Runs rougher when above freezing... - Snowblower Forum : Snow Blower Forums
 
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post #1 of 9 Old 01-27-2020, 05:25 PM Thread Starter
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Runs rougher when above freezing...

We got hit with lots of that soft wet heavy snow on the weekend. It's hard on any machine because it's so dense, sticky and weighs a ton. Even my 10HP Tecumseh had a tough time and I had to make sure I didn't ram too much snow at a time into it or it would choke and die. But besides that I noticed it seems to run a bit rougher when it's warm (above freezing) than when it's cold. Has anyone else noticed this and if so what is the cause/remedy. Thanks!
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post #2 of 9 Old 01-27-2020, 05:31 PM
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that's normal; your carb is dialed-in for lower temps at which the air is more dense (requiring more fuel for the mix).

when it warms-up, the air is less dense so you need less fuel.

If you have an adjustable main jet, you can lean it out (turn-in) a bit.


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Last edited by classiccat; 01-27-2020 at 07:17 PM.
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post #3 of 9 Old 01-27-2020, 06:28 PM Thread Starter
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No adjustable choke unfortunately. What about leaving the choke open a bit when it's warm outside?
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post #4 of 9 Old 01-27-2020, 06:56 PM
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Have you considered trying the aforementioned $12 aftermarket carb with the adjustable main jet? You don't want to choke it more if it's already running rich.


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post #5 of 9 Old 01-27-2020, 07:02 PM
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Quote:
Originally Posted by Dannoman View Post
No adjustable choke unfortunately. What about leaving the choke open a bit when it's warm outside?
You should have the choke fully open ..it's only used for starting and to provide the extra fuel need while the engine warm..you should be able to fully open the choke after a minute or so.




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post #6 of 9 Old 01-27-2020, 07:15 PM
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Quote:
Originally Posted by Dannoman View Post
No adjustable choke unfortunately. What about leaving the choke open a bit when it's warm outside?
Hi Dannoman, Not choke...main jet. if you look at your carb, does it have an adjustable jet on the bottom of the bowl?

if so, in the image below, the slotted screw adjusts your main mixture. In your case, after warming-up the engine for a few mins, you'll want to turn that in (clockwise) in 1/8 turn increments until it smooths out...wait a few seconds between adjustments.



Remember how much you turned the screw so that you can set it back when things cool off again!


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post #7 of 9 Old 01-27-2020, 08:06 PM Thread Starter
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I have a replacement carb in my cabinet that has that. The old one on the machine does not. The old carb has served me well but it may be time for a swap soon...
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post #8 of 9 Old 01-27-2020, 08:10 PM Thread Starter
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Quote:
Originally Posted by Shovel View Post
You should have the choke fully open ..it's only used for starting and to provide the extra fuel need while the engine warm..you should be able to fully open the choke after a minute or so.




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I get mixed up when it comes to what's open and closed on the choke...
Usually the choke is all the way to the right for start up and then I ease it gradually back all the way to the left to run.
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post #9 of 9 Old 01-30-2020, 09:07 AM
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Choke makes the fuel mixture more rich not by adding extra fuel, but by restricting the air intake.

As mentioned before, warm air is less dense, effectively making your mixture more rich. At some point, leaning out by running a smaller jet may become required. Also note that even once the fuel ratio is adjusted back with a smaller jet, a naturally aspirated engine like those on our snowblower will still produce less power than it would at lower temps..

To sum up:
Warm air = less oxygen, less power + potentially overly rich mixture = even less power.
Colder air= more oxygen density , more power but only if you are jetted to keep the mixture properly rich...

If you jet leaner to fix your actual problem, be careful the next time you use it in really cold temps as you risk being too lean, potentially damaging the engine.


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