New engine won't start

[Jere814]

I have a brand new motor that took me 5 months of buying parts and building it up. I bought a bottom end online. Anyway I have spark I have compression. It's not firing. It's wants to it almost does. Everything seems right. The only thing I didn't do was put the new gas oil ratio in. I just used my old carb am gas tank that I already had hooked up. Does anybody know if that's what the problem is? Because I k own your supposed to use less oil to break the engine in. But I only had what I had an I figured it would at least start.

 

[crassius]

depending on what kind of gas is sold where you live, that 5 month old fuel may have gone bad - try fresh

 

[Jere814]

No the gas isn't old. I took my old motor off an put my new one on with the old carb still attached to the fuel line. When I very first tried to start it it did fire for a second. But that was it. Maybe you think I broke a ring? Because I did that the first time an had to reorder another set of rings. I just don't want to pull the head off an it not be broke an break it putting it back on. Idk

 

[crassius]

I'd probably do a compression test next - there are so many cylinder & connecting rod differences out there that changing top ends can be tricky

 

[Jere814]

I definitely have compression. You can hear it

 

[crassius]

well, you need up around 100 or 120 pounds to run it - a good mechanic can put his thumb over the plug hole & tell by the way the air blows his thumb off the hole it there's enough, but most folks should use a compression gauge

if the old top end doesn't match the new bottom end, you may have low compression