Gremlins in 7HP Briggs on Husqvarna W/B

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Old 04-21-16, 04:08 PM
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Gremlins in 7HP Briggs on Husqvarna W/B

Another case of gremlins invading lawn mowers!
7HP Briggs OHV, will start and run ok with occasional misses but will go until you shut it off. It will start right back up, but if you let it sit for 5 mins or so, it will not start, only puff a bit of smoke either out the carb or the muffler.
Originally I tested for spark and did not see any, so I disconnected the kill wire at the cable kill spot. Same result. So I order a coil, install and test again and am able to repeat the no start. Chased it around another few hours and decided that maybe a bad coil, so coil no.3 basically, two new ones and still able to reproduce. While I had it apart I went so far as to replace the kill wire as well. Still we test for spark with inline, and grounding a plug with test lead...neither method shows spark, HOWEVER, plug the lead back on the plug and voila it will start. Test for spark, no spark, plug it in, fires right up...!!!!!????
During the no start it is still getting fuel to the carb and into the engine, fuel cap fuel lines etc. all ok.
I have it down to the head which will come off in the morning....valve seat loose, sticking valve..???
 
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Old 04-21-16, 04:26 PM
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Just an IMHO it must be the ignition since you get a start with the reattaching of the lead wire to the plug. If you put the tester inline and the plug grounded with no spark, then either the voltage can't jump two gaps (plug gap and tester gap) or the plug or tester may be have a problem.

You might try grounding the tester without the plug and see what you get.

Or you may just need a bigger hammer.
 
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Old 04-21-16, 04:30 PM
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Also tried using a test lead, connection to the hex on the spark plug other end to ground. (this is my main way to check for spark, no guessing) as well as the old fashioned way, holding the plug to ground. I personally do not trust inline testers as they have foiled me before, however, in this case we did test the inline tester and it is accurate on other engines.

Oh, and trust me I have a bigger hammer handy lol!
 
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Old 04-21-16, 05:14 PM
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I know magnets can loose their juice, but I have never seen one on a flywheel...anyone else?
 
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Old 04-21-16, 08:59 PM
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Never seen it and if it was the problem, it wouldn't come and go. Either the magnet is strong enough or it isn't. With no spark on the tester, but then it starts when you connect it to the plug, that doesn't compute. Does this have autochoke?
 
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Old 04-22-16, 05:16 AM
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It has a primer, which is only needed when cold.
 
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Old 04-23-16, 09:04 AM
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Went ahead and pulled the head and found nothing out of the ordinary, lapped the valves and polished the stems and it sure ran alot smoother...until it didn't run

Last resort was to throw another carb at it, only reason being is when I first inspected and cleaned the original carb there was a welch plug laying in the bowl. I installed it and peened both plugs, which are still in place. However, so far, the carb is doing the trick, not able to repeat the no start. Going to give it another day of trial before I declare success though....
 
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Old 04-28-16, 05:26 PM
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Once again, a new carb solves the issue.
 
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