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Paul_B

Missing 16hp briggs when warm...FIXED!!!

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Paul_B
UPDATE: Thanks for all the help! I installed a new coil and a universal electronic ignition module and I mowed my entire yard w/o a problem. The real culprit was a badly worn points actuator rod/bushing that caused my point gap to wander. The only thing I did like about the battery ignition was the way it started. *************************************************************** I've got a rebuilt 16hp briggs on a 917 allis chassis. After 30-45 minutes of mowing it starts missing and will then only run at low RPM's. I don't get any backfires it just does seem to "hit". It's been converted to a battery points ignition a while back. After it's allowed to cool it'll run just fine for 30-45 minutes again. This motor had been running perfectly last year and up to a couple weeks ago. Today after it acted up, here's what I tried: 1) Disconnected fuel line from carb and I was greeted with a nice flow of fuel. 2) Checked battery voltage (about 14V). 3) Swaped out the condensor for one out of an old BB mopar distributor I had. No difference. 4) Point gap checked out at .020" 5) Sprayed carb cleaner in carb and didn't seem to make motor smooth out at high rpm's (checking for lean condition). 6) Sprayed carb cleaner around carb and intake (checking for vacuum leaks) 7) Check ignition coil resistance 2.5ohms primary and 11.3k ohms secondary. 8) Before mowing today I had installed a new spark plug. Any ideas?

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HubbardRA
If none of the other things work, try checking the clearance on your exhaust valve. I have fixed a couple engines that would cut off after running for a while, that had almost no clearance in the exhaust valve. After the engine got hot enough, it would run very rough. Valve stem gets longer as it heats up. Put clearance in the valve, and engine ran fine.

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Paul_B
Update: I still have the problem, but here's what I've tried. 1) Installed new external automotive style coil to replace old automotive coil. No change. 2) Checked exhaust and intake valve lash. Intake lash was around .008" and exhaust was around .010-.011". A book I have says exhaust lash should be .017-.019". Would this be the problem?!? -How do you grind off tip of valve and is there any way to remove the valve w/o the briggs valve spring compressor? 3) Checked compression after it acted up and got 115 psi. 4) Cooling fins are clean.

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tec2484
I would thing that the ext valve could be the problem then. If not, Have you got a resister on the coil? If not they will burn and pit the points and .020" on the gauge will become more like .025".

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HubbardRA
I usually just put a double sided file between the valve tip and the follower and file till I get the necessary clearance. The reason that clearance is needed on valves is to allow for temperature changes. Remember that as a valve gets hotter, the stem gets longer and this makes the clearance decrease accordingly.

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MPH
Though it can test your will power, it is possible to remove the valves using two screw drivers to compress the spring. Reinstalling can take some time if your cards aren't 'right' for the day. This is the only way I've ever done them, sometimes it takes 5 min, sometimes, well, we won't go there.

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msiebern
quote:
Originally posted by MPH
sometimes it takes 5 min,
30 sec. to install . . . . . . . . . . . . . .after spending 45 minutes numerous times finding the keepers after their latest trajectory!:D

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ehertzfeld
quote:
Originally posted by msiebern
quote:
Originally posted by MPH
sometimes it takes 5 min,
30 sec. to install . . . . . . . . . . . . . .after spending 45 minutes numerous times finding the keepers after their latest trajectory!:D
Been there, done that!:D

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stevenj
Can't you check the compression cold and then again when it's hot and the engine is missing to see if the compression has dropped. If the valve is indeed slightly open the compression would be lower. Right?

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firefoxz1
quote:
Originally posted by Paul_B
Update: I still have the problem, but here's what I've tried. 2) Checked exhaust and intake valve lash. Intake lash was around .008" and exhaust was around .010-.011". A book I have says exhaust lash should be .017-.019". Would this be the problem?!? 3) Checked compression after it acted up and got 115 psi.
The valve may float a little when running so yes it may be the valve clearance even though you had 115psi compression when checked. I would take Amblers suggestion and plug the oil drain hole in the spring housing. wouldn't want to tear the engine out because a keeper went into the crankcase.

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Paul_B
Tonight before mowing I checked my point gap and it was really tight. I regapped and mowed for a while before it acted up. I then checked the point gap and it had opened up. I regapped and then it ran great again. I did have the jam nut tight when I started I had everything set out to do a very quick regap so it wouldn't have a chance to cool down much. I'm beginning to think my problem is due to a varying point gap. Is this due to a worn points plunger or points? Maybe it's time to go to an electronic ignition! B)

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wminmi
quote:
Originally posted by Paul_B
Maybe it's time to go to an electronic ignition! B)
Best $20 i ever spent :D When i rebuild my 16hp, or ANY other lawn tractor engine for that matter, the Mega-Fire will be put on it :D

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