# Runs great under load, but sputters without...



## KATfishing

Looking for some help... I have a Craftsman 9 hp 28" snow thrower, model 247.887900 made by MTD in 2007. Motor is Tecumseh. It always starts fine, but this year is running rough when NOT under load. I just replaced the carb and it's a bit smoother, but at times when not under load (crawling in F1 without auger running) it sputters and even will kill at times. It is sporadic and this is with choke off. There is some Sea Foam in fuel (had good luck with this in past) and fuel is ethanol free. New spark plug. Again, seems to run well under load, bigger the better. Any ideas? There is no fuel filter from what I can see and fuel is fresh.﻿


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## e.fisher26

Does the replacement have adjustable bowl jet?


-efisher-


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## KATfishing

It looks identical to the OEM but the new non-OEM 640349 carb is an Everest carb.

I'm not sure the bowl jet can be adjusted in either of them... just unscrewed and cleaned. The other jet (for idle?) on the side with spring is the same with both also.


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## e.fisher26

Watch youtube on how to check valve clearances. When was last oil change?


-efisher-


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## Kiss4aFrog

:welcome: to SBF KATfishing, fellow cheese head !!

It's best to check valves and anything else you can to make sure it's adjusted properly. If everything else checks out it might be running lean. Have you tried to apply the choke a click or two to see if it smooths out ??


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## KATfishing

e.fisher26 said:


> Watch youtube on how to check valve clearances. When was last oil change?
> 
> 
> -efisher-


Changed oil one month ago. It was pretty dark. Might have missed last year's oil change but it wasn't run much with El Nino. Changed prior to using this year.


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## KATfishing

Kiss4aFrog said:


> :welcome: to SBF KATfishing, fellow cheese head !!
> 
> It's best to check valves and anything else you can to make sure it's adjusted properly. If everything else checks out it might be running lean. Have you tried to apply the choke a click or two to see if it smooths out ??


Go Packers! And thanks for the welcome. I'll have to research how to check valves, including YouTube videos. On the old carb it ran better half choked. With new carb, runs best with no choke and under load is nice and smooth. I'm just scratching my head as to why once the auger is disengaged it sporadically spits, sputters and at time loses power. I read somewhere that Tecumseh gas tanks have a little built in screen in the bottom that acts as a built in fuel filter. Thought maybe I should drain tank and see if there is a blockage although that back to why is it running fine under load... perhaps it's sucking more gas and only runs lean when not under load? If it's running too lean and that's the problem, is my only option to drill the jet hole bigger if carb is nonadjustable? No problem starting. Fires right off on one pull. BTW - I know just enough to be dangerous, but I am a DYI-er because I hate paying someone else when I can learn to do it myself. Guessing I'm in the right crowd here


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## Vermont007

Since the OP's Tecumseh Engine has a non-OEM version of *Carburetor 640349*, which is on many Snowblowers, it should have the hidden *Idle Restrictor Screw* on it's side.

When allowed to collect fuel deposits in blocked passages of this screw, it causes chronic surging conditions, especially when NOT under load . . . . which sounds very similar to the problems with being encountered in the OP's machine.

Here's a Donyboy video showing the correction of this surging . . . . just in case it's the cause of the OP's surging and sputtering at idle:






I now find myself cleaning this valve about every 2 years !


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## drmerdp

Regardless of the carb being new, the float needle doesn't always seat well at first. 

I would physically exercise the needle and seat a few times then set the float height using a 5/32 drill bit before trying anything else.


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## e.fisher26

Ive bought a few ebay replacement carbs off ebay that have adjustable bowl jets just to have added adjustability. I like them for the cost of a rebuild kit


-efisher-


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## Mike C.

Does this bower have a flat-head or an OHV engine?In 2007 I think Tecumseh was just about out of business but they were making OHV engines-pretty crappy ones,so I understand.


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## KATfishing

Mike C. said:


> Does this bower have a flat-head or an OHV engine?In 2007 I think Tecumseh was just about out of business but they were making OHV engines-pretty crappy ones,so I understand.


Good question. It's a Tecumseh Snow King 4-Cycle, Horizontal Crankshaft, Air-Cooled, Model 31AE5HTG799. Hmmm.... did I mention I know just enough to be dangerous?!


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## Yanmar Ronin

Hold my beer and watch this... Remove freshly installed Chump-ion, throw as far as you can. Install NGK./


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## KATfishing

Yanmar Ronin said:


> Hold my beer and watch this... Remove freshly installed Chump-ion, throw as far as you can. Install NGK./


OK - Can you please explain more? I can get a new plug, but I'm interested to know more about this (Ironically, it is Champion plug I put in J19LM)... You think the engine responds better to an NGK plug?


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## Mike C.

I believe he's just suggesting you try a different plug.He obviously prefers NGK.

Certain type numbers of Champions suck-I agree. H10 Champions are terrible plugs.But I regularly use Champion RJ-19s and have had few problems with them.

We ARE talking about a flathead engine according to the parts breakdown.If it was a Tecumseh OHV,I was going to suggest junking it for a Predator.


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## DriverRider

Your engine is probably now running too rich and might even have a partially fouled spark plug. When under a load an engine consumes more fuel and the excess unburned fuel with no load which causes your symptoms can now run correctly with load applied.

Your description of needing the choke fully open also lends credence to this.


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## e.fisher26

Alot of ppl may disagree, but i tried the E3 diamond fire plugs from weed wackers to snowblowers and i like them.... one chainsaw that smoked, did considerably less. Maybe because of new plug in general but im sold... 


-efisher-


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## KATfishing

DriverRider said:


> Your engine is probably now running too rich and might even have a partially fouled spark plug. When under a load an engine consumes more fuel and the excess unburned fuel with no load which causes your symptoms can now run correctly with load applied.
> 
> Your description of needing the choke fully open also lends credence to this.


That makes sense. If it's running rich, wondering if there is anything I can do about it since these carburetors seem to be not adjustable (please correct me if I'm wrong).


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## Vermont007

KATfishing said:


> ". . . If it's running rich, wondering if there is anything I can do about it since these carburetors seem to be not adjustable . . ."


Did you look at the video I mentioned in post #8 above ?

It's for the non-adjustable carburetor . . . . like yours !


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## KATfishing

Pictures of old carburetor. New aftermarket (Everest) looks identical. Adjustable???


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## bad69cat

Quick check is pull the plug and look at it for rich/lean condition - when it's sputteing/bogging is the muffler red hot? (Lean) or smoking from unburnt fuel. (rich)


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## KATfishing

Vermont007 said:


> Did you look at the video I mentioned in post #8 above ?
> 
> It's for the non-adjustable carburetor . . . . like yours !


Thanks Vermont007... I'll check the video out again from that aspect. Very appreciated!!!


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## KATfishing

bad69cat said:


> Quick check is pull the plug and look at it for rich/lean condition - when it's sputteing/bogging is the muffler red hot? (Lean) or smoking from unburnt fuel. (rich) https://www.youtube.com/watch?v=uMYAEtxiYfc


Thank you! I'll pull the plug again and check. The muffler is NOT red hot... I recall seeing a few puffs of smoke from exhaust when it sputters, which again makes sense that it's running rich when not under load, and also choke is wide open. It bogs even more if I try pushing it to half choke at that time. This is very helpful. I will watch the couple of videos posted on this thread, especially for adjustments to the new carb. I REALLY appreciate the insight of everyone who is posting and helping me learn! I welcome ALL advice. Merry Christmas!


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## Mike C.

Interesting that the engine basically runs the same with both carbs on it.

This rig is going on ten years old,how many hours would you say are on it?Has it been used a lot?

I'm wondering if the valve clearances should be checked and maybe the head pulled to check for deposits around the valves/seats,especially if clearances are on the generous side.

I would would say that restricted carb idle fuel or air bleed orifices could be an issue on the old unit,but hard to believe the same thing could be wrong with the new carb-unless your gas tank has 1/2 a pound of dirt in the bottom of it and it's getting past the tank screen/filter.

Someone else already mentioned the float and inlet needle.


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## Yanmar Ronin

KATfishing said:


> OK - Can you please explain more? I can get a new plug, but I'm interested to know more about this (Ironically, it is Champion plug I put in J19LM)... You think the engine responds better to an NGK plug?


Undoubtedly, at least for me (flathead B&S). Missed like crazy from new at idle with any J19 I installed, the NGK fixed the problem instantly and permanently. Not saying 100% it'll clear up your problem but it's only a couple of buck hassle-free try.

The J19LM NGK equivalent is B2-LM, or resistor-type BR2-LM.


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## KATfishing

Yanmar Ronin said:


> Undoubtedly, at least for me (flathead B&S). Missed like crazy from new at idle with any J19 I installed, the NGK fixed the problem instantly and permanently. Not saying 100% it'll clear up your problem but it's only a couple of buck hassle-free try.
> 
> The J19LM NGK equivalent is B2-LM, or resistor-type BR2-LM.


Thanks for that info. Does it matter whether I go with resistor or non-resistor type? Do you recommend one over the other for this type of application? I will give it a try!


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## KATfishing

Mike C. said:


> Interesting that the engine basically runs the same with both carbs on it.
> 
> This rig is going on ten years old,how many hours would you say are on it?Has it been used a lot?
> 
> I'm wondering if the valve clearances should be checked and maybe the head pulled to check for deposits around the valves/seats,especially if clearances are on the generous side.
> 
> I would would say that restricted carb idle fuel or air bleed orifices could be an issue on the old unit,but hard to believe the same thing could be wrong with the new carb-unless your gas tank has 1/2 a pound of dirt in the bottom of it and it's getting past the tank screen/filter.
> 
> Someone else already mentioned the float and inlet needle.


Hi Mike - Good thoughts. I would say 50-75 hours on the machine, tops. There can't be much sediment in the tank, although I've never drained/pulled the tank to see what that little screen looks like. I suspect that's not the problem, but obviously something is causing the symptom. I came across a video for lubricating the valves just by pulling the spark plug, turning them with a slotted screwdriver through the plug hole and spraying WD-40 down the sides of each valve in case there is sticking. Think this is a legitimate way to go about it more conservatively without pulling the head?This of course is aside from any clearance issues, which seems overwhelming to me. I'm a bit of a novice - lol!


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## Yanmar Ronin

KATfishing said:


> Thanks for that info. Does it matter whether I go with resistor or non-resistor type? Do you recommend one over the other for this type of application? I will give it a try!


Not really, unless you have a preference for either grey or blue letters/which one's cheaper/on sale.










External dimensions are identical.


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## Mike C.

KATfishing said:


> Hi Mike - Good thoughts. I would say 50-75 hours on the machine, tops. There can't be much sediment in the tank, although I've never drained/pulled the tank to see what that little screen looks like. I suspect that's not the problem, but obviously something is causing the symptom. I came across a video for lubricating the valves just by pulling the spark plug, turning them with a slotted screwdriver through the plug hole and spraying WD-40 down the sides of each valve in case there is sticking. Think this is a legitimate way to go about it more conservatively without pulling the head?This of course is aside from any clearance issues, which seems overwhelming to me. I'm a bit of a novice - lol!


Small engines need to have the heads pulled off occasionally so that carbon deposits can be removed from the top of the piston,bottom of the head,valves and valve seats.If there's crud on the mating surfaces of the valves,they won't seat completely to form a perfect seal,and performance suffers.Although your engine has relatively few hours on it to be concerned with that,I've owned engines with low hours that needed this done.

Squirting the valve stems with wd-40 is not going to do much for carbon deposits in the combustion chamber.If you have a valve sticking because of lack of lubrication of the valve guide or stem (or crud),the wd-40 might help.I don't think this is your problem,but won't hurt to try.

Did you use new gaskets when you replaced the carb?When you removed the carb,did you remove it from the end of the intake pipe,or did you remove the intake and all from the engine?Did you make sure the two bolts/screws that secure the intake to the block are good and tight regardless of how you removed the carb?

If you don't feel you can take on the task of checking valve clearances and pulling the head,it may be time to take it to a shop.However,you say it runs well under load,it just doesn't idle well.That describes better than 40% of the Tecumseh engines I've owned.Some I eventually cured,some I never could and just lived with it.

One more thing you could try:With the engine running about 3/4 throttle or so,take carb cleaner or Seafoam and spray it right into the intake.You have to have the engine running at a good clip because it's going to want to try and stall.If there's gunk on the intake valve or seat this may help clean it off.It worked for me on a couple of lawnmowers using carb cleaner.Give it good blasts.You have to learn how much of a snort you can give her without killing it .On the carb cleaner,don't use the straw,you want a mist.I use a household trigger sprayer for Seafoam.


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## fIXaNYTHING

I agree. Champion spark plugs are pure crap! Always amazed me that Harley Davidson uses them, go figure. Autolite, NGK, Bosch (except in Corvettes)are all good plugs. Stay away from Diamond Fire, as they work well in some applications and cause problems in other. Subaru engines in particular hate Diamond Fire. Split Fires always work well- if you can find them for your application.
On another note- ALWAYS.....ALWAYS use synthetic oils!
-Barrett in Tooele, UT


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## fIXaNYTHING

BRAKE CLEANER, yes good old brake cleaner (The chlorinated type is best if you can still find it). Spray some into the carb while it's running. Lightly at first. after 1/2 dozen times or so run engine up to full speed and do it again several times, just to the point of it dying. Let run until smooth and then drench it until it does die. Remove spark plug and add a few drops of light oil (Marvel Mystery oil is best), and then spray some brake cleaner inside the cylinder. Piston at TDC is best but doesn't make a lot of difference. Screw the plug back in a few turns and grab a cold one. Give it a bit and take the plug back out and rotate the engine several times. More is better, but keep the spark plug grounded. Reinstall the plug (or a new one) and start it up. Do remove the air cleaner before doing this! This works a great deal of the time. Good luck!
-Barrett in Tooele, UT


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## Vermont007

fixaNYTHING said:


> [". . . Do remove the air cleaner before doing this! . . ."


But most Snowblowers ARE NOT equipped with Air Cleaners.


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