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Hey everyone first post !

I have a John deere 318 repowered with 25hp Subaru eh72 twin engine. I have a 50" deck, model 30 tiller, model 49 snowblower, rear blade & also a custom made FEL.

My tractor works amazing in the summer, but in the winter I have issues. Today we got 4-6" of snow -10celcius in SE Ontario and I thought great op to try out the 49 and rear blade. Worked great for the first thirty mins or so then it began to surge mildly and I thought I was out of fuel. Left it idle while I got a jerry can, dumped in a few litres and I'm on my way. Worked ok for another five mins then started surging agan and also backfired a bit then stalled and turned off during use. I restarted it immediately and let it idle for a few mins then full throttle and it started surging again so I revved down let it cool then turned it off. I checked my fuel after all this and I had over a half tank left so when I topped up before it wasn't nessessary

Now I went through all the same issues last year and I never found the issue. But warm weather comes and problem goes away and tractor works fantastic again.

Could this be a jet problem in the carb? Maybe I need to get winter/ summer jets ?

Thanks in advance for the suggestions
 

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I can't imagine needing different jets for different temps, but surging does indicate a clogged passage...possibly the difference in temps contracts the jets just enough to cause the problem...possibly if you drill the passage out just a tiny bit you can overcome the problem
 

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Here are some things to look at too, get an unlit propane torch with gas open and run it around the intake manifold while it is surging and see if that reduces or eliminates the surging. Can you eliminate the surging by pulling out on the choke? If so, then may be that the fuel pickups in the tank are clogging up and that is causing it.
 

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Here are some things to look at too, get an unlit propane torch with gas open and run it around the intake manifold while it is surging and see if that reduces or eliminates the surging. Can you eliminate the surging by pulling out on the choke? If so, then may be that the fuel pickups in the tank are clogging up and that is causing it.
I recall that you suggested that to someone else recently....the propane tank thing...if it causes a favorable response, ...what is the indication?...A warped manifold or bad gasket?
 

Kish JD 318/420/430
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Check the intake manifold, it is a two piece unit, split in half, the two parts are sealed and riveted together. After so many years the sealant rots away. Also check on the front of the carb, there is a plug that can come loose allowing air into the carb. those are the easiest to work on, followed by getting into carb. Oh, check the governor / carb linkages for slop. The holes enlarge over time
 

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Discussion Starter #10
Hey my 318 has been repowered with a new 25hp Subaru engine. I don鈥檛 have the 18hp Onan that鈥檚 notorious for leaking intake manifolds etc.

I think my problem is more leaning towards a lean jet issue. Yesterday was much warmer only -2C and my tractor worked amazing for the 90 mins it took me to blow about 6鈥 of snow from my driveway, no surging etc
 

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Always high test, and sometimes I鈥檒l dump some sea foam into the tank

I ordered some carb seals I鈥檒l be getting them Monday. I might try to widen the jets ever so slightly
 

Kish JD 318/420/430
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Ok, "high test" like aviation fuel, so octane of 104 right???? Onans like an octane rating of 89 to 91, no ethanol to draw water into the fuel and if sitting for a long time Stabil 365, which helps with cold conditions also.
 

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Subaro, DO NOT WIDEN JETS!!!! Carb jets have very specific angles and finishes to make them flow correctly. NEVER open them with a drill or clean them with anything metal...cleaner and/or compressed air ONLY.

So,ething else you mentioned was topping fuel from jerry can. Plastic or metal? Metal will sweat/condense moisture. Also, treat jerry can with seafoam also, not just tractor tank. Bob
 

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Only plastic jerry cans. Rw, could I experiment widening an extra set of jets if I was to order them? Then if it fails, switch back? Any research I鈥檝e done is pointing to over lean carbs for summer use & emissions standards. In my dry winter climate, how could they perform?? Is there a way to richen the mixture in a fixed jet carb without drilling the jets? Thanks for your reply, p.s did u watch the video did the link work?
 

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Hey Subaru, and welcome! With this only happening at a specific temperature, I'm wondering about carburetor icing... I'm not familiar with the engine you repowered with, but it looks like its carbureted from the owners manual here. Odd that it would happen around -10 (usually its around +2 or so), but are you coming from a heated garage to outside with it? How much space around the repowered engine? How well does it do heating under the hood? You said dry climate, what kind of relative humidity are we talking about?
 

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Subaru, I'm not all all familiar with the Subaru engine and any experience I've had with carb was in the late 60's, early 70's...but jets are jets!

OK, plastic gas can, that's good. I'd still recommend treating EVERY refill of your gas can with a fuel additive...MANY out there, so your choice.

"Playing" with an extra set of jets is a good idea. You may have 2 issues: size and speed of the drill. Do you have a drill press and a decent vise for it? Do you have, or have access to, number drills? The first thing you'll need to know is what size they are now. They may or may not be identified by a number but this may not be the size of the hole. You're going to have to try different size drills...use the shank end just to be safe...to find the size. I'd go one size larger, or maybe .005" max, and try it. Let's say a number 65 (.035") drill fits nicely in the hole.I'd try a #61 (.039") drill. If the engine doesn't get better, go larger. It's gonna be a "How's this work!" kinda deal with much trial & error.

Your other issue is speed. Your using a small drill in brass (??) and the "ideal" rpm is up around 14,000 which is far more than any commercial drill press or hand drill is capable of. The correct speed will give you the best finish but you're kinda stuck with what ya got! Use VERY light feed/pressure and be prepared for the drill to "grab" and pull through the existing hole.

You mentioned summer/winter & dry/moist air. No "scientific data" to support this, only my logic! Your carb mixes the "correct" amount of air and fuel for proper operation/combustion. The air going into the carb can contain moisture, which actually reduces the amount of air, more precisely oxygen, available for proper combustion. To me, dryer aire is better. To add more confusion, winter operation should give you a slighter richer mixture! A liquid expands when warmed and contracts when heated. In the 60's, we had "cool cans"...a container filled with ice that cooled the tubes the fuel ran through... to provide a richer mixture.

So far, everything I've said is contrary to what you're experiencing! It's definitely a temperature related issue, but I can't figure out how or why! Bob (btw, sorry., didn't watch video. You say it's dying, I believe it!)
 

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After reading Littletractorguy's post...and digesting it!... he may be onto something. AND it makes sense for your conditions. If your tank isn't full, the rest of it has air in it. Running for a while in a cold temperature, ANY moisture in this air will condense. This condensation can cause small ice crystals to eventually, like 1/2 hour after running, block your carb jets. At best, they'll give you a very poor fuel mixture which may lead to sputtering/dying. Just a thought!

When you use your tractor, try topping the tank off before putting it away. This will eliminate a lot of air that may lead to issues. Bob
 

Kish JD 318/420/430
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Found an interesting video on fuel, additives for water contamination: https://m.roadkillcustoms.com/water-contaminated-fuel-seafoam-heet-isopropyl-alcohol/ I'm with rwmeyer and littletractorguy on carb icing is the most likely cause. As in video you may try to adjust the choke to "rich" and see if that makes it run better. That may confirm water and the temp causing icing. Then to find a practical workable solution. I wonder if the carb maker has high altitude jets available??
 
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