Hi , I need some help Please . I bought an 89 XT 600 with the top end off and needing to be rebuilt.

I just put new Yamaha .50 piston and rings in it and new timing chain , new valve seals, also lapped the valves into the seats. put it on the bench put diesel and it did not leak though the valve seats . we put the engine together ,, cam lobes all pointing down , piston up top dead center and the marks on the cam sprocket and fly wheel lined up. adjusted the valves to maximum clearence specs . I also cleaned the carbs , put a 130 main jet in and turn out the mixtures screw to 3 full turns . I even put on brand new intake manifolds/boots on it and siliconed the rear air box boots around the seal where it meets the airbox. I used propane to see if there is a leak somewhere , never made a difference in the way it ran.

it kick starts fairly easy , seems to idle but it with pop back through the carb , the plug is white when I pull it out to check it. the engine heats up really fast .

we couldn't do a air leak down test or compression test because my buddys fitting didn't fit where the plug went , his fitting was to big . but starts easy and the deisel didn't leak through the vavles while on the bench . he did have a fitting to just put air in the cylinder though , he put 45 lbs going by the commpressor guage and we did get some air through both intake valves and 1 exhaust valve .

Can someone point me in the right direction , am I having carb problems or head problems ,, I'd hate to pull that head back off , but if it has too , then it has too.

Thanks Randy