Nearly New Rider Mower won't run smooth

[Retired Pedler]

Hello, My very first post as new member. Hope someone can help me.

I have a Craftsman YT3000, model no. 917.271635, 2014 model, engine B & S, 33187,type no. 2371-G!, 21 HP single cylinder. I bought it last year at end of the season & used it 1 1/2 hrs. and then stored it. Upon starting it backup this year,
the engine is surging at idle, bad. Under a load or when engaging the blades it does much better & runs pretty good but still surges lightly. I have taken the carb. apart cleaned it, new kit, new fuel filter,new spark plug, fresh fuel, adjusted the idle screw which nothing seems to help. It looks like the governor arm is moving the throttle back and forth-without a load on the engine. A retired mechanic told me that the values may have seated in after running a while and no value clearance. I told him I might need to adjust the value clearance. He said you cannot, that type engine has no adjustment on them. I do seem to smell a rich exhaust mixture when it running & in idle. I don't think it is carburetor related, as
everything I have done to it, does not seem to help. It now has 3 hours on it and still surges, bad, at idle. I am thinking it might be the governor? It is still in warranty but I must haul it some 75 miles to a Sears repair facility and my last experience, I never got my mower back, after several months and got a refund. I do like the mower and would like to keep it, if I can fix this problem. I last week looked at the new mowers this model & they used a different engine than mine.
I have heard of a 2013 same model & engine with very same problem. Any ideas of what is my problem and solution? Thanks!

 

[7394]

IDK ? My former 2008 craftsman, had a 20 hp single B&S, & I did adjust the valves after years of use. Not sure I believe that info about not being able to adjust.

Your owners Manual 'should' give you valve clearance specs. At least mine did.

Did you treat the gas before storage & run it in, or drain it & run it till she quit ? I think this is a gas/carb issue. those lil carbs have tiny orfices that if anything gets blocking one, could give you those symptoms.

 

[cpurvis]

Not the governor; it's just doing what's being asked of it. Not the valves, either. There is no way in a year and half of use that the valves have recessed and lost their clearance, unless you've put 1500 hour on it in that length of time.

There are two "circuits" through which the carburetor sends fuel to the engine: One for low power loadings, like idling or medium rpm, low load situations. The other is for high power requirements, such as mowing. The throttle plate is what determines which circuit will be used. If the throttle plate is below a certain setting, the low power circuit is used. Above that, the high power setting is used.

The governor controls rpm by opening or closing the throttle plate. Once the rpm drops below that set by the operator, it opens the throttle plate to send more fuel/air to the engine to make it speed up to the desired rpm. If the rpm keeps dropping, it will progressively open the throttle plate all the way. If the engine isn't getting any fuel from the low power circuit (aka primary or idle circuit) the rpm drops until the throttle opens enough to engage the high power circuit (aka secondary or main), then the engine accelerated rapidly up to the rpm the governor is trying to maintain and closes the throttle. Once again, the primary circuit provides no fuel and the whole rev up/slow down cycle begins again.

My guess is that your primary circuit in the carburetor is clogged. With what, I don't know, because of the relative newness of the engine. You can take it apart and clean it or simply replace the carb. The good news is, Briggs carburetors are cheap. The bad news is, there's a reason why they're cheap.

edit: deleted.

 

[bertsmobile1]

Surging is always fuel related.
As above, clear the carb there will be crud in there somewhere

 

[SkipD]

Also, don't forget to look at your air filter.

 

[Retired Pedler]

Thanks for the replies,

I did ran the engine to burn out the fuel for storage. That's what the Owner's manual says to do. That did not work on fuel available around me.
I did clean the carb and new kit installed along with the other new standard parts. Air cleaner was perfect, only running 1 1/2 hrs. It appears some of
the fuel must to have been left in the carb and caused some damaged to the small jets, not visible to the eye. Nothing in manual about values.
At this point, I agree it is a carburetor issue as some of you stated.

Replacement carb is Nikki 796587 or 591736 and not cheap. I see a lot of model no. 794572 online but don't know it they will work for me.
The 794572 is a replacement for 19HP and lower, but not sure it would work for me. Only about $60.00 online. All of these carbs are Nikki.

Any thoughts on using the Nikki 794572 in my application?

Thanks, Again!

 

[7394]

I would suggest after this, prepping for storage to use Seafoam* (found at local auto parts) to stablize the gas, & make sure it is mixed properly & run the engine long enough to get it into the carb. I NEVER empty my mowers or etc for winter. Seafoam not only stablizes the gas, but it also Cleans the internals.

I have no issues using it, it has been around since about 1942.

 

[cpurvis]

I think you're in for another carburetor cleaning. You probably won't need any parts if you're careful not to destroy anything. Even if you do, you still have the take-outs from the last "cleaning," that can be re-used, no older than this engine is.

This time, you've got to look close for fuel passages you probably didn't notice before. All fuel enters the engine through very small holes near the venturi, near the throttle plate. A venturi is a narrowing of the air passage into the engine. Narrowing causes the air to speed up, which reduces the pressure of the air at that point, which sucks fuel into the air, creating a combustible mixture.

To clean it, disassemble the carburetor as completely as you can. Count the turns on any adjustable jets by slowly turning the jet to the closed position, counting the number of turns to the nearest 1/8th turn. Do not overtighten. Remove all non-metal parts. Soak the stripped-down body of the carburetor in carb cleaner, followed by blowing compressed air through every passage you can, preferably with a non-OSHA air nozzle. If possible, run a small wire through all these passages to make sure they're clear.

Reassemble the carburetor. (Hi-rez close-up pictures of the carb as you took it apart can be very helpful at this step.) Set the jets to what they were went you disassembled. Re-install carb and fire it up. Should run OK now.

If it doesn't, remove carb again and pulverize it with a sledgehammer or crush it in the nearest vise. This relieves stress immensely.

Then go pay the big bucks for a new carb and be done with it.

 

[RJL1]

I was having alot of problems with one of my older snowblowers last winter. Took the carb apart and cleaned it real good. Reinstalled it and it continued to surge at idle, much like you describe. I called a friend of mine that used to work at a small engine repair shop. He suggested I take a cap full or two (thats it, its strong stuff) of plain white ammonia and add it to a full tank of gas. By cap I mean the cap on the ammonia bottle. Run your motor for awhile and is should clear it up. If not than it's new carb time. It worked for me. Can't hurt in your situation either.

Good luck

 

[Retired Pedler]

Re: PROBLEM SOLVED!

PROBLEM SOLVED! AFTER 3 CLEANINGS!

Cleaned carb this way. First time: removed anything and sprayed with carb cleaner. Installed on mower-still running bad. Second time: Removed everything, cleaned with carb cleaner
and lower pressure air. Installed on mower- still running bad. Third & last time: Removed everything cleaned with carb cleaner, washed in solvent, running small sewing needle in idle jet,
next to carb butterfly and all other small holes. I last blow high pressure air through all holes to make sure all of them were open. Everything seem to be open. Installed back on mower.
PROBLEM SOLVED! Runs good.

The problem hole was the idle circuit-I think runs about 3/4" and into area of the large welch plug. This is the area I thought might be stopped up. Then using high pressure air, about 85 psi,
check all holes, again. Installed carb back on mower, now running very good.
I was able to adjust the idle-jet, only had to move it a 1/8 of a turn. I was able to bring idle back down to a reasonable rpm. Runs very good, now, better than ever.

What did I find?
I caught everything in third cleaning, coming out with a rag. There were two small slivers of white plastic which I think may have been mold flashing from the molding of the white main
internal housing. I think they have been in it every since it was new and starting to lodge in the idle circuit. The high pressure air did the trick. If my memory serves me, I don't think it really
run right since it was new and probably partial-blocked, even new. Runs very good, now and did not have to buy a new carb.

No, I did not pour ammonia or urine in it. Just a good cleaning in step #3, above.
I now use fuel stabilizer in all my fuel.

Thanks for everyone's help.