Export thread

Still having fast idle when engine is warmed up. Cold idle is normal.

#1

B

bodean

I’m still having a fast idle when engine is fully warmed up on my 12 year old 26hp V-twin B&S. The hotter the engine…..the faster the idle until it reaches about one third to half the throttle range. I’m figuring an intake leak, but all my attempts to locate it proves nothing. I’ve tried s50 weight oil on the entire outside of the intake and no change. I’ve tried using propane gas from my unlit torch all around the intake and carburetor areas and still no change. The throttle linkage and all related brackets and connections have been checked to ensure complete closure. Any ideas or suggestions?


#2

StarTech

StarTech

Have you gone thru the idle speed setup in the service manual as you probably have a governed idle issue?


#3

B

bertsmobile1

Idle or no load speed.
Your engine is supposed to idle at its full running speed
You can slow it down to around 1/2 the full speed by moving the throttle lever to the slow ( Turtle ) position .
Why are you trying to make an engine that wants to spin at 3400 rpm run at a slower speed ?


#4

B

bodean

Because the idle was considerably lower when it was new. It’s 12 years old now(350 hours ) and the idle is at least 3 times faster than the 5 year old model which still idles normal. It idles normal RPM until the engine reaches full operating temperature. and then when the outside temps get into the 80° to 90°F range, I can almost mow tall grass at idle.


#5

StarTech

StarTech

What the OP is referring to is the engine's idle speed (turtle mode as you call it). These engines usually idle at a governed idle speed of 1750 rpms with a dead flat idle speed of 1200 rpms (throttle against the idle stop screw). When the dead flat idle is set incorrectly due to either messing the idle speed stop screw it can cause this and usually they will settle back down to the 1750 but it can take a while. Many operators and techs mistakenly adjust the idle speed stop to the 1750 rpm which is wrong for the governed idle setup.

This adjustment does take a RPM meter to set it, you can't just guess at it. I know I had several engines here that would do similar things and took me following the SM instructions to stop them from this. For some reason these can get in a self feedback loop and don't want to return to governed idle speed right away. This very to the problems we can have with the old updraft carburetors and they too had to be tuned a particular way for them to operate right. I know reading and following the SM instructions are a pain for us know it all types. It took me a year to learn to set this adjustment as I just over looking it in the service manual.

Now if once you perform this adjustment and the engine still does this then I would for worn carburetor parts like the throttle shaft, linkages, or some other item. But you got to start with the basics first and troubleshoot from there.


#6

B

bertsmobile1

At minimum idle speed the engine is just barely getting enough air flow to keep a new CLEAN engine within the operational temperature .
They are not car or motorcycle engines and are not suppose to be run at any speed other than full throttle.
My guess is you are running the engine two slow so it is overheating thus running fast .
Apart from bleeding the hydros there is no other time that the engine should be run at any speed but full throttle.


#7

B

bodean

bertsmobile1 said:
Idle or no load speed.
Your engine is supposed to idle at its full running speed
You can slow it down to around 1/2 the full speed by moving the throttle lever to the slow ( Turtle ) position .
Why are you trying to make an engine that wants to spin at 3400 rpm run at a slower speed ?
bertsmobile1 said:
Idle or no load speed.
Your engine is supposed to idle at its full running speed
You can slow it down to around 1/2 the full speed by moving the throttle lever to the slow ( Turtle ) position .
Why are you trying to make an engine that wants to spin at 3400 rpm run at a slower speed ?
Click to expand...
Click to expand...
bodean said:
I’m still having a fast idle when engine is fully warmed up on my 12 year old 26hp V-twin B&S. The hotter the engine…..the faster the idle until it reaches about one third to half the throttle range. I’m figuring an intake leak, but all my attempts to locate it proves nothing. I’ve tried s50 weight oil on the entire outside of the intake and no change. I’ve tried using propane gas from my unlit torch all around the intake and carburetor areas and still no change. The throttle linkage and all related brackets and connections have been checked to ensure complete closure. Any ideas or suggestions?
Click to expand...
I just realized that I failed to mention in my title that cold idle is normal.


#8

R

Rls8836

bodean said:
I just realized that I failed to mention in my title that cold idle is normal.
Click to expand...
Bodean my 37 hp. Briggs and Stratton does this also. When cold and newly starting it the idle speed is ok. But after mowing awhile and returning to park it the idle speed is a great bit higher than what I like. Someone who is more knowledgeable here please explain and respond how to remedy this. I forgot to add, this is a twin cylinder motor on my 2013 Scag zero turn.


#9

B

bodean

Rls8836 said:
Bodean my 37 hp. Briggs and Stratton does this also. When cold and newly starting it the idle speed is ok. But after mowing awhile and returning to park it the idle speed is a great bit higher than what I like. Someone who is more knowledgeable here please explain and respond how to remedy this. I forgot to add, this is a twin cylinder motor on my 2013 Scag zero turn.
Click to expand...
That’s exactly what mine is doing


#10

B

bodean

This is exactly what mine is doing. I’ll post it here when and if I get it figured out. Warmer days are coming soon, so I’ll be doing a complete maintenance on it sometime this month.


#11

R

Rls8836

bodean said:
This is exactly what mine is doing. I’ll post it here when and if I get it figured out. Warmer days are coming soon, so I’ll be doing a complete maintenance on it sometime this month.
Click to expand...
Thanks I hope for good results.


#12

shadetree#1

shadetree#1

What is the model, type and code of your engine????????

As star tech mentions in post 5 the governor idle adjustments have to be correct. If you make these adjustments with a bad carb it just makes things worse.
AND
I've seen Nikki carbs have those symptoms and most generally it is the Clone Nikki's types.
Wondering if you have ever seen this engine carb combo operate correctly?
Did it just start doing this all at once or ?????????????


#13

B

bodean

This happened gradually over time and seems like it’s getting worse. Nothing has been tinkered with as far as governor adjustments….only backed the idle adjustment down. I did remove , clean, and replace the intake to insure that it was sealing properly, but that was after it had already started doing this.


#14

shadetree#1

shadetree#1

Did I overlook where you posted this info?

What is the model, type and code of your engine????????


#15

B

bodean

I think I must have overlooked the request for this information. The first vide is cold start up and run. The second video is after fully warmed up from cutting grass for 15 minutes. 864FFFC1-2B92-492A-BE6F-71CA5B51D4C1.jpeg


#16

B

bodean

bodean said:
I think I must have overlooked the request for this information. I tried attaching a short 25 second cold run video and a hot run video, but it won’t allow that or posting more than one still photo, so this is probably the most important one as far as engine information goes. View attachment 63367
Click to expand...


#17

B

bodean

F5CAD38A-E62E-4705-B590-CA456CE100F4.jpegF5CAD38A-E62E-4705-B590-CA456CE100F4.jpeg


#18

shadetree#1

shadetree#1

HMMMMMMM
Dual throat Nikki carb. I've seen the o-rings inside those Nikki carbs cause that engine speed changes.

I did not say that carb is your engines issue but it's a good suspect.
Here is a link to review about your 796997 Nikki carb. (repairs, etc)

Small Engine, Lawn Mower, Snowthrower Troubleshooting, Repairs and Safety

outdoorpowerinfo.com outdoorpowerinfo.com

Here is some info I have saved from my files about those type carbs FOR YOUR REVIEW.
Nikki dual throat carb repair/rebuilding links

Nikki dual throat carb tips and re-building LINK.

Guy asks about jets sizing and re-building a dual throat Nikki carb

https://www.lawnmowerforum.com/threads/nikki-dual-carb-main-jets.29187/



You tube video part 1: (newer style aluminum float bowl Nikki) USE KIT 54832 @ $7




part 2 (older model with steel float bowl) USE KIT 54833 or 54834 @ $9 each depending on the style of Nikki. See part 2 of the video to determine which kit needed.

Nikki dual throat carb repair/rebuilding links

Nikki dual throat carb tips and re-building LINK.

Guy asks about jets sizing and re-building a dual throat Nikki carb

https://www.lawnmowerforum.com/threads/nikki-dual-carb-main-jets.29187/



You tube video part 1: (newer style aluminum float bowl Nikki) USE KIT 54832 @ $7




part 2 (older model with steel float bowl) USE KIT 54833 or 54834 @ $9 each depending on the style of Nikki. See part 2 of the video to determine which kit needed.



Footer Links 1

Top