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RUNS ROUGH AFTER 1/2 HOUR

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8N238409

10-16-2000 20:10:45




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My new, old 1949 8N starts with some difficulty, runs ok for a while then begins to run more and more rough until its basically sputtering with out any power, barely enough to limp back. This generally occurs after a half-hour or so of running. The manifold & exhaust was replaced last month, and Spark plugs last week. The air filter door is stuck shut. So I shop vac the slots on the door and changed the air filter oil. Any theories.

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Kev8N

10-17-2000 18:44:05




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 Re: RUNS ROUGH AFTER 1/2 HOUR in reply to 8N238409, 10-16-2000 20:10:45  
You might want to check your point gap. I've have my points slide together and act as you describe. Worked great for about an hour.. then lost power, missed, and backfired.

Good luck and post back the results.

Kevin



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Dave 2N

10-17-2000 04:09:16




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 Re: RUNS ROUGH AFTER 1/2 HOUR in reply to 8N238409, 10-16-2000 20:10:45  
In my experience, this is a coil problem. And don't automatically assume that a new coil is a good coil. I went nuts on my JD 70 tring to get it to keep running. Put on a new coil and it still shut down. Tried another new coil from another supplier and we're OK now.



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Salmoneye

10-17-2000 02:17:56




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 Re: RUNS ROUGH AFTER 1/2 HOUR in reply to 8N238409, 10-16-2000 20:10:45  
If you have replaced the manifold, we can rule out a hairline crack that opens when hot.
The 2 easiest and most common other problems that come to mind are the key switch (notorious for this problem) and the coil (another likely suspect).
Next time she acts up, jumper around the switch. If this cures it, replace the switch. If it is not the switch, try a known good coil (I have seen brand new ones that were no good). The coils are known to be the weak link in the front-mount distrbutor setup. They get hot and boil the tar insulation between the windings and short out decreasing the sparks and causing just the symptoms you are seeing.
Try jumpering the switch first, and post back what you find...

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8N238409 in Indiana

11-06-2000 15:23:43




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 Re: Re: RUNS ROUGH AFTER 1/2 HOUR in reply to Salmoneye, 10-17-2000 02:17:56  
Since your reply last month, I've checked the manifold bolts to make they were properly torqued and tightened up the muffler pipe/manifold clamp. Installed and new key switch, push button switch, solenoid because it started to smoke, coil, distributor cap, rotor, pts. condensor, plug cables, rebuilt the carb. Ran a bit better until it I tried to restart it. Then the battery ran low. Put in a new 6V battery and it cranked much stronger but no go. Checked it over and found one of the new plug cables got worn thru by being too close to the fan belt. Replaced it. Cranked strong again then, nothing, not even a crank. I'm getting very frustrated. Is the new coil and/or distributor cap a likely culprit?

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Gene

10-17-2000 00:18:59




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 Re: RUNS ROUGH AFTER 1/2 HOUR in reply to 8N238409, 10-16-2000 20:10:45  
Check the fuel tank cap. If the cap is not venting the tank properly, the fuel will not be able to flow to the carb.



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Salmoneye

10-17-2000 02:13:48




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 Re: Re: RUNS ROUGH AFTER 1/2 HOUR in reply to Gene, 10-17-2000 00:18:59  
The cap is not supposed to be vented as the tank itself has a slight 'crown' with a small vent hole in it.
If the cap is tight, this hole may be plugged.



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bg

10-16-2000 20:35:52




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 Re: RUNS ROUGH AFTER 1/2 HOUR in reply to 8N238409, 10-16-2000 20:10:45  
Most often, such a syptom is indicative of a bad coil. Once the coil heats up(resistance)it loses its capacitance. It must have a high enough capacitance to convert a low voltage(from battery) to a very high voltage(to spark plugs). The easiest way to check the coil is to replace it. Another possibility, if you have eliminated the coil and fuel problems, is a faulty keyswitch.



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MadMax

10-16-2000 20:22:50




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 Re: RUNS ROUGH AFTER 1/2 HOUR in reply to 8N238409, 10-16-2000 20:10:45  
First check the fuel delivery rstricted filters maybe? If all is clear to the carb there is a small filter in that elbow fitting that goes into the carb (unless someone cut it off) see if that's clogged, P.S. carefull with the elbo it's made of brss.



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