occasional miss when mowing

Messages
30
Location
iowa
i have a 190cc 6hp flathead briggs quantum .for a long time i thought i had a exhaust valve going bad or a faulty ignition module.i really thoght the spark plug wire was worn and jumping to ground occasionally.i replaced the ignition module with no improvement in performance.then one day it ran perfect for my entire mowing.i always have fresh gas treated with stabil.gas is always a no ethanol blend and fresh.i now wonder if i had a small air leak on the intake side somewhere.my guess is the o ring between the carb and the block is faulty. (hard or brittle). the mower is ten years old with low hours.is this o ring ever a issue with anyone else? any other possibilities? thanks for any input.
 
Messages
6,550
Location
Connecticut
I've never had a problem with the o-rings on the Quantums, but that doesn't mean it isn't possible. You said you use ethanol-free fuel, but there could still be a little piece of junk that got stuck somewhere in the carb. I'd also replace the plug if you haven't already. For what its worth, I had a 6hp Briggs Quantum on a log splitter than would run okay for a bit then run terrible. I cleaned the carb probably 4 times with no luck. I took the shroud off to swap the ignition module with a known good one and I found that the intake pipe was loose. The two bolts that hold the pipe to the block had vibrated loose causing a leak. I replaced the gasket, tightened everything up and it ran perfect.
 
Messages
17,501
Location
Clovis, CA
<span style="font-family: 'Verdana'">I'll give you a little hint: carburetors get contaminated VERY easy. One little microscopic foreign particle in the wrong place and suddenly the carb won't be metering fuel properly.</span>
 
Messages
6,638
Location
South Florida
Start with the basic maintenance first and see if that fixes your problem. 1) Spark plug, Champion RJ19LM gapped at 30 thousandths, $1.90 at Wal-Mart 2) Air filter, Briggs 491588S, available in a 5 pack off Amazon for $13.19 http://www.amazon.com/Rotary-5-Pack-Cart...eywords=491588s 3) Change oil $2. Manual calls for synthetic 5W30 or SAE30 If you still having problems, flush the gas tank, replace the 10 year old fuel line, and replace the carburetor with a new one. You can do all that for about $25.
 
Messages
767
Location
Nebraska
Don't you hate it when that guy says "maybe the flywheel key is sheared" for every problem under the sun? Well, here it goes. The flywheel key may be sheared just a hair. It can cause the occasional flutter without really interfering with the operation of the mower. At times the mower can sound perfect, then the "flutter returns. Can't hurt to check. The intake tube sucking air also rings a bell...
 
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