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B&S just won't start


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#16 Sawdust OFFLINE  

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Posted March 07, 2015 - 11:24 PM

On this Nova module thing.....you have right magnets on flywheel to use it? Seems there are one, two and reversed magnets depending on year or engine and systems. Mine had wrong magnets and would not fire right on a module I put in AND, also not on a coil with the electronic bump on it. Had to find orig type coil number.

I have the one magnet. It ran great when I first installed the Nova II. It wasn't until I put everything back together it gave me problems.



#17 Sawdust OFFLINE  

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Posted March 07, 2015 - 11:31 PM

All great suggestions!

 

I had this issue on my 16 hp Briggs, I needed it for snow plowing and didn't want to take everything apart to get to the mag so I put a battery ignition on it. I took the coil and condenser from a Kohler K engine, at first I used the magneto ignition switch and wired in a toggle switch for the 12 volts to the coil + terminal ( I did this all during a snow storm). But have since put a non magneto ignition switch in and eliminated the toggle.

 

It was a very easy install, and the engine runs great!

I'm starting to wonder now about my ignition switch. When I first got this the original one was corroded & I jumped it to start. It ran well after I installed the Nova II. I have since replaced the corroded switch with a new one from MTD with the same part number from the manual. Maybe I will take the yellow kill wire off the switch to see if this makes a difference. My wiring was a mess when I first got this tractor. I really don't see how this would be a problem since I'm getting a good spark though.



#18 chris m OFFLINE  

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Posted March 08, 2015 - 12:26 AM

I'm starting to wonder now about my ignition switch. When I first got this the original one was corroded & I jumped it to start. It ran well after I installed the Nova II. I have since replaced the corroded switch with a new one from MTD with the same part number from the manual. Maybe I will take the yellow kill wire off the switch to see if this makes a difference. My wiring was a mess when I first got this tractor. I really don't see how this would be a problem since I'm getting a good spark though.

unless the key is sheared and the timing is off? Then you would still have spark just not at the right moment. I had an old 11hp Briggs (vertical shaft) that was forever shearing the flywheel keys. Now that I am running Battery ignition on my 16, shearing keys won't make a difference in the timing anymore. :dancingbanana: If it was a restore then I would go original magneto, but this is just a worker. :D


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#19 New.Canadian.DB.Owner OFFLINE  

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Posted March 08, 2015 - 09:53 AM

To my mind, it is more significant that you have a dry plug, gas pooling & are missing an intake gasket.   If there is fuel pooling in the carb, and air is moving over it, fuel will end up in the cylinder & on the plug, even if the main & idle jets are plugged.  If your plug is dry, you can't be sucking air through the carb and into the cylinder.  I would spray carb cleaner around the carb/cylinder joint & give it a spin.  You might also want to put your hand over the carb air inlet & give it a spin to see if you are sucking air into the carb. 


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#20 HDWildBill ONLINE  

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Posted March 08, 2015 - 10:14 AM

Reading through all the this, I think Ben has the best idea.  Isolate they systems and figure out which system is not functioning correctly.  Like Ben suggested spray some starter fluid down the throat of the carb and if it starts then the problem is in the fuel system some where.  If it doesn't then the problem is either in ignition or valve train.  If you spray starter fluid down the throat and then pull the plug and it is not wet then I would suspect something on the intake or intake valve.  If it appears to be the ignition then try starting it with the engine disconnected from the tractors electrical system.  It it starts then you know the problem is with the tractor, if it doesn't then the problem is with the engine.

 

I how ever suspect the problem will be with something you have done during the tear down and rebuilding process.  A crossed wire, bad switch, bad ground (not just the module), loose connection etc. 


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#21 Bruce Dorsi OFFLINE  

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Posted March 08, 2015 - 03:43 PM

 16 HP B&S model 326431

* Installed Nova II module tractor ran very good no problems at all. Electronic components can fail intermittently, despite manufacturer's claims!

* I never removed the flywheel.  There is a good possibility the key is partially sheared.  ....Any indents in the key are enough to affect timing - it does not have to be sheared completely.

* When I installed the coil I put three layers of painters tape between the coil & Magnet because of no business card handy. The air gap should be .010"-.014" for this engine.  ...The air gap will affect ignition timing.

* First time start up last week, hard to start, back fired a few times but started several times & ran well. Backfiring could have caused the flywheel key to shear.

* Tried a few days later but wouldn't start just backfired through muffler a few times. Backfiring through the exhaust is caused by late ignition timing (Nova module, magneto air gap, or flywheel key), or exhaust valve not seating (burnt valve, loose valve seat, carbon build-up, or improper valve lash).   ....The intake valve lash should be .007"-.009".  ...The exhaust valve clearance should be .017"-.019".

* Rebuilt carb still won't start. While turning over I open & close fuel/air mixture valve, when I get around 2 1/2 turns out it starts back firing again. With the mixture valve closed, no fuel mixture is getting into the cylinder.  ....The large opening is allowing fuel to get into the combustion chamber, allowing the engine to backfire.

 When I turn it to 1 1/2 turns out no back fire. But it still doesn't run!  .....This setting may not be open enough to overcome a vacuum leak.

* I have hot blue spark Always?  .....While the plug is installed?  ....At the proper time?

* Full tank of gas (990 owners know about having no less than 2/3rds tank) Clean, fresh gas? ....No water in gas?

* Float level was adjusted to level when turned upside down. That's correct.

* Gas in carb.

* Plenty of compression. How did you determine that?  ...Does it forcefully blow your thumb off the sparkplug hole during the compression stroke?

* I can see the intake valve going up & down as normal.  ....That does not confirm proper seating of the valve, correct valve lash, or correct valve timing.

* Pulled the exhaust pipe off & could see the exhaust valve stem going up & down as normal.  ....That does not confirm proper seating of the valve, correct valve lash, or correct valve timing.

* When I pulled the spark plug it looked dry not flooded as expected concerning the amount of gas in carb. ....A vacuum leak or insufficient compression will prevent fuel mixture from being drawn into the cylinder, as well as a carb fault.

* I put a few drops of gas in the intake then put the plug back on & it back fired a few times then nothing still wouldn't start. ....Backfiring, again indicates ignition does fire, but is it constant and at the correct time?  ....Does it always backfire though the exhaust, or does it sometimes backfire through the intake?  ....If only through the exhaust, see my comment above naming possible causes.  .....If it backfires through the intake sometimes, and exhaust sometimes, I would be 99% sure your problem is in the ignition. 

* I blocked the drive shaft & tried to turn the engine at the pulley in the front to see if a pin had sheared. ...This will not detect a bad flywheel key.

* I have two concerns about what I done:

     1. When I installed the carb there was no gasket between the cylinder & metal plate. The only gasket is the thick one between the carb & manifold pipe.  There needs to be a gasket on both sides of the metal plate, as well as a gasket between the manifold and carb. 

     2. Could the three layers of painters tape be a problem instead of the typical gauge of a business card? ...The correct air gap spec is named above.  ....Too much gap is as bad as not enough gap!

 

My thoughts are what would keep a large amount of gas to not be in the cylinder head area when I removed the plug. ...There should never be large amounts of liquid gas in the combustion chamber!  ....Too much liquid will not ignite, and is known as "flooding" an engine.

 I made sure I cleaned everything & air blasted all openings when I rebuilt the carb. Maybe I'll take the carb off & clean again to make sure I have no blockage.  ...If you're sure you did it correctly the 1st time, and your fuel is clean with no water, what would have changed?  ...I would be more suspect of the missing intake gasket.

If I haven't sheared a key & didn't remove the flywheel is there something else that could cause the timing to be off. ...Yes, as described in above comments.

 

At this time, my only other suggestion is to disconnect the wire that grounds out the ignition, at the engine.  ....Sometimes safety interlock or key-switch problems can cause ignition problems to occur.  ....If the engine starts and runs without backfiring, most likely the problem is in this area.

 

My thoughts and comments are in red above.

 

Without further testing, we are all just naming possibilities!

 

Don't get disgusted, just rule out one possibility at a time!  ....And, don't make assumptions that anything is correct!

 

edited for spelling.


Edited by Bruce Dorsi, March 08, 2015 - 03:51 PM.

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#22 Sawdust OFFLINE  

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Posted March 08, 2015 - 08:08 PM

Thanks Bruce Dorsi that's a heck of an outline you done. I want to thank everyone for your comments & suggestions. Like most on this forum someones problem is like everyone else's problem until it's solved.

 

Well guys I have some good news, it's a runner! Sunday's between church, family & friends the day is pretty much full. I couldn't stand it when I got home I went out & cranked it hoping for a miracle but no go again. I dreamed last night my needle valve was bent like a fish hook but it wasn't of coarse. I did take the needle valve & main jet out to drain the gas out of the bowl. I took a small empty plastic bottle with a long nozzle on it & pushed it into the carb opening where the main jet goes & gave it a few good blasts of air. I put everything back together & within two cranks it fired right up like it had been running all day. It actually scared the crap out of me because I wasn't expecting it to run & I still had the muffler off.  :firejumper:

 

I let it run for a couple of minutes then I adjusted the carb & oh was it a sweet sound. I let it cool off & went back out & it fired right up again. I have a 1"  90 degree conduit elbow that has a 1 1/4" OD  I'm using coming off the engine. I recently bought a Stanley IH-1 muffler stack for it. When it was running a stuck a 3' section of a 1 1/2" tubular chain link fence rail on top of the elbow & I have to admit the straight exhaust sounded pretty good. 

 

Once again thanks to everyone for your help & I hope this thread helps someone else because I don't think you guys left out any possibilities this could have been.  :wave:


Edited by Sawdust, March 08, 2015 - 08:09 PM.

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#23 HDWildBill ONLINE  

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Posted March 09, 2015 - 10:09 AM

Glad you got it running.


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#24 KennyP ONLINE  

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Posted March 09, 2015 - 12:10 PM

Congrats, Jim! We need a pic of that bottle so we all can have one stashed away for issues like this!


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#25 Sawdust OFFLINE  

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Posted March 10, 2015 - 11:31 AM

Congrats, Jim! We need a pic of that bottle so we all can have one stashed away for issues like this!

Here ya go Kenny as requested. These are hair color bottles my wife uses once in awhile. I have her save them for me. Just a side note to prove how strong that hair color is I have kept gas, oil, & the trans fluid with acetone mix in these bottles & have seen no melt down at all. 

20150310_121603.jpg


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#26 TAHOE ONLINE  

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Posted March 10, 2015 - 11:36 AM

... Just a side note to prove how strong that hair color is I have kept gas, oil, & the trans fluid with acetone mix in these bottles & have seen no melt down at all. 

attachicon.gif20150310_121603.jpg

 

have you seen what it does to their hair, gas and acetone are no match  :bigrofl:  :bigrofl:


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