5020 hard to start

I'm working on a 5020 I've had sitting for a few years. It runs well, but it is a real guessing game if it will start. If it were a gas tractor, I would diagnose that the timing was a bit retarded. When cranking, it smokes black fuel smoke. It will hit occasionally, but acts a little late, and doesn't hit enough to actually start. When it does start, it acts like it has to gain momentum, like a gas tractor working through a flood, then it cleans up and runs good. I put new glow plugs in and use them according to the decal. Is there a trick to starting them, or a way to check the advance or timing or?? Thanks in advance.

Low compression will make them hard starting also. And make sure glow plugs are working!!! Good Hi Capacity battery, good cables and connections helps also. They won't start without heat! I always crack throttle a little & crank a couple revolutions, then pre heat at least 30 seconds, Bright orange on indicator! More when COLD weather. Next step as Ed said injectors!

Adam, I think one of the suggestions made have to be it. Not that it makes any difference, but I lean towards the low compression idea. Years ago when Cummins was trying to reach the gov. standards, mandated by politicians who didn't know beans from bull foot, they had the same problem, hard starting, and when you would get them started they would slobber, and miss, and carry on until they built some compression and warmed up. I got to checking and the dang things only had about 13 to 1 comp. They weren't all that bad but if you had a smoker that's what you had. Not being from this world and hypnotized by their B.S. when I rebuilt my old 290 I went to Cummins and we dug thru. the specs. and found a piston that built if I remember right about 16.5 to 1 comp. By the way they were pistons built for a 270. Not much power there you say. Well I admittedly was building a mini hot rod, jest a little old cab over International. However, after turbo adjustment, injector adjustment, major pump adjustment, much bigger air canister and filter, snorkel, retarding the timing, match timing the injectors not just 1-3-5 but all six right down to half a 1,000 plus other things I don't remember, the dang thing ran well enough to send users of 425 Cats to the Cat house to get some work done. Not saying it was a 425 Cat, but we didn't get in everybodys way. And start? I quit the road in '86 and went into a shop and later when it got cold I would start it every two weeks and warm it up. I came from work one day and I don't think it had reached 30 degrees all day. With no either it rolled over and fired right up. No miss, no slobber, no smoke. Here I've run off at the mouth just trying to say, compression. Leon R  Cmo