Outdoor Power Equipment and Small Engines - Toro HMR1200 rider starts rough, runs fine

I ahve a Toro HMR 1200 with a 12 HP Briggs and Stratton Engine - The mower starts rough (requires continuous cranking for almost 90 secs and starts rough once the engine responds), but once it gets to full speed runs fine. I have verified that the choke butterfly closes all the way when the throttle lever is moved to choke. I have also verified that the spark plug fires when the engine is cranked. I have adjusted the carburetor per the owner's manual at full speed (needle valve at bottom of float carb) and slow idle. I have replaced the spark plug, fuel filter and battery. The mower used to start reliably on the first crank up until 4 weeks ago. I am wondering what might be the cause of this rough starting behavior. Thanks for your help!

I'd say you have a carburetor that is dumping fuel at a rate that only shows up at lower demand (RPM's). I'll bet you have a inlet needle & seat or a float that needs to be replaced in the carburetor. By any chance have you noticed the engine smoking lately, particularly a white smoke? Can you smell any gasoline in the oil sump? These would be two indicators that the carb is dumping fuel.

While you got the carb off check the valve clearances.

Thank you for your responses - I think you're right. I took the air cleaner off today and noticed a puddle of fuel right by the choke. The oil also smells like gasoline, but there is no white smoke while the engine runs (only a brief run of black smoke right when it starts, indicating a rich mixture). I took the whole carburetor apart, cleaned everything out with carburetor cleaner and put it all back together again. The needle valves were clean and did not appear scored. The float did not have a leak, moved freely, and the inlet restrictor to which it was attached looked fine. The engine still took a little while to start - I guess I will purchase a carburetor rebuild kit and see where that gets me.

-Mark

Any favorable results with the rebuild kit? Also, if you suspect that you have fuel in the oil, be sure to change this before you run the engine again but after you service the carb.

Actually I may not need it - After reassembling the carburetor two weeks ago I looked under hte air cleaner today and saw no fuel. Mower started right up. I'll keep an eye on it though and rebuild if any issues. Perhaps I had a stuck float or some dirt in teh area where its needle valve sat. I did change the oil. Reeked of gasoline.

-Mark

Puey61:

Well, it started acting up again - Still dumping fuel and running rough after starting as well. Adjusting the inlet needle got it running smooth for a little while, but engine would die shortly thereafter. Rather than rebuild the carburetor (which I have read doesn't give you as good a result as replacement), I decided to just buy a new one since it wasn't that expensive, and Partstree.com had one. Actually this is a great website - I was able to find all kinds of parts for this mower even though Toro stopped making it many years ago (the mower was purchased by my father in 1989). I put the new carburetor on (and replaced the inlet gasket and fuel filter for good measure) and now this tractor runs just like it was new! Thanks very much for your help - I fixed this for less than $200 and I'm sure it will be good for another few years at least! Given that modern zero-turn radius riders go for ca. $4000, this was a great investment!

-Mark

Glad you got it fixed! Thanks for the update!

Good news and now you need to prevent future varnish buildup by using fuel stabilizer regularly.