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dmcluckie

SnowThrower engine problem

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dmcluckie
This is not Simplicity, but some of you guys are the best small engine mechanics I've found on the net, so I thought maybe you can help me out. I am working on my Ariens snowthrower with 8HP Techumseh Sno King motor. The previous owner had the same problem I am having. He spent a lot of time trying to figure it out, and paid good money to a shop also. No one has fixed it. If I let it idle for more than 10 or 15 seconds, then move the throttle up slowly, at mid-throttle it loads up, sputters, and belches a few puffs of black smoke. Then it dies or else stumbles back to a smooth RPM. OTOH if I let it idle just for a few seconds, then move the throttle, it does not do this, it only has a slight stumble in the midrange but nothing you couldn't live with. If I let it idle for a longer while, then move the throttle rapidly to full, again it only has a slight stumble in the midrange but nothing you couldn't live with. Most of the time it will idle forever, it just won't accept mid-throttle after that. So far, you could say: "Don't let it idle", and "if you do, then don't move the throttle to mid-way". :) And, so far, that's the best anyone can do. It has fresh gas. Ultra clean fuel system. The inside of the carb is spotless, looks like new. Welch plugs and ball plugs do not look leaky. I changed the needle and seat. Pressure tested it, it works. Gravity feed, no fuel pump. Float is hollow brass but not leaking. Tried leaner float positions. Tried different idle mixture settings. Tried different high speed mixture settings. Tried combos of the last 3 things. There is a stock primer connected to the carb by a hose. It seems to put pressure on the float bowl when you push it. I disconnected the hose at the carb, no difference. There is no air filter. Like most motors the throttle cable actually moves a spring loaded lever which is connected to the governor which is connected to the throttle. I cannot come up with a governor theory to cause the problem. ?? I'm not sure on this next clue, but I *think* it doesn't cold start well. Tonight it took forever to start. It has a 110v starter so it can crank pretty good. I kept thinking it must be flooded but finally I got it to fire with the choke, then it was loaded up and I had to floor it to start it. So that could be just poor technique on my part tonight. I have not checked compression or ignition. It is like new and runs fine when you work around the loading up problem. Could ignition adjustment lead to this problem??? I can't see it, but... I don't like to be a "parts replacer", but I am tempted to buy a whole new carb. It seems like there must be a circuit leak somewhere. Any suggestions? Thanks!

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HubbardRA
The only other thing that I can think of is the spark plug. If it has the wrong heat range plug (probably too cold) it might have a problem like this. A long idle could cause the plug to cool down, causing the stumble. It would remain hot for a short idle. This may not be it, but I have had similar problems with motorcycles that are very sensitive to plugs. Rod H.

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powerking_one
Don, If it's any consolation, my VERY early HM-80 (on a pressure washer I built) does the same thing. The carb is checked out/rebuilt/ as good as I can make it. On the other hand, my much later HHM-80 engine and newer revision of carb doesn't have the problem. I suspect it was a rush to market and early rev of carb design flaw. Root cause probably has something to do with the idle circuit well restricter and/or the graduated idle oriface holes placement in the throttle bore. They look different on the two motors I cited. Like Jeff mentions, the latest(er) rev replacement carb will problably fix it. Spark plugs don't typically affect an off idle/low to high speed circuit mixture transistion condition. Hope you are feeling like Mr. "McLucky"! (LOL) Tom(PK)

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BigSix
Tom: My experience with sparkplugs affecting off-idle throttle transitions has been consistent, on a few engines, with this situation, so no offense intended whatsover, I just want to second Rod here. This has only occured, to my memory, re: two stroke engines, and I bet when Rod mentions motorcycles, he's talking two strokes? So you may be 100% correct re: fourstrokes, 'cause I can't remember any that did that. With two strokes though, with my persnickity 25 year old Poulan Micro 25 (good power, ticklish carb) if it's not got a good strong plug, you get periods of idle but she won't take the gas. Same with a '70's "Harley" AMF imported, which was a little 65cc Armachii two stroke, rebadged as a Harley (can you feature that?). Very picky re: plugs, and it could sniff out those that had been "vapor honed" or sandblasted. Didn't like them much either. I'm still wondering which way this snowblower is "leaning," no pun intended, if it IS a carb problem, lean or rich? I assume the carb is not loose? I've seen loose carbs or otherwise leaking intake manifold gaskets cause some goofy, intermittent symptons. Just my .02. Peter

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dmcluckie
Guys, thanks for the replies! PowerKing, it *is* a fairly old HM80. The serial number indicates it is a 1979, according to my manual. The owner hardly ever used it, you would guess this unit is just a couple years old, it looks so good. I was actually wondering if this could just be the way it runs. There is a 4-star Ariens dealer near me and I will check on the revised carb. Do I feel "McLucky"? I guess I should, even if I don't. ;) BigSix, it seems to be rich. It puffs out black smoke when in stumbles. Thanks again.

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powerking_one
Peter, Rod: I didn't mean to discount your suggestions about spark plugs possibly causing this, but Don's graphic description of the problem perked my ears up to make me think he had my engine! I'd think Don and previous folks have swapped plugs in troubleshooting this. My engines are not the Sno-King type however and don't have the primer bulb setup. As far as spark plug finickiness on 2-strokes, I couldn't agree more. Personal experience has seen many battles with brand, heat range, and over-rich oil injection reeking havoc with plugs fowling causing many weird performance problems(dirt bikes, chain saws, etc). You may remember the discussion a few months back. http://www.simpletractors.com/club2/topic.asp?TOPIC_ID=8035 Peace! Tom(PK)

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Cheap_Dave
Check the governor meaning is the little piece with the screw tight on the governor shaft, had these problems on mine. also make sure the linkage is not touching anything it's not supposed to had a POS craftsmen tractor no one could make run right untill i found the carb linkage was rubbing on the fuel line and the governor was either wide open or closed tight, it would start and just about explode or it would start and idle nice but die after throttle up. easy fix just bent the linkage out of the way (not supposed to but it worked) re adjusted linkage on the governor shaft and ta da fixed. Hopes this helps. Dave

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dmcluckie
quote:
Originally posted by dlcentral: If you or someone else took carb bowl apart you ''monked''up the hi speed assy.,,Will get back later for a fix on it..,,
I'll be interested in your advice, I don't think I monked anything, but I'm not perfect. Ask my wife. ;) However, I think I got it fixed. The problem was, it was idling with the throttle butterfly completely closed. Based on the tuning instructions in the service manual, that is not the way they want it. It looks like the airflow past the idle and intermediate fuel ports is screwed up with the butterfly closed. That was my first clue, when I saw that. The book says to adjust it slightly open as a starting point, that was my second clue. :) I did have a hard time with the governor linkage adjustment. The book was not too clear on it. I did it by trial and error and think it is close enough. I will see when I get put it under load. I am going to wait for winter to fine-tune the jetting, otherwise I'm declaring it "done". Thanks again for the great suggestions!

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