You webserver will limit the maximum response size limit. You should refer to documentation on your web server of choice to see how best to increase that limit beyond whatever it is set to today.
The JsonResult class does have a property (maxJsonLength) you may also try changing
var jsonResult = Json(dataPlot, JsonRequestBehavior.AllowGet);
jsonResult.MaxJsonLength = int.MaxValue;
return jsonResult;
Possible configuration change
<configuration>
<system.web.extensions>
<scripting>
<webServices>
<jsonSerialization maxJsonLength="1000000" />
</webServices>
</scripting>
</system.web.extensions>
</configuration>
Most importantly - you may want to reconsider your call to limit or somehow partition the responses into more manageable chunks as a default response limit is fairly large and can take a long time to return (network latency)
Generally speaking it's usually not a good idea to increase your response size limit. But that is probably the problem you are experiencing.