Briggs thats hunting

[dunoon2]

I serviced a Troy-Bilt with a 17.5hp Briggs single cyl, ohv It constantly is hunting, speed up then backs off. Thinking that the idle curcit was plugged I removed the carb, it looked clean then cleaned it in my ultrasonic. No difference. Any suggestions? Thanks
Rich Davis
Mobile Mower Maintance

[38racing]

Static governor adjustment.

[bgsengine]

Ultrasonic cleaner is not a miracle cure - it won't fix bits of debris, dirt, rubber fuel line that have worked their way to a jet and jammed in there, won't fix worn throttle bushings or corroded carburetor - ultrasonic pretty much will break up and clean away bits of varnish and build up that you can't get to otherwise and won't dissolve, but it wont fix everything - you need to go through the carb with a fine tooth comb and an otoscope sometimes - but for most shops the time it takes to do that will cost more than slapping in a new carburetor. I have actually found a piece of *animal hair* stuck in a tiny idle circuit jet that was causing a lean surge - would not have found it without otoscope.


Could also have an air leak, or as noted a mis adjusted governor - have you eliminated the governor from the equation by holding the carb throttle lever steady so it won't move and see if it smooths out or dies?

Got to do the diagnostic work before the fix can be done.. first step is to separate governor trouble from carburetor trouble with the simple test noted above and go from there.

[Arkie]

I seen same thing awhile back. (hunting briggs single cyc and also a twin carb)

First hold throttle at closed pos to eliminate mis-adjusted static gov.
One of the carbs I had ultrasoniced it about 4 times and still same. finally took out the idle ckt welch plug and used a tag wire and cleaned all the small passages, re-used the same steel welch plug by soldering the small hole in the center that I made for removal and carefully re-installed and sealed. (did not have a replacement welch plug of correct size readily available) The welch plug can be re-shaped using hand pressure and a round nose punch with leather backing. Carb worked ok. (be real careful and don't break off a tag wire inside a long carb passage or you are SOL)

The next carb was same type carb but no go after several ultrasonic cleanings. Found the idle ckt welch plug was leaking. (sucking air) Found this by holding finger over the welch plug while engine was running. The STEEL plug had a small rusted pin hole at edge. Replaced the welch plug and applied sealer.
Like bsengine says thou, best to do the troubleshooting and if carb is bad replace with new, then you can repair the old one in your spare times as a spare for future testing or replacement.
Sometimes adding some choke very slow little bit at a time will stabilize a hunting engine and this gives a hint that Carb/air idle circuit issue and not the governor.
I've had some OLD cruddy carbs that had pitted carb bowls that are part of the carb body (bowl made onto the carb) and the ultrasonic would make them ok for awhile, like couple weeks and a small piece would turn loose and re-clog and they would have to go back to the cleaning again, especially if the bowl and or casting was flaking small pieces. (patience) I had installed new fuel filters and hoses going to these carbs and this told me the carb was still the producer of the small pieces. (seen this re-occurrence several times with old carbs)
Old carb reoccurring issues is main reason why customers get new carbs and the old carbs only used as a temp test run or used on my own eq. (New carb also helps reduce chance of Murphy's law) Some of my old carbs are stored with small amount of oil inside the carb so as to keep the casting from making the white corrosive powder flakes that clog the small ports, than place the carb in a sealed plastic storage bag.

Also some welch plugs can be blown out or sealer broken loose at their edges if too much air pressure is used when cleaning the small briggs carbs. I only use about 15 psi and keep the air nozzle back away from the carb openings so as direct full pressure is not going into a orffice in the carb body. I sometimes purposely use high air pressure to remove a welch plug for cleaning inside and catching it in a large zip lock plastic bag. (wear eye protection)