Hard starting

[Kachess]

My original Ton with 9800 miles has recently becoming harder and harder to start. None of our Tons have ever had a problem starting, ever, but I attributed it to some clogged carburator circuit and hadn't taken the time to trouble shoot it. Once warm the engine pulls harder than any of them. This last trip to McCall tit was cold a couple mornings and I really struggled to get it running. It took starting fluid, new plugs, and a jump one morning. Once warm it ran great. I finally pulled plugs, yesterday, and checked cold compression. 40 and 60 psi in two of the cylinders. I ran air into the weak cylinders and hear an exhaust valve leak in one and an intake valve leak in the other. I started the engine up, let it wrm up and all show equal compression around 150psi. I'm assuming I need to re-shim valves at this point, but am a little amazed that warming up the engine makes that much difference.

 

[kinger]

Sure you did the test correct on the cold one? If they are even when warm and at 150 psi that is ok.

If the valve shim was a issue it wouldn't go away when warm.

Wondering if your fuel pump is leaking slightly internally losing some vacumn when its hard to start do you ever pressurize the fuel tank by blowing air into the vent tube by the left footwell and sealing with your thumb? This will force fuel to the carbs and tell you if the sled is basically draining fuel back to the tank every night (losing the vacumn in the fuel pump).

If she fires right up that is your problem.

 

[Kachess]

I checked the compression twice, cold. It blew me away. And when I finally get it started, it barely starts, and it runs really, really rough. Sounds like it's coming apart. I have to hold the throttle to keep it running. Gradually over 10 minutes time, it will run smoother and smoother. Not until it is FULLY warmed up will it idle. And once warmed up it starts perfectly, and idles perfectly. I've checked that the fuel pumps are both operating, and the way it gradually smoothes out over a long period of time is not what I've experienced when a pump is going. I was guessing that maybe the difference in the coef of expansion of the alum head and the steel valve stem might make then close up at temp. I really don't want to break it open until the snow stops flying, and it happens to be really flying, lately.

 

[kinger]

Try the pressurizing gas tank trick and see if it helps and let me know. Only then can you rule out the pumps. To me that is exactly how I have seen vacumn style pumps fail.

That is why no one tests CR cold its always reccomended while warm.

Although not as accurate did you add oil to the cylinders with low CR and test again cold? That would eliminate rings and help to get you to think valves but still not real accurate. True compression is on a warm engine.

 

[Utah Stilley]

I have had my Ton on 2 occasions soo far. a bit hard to start and wont idle until it was warmed up. Then for no reason it would cough and sputter and die. finaly blew int the tank a bit and it would start to run then clear up and run fine for 100 mils or 2 or 3 trips. this has happend twice. Cant seem to find any Vacume line problems. Maybe the fuel filter? or the pump? not sure.