Savage3

Compression is an important factor as you know. I'd check it again, make sure no mistakes were made in top end.

Have you looked closely at the spark? For instance, when it dies, is it because it is losing spark?

Is something grounding the circuit or is it losing ground?

How about fuel? Is it losing fuel after start? For instance, if you sprayed fuel source directly to intake after start will it keep running?

Is there a safety switch shorting to ground immediately after starting?

Verify these things and get back to us. Maybe someone else has some ideas as well.

Hope this gives you some ideas Boss

Well sir, assuming your assessment and troubleshooting is top notch, the next possible issue could be a loose wire.

I'd check the ground circuit 1st.

Follow positive wire to starter solenoid, make sure it is tight.

Follow ground wire to frame, make sure it is tight.

What was the voltage reading on battery?

Did you find the main fuse when you checked the fuses?

Does the neutral light come on? 

Great success with Startron.

No problems, I also use non ethanol gas.

I use the regular tools in any small engine shop. DVOM, compression tester, leak down tester...etc.

I use a GTC 505 for ignition related issues.

7 hours ago, Redfox said:

My fuse holder was badly distorted as well, but I was able to remove all the old fuse pieces and replace with a new 30A fuse. After a charge, the fuse was still intact and working properly 

I suspect this problem will reappear. When it does, check the current draw on the starting circuit.

The destroyed fuse is the machines way of making you aware that an electrical problem exists.

I would find the problem before it causes more damage.

Begin by finding a service manual. 

Next, use ohms law and begin testing.

Good idea! Worth a try for sure! No cost, no harm, no foul!

This is not the same equipment, but, will get you in the ballpark! You will have to research the specs for Axis.

The concept is the same, basically, the TPS is a potentiometer that is feeding information back to PCM that controls timing. ( In a nut shell)

Trying to keep it simple......

Use this link to grasp basic fundamentals, then study how tps works.....then perform test

The definition of insanity is to continue doing the same thing and expect a different result. 

You already performed the TPS replacement twice! 

I agree, that diagnosis doesn't sound reasonable.

Is there information we haven't heard of this far?

Hate to see you spend more money and not correct the problem.

Look for low voltage input at the TPS. Must be a poor signal.....

What is the voltage coming into the TPS?

Is fuel making it to the throttle body?

Is fuel making its way to the spark plug?

If so, how much?

Decel pop is usually a result of unburnt fuel in chamber.

Your air fuel ratio is off

Now that sounds more like it!

I ended up ordering parts through Amazon. Sorry for double post, was having issues with phone.

I received no response from "Hisun" in TX. Take a close look at the facility online.

I received no response from "Hisun" in TX. Take a close look at the facility online.

Do you have the service manual? I've had a few of those engines apart. Not a 500, but, a 550 and 700.

Awesome! Sounds like a plan!

Hopefully, the valves are ok. Sometimes they survive without any damage.

Good luck!

Good job, ya found the problem. Take a good look at the tensioner when you put chain back on. They often melt! 

Hope that helps .....page 195

https://www.manualslib.com/manual/1113756/Hisun-Hs800.html

Set timing, turn motor slowly by hand ensuring valves move free. (At least 2 revolutions)

The key usually shears if wheels locked up or abruptly stopped. Generally, abuse causes key to shear.

Sometimes the chain tensioner loosens. The key doesn't always shear.

Hot tip, a bad sensor does not create popping noise.

Also, the crank sensor will not know the chain has skipped a tooth.

If you want to test the sensor, I'm sure the service manual has specs. 

8 hours ago, Dumbfounded said:

I have similar problem only mine died while in use. I heard a slight pop right before it died. Then it would not start. 1st I checked was oil level and it was a bit higher than normal.  Removed spark plug boot placed test light in between and good. Removed plug and tested compression and had real good number considering it has less than 300 hrs. Listened for evi pressurizing and sounds good.  Added fuel since it was 1/3 on gauge and turned to on and off position 3 times then cranked but same issue.  What could have caused this and what to do next?

Ok, so we go back to his original post. I was basing troubleshooting on this post . The popping sound is important. 

If it has fuel, spark, and compression ( assuming he made sure fuel is reaching combustion chamber and it's fresh) I would personally check timing next. The last one I rebuilt, the chain tensioner had a total meltdown with only 200 hours. Same symptoms as described.