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

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

trouts2,

when l set points l do it this way, the rod that open the points make sure its fully extended out (points fully open) which should be TDC, then take your feller guage (.020) and move the capacitor up tight to the feller guage then tighten down the bracket, and that should do it. theres nothing that l can think of that  would cause the engine to pull back other than pre igintion and if you want to test if its the igintion system take the plug wire off and turn engine over serval times and see if it pulls back. and as far as valve adjustments there isnt any (non adjustable). 

friiy,

It's silver. ? Never saw a gold one.

niper99,

There is no "rod that open the points". The points are opened by an enlarged portion of the camshaf, at the peak of the dewll. The .020 was set there at the point of the enlarged portion that opens the points the most.

The capacitor is mounted on the coil and has a lead running outside the points housing. It's not near the points so impossible to make touch the feeler gauge. You must mean the movable part of the points bracket which the point arm attaches to and is moved by loosening it's holding screw.

The Tecumseh manual says get the .020 set at TDC then move the piston to BTDC. That position backs the points arm off the peak of the dwell and the place where the points should just open.

The ignition holder (not the points) then gets untightened and moved until a lead connected to the points and ground reads a break of resistance with a mulitmeter. That will cause a break in the field and excit the secondary of the coil. That's supposed to be what happens but given the way the thing runsI have something wrong in this. The spark is fine. It's got gas and air and does fire but not strongly. Compression is leaking someplace. Hopefully it's not the rings.

So, no adjustment for the valves. Maybe they need cleaning on the underside or refitting.

trouts

trouts2,

l'm sorry my example was on a briggs stratton, l would set the points when the camshaft opens the points the most (that should be close to TDC) then set  to .020 try that. the timing (DWELL ) can be changed a little by using a bigger gap or setting the gap a little early or late, it sounds like you have it a bit early which explian the pull back.

The Tecumseh manual says get the .020 set at TDC then move the piston to BTDC. That position backs the points arm off the peak of the dwell and the place where the points should just open.

if you set your points to the peak of the dwell (TDC) then your points will start to open just before before TDC and come off just after. the points if my opinion cannot start to open at BTDC its to early, you could check and see if the points are open before TDC because if they are its gonna spark. 

Niper99 wrote:

>>The Tecumseh manual says get the .020 set at TDC then move the piston to BTDC. That position backs the points arm off the peak of the dwell and the place where the points should just open.

 

Above, Yes.

 

>>if you set your points to the peak of the dwell (TDC) then your points will start to open just before before TDC and come off just after. the points if my opinion cannot start to open at BTDC its to early, you could check and see if the points are open before TDC because if they are its gonna spark.

 

Above, No, at lest not as I understand things.  The first paragraph conflicts with the second.

 

   The points opening at BTDC is what is called for so although early is not early enough to cause pullback. 

 

   To get the points to open right at BTDC there is a process to do that.  The metal enclosure that houses the points and is bolted down by two bolts.  The bolt holes are not round but oval and oval enough that the housing can be moved about 20 degrees.  The points are screwed to this housing so moving the housing affects the points. 

 

   After the .020 is set at the dwell the crank is rotated to BTDC and that is the spot the points should open not TDC.  To insure that happens the bolts of the housing can be loosened and the housing rotated slightly to get the point to just open at BTDC.  A mulitmeter is used to monitor the points.  The housing is rotated and just when the mutlimeter indicates the point opens is when the timing is right.  That’s at BTDC and when the start of the process of firing the fuel happens. 

 

   The spark creation is instantaneous with the opening of the points but the firing of the gas is not.  As the firing occurs in time the piston moving fast with a lot of mass.  Having the spark at BTDC is just the start of the explosion, not the middle, or finish.  They happen later.

 

  The explosion takes time and after the ignition spart the piston moves past BTDC.  There is still compression going on as the piston moves from BTDC to TDC.  The gas is starting to ignite but not completely ignited.  The piston gets to TDC, the compression complete and the gas completed exploding enough to drive the piston down for the power stroke. 

 

   That’s what should happen but since there is a lot of pull back something is wrong.

trouts2

All I know is that kick-back of the motor when starting is wrong,

Try top dead center, this engine only runs at 3500 rpm max, it does not need any advance anyway... it's not a  2002 Kawasaki cycle with smog junk on  it.

Do you have any Tecumseh motors that have been made in the last 20 years?  Maybe you can try one of the cdi units off of it, and put this painfull chapter behind us.

Good Luck,

Friiy