Exhaust popping in cold weather

[Alrashid2 431]

Hey guys. I've noticed this phenomena with my Horse before, but not nearly this bad. 

 

When it is cold out, despite warming the tractor up, my exhaust will constantly be popping during operation, almost sounding like a backfire. Usually it only happens once a minute or so, but today in this <20F weather, it was happening every few seconds. On top of this, the RPMs seemed to be really fluctuating, and I even had a few cases where it dropped for a few seconds then sped back up. It almost reminded me of when youd engage the PTO in wet grass, but I was just standing still when this would happen.

 

I took a video, but now that I'm watching it it isn't doing it justice. Can't really hear the pops, but if you listen closely you can kind of hear the fluctuations in RPM.

 

This never happens in the summer, only winter. Any ideas here? My only guess was that this was actually backfiring, and my carb might be running rich when in cold weather, but not in warm weather? Not sure if that makes sense though. I suppose I could try tweaking the carb adjustments but wasn't sure where to start.

 

Thanks for the advice fellas!

Edited December 15 by Alrashid2
Video

[ebinmaine 75,867]

2 hours ago, Alrashid2 said:

running rich when in cold weather, but not in warm weather?

 

The opposite actually. 

Cold air is denser so more can get in. 

Cold fuel doesn't atomize (spray) as well either. 

Sort of a double negative. 

 

More air and less effective fuel spray means you're likely running lean. 

Not the best for an engine....

 

Try turning the adjustment screw(s)

Just a tad... out. 

 

Experiment and report back.  

 

 

[Alrashid2 431]

2 minutes ago, ebinmaine said:

 

The opposite actually. 

Cold air is denser so more can get in. 

Cold fuel doesn't atomize (spray) as well either. 

Sort of a double negative. 

 

More air and less effective fuel spray means you're likely running lean. 

Not the best for an engine....

 

Try turning the adjustment screw(s)

Just a tad... out. 

 

Experiment and report back.  

 

 

 

Thanks @ebinmaine! That makes sense to me. I bet my carb is set "perfectly" for warm weather but the cold is throwing it slightly off. As you said, double negative. I'm sure I can richen the main jet a bit and it'll still run well in summer too. I won't have time to tinker until Fri but will report back then! Thanks!

[Handy Don 15,273]

All of the above, and...

I’d make very sure there is no water in the fuel lines. Condensation can occur in the tank, the pump, and in the carb bowl. If the tractor storage is below freezing that can cause ice. 

Me? I’d try for a warm enough place for the tractor for 24 hours, then dose the fuel tank with dry-gas per the instructions on the bottle. Then burn through ALL of that fuel before re-fueling. 

 

[Alrashid2 431]

@Handy Don how quickly does that happen? I burn through fuel pretty quick and just put fresh fuel in the tank 2 weeks ago. Store my wheel horse in the same place as my snow blower and lawn mower, and they've never had any issues with water or ice in the fuel system. 

[ebinmaine 75,867]

6 minutes ago, Handy Don said:

dry-gas

 

@Alrashid2 do you use ALL ethanol free fuel?

 

@Handy Don I've never seen ethanol laced fuel with water in it - but we have older machines with higher tanks, except one. 

[Handy Don 15,273]

8 minutes ago, Alrashid2 said:

@Handy Don how quickly does that happen? I burn through fuel pretty quick and just put fresh fuel in the tank 2 weeks ago. Store my wheel horse in the same place as my snow blower and lawn mower, and they've never had any issues with water or ice in the fuel system. 

Fueling and using that often, ice in the fuel system is probably not your issue.  

We have had members report carb icing in very cold but humid weather. It’d be visible as frost on the outside of the carb and the symptoms would be similar as it affects both air and fuel mixing in the carb throat. 

Edited December 15 by Handy Don

[lynnmor 8,270]

28 minutes ago, Handy Don said:

Fueling and using that often, ice in the fuel system is probably not your issue.  

We have had members report carb icing in very cold but humid weather. It’d be visible as frost on the outside of the carb and the symptoms would be similar as it affects both air and fuel mixing in the carb throat. 

 

During a week long Christmastime power outage, I ran a generator the entire time except for fuel and oil stops.  Carburetor icing was a real issue since a generator might run at the same throttle opening for some time and then when more power is called for the throttle plate is froze fast.  My solution was to build a cardboard house to keep the heat in.  I believe that ethanol laced fuel did stop nearly all of the ice in the fuel lines problems, but my example with the generator was not within the fuel touched parts.

[gwest_ca-(File Mod) 11,858]

1985 312-8 would have a K301 with points and condenser. Have another condenser you could try?

 

Have you checked the valve clearances? They do not need it often but if never done a 1985 model is due.

 

Have had success adding a shot of Marvel Mystery oil to the fuel or 2-stroke oil if you have it. Lubricates the valve stems in case they are lazy at closing.

 

Do one thing at a time so you know what the fix is.

[Retired Wrencher 6,180]

On 12/15/2025 at 5:56 PM, ebinmaine said:

 

@Alrashid2 do you use ALL ethanol free fuel?

 

@Handy Don I've never seen ethanol laced fuel with water in it - but we have older machines with higher tanks, except one. 

Eric the best thing I ever did is starting using that non-ethanol fuel. I’ve only had one bad day so far on start up. It was really cold. Yesterday I put the block heater on and it started right up about an hour. With the non-ethanol do you use dry gas?

[ebinmaine 75,867]

6 minutes ago, Retired Wrencher said:

With the non-ethanol do you use dry gas?

 

 

 

NEVER.  

 

Why add alcohol to the elimination of alcohol?

 

 

[Alrashid2 431]

Yup, only 100% ethanol free fuel used on all of my small engines! I found a gas station about 40 min round trip that has it. Every November, I go there and fill up 18 gallons of ethanol free fuel, and stabilize it all with Stabil. That lasts me the year, between the Wheel Horse, snow blower in the winter, lawn mower in the summer, and all the other small engines used throughout the year. Usually I have a few gallons left by next Nov, that I throw in the car and I restock again!

 

Only case where I may use 10% ethanol fuel is in my generator, as she burns a lot of fuel. If we lose power for 2 days I'll go through at least 10 gallons, so usually I throw in normal fuel as I know it'll get burned through quickly. If any gas remains in the tank by the time the power comes back, I'll typically drain it and throw it in the vehicle. 

[Retired Wrencher 6,180]

Only case where I may use 10% ethanol fuel is in my generator, as she burns a lot of fuel. If we lose power for 2 days I'll go through at least 10 gallons, so usually I throw in normal fuel as I know it'll get burned through quickly. If any gas remains in the tank by the time the power comes back, I'll typically drain it and throw it in the vehicle.                    @Alrashid2 I do the same with the generator. I have construction type generator, noisy as all heck but it starts first a second pole every time. Any kind of storm that would knock you out from one to two days that’s a lot of  ethanol, free gas. I usually turn valve off and run it out of fuel.

[Alrashid2 431]

Finally had a chance to look at the Horse with some colder weather. Warmed her up, moved some wood, and that exhaust was popping! Popped the hood and tried to make the main jet screw richer (which by the way, very difficult to adjust it when the throttle linkage is directly over it!)

 

Didn't make a difference! I made it richer and richer until the RPMS started to fall off. For the heck of it, did the same thing the lean way (turned in) and didn't make any difference. Sweet spot is pretty much where it was already. I left it a tad richer just to see. Exhaust still popping. If throttle isn't at WOT, it seems to jump in RPMS a bit and sounds funny, but if I go full throttle it just pops a lot and keeps going. Only when cold out. 

 

Not sure what else it'd be? Fresh fuel filter and I get fuel delivery just fine

[sqrlgtr 1,372]

15 minutes ago, Alrashid2 said:

Finally had a chance to look at the Horse with some colder weather. Warmed her up, moved some wood, and that exhaust was popping! Popped the hood and tried to make the main jet screw richer (which by the way, very difficult to adjust it when the throttle linkage is directly over it!)

 

Didn't make a difference! I made it richer and richer until the RPMS started to fall off. For the heck of it, did the same thing the lean way (turned in) and didn't make any difference. Sweet spot is pretty much where it was already. I left it a tad richer just to see. Exhaust still popping. If throttle isn't at WOT, it seems to jump in RPMS a bit and sounds funny, but if I go full throttle it just pops a lot and keeps going. Only when cold out. 

 

Not sure what else it'd be? Fresh fuel filter and I get fuel delivery just fine

Sounds like its leaning out to me but a bad condenser will make um act funny also. I always heard its very rare for a condenser to go bad, but I've had 3 go bad myself, two where on a 6volt VW bugs and one was on a k341 Kohler. Might be worth a try if you have a known good condenser to swap just to see if anything changes, but if I was a betting man I'd say carb is full of drugs. 

[lynnmor 8,270]

You may have crud in the carburetor that limits the fuel flow more than any adjustments can overcome.  I would pull the carb and give it a good cleaning at this point.

[Alrashid2 431]

Thanks guys for the advice here! It's all appreciated.

 

Any other symptoms of a bad condensor? I assume it's easy to replace? This only seems to happen in cold weather, so I wasn't sure if that was true of a failing condensor or if a bad one would cause sputtering all the time, any weather. 

 

I just tore apart and cleaned the carb about 8 months ago, so I highly doubt I have crud in there. Doesn't hurt to check though. 

[sqrlgtr 1,372]

1 minute ago, Alrashid2 said:

Thanks guys for the advice here! It's all appreciated.

 

Any other symptoms of a bad condensor? I assume it's easy to replace? This only seems to happen in cold weather, so I wasn't sure if that was true of a failing condensor or if a bad one would cause sputtering all the time, any weather. 

 

I just tore apart and cleaned the carb about 8 months ago, so I highly doubt I have crud in there. Doesn't hurt to check though. 

Just a miss is all that I can remember.

I still would bet on carb full of trash.

I have been going through the fuel pumps on my tractors, rebuilding them and can't believe how much crud was inside them. Was having trouble with crud getting in carbs every month are so. I had bought fuel line off of jungle site and thought I had fuel line breaking down and filling my carbs up with junk but have come to the conclusion it was coming from fuel pumps instead. I have not had to clean carb out of any that I have rebuilt fuel pump on so far but hasn't been too long since rebuilding them.  

[ebinmaine 75,867]

8 hours ago, Alrashid2 said:

tore apart and cleaned the carb about 8 months ago

 

I've had to clean a carb literally 3 times IN A ROW to get one particularly bad one right. 

 

Your tractor had ethanol at one point. We live on a dirt planet. 

[peter lena 9,575]

@Alrashid2  something  I  regularly do to an engine pick up , is to run it separately  on a gallon of heavily treated fresh gas , drop carb bowl clean out first , typically there is so much incremental  fuel tank debris , and related fuel hose break down , this a way to eliminate  tractor fuel tank  issue , always expect  to find another point of issue , something else , verify what you might have gained on ?  very rarely a one and done , this another reason for me to suggest , running a 5/16 steel  brake line the entire length of  the frame , tucked into the upper  frame corner ?  extend out with a  90 deg bend , cap off  ?  its now in place for  later hook up  , filter in each end , short run to carb and tank , like a clear  fuel rated hose there , personally have zero fuel issues , and maintain  what I do for that , love a repetitive problem ?  track it down and eliminate it  . done a lot of that , pete 

[Alrashid2 431]

Thanks guys! I'll pull the carb bowl after the holidays and give it a look. I assume I would see actual debris in there if this were the issue correct? Is it as simple as pulling the bowl, blowing it out with brake cleaner, wipe down, reinstall? 

 

Merry Christmas all!

[sqrlgtr 1,372]

1 hour ago, Alrashid2 said:

Thanks guys! I'll pull the carb bowl after the holidays and give it a look. I assume I would see actual debris in there if this were the issue correct? Is it as simple as pulling the bowl, blowing it out with brake cleaner, wipe down, reinstall? 

 

Merry Christmas all!

not really carb needs to come off and have thorough cleaning. Might need to purchase kit first before you start project .