Jump to content

Nominations for Tractor of the Month
Garden Tractors and Parts on eBay



Photo
- - - - -

B&S just won't start


  • Please log in to reply
25 replies to this topic

#1 Sawdust OFFLINE  

Sawdust
  • Senior Member
  • Member No: 36549
  • 4,521 Thanks
  • 2,829 posts
  • Location: Butler, Kentucky

Posted March 07, 2015 - 07:14 PM

I'll try to eliminate all the ideas so I'll list what I have tried but first a little history.

1976 MTD 990 16 HP B&S model 326431

* When first purchased low to no spark due to bent points push rod & damaged cam lobe.

* Installed Nova II module tractor ran very good no problems at all.

* Dismantled tractor to rebuild, repair, sand blast & paint.

* I never removed the flywheel.

* When I installed the coil I put three layers of painters tape between the coil & Magnet because of no business card handy.

* First time start up last week, hard to start, back fired a few times but started several times & ran well.

* Tried a few days later but wouldn't start just backfired through muffler a few times.  

* 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. When I turn it to 1 1/2 turns out no back fire.

* I have hot blue spark

* Full tank of gas (990 owners know about having no less than 2/3rds tank)

* Float level was adjusted to level when turned upside down.

* Gas in carb.

* Plenty of compression.

* I can see the intake valve going up & down as normal.

* Pulled the exhaust pipe off & could see the exhaust valve stem going up & down as normal.

* When I pulled the spark plug it looked dry not flooded as expected concerning the amount of gas in carb.

* 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.

* I blocked the drive shaft & tried to turn the engine at the pulley in the front to see if a pin had sheared. 

* 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.

     2. Could the three layers of painters tape be a problem instead of the typical gauge of a business card?

 

My thoughts are what would keep a large amount of gas to not be in the cylinder head area when I removed the plug. 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 I haven't sheared a key & didn't remove the flywheel is there something else that could cause the timing to be off. 

 

I wanted to rebuild this engine later but not now because it ran so well before. I wanted to get some seat time on this for awhile. It may not run but it sure is perdy. Any help please it would be greatly appreciated. I have exhausted everything I know to do.

If you need to research anything here is my rebuild. I warn you it's lengthy.

http://gardentractor...d-up-a-mtd-990/



#2 boyscout862 ONLINE  

boyscout862
  • Senior Member
  • Member No: 8923
  • 9,770 Thanks
  • 7,537 posts
  • Location: N.E. Connecticut

Posted March 07, 2015 - 07:22 PM

Could the flywheel key have partially sheared? Check the magneto gap with a feeler gauge. Can you check the valve lash? Any of these can mess up the timing which will make the engine difficult to start and run poorly. Check out the engine manual. It will have a troubleshooting guide. Good Luck, Rick


  • Sawdust said thank you

#3 Bolens 1000 ONLINE  

Bolens 1000

    DR. Bolens

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 7
  • 12,681 Thanks
  • 17,202 posts
  • Location: Western NY

Posted March 07, 2015 - 07:30 PM

Have you put an inline spark tester on the engine, many times a blue spark is present outside the engine but under compression its a different story.


  • boyscout862 and Sawdust have said thanks

#4 glgrumpy OFFLINE  

glgrumpy

    Getting Out!

  • Senior Member
  • -GTt Supporter-
  • Member No: 8360
  • 6,660 Thanks
  • 6,474 posts
  • Location: Huntington, IN 46750 North East in State

Posted March 07, 2015 - 07:30 PM

I've had these and similar problems. One thing to check is that little breaker box thing hanging off the bar that goes from dash to grill as a support. It's usually hanging underneath the bar, back nearer dash. One I had, I used to have to jump that with a wire to make work. I later pulled it and put in a fuse block for spade fuses. But, you say good spark.  I've also had to replace ignition switches on these that are intermittent in operation. They are easy to find generic type, just need to make sure for Magneto ignition. Safety switches on yours?  Usually one for the pto lever and sometimes for the pedal down below. Seat switch?  Again tho, you say you have spark. Tried a diff brand spark plug, not a champion?  Maybe not firing when screwed in? Two of mine didn't want to start with throttle half-way open, but would on idle only, try that?  One I had would change tune all the time while running around. I'ld set richter to smooth it out and later have to open more or close again to set high speed. Never did like that tractor, ha!


  • boyscout862 and Sawdust have said thanks

#5 lyall ONLINE  

lyall

    Tractorholic

  • Senior Member
  • -GTt Supporter-
  • Contributor
  • Member No: 2180
  • 1,747 Thanks
  • 1,398 posts
  • Location: State Center, Iowa

Posted March 07, 2015 - 07:44 PM

the needle valve might be one of your problems

check the seat of the needle valve and clean the needle valve and seat 

then blow out the gas line for the carb

 

have you checked the gas line?

if you have a tank filter/screen it can cause problems, too


  • boyscout862, HANKG and Sawdust have said thanks

#6 classic ONLINE  

classic
  • Senior Member
  • Member No: 52970
  • 3,455 Thanks
  • 1,605 posts
  • Location: New York

Posted March 07, 2015 - 08:02 PM

Definitely try another spark plug first.
  • boyscout862 and Sawdust have said thanks

#7 jabelman OFFLINE  

jabelman
  • Senior Member
  • Member No: 38843
  • 1,472 Thanks
  • 1,134 posts
  • Location: nj

Posted March 07, 2015 - 09:02 PM

Unbolt the head check the valves and gasket?
  • Sawdust said thank you

#8 superaben OFFLINE  

superaben
  • Senior Member
  • Contributor
  • Member No: 11204
  • 7,664 Thanks
  • 5,677 posts
  • Location: Shenandoah Valley, VA

Posted March 07, 2015 - 09:08 PM

Jim, I've been thinking about this one for a little while.  It has to be something simple.  Is your Nova module grounded well?  I can't remember if it was the Nova module or the Stens Megafire that I fought and fought with similar issues before I realized that it didn't have a great ground.

 

Do you have a new spark plug or an old one?  What type of spark plug are you running?  classic is right.  That can make a huge difference.

 

Adjust the carburetor to 1 1/2 turns on the main adjustment and 1 1/4 on the idle side.  2 1/2 is far too much.  The engine won't like it. 

 

Is there gas puddling in the bottom of the carburetor or not?

 

Ben W.


  • boyscout862, HANKG and Sawdust have said thanks

#9 petrj6 ONLINE  

petrj6
  • Senior Member
  • -GTt Supporter-
  • Contributor
  • Member No: 53717
  • 3,808 Thanks
  • 2,219 posts
  • Location: petersbrgh ny

Posted March 07, 2015 - 09:17 PM

:ditto: :iagree: change the plug, one more thing to look at are the valves. check the clearances and make sure they are seating correctly.  I rebuilt a single cyl briggs and didn't get the valves correct the first time around and it did the same thing.  drove me nuts for a while before I got that figured out.


  • boyscout862 and Sawdust have said thanks

#10 TheFarm2004 OFFLINE  

TheFarm2004

    Member

  • Senior Member
  • Member No: 642
  • 129 Thanks
  • 124 posts
  • Location: Lanesville, Indiana

Posted March 07, 2015 - 09:36 PM

I have a '74 990 with the Nova II, that I had to  replace the flywheel key 4 times. Every time the carb messed up and it backfired the key would be slightly dented. Parked that one and bought a 73 model 2 years ago, never had the points cover off of it and it starts every time.

David


  • boyscout862 and Sawdust have said thanks

#11 Sawdust OFFLINE  

Sawdust
  • Senior Member
  • Member No: 36549
  • 4,521 Thanks
  • 2,829 posts
  • Location: Butler, Kentucky

Posted March 07, 2015 - 10:07 PM

I appreciate you all as most have mentioned before. I knew I would get a good response so I will try to respond to each.

 

Boyscout862- checking the valve lash & the key will be something I'll consider if all else fails.

 

Bolens1000- I have heard of this but never had that problem before. I know it exists but never could understand why a plug would fire outside the cylinder but not inside under compression. I guess it's a resistance thing from the compression.

 

GL- My circuit breaker is good, I installed all new safety switches, & new correct ignition switch. As you mentioned these would not allow a spark or starter to work. I did notice like you mentioned when it was starting good it preferred a small amount of throttle rather than full...weird.

 

Lyall- Cleaning & blowing out the carb is one of the things I will do next once I check the spark plug. I have a freshly clean tank with no deposits, new filter & new fuel lines.

 

Classic- I tried one other plug from another tractor that I knew worked but didn't help. I will be picking up another plug to make sure.

 

Jabelman- After I cleaned the engine I took the head off. It was fairly clean just minor deposits. I did notice it had a .20 over stamped on top of the piston so it's been bored. I did notice when I was wiping off the top of the piston it moved slightly from side to side like looking down on the face of a clock 12 to 6, 3 to 9 etc. I'm not sure if this normal, I was concerned but not worried about it since it ran so good before & never smoked. I did use the old head gasket because it looked fairly new but I will be replacing that too if all else fails.

 

Superaben- My module is grounded good. Most of these are mounted on the engine don't know why I guess it's just convenient. I mounted mine under the dash where it would be cooler. I have searched to see if the distance from the engine makes a difference. I took it off & mounted right on top of the engine but still no start. I'm running an Autolite ( sorry Champion guys). I will be trying a new one. I started out with the typical carb adjustments but nothing worked. Yes gas did puddle in the bottom of the carb but only after I cranked it for awhile.

 

Petra6-I'm thinking if the little stuff don't work I'll check the valves.

 

TheFarm2006- That's what I'm worried about. Another member Vxrider had the same thing happen to him...kept shearing keys. If I rebuild this I'm going back to the points.

 

I hope I didn't skip anything. I probably won't be at it again until Monday or Tuesday except in my dreams. You all have come up with some possibilities. I'm hoping it's something simple but if not I guess I'll just start taking things apart. I was happy using the Nova II module mainly because it worked. But I just can't seem to wonder how such a tiny little thing can make such a huge difference. If I do rebuild this engine I think I'll replace the cam & go back to the old fashion points & condenser....something I can see work  :D  Thanks again to everyone.


Edited by Sawdust, March 07, 2015 - 10:12 PM.

  • boyscout862 said thank you

#12 glgrumpy OFFLINE  

glgrumpy

    Getting Out!

  • Senior Member
  • -GTt Supporter-
  • Member No: 8360
  • 6,660 Thanks
  • 6,474 posts
  • Location: Huntington, IN 46750 North East in State

Posted March 07, 2015 - 10:18 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.


  • Sawdust said thank you

#13 superaben OFFLINE  

superaben
  • Senior Member
  • Contributor
  • Member No: 11204
  • 7,664 Thanks
  • 5,677 posts
  • Location: Shenandoah Valley, VA

Posted March 07, 2015 - 10:38 PM

Jim, humor me and try a Champion J8C on that engine.  With condenser and points, that engine loves a J8C.  I'm not for sure if a Nova would change that. 

 

Old Briggs do like Champions.  J8C was the original spec for that series engine.  But I am also a Champion guy.  (Yes, George, we won't derail this over spark plugs again.  :dancingbanana:

 

Get yourself a can of spray carburetor cleaner (ask for 2+2, most auto stores sell that behind the counter) and make sure the engine is not flooded.  Do this first with a fresh spark plug.  Spray a little taste of 2+2 into the carburetor air intake and see if the engine starts on that.  If it does, you have a fuel problem.  If it doesn't, chances are you have ignition woes. 

 

Ben W.


Edited by superaben, March 07, 2015 - 10:38 PM.

  • HDWildBill and Sawdust have said thanks

#14 chris m OFFLINE  

chris m

    Tractorholic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 8148
  • 3,277 Thanks
  • 4,033 posts
  • Location: Charlestown,Rhode Island

Posted March 07, 2015 - 10:39 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!


  • Sawdust said thank you

#15 Sawdust OFFLINE  

Sawdust
  • Senior Member
  • Member No: 36549
  • 4,521 Thanks
  • 2,829 posts
  • Location: Butler, Kentucky

Posted March 07, 2015 - 11:21 PM

Jim, humor me and try a Champion J8C on that engine.  With condenser and points, that engine loves a J8C.  I'm not for sure if a Nova would change that. 

 

Old Briggs do like Champions.  J8C was the original spec for that series engine.  But I am also a Champion guy.  (Yes, George, we won't derail this over spark plugs again.  :dancingbanana:

 

Get yourself a can of spray carburetor cleaner (ask for 2+2, most auto stores sell that behind the counter) and make sure the engine is not flooded.  Do this first with a fresh spark plug.  Spray a little taste of 2+2 into the carburetor air intake and see if the engine starts on that.  If it does, you have a fuel problem.  If it doesn't, chances are you have ignition woes. 

 

Ben W.

Sounds like a plan Ben if this works you'll be the first to know. If I have time tomorrow I'm going to pick up a new plug & the carb cleaner you mentioned. 


  • superaben said thank you




Top