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

After reading about your problem.. a few thoughts!
Are you sure that your exhaust valve is not hanging up..  perhaps due to carbon on the stem or in the valve guide ??  Also, has the air temperature changed dramatically during the run and no run time ??
An engine which runs well in the summer will not always run well (if at all) in the winter without increasing the fuel flow. Did you say that you did replace th coil ?  I have had a few cases where mice, etc.
have chewed the coil wire causing a weak or no spark !!  Finally, some TEC's have a jet in the carb. which have an almost imposible to see hole in it which can plug up very easily !! Even seasoned mechanics have been known
to miss this one !!

>>Are you sure that your exhaust valve is not hanging up..
I'm not sure about that at all and don't know how to check that. I've watched the valves cycle many times by hand and they were opening and closing ok. When I removed the head I scrapped off all the surface buildup and tried to get under the valve and clean the seat as best I could. They opened and closed but I'm not sure it was properly.

This all happened in the last two weeks here in Massachusetts and the temp difference might have ranged between 50 and 75.

The points were replaced with no improvement. The coil was then replaced with no improvement. I've got the old coil back on now and it's the same. The spark jump outside the engine looks passable but not the best. It looks better than other engines that run fine though so I'm pretty confident the spart is ok. There are several new plugs around so I'm swapping and cleaning them constantly to insure I'm using a clean dry working plug.

>>An engine which runs well in the summer will not always run well (if at all) in the winter without increasing the fuel flow.

This is not about trying to run smoothly or well so much as going from health combustions to extremely weak combustions in a matter of days.

If I remember right this carb has a fairly large hole close to the base of the nut. I've seen some that have one or a few very tiny holes and always check for them.

I think I'm bypassing the carb altogether by dumping gas into the plug. Based on niper88's post I did some more tests. The older machines do not have a rubber button push prime. They had a spring loaded bakelite button attached to a carb throat cover. The manual says to get a prime you push the cover onto the throat and pull the start cord through a compression cycle.
I had a few engines like this and they were a bit tougher to start than engines with the soft rubber primes. I put gas directly into the throat and then tried starting. The machine got a couple of very wimpy puffy combustions a tad weaker than dumping gas through the plug but basically the same thing.

I'm under the impression that I could remove the carb altogether and still test the combustion part. I think if I removed the carb I should still get healthy sounding explosions from the engine. By dumping gas in the plug I should get a short run of decent explosions and I can't get that with this engine.

The explosions sound very weak like the combustion is happening way off BTDC or TDC. May this started happening as you suggest because one of the valves is not closing properly so it can't get a full combustion. When I had the head off I looked for cylinder wall and head cracks but did not notice any.

It's evening now and I just went out and checked the spark and it's great. Nice whitish blue thick jumps and I can hear the air snaps. I put in a fresh plug and unfortunately it did not tighten to a stop so the threads are now hosed. I've got to pick up a helicoil kit.

   I feel a bit defensive about gas through the plug given some of the posts above returning me to a possible carb problem.  I’ve picked up number of snowblowers from people who want to get rid of their machine so give them away or sell them for $50.   

 

  Today a person was selling an older Toro 724 for $25.  Those were very well made and dig into the end of the driveway pile very well unlike the lighter new machines.  Chances are always high if the engine is ok the rest can be made to work very easily and without much expense.   Today was a good example of using gas through the plug as a fast check on things. 

 

   The first thing I do when I get something like this home is check for spark and I do that quickly by dumping gas in the plug.  People generally are dumping these because they don’t start or run well because of carb problems.  Most have been sitting around for a few years and never had proper maintenance.  The gas in the tanks is usually old or dried up.  The carbs generally have varnish crud buildup or white cake buildup.  The carb jets are usually screwed up from tinkering so there’s no sense in pull starting till my arm falls off or heating up the starter until it melts trying to start the thing.  Dumping a bit of gas in the plug lets me know there’s spark and the thing can usually be made to run if it fires up well.  As long as I get a healthy sounding combustion there’s hope to go further. 

 

   If I get a short run of good fires it’s very positive.  I used to at this point put gas into the tank and try to run.  Over time I’ve found that sometimes some of these things would run but very soon develop gas related problems.  It was sort of a waste of time to put gas in the tank as I’d have to later drain the bowl, line and tank which is messy.  I found it was better to assume dirt everywhere so now if I get a machine to fire well I just take off the carb and clean it.  If the gas tank has a lot of crud I’ll drain the line and tank and flush it out with a garden hose. 

 

     I should add that I did a compression check right after I got the run of good combustions which on this machine was a not so great 75 cold by the hand pull.

 

   I’ve found the majority of these machines don’t need a rebuild kit, just a through cleaning.  So today after getting a short run of good combustions I pulled the carb and gave it a good cleaning along with the tank and line.  I put the carb back on and it ran rough and hunted for several minutes but settled down and ran fine. 

 

   I got in the habit of using gas through the plug often as a quick check I guess because I’m always worried about spark and the pain in the neck of pulling the covers and removing the flywheel to get at the ignition area.

 

   Today’s combustions with gas through the plug were similar to the usual I get with an engine that is healthy.   They were quite different than the stubborn 5hp that has the wimpy combustions.  I’ve pretty much given up on that unless I can figure out how to check for a sticking valve which was suggested.  Other than that the only thing I can think of is to take out the valves and inspect the underside and the seats.  So it’s sidelined for consideration. 

 

    I’ve got another just like it, another old Ariens ST520.  It was a free rig as it would not start for the owner.  It got the gas through the plug treatment and it’s compression test was 145 so impressive.  I pulled the carb right away and cleaned it along with the gas tank and it been a great starter ever since.  It also had healthy combustions on it’s initial test. 

Tecumseh engines have a compression release, don't wory about the compression.

Take the bowl off the carb, the bowl nut is the inlet for the main jet,  take a piece of wire from a wire brush and clean the holes out with it, top and sides, then blow through it with carb cleaner.  I think that is all it needs.  timing is nonadjustable on 95% of the engines that TECUMSEH makes.

just put it back together. and run it..  let me know what happens.

Good luck

Friiy

   Most second hand older engines I've seen don't have compression release.  The ones that do test around 45psi but I'm not sure how consistant that is.  What is consistant is wet and dry test the same on the ones I've tested with compression release.

   Maybe you did not read the top posts.  I'm just giving a test to the engine and not looking ot make it run.  The carb may be all screwed up.  What I'm looking for is healthy combustions by dumping gas directly into the plug.  That should happen.

Almost all engines have compression release.   One type is a mechanical release that is spring loaded to pull aside at certain engine speed.

The other is un-noticeable rise ( intake side ) in the camshaft just before top dead center,  The second also is very critical to valve clearance.  Have you ever noticed that a engine with very little  Valve clearance is easy to pull over and a engine with too much clearance his hard to pull throught  (jerks back)..

Good luck,

Friiy

triiy,
>>One type is a mechanical release that is spring loaded to pull aside at certain engine speed.

What gets pulled aside?

I don't understand compression release so I'll have to dig into that.

>>The other is un-noticeable rise ( intake side ) in the camshaft just before top dead center, The second also is very critical to valve clearance.

When trying to imagine what's going on it always seemed a problem that once the engine fires the compression release could have to be disabled to close things off to maintain pressure. ??  Something obviously has to disengage this after the engine fires but I don't have a clue to what that is.

>>Have you ever noticed that a engine with very little Valve clearance is easy to pull over and a engine with too much clearance his hard to pull through (jerks back)..

This is pretty interesting if we're both on the same page here on the jerking back part. I think you're saying the pull out locks or tries to pull back the other way. On this engine that happens all the time. On some engines it's occasional but this one very often. It would make sense if the valve clearance being to much causing jerk back would also cause so low compression that an engine would not fully fire like a healthy engine resulting in  very weak combustions. Is that expected?
trouts

mechanical compression release is wieghts attached to the camshaft with springs so when the engine fires it reaches rpm and the wieghts fly out and disengage the mechanism, which closes the vavle. some of the old engines had a rod which you pulled out or pushed in to to achieve the same result. any how your tecumsech 5 hp does not have a compression release. as for the engine pulling back  when cranking (out of your hands) thats not a valve clearnace problem, its more likely a sheered  flywheel key which sounds like it could be causing pre ingition which in return will pull starter out of your hand when your cranking. and if so your timing will be off and is probally causing you all your problems.     ie good sounding compression.

niper99,

    The flywheel shear pin is ok.  The flywheel has been off a few times for replacing the coil and points.  As mentioned above I set the timing after installing the points at BTDC with a multimeter.  The point gap of .020 was set on the peak of the dwell then the crank rotated several times to get to the proper place in the stroke BTDC.  The point housing was then loosened and the points gotten to just open at BTDC.   

    I don't have a gauge to measure BTDC so it's a guess.  The timing will not be per spec but I think should be close enought to get a heathy combustion.      

   The pullback is very stong.  It's tough to say exactly but it's like an immediate lock up of the cord so it gets ripped out of my hand.  I don't hear any combustion or see any smoke out of the muffler so don't think it's firing slightly but it might be.  The timing could be off and the problem.  I've set it and gone over it a number of times but when you've missed something you don't always catch it on a recheck.  It's been raining for a few days so on the next decent day I'll go back over the timing and possibly adjust the vales.  As I remember valves in a car engine there was a nut and the valve could be screwed in or out then locked down with the nut.  I'm not sure how to adjust on a small engine so will have to look into that also. 

   The picture is of the 5hp valves.

I beleive the points are to be set AT top dead center,  What color of flywheel key does this have (gold or silver)..

Good Luck ,

Friiy