Temp snowblower problem
I have a 2004 Craftsman 27” 8hp snowblower that has seen little use. It began this year running weakly, and tending to surge rhythmically. It made it through the first snowfall, but halfway through the second it quit. It will restart OK, but dies about 15-45 seconds later. Successive restarts die a bit quicker. Going to half choke makes it last slightly longer. I’ve pulled the carb, blown out all the passages, hit them with carb cleaner as well and run a fine wire into all the passages I could get to. Also blew out the fuel line back to the tank. Nothing appeared gunked up at all, but since it seemed likely to be a fuel problem I did all the above anyway. No change whatsoever in the symptoms following the above. I then tried spraying some fuel directly into the carb after starting it (as it began to quit), and that only kept it running a few seconds longer. My conclusion is that it isn’t a fuel problem after all. While I had the carb off I did notice that there was some bluing on the stem for the intake valve (just above where the valve widens out). So now I am thinking that perhaps the intake valve begins to stick as the head heats up (resulting in some burning of the fuel mixture before it enters the cylinder, thereby heating the valve stem). A compression check yielded 55-60 psi while the engine was cold. Your thoughts/suggestions?
OK, thanks all. Lots to cover:
bgsengine – I agree about the coil, but none-the-less I’ll try to rule that out using my timing light.
I kind of ruled out the carb when I couldn’t keep it running by spraying fuel into the carb. In my experience if it is a fuel problem, when you squirt some fuel into the carb as an engine starts to quit it will revive with a burst of power for several seconds for each squirt. In this case it died quickly regardless and to the extent it ran a small amount longer, it was still very weak – no surge of power. Based on that do you still think the carb is the likely cause?
deere2me – I haven’t pulled the valve cover yet to check clearances or look for anything else amiss in there. Do you know what the spec clearances (intake and exhaust) are for this engine?
First thing I did (before even pulling off the carb itself) was to pull the bowl and check/clean the bowl nut/jet. It wasn’t junked up at all, but I cleaned it anyway and that had no effect on the problem. I do have some very fine drill bits, but it really looks completely clean and air blows through it freely.
peanut budda – I wasn’t sure what compression is normal for this engine, so thanks for confirming that it appears to be ok in that respect. I had thought about the tank venting so I tried starting it with the fuel tank cap off but that made no difference. Also, it is hard to imagine it sucking much of a vacuum in the tank in less than a minute.
I used a rubber tip in blowing things out. For most of the orifices I was able to get a pretty good seal and feel air blowing through. I also ran a fine wire into each orifice and found no obstructions (other than bottoming out where a passage makes a turn) and the wire tip didn’t come out with any gunk on it at all for any of the passages.
Again, thanks for the responses. Has anyone seen bluing on a valve stem as I described above, and if so what turned out to be the cause of it?
Joe