do you have a Clymer manual to get the specks? If no I recommend getting ne because the next thing I would check is the stator and coil with a ohm meter.

 

I ordered the factory manual to become more familiar with the details of this engine. I removed the recoil starter to see the TDC mark. I found the T mark and I made a reference mark on the starter cup(which rotates) and on the housing (which is static). This would indicate TDC whenever the 2 marks lined up. I hooked up a timing light and cranked the engine and watched the marks while cranking. The plug fired right at my TDC mark, maybe a few degrees before. So the ignition timing should be close enough to do something. Checking the valve timing may be a little more difficult, and I will try to check that. But as I said before I have plenty of compression-checked with a gauge), and very good spark. My confusion is that with good compression,good spark at the right time, I sprayed starting fluid in the carb and nothing happened, no pop, no backfire, just the starter turning the motor over! Confusing! Thank you for following up my mystery!

 

did you pull the time gear cover off? I could care less abut what the timing light says You are getting too technical at the moment line the marks up on the flywheel and look at the gear. Are the marks on the gear lined up with the mark on the head? It is a simple thing to check Your timing chain could be stretched out and maybe your chain tensioner is not plunging in like it should and it could've jumped a tooth. Check that simple thing and get back to us.

 

Looks like I was writing to myself. Told you how to check ignition timing. No good checking valve timing if flywheel has moved, so check T mark is right, via piston through plughole first. Had an engine with flywheel spun 180 degrees out, strobe would still agree with T mark, piston didn't.

 

Got more confusing info! When the T mark is lined up in the hole, the engine is not on TDC, actually it calculates to BDC( using a wire in the cylinder on top of the piston) TDC was found almost exactly 180 degrees from the T marker! I am assuming that the T mark was TDC and that's where the valve adjustment was made. Of course the cam timing does not match up. The cam dot and mating slash mark on the housing is in the proper place when the motor is halfway between TDC and BDC. I have made a mark on the starter cup(which rotates with the engine) and 2 corresponding marks on the housing behind it to represent TDC and BDC, to keep things clear in my mind. It would seem odd that the flywheel would be almost perfectly off by 180 degrees if something like a key stripped off. And I don't even know what to think about the camshaft timing. Thank You for helping and challenging my diagnostic and thought process!( Almost seems like the repair info regarding TDC is inaccurate.)