Honda GX620 back fires and wont run

Hello Everyone,

I have a Lincoln red-D-arc ZR-10 welder with a Honda GX620 V-twin 20.0 engine sn:GCAD-1093945, We loaned it out and when it came back the engine was locked up tight, so I pulled the engine out thinking it kicked a rod out, and disassembled it and I found the engine did not kick out a rod like I thought however someone had a chain with hooks on both ends and one of the pins from the chain hook came lose and worked its way down and got lodged on the inside of the flywheel to a magnet (go figure).

I checked everything out since I was there and put new gaskets and reassembled the engine and installed it and when I tried to start it if back fires threw the intake and when it did start it barely ran, just popping threw the intake valves, so again thinking maybe somehow I got the cam to crank timing wrong I took it back apart and I found that I the timing correct and the valves were adjusted correctly too, I looked at the camshaft centrifugal compression release, it is spring loaded however It moves free and when its moved out the compression release pins drop down like they should to release the valves, I saw where on the end of the camshaft is a hole where oil pressure is forced by engine oil pressure and it seams to hold the compression release part off ? the engine has good oil pressure,

since the engine ran great before the pin got lodged I have to believe that this is a mistake that I caused or over looked ? I checked the crankshaft key way and key and they look good, I see where the only timing per say that could be changed is the cam to crank timing and since the crank key only goes in one way as the coil mounting only mounts one way (bolts). I feel the compression release is not coming off and its holding the intake valves open just slightly, oh I am a heavy equipment mechanic for 30+ years now I just wanted to throw it out there so you know that I'm not a dummy completely LOL.

Here is some pictures of it and please if any one with Honda knowledge has any ideas please let me know, has any one had a problem with this type of honda like this ? thank you gtxtim

Pull the flywheel under it is a key the key is probably sheared this affects timing. Replace key I bet it'll work great

when I reassembled the engine and after noticing the problem I pulled the engine back apart and checked the cam to crank timing and the flywheel key and they are ok ? I tend to lean towards the compression release not releasing ? let me ask a question, does the engine really need the compression release ? I noticed the earlier GX's didn't have that ? I am temped to remove the two compression release pins from the cam shaft and try starting the engine so I know ?

That's a bit beyond anything I've ever done with an engine. My opinion is that you should not remove or modify anything internal it was built to have a compression release so it should function with it. Pm Robert@Honda he is a user on this forum and can probably get you going

Hello again, I have some more pictures to put up and I still haven't found the problem yet the crankshaft key is good and I need to get it fixed so I can use it , I did a leak down test and the valves and rings are not leaking, when I do get it to start it barely runs and pops from the intake and exhaust until it dies , the longest I had it running is about a minute at a idle if that, any help would be good thank you very much.

Have you cleaned the carb the compression release is unlikely going to fail. It has spark? Has good compression? And that leaves fuel. Another thing to check is the kill switch could be broke or malfunctioning not letting it fire.

it has good compression and spark and there gas to the crab, if it was a lean condition I could see the intake popping (backfiring) but not the exhaust, we used to see the exhaust pop or backfire when we had points but this has electronic ignition and it pops from both intake and exhaust ? I have the valves set at .015 and .020 I got this out of the honda book ?