Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

  A newly acquired 5hp 70’s Ariens snowblower started fairly well over several days with test starts and running the engine for a minute.  Then it started a bit harder and just barely putted along having very week combustion after 10-to 16 cycles and died.  It’s been about the same every since then.  It won’t start easily now with gas through the carb.  I can get it going with gas through the plug but it only sputs along for about 10 cycles, very faintly and dies.

   It has 60psi compression after 5 pulls cold.  There was no to  very faint spark so I replaced the points which were pitted.  The spark is good but the same thing of running faintly for a short time and dies.

   My test of the coil was a little fuzzy so I replace the coil but the same thing happens.  It only starts by dumping gas through the plug and it does so in an unusual but consistent way.  I have to pull about 10 times and I hear a faint put or two with a slight breath of smoke.  The next pull or two a few more puts, the next pull about 6 to 10 puts, the next a couple then nothing.  I can do that over and over.  What’s unusual is that it never fires quickly but takes many pulls. 

   If I change the plug often it does not change things.  I check the spark and it seems very fine. I have a plug with the arm cutoff so the spark jumps to the rim.  I test the tester on other machines and their spark is about the same as on the 5hp. 

   Gas is not an issue, spark is not an issue, air is there.  I pulled the head and the gasket is fine.  The valves look ok.  The intake lightly covered with black carbon, the output a light brown ash.

   The timing is set as best I can set it.  The points gap is correct.  I don’t have a dial indicator so guessing BTDC, take off the point wire and use an ohmmeter so just get the points to open at BTDC.  I’m sure I’m at the right cycle as I’ve checked it over and over with a flashlight through the plug watching the valves and watching the key turn on the crank. I’m probably not on the money for BTDC but think I’m close enough.

   The only thing I can think of is if there was a compression leak from a wall crack or rings.  With 60 psi I think I should be running with no load fine.  It should at least run and sound like a good motor even it did not have any power. 

    I’ve obviously missed something so the reason I’m posting.  This business of running fine then within a few days very hard to start or no starting with running only for a short period and with very week combustions has happened before with a lawnmower and a chainsaw.  All very quickly deteriorated to non-starters unless gas was dumped into the plug.  When they did catch and only after many pulls they ran only for a short time and very weakly.  Since it’s happened three times it must have happened to someone else and be a fairly common thing but I’ve never seen a write-up on the web similar.

trouts

Crew,

   There were a lot of problems with this engine and fairly difficult to deal with.  The carb was messed up, valve problems, and intermittent spark causing some confusing problems.  When this was posted I was still ramping up on rebuilding so this engine got put in the background several times.  Over time I’ve rebuilt 5 engines and finally got back to working on this engine again. 

    I relapped the valves, water tested them and put in rings.  It sill sucked, barely started and ran weak.  Since starting this thing I’ve picked up a leakdown tester and after testing this one last week found a big ring leak into the crankcase.  Evidently besides it’s other problems which were worked off it also has a worn bore.  You can’t win them all. 

    The good part was I’ve learned quite a bit and rebuilding and getting strong engines – aside from this one.  I’ve now ordered a decent bore gauge which should be here in a few days and prevent any false rebuilds in the future. 

     Thanks for all the help it’s very much appreciated.

Trouts2

I assume the bore was oval shaped.  This is a fairly common occurrence caused by piston wearing  as a result of poor lubrication.  When it wears, it begins to rock  in the bore usually wearing front to rear.  It's not a readily observable condition but, as you've learned, can seriously effect engine performance.  Was the cylinder beyond a re-bore or just not worth the expense.  I work on old 1970's two stroke motorcycle engines.  When originally produced, they were designed to be over-bored several times.  Max number of over-bores on the Yamaha RDs is eight (2mm).  Which is incredibly robust considering that you can get 10000 to 20000 miles per over-bore providing the bike is ridden sensibly and good quality oil used.      

What does you local machine shop charge to oversize the cylinder?   I have not done it in quite some time..   but if you fine a hungry machinist it can be done cheap..

Depends on you location and their workload, you may want to give them a call.

Friiy