Engine surges... help!!

[Steve (Magnolia, TX)]

OK, so I've got this Murray 20" push lawn mower with a 4HP Briggs&Stratton engine.
I've got nothing (but gas) invested in this thing (it was given to me), but I'd like to get some use out of it.
I last used it almost 3 weeks ago, now, and it worked fine (this was the first time that I'd used it).
Then this past weekend, I got it out to use it again and that's when the problems started... the engine is surging.

It's got fresh gas.
It's got plenty of oil (which is nice and clean, by the way).
I cleaned the air filter.
I sprayed some carburetor cleaner in the carb (it didn't look too bad, anyway).
I pulled the spark plug (it looks good, no oily soot... basicly normal "carbonization"), but I hit it with a wire brush a bit, before putting it back in.
I messed around with the throttle/choke linkages (I sure do miss the "good ole days" with an adjustable throttle on a lawn mower, instead of these danged ole preset things with the "safety lever", but I digress).

Anybody got any good suggestions?

Thanks...

[Mickey]

Surging is usually a sign of a lean condition. You might be able to help the problem with a little turn of the mixture screw but it would be better if you dug into the carb and find what has caused the lean condition. Most likely something in a gas that has found its way into the carb.

Just a guess.

[Steve (Magnolia, TX)]

I'll give it a shot....


Thanks...

[Archdean]

I concur with mickey, but no mixture screw on that little varmint , Surgeing is generally caused by a pinhole in the diaphram (Caused by age/carb cleaner)or both and or the governor tab (the little springs "you messed with":fing20: ) just kidding ! The fix is to (you guessed it Bend the tab the old fashion way provided you put the springs back on correctly)!

one othe thing you might do depending on the age is to replace or other wise reseal the gaskets to the tank and the little hose thingy that feeds the mixture from the carb into the block!! Carb cleaner is/was generally not your friend for small engine carbs (dirt , gunk covers up a lot of sins!!

Hope this helps you and a B&S parts list is included Here!!
http://shop.briggsandstratton.com/BShopProductPage.asp?CatalogID=39EC87CC-8003-4B08-ABB8-61BB0ADB5155&MECID=100&SessionID=94F5F0BE-6B41-44F5-866B-A861C3A52CE8&CategoryID=&lrid=1&ProductID=56B2BB5E-283C-11D4-8886-00B0D0203414#

[mbkerk]

I had the same problem with my snowblower a few months back. It literally started acting up between passes!

After some research, I ended up pulling the carb off, taking it all apart, and cleaning it with carb cleaner and an air hose. It runs great again.

A friend of mine (small engine mechanic) told me these new pollution friendly carbs, without any adjustments are very temperamental. He thought a piece of varnish broke loose and got itself into a passage somewhere and plugged it up. I could not see anything like that, but it ran fine when I put it back together.

BTW... Mine engine would run fine under heavy load, it just surged when it was under no load. The problem was in the "idle" fuel passage somewhere.

[jodyand]

The pressure washer i have was doing it with or without a load. I took the carb off a mower i had and did the same thing. I let my boss use it and i told him what it was doing and how much of a pain it was to use. He said he didnt care that he need to get his house cleaned. When he gave it back i asked him how much troble it gave him and he said none. He said he change the spark plug and it ran fine and has been running fine for over 1 1/2 years.

[Carl]

I looked all over the site, and found nothing that would fit chipper/shredder. Since the surging symptom fits my problem I'll tack on here.

Have a 10 hp Yardman chipper. Last time I used it it started running bad. Backfiring at full throttle, and surging at part throttle, and quitting at idle. The engine is one of those Tecumseh 10 hp XL/C engines. Since it was a surging problem mostly I figured that I would take the carb apart and clean the passages. (I think that they should opt for fuel injection on these guys too!) Simpler than these stupid antipolution carbs. [my opinion]

Since the problem manifested itself mostly at idle to half throttle and then started to smooth out, I figured that it was in the low speed jet. Found out that my old 63 year old eyes can hardly see the idle passage. Blew it out with carb cleaner and put it back together - - no change.

Yesterday I decided to try again. Squirted some carb cleaner in small container and put low speed jet in the fluid and swished it around for about 5 minutes. Shot carb cleaner through it again and found that it came out some places it hadn't come out before.

Now it works again. I'm thinking that is some kind of a miracle after reading about carb problems on an small engine repair site.

Sorry now that I didn't save all those small engine carbs that I've chucked through the years. Go figure