I bought a used 50cc Kuzuma Redcat that will not start.
I have spark, gas,and air just won't start. Any suggestions?

 

let's define "no start". judging from your verbiage, i presume it cranks/turns over the engine cause you say you have spark. ok.
you have gas? where? in the tank, in the carb, or is the spark plug getting wet when you crank it? if you can crank it and give it a small shot of ether/starting fluid in the air filter and the quad starts and runs on ether, then you have a fuel delivery problem. that would mean your jets are plugged and not delivering fuel to the engine. seeing how it's a smaller quad, i hope you've checked for spark and that one of the safety interlocks ain't holding you out. but anyways, holler back with any other information.

 

I've worked on small engines before (lawn mowers etc) but this one I can't figure out. It cranks good, the spark is good, I get gas to the cylinder and I've sprayed starting fluid into the carb manifold and it just won't fire.
I tried pulling it while in gear and it will sputter a couple times but wont start. ???????????????????????

 

Given your symptoms (after getting answers to Jaster94's completely valid questions), the first thing I would do is adjust the valves. Tight valves make for hard starting (or no starting) when cold.

Do you have any history on this quad? Have you ever seen it run?

 

Just bought it a couple weeks ago. It didn't have a battery so the owner said he always just push starts it. Which he did by pushing it down the street and jumping it in gear and it started. He drove it up the street, sounded good so we bought it. Hasn't started since.

 

Do you have a battery now? Or are you still trying to push start it?

I would still check the valve adustment. If the quad engine was warm (even slightly) when the previous owner demonstrated it for you, and the valves were tight, it would start up and run like a champ. Until it cools all the way back down...

Valves on these engines tighten with wear, and tighten more when the engine is cold. So the symptom of tight valves is hard starting (up to and including no starting) when cold. Adjusting the valves is a periodic maintenance requirement.

Sometimes a defective spark plug will spark outside the engine in atmospheric pressure, but fail to spark inside the engine under compression pressure.

Have you measured the compression?

 

I've been trying to start it from a battery. I have also used two new spark plugs and I have not checked the compression. Do you know what the valve gap should be? Thanks

 

Set the engine to TDC on the compression stroke (both valves closed). Adjust the clearance to 0.004" intake and exhaust with the engine cold.

If the valves get set too tight the engine won't start, or is extremely difficult to start, when it is cold. Remember they get tighter when the engine is cold, and they get tighter as the engine wears. They get looser when the engine warms up, hence the oft stated symptom of "its a bugger to get started at first, but once it is running it always starts back up just fine".

If the valves get set too loose you will hear valve clatter - especially when the engine is warm.

You tube is your friend. Search for chinese ATV valve adjustment. You might even find a video for your specific quad.

 

Thanks for the info I'll work on it this weekend....