Craftsman no / intermitant spark

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  #1  
Old 01-07-08, 06:12 PM
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Craftsman no / intermitant spark

Hi guys, I need you're help on this one. Big Time!! Its a Snowblower with a 8 h.p.Tecumseh #143 736132 ser 5265D. It came to me as a run rough problem. I looked & it has a BRAND new carb on it, but runs like crap, misses, backfires from the carb, sometimes flames from the exhaust too. Checked & intermittent spark. (checked with an air gap tester @ .020") Replaced the already new plug & same. Pulled the flywheel & I find new points, condenser & a coil. I cleaned the points with alcohol ( not beer, but soon) & checked the point gap & tried. No good. The laminations the coil are on do not show any sign of the timing being moved & the flywheel key is good. Put in a known good coil from a blown eng, same. Changed the condenser from blown eng, same. The points seem to open & close when checked with an anolog ohmmeter. The stop wire is off of the stator the points are connected to & the flywheel magnets seem to pull good. I'm at a loss here. This thing should run!!. Sorry about the long post & I've probably tried other stuff too. I Need your help, Thanks Lots, Roger
 
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  #2  
Old 01-07-08, 06:44 PM
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Lightbulb Ideas.

Hi,
I would try new points and especially the condenser as you don't know how old they are.
Ensure the key way on the fly wheel is not sheared.
Check the valve clearances. I believe .007-.010" at 1/4 stroke past TDC. Check manual for this.
 
  #3  
Old 01-07-08, 07:47 PM
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It has new points & condenser & even a coil as stated in my post. Flywheel key is perfect. I even tried parts from an old engine that thru a rod & I have to assume the parts from the doner engine where O.K. if it flew apart!! The only thing I don't have is a doner flywheel, but the one on it pulls a screwdriver as well as any other I've seen. I have 125 + lb comp when using the electric start, I'm thinking the valves aren't an issue 'till I can get spark. I just tried it again & no spark / intermittant spark over a .010" gap. I'm not going to let this one beat Me!!! Thanks, Roger
 
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Old 01-07-08, 09:56 PM
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I wouldn't suspect the flywheel as a cause. The problem pretty much has to lie in the points, condenser, coil, plug, or the air gap/setting of the coil. I think you may need to check the setting on the coil. Does the crankshaft have a good bit of side play?
 
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Old 01-08-08, 03:47 AM
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Thanks, I don,t have anymore crank endplay than I,ve seen on any other. This unit has the coil under the flywheel. I dont see how I would adjust the coil air gap. I,v never ran into this much trouble. Thanks again, Roger.
 
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Old 01-08-08, 01:28 PM
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I would check my wiring on both the coil and the condensor for a rub through or pinch. Sounds like intermittent grounding. If the condensor wire is not routed correctly and gets pinched it can ground out. Also take a good look at the lower carb nut and screw. Make sure the holes, especially the small hole in the grooved out area on the brass nut are open and set the screw about 2 turns out from snug. I have seen too many people with the carbs set too lean this year.
 
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Old 01-08-08, 01:52 PM
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Thanks, I've looked @ the carb & as I said, It's BRAND new. The wiring is good under the flywheel, & I've had it apart so many times I think the flywheel knows how to come off by itself . The owner tells me it was like this before before the tune-up. Done @ a dealer. I'm sure it's something simple, I just can't seem to put my finger on it... Thanks for the help, guys. Roger
 

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  #8  
Old 01-08-08, 03:14 PM
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Cheese, Crank end play

Thanks, Cheese. I just tore it apart again & measured the crank end play with a dial indicator & magnetic base to be accurate. It's 0.022". A little high, but my manual states 0.027 max. Does that sound right?? The points still seem to operate O.K. with the crank @ max travel both ways. Thanks for the help, Roger
 
  #9  
Old 01-08-08, 03:50 PM
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Hopkins, from your answers to past questions, I know you know what you are doing. I don't mean to insult you at all.
I would closely check the kill switches to see if they are loose and are vibrating to ground on & off while running. I know it sounds simple & stupid, but this is often overlooked.
 
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Old 01-08-08, 06:43 PM
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I have done the same thing way too many times putting in what I "am sure" are good parts but it can make you go in circles. I work on a lot of older Ariens snowblowers and have resigned I will only pull flywheel ONCE. If I am pulling it, I install new points and condenser and set the timing. I know it can be a pain on the older Tec's but I am 100% convinced it is worth the effort. I would also be sure the "new" carb is the correct carb. Although it would have nothing to do with intemittent spark. For that I have on occasion removed spark plug boot, cut wire and installed a new end being sure to pierce wire. Although you swapped coils so that should not be an issue. Grounding could be the issue, so while installing new points and condenser carefully inspect coil wires. Had a break on a mower last summer I needed a magnifying glass to see but it was grounding.
 
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Old 01-08-08, 06:58 PM
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hopkinsr;
You know what you're doing so I can't add much, however below is a good link to ignition trouble shooting, ignore the outboard caption. Have a good one. Geo
http://assets.fluke.com/appnotes/ele...r/B0271b_u.pdf
 
  #12  
Old 01-08-08, 07:10 PM
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You measured end play, but I was asking about side play. I doubt it's the problem, but it could be. I've seen some engines with so much side play that it drastically affected the coil air-gap, causing ignition problems, but it is rare for one to be this worn. Usually it happens when there is a fin or two broken off the flywheel, causing it to be out of balance, and then it wears the bushing accordingly.

The timing on that engine is involved to set, but I think it would pay to go ahead and check it...especially since you mentioned you already have a dial indicator. Follow the directions in the manual (got one?) and see what that nets you.

Also, double check the contact surface on the points. Run an emery board across the areas to be sure there isn't a spot of carbon or foreign material causing an intermittent resistance across the points.
 
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Old 01-08-08, 09:25 PM
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Thanks to guys

Thanks Guys, Indy, I have the entire kill circuit disconnected, If this thing will run, the owner won't be able to turn it off, altho @ this time, that would be a good thing!! S.M.E.guy,That is a great idea Just because they are new does't mean there installed properly. I'll have a closer look. Geo, Thanks for the link. I'm going to save it for future referanace.There is a lot of info there. Cheese, Sorry I didn't check the side play. Read you're post wrong, I'll check the side to side movement tomorrow & get back to you. I have to thank all of you for you're help & tolerence while I fight thru this, Thanks, Roger
 
  #14  
Old 01-09-08, 02:12 AM
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I'm leaning toward a stator that is off time. Here is a link to Tecumseh service manuals, http://toprake.com/index.php?module=...position=11:11 refer to the 692509 manual for yours and follow the prodecures for timing the stator. I believe the manual shows a special, spark plug hole inserted dial indicator and if you have only a standard dial indicator you will then need to remove the cylinder head in order to mount your dial indicator to one of the head bolt holes. Further along in the manual you will find the specific specifications for your engine and further yet in the manual you will find the Craftsman cross reference in order to change over the 143 model number to a useable Tecumseh model number, which I've done for you and is a HM80-155247J. Use the HM80 (and possibly the "J") to find your timing, BTDC spec.
 
  #15  
Old 01-10-08, 05:58 PM
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It Runs Again!!! Thanks to all!!!

Thank you to everyone for all the help!! I changed the entire stator assy last night, transfered the new parts to it & set the points & timing ( I do have the tool to set it thru the spark plug hole) & this thing starts well & runs like a top. I can't see anything wrong with the stator or the laminations for the coil, as that's about all that's there after you take the other stuff off. I tried it again tonight & it's GREAT!! I can't see there being any thing with the stator or laminations?? I'm almost thinking there was an issue with the points that I couldn't see. They apeared clean & I cleaned them again. I'd really like to see a fault that caused my problem so I can look for it next time if it happens again, Thanks guys, I owe you LOTS!!!....Roger
 
  #16  
Old 01-10-08, 07:21 PM
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Great news Roger!, As I had said, been there myself, just toss the old ones in the circular file and tell yourself they were possessed!
 
  #17  
Old 01-11-08, 12:49 AM
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Good news! I know what you mean about wanting to know what the problem was. I have cut into sealed units, broken open electrical components, etc... just to see what went wrong inside. For some reason, I always want to know "WHY". Just one of those hang-ups that mechanics have I guess, lol.
 
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