Thank you for taking the time to reading my problem.
I have 2 Yamaha bikes right now both with the same problem. When I first start them they only run on 3 cylinders. Once it warms up or if I rev it high the 4th cylinder kicks in. And once hot it runs on all 4. I've went through both carbs with carb cleaner, carb wires(for making sure jets are not clogged) and compressed air for testing the jet passage ways. Both bikes had been sitting and the carbs were gunked up. Even replaced with new gas and some sea foam in it also. The Seca II has Mikuni carbs, not sure of the brand of the Maxim. The left cyl on the Seca is the one and the right cyl on the Maxim are the ones that start off cold. I've swapped the plugs, tested compression(with my thumb), and tested spark. Not sure what to try next. I've went through carbs before with good sucess but found it odd that I have two Yamaha's doing almost the same thing. I do not have a carb sync tool but would like to get one, any recomendations on this would be great too!
Thank you for any advise you can give me here!