Tecumseh hmsk80 will idle all day, but won't run at full speed.

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  #1  
Old 03-12-17, 05:28 PM
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Tecumseh hmsk80 will idle all day, but won't run at full speed.

OK So I got this old snow blower given to me that should have just gone to scrap. Now that I've gotten it this far I'm WAY too stubborn to just walk away. I've got all the running gear rehabilitated and working well. I replaced all the fuel lines, new plug and new cheap aftermarket carb. It's the model that does have main mixture screw and and idle mixture screw.

I had it running a couple months ago, but when you went to transition from idel to full throttle you had to go very slowly or it would just immediately surge and die. I did get it to full throttle and set mixture screw. All seemed to be OK, although i wasn't 100% confident with that weird transition issue.

First snow comes, it runs for a bit then dies. Restarts right away but just not right. I play with it for a bit and have it purring so I think I'm good, then surging and dead. No snow anyway so leave it. Now the Apocalypse is coming so I'm trying again. I take the carb apart and run cleaner through it, runs terrible. Look at some more pictures and realize I did not clean out the little holes on the main mixture pieces. Clear that out and now it's back to running fine at idle but crazy surges on transition and won't run right. After staring at this thing for most of the afternoon I realize the throttle return spring on the carb itself is NOT on. I put this on, now when you go to transition it's much smoother and doesn't do the crazy surging but still the same thing. Runs at full throttle for perhaps 10s then dies out. If I can get it back to idle fast enough it will recover.

I am now overly familiar with the names and locations of everything. I've played with all the linkage screws, governor arm & mixture screws.

As it stands with a warm start you have to close the choke to get it to start, but the second it starts you can go full open and it will idle all day. I can get it to run at part throttle for seemingly forever now, without surging. you still have to apply throttle slowly or it wants to go full open on throttle and die. At full throttle it will run for a bit, then just go full throttle open and done. In all my messing around I'm not really seeing any black smoke, what I tend to see is white puffs.

Does this sound like carb and linkage issues or could there be something else wrong that means I'll never get it? Any ideas what I'm missing? I'm confident that it's close now. There's no question that spring was off the whole time. But it just won't run at full throttle and I'm not sure if it's lean, rich or something else entirely.

Thanks in advance!
 
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  #2  
Old 03-12-17, 05:48 PM
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It's a carburetor problem. Does gas enter the bowl at a steady rate? The inlet seat could be swollen nearly shut, allowing just enough fuel flow to feed the engine at idle but not at higher speeds. If it has a high speed mixture screw under the bowl, it could need richening. If it has a fixed jet in the bowl nut, it may be partially clogged.
 
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Old 03-12-17, 05:54 PM
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The carb is new so hopefully nothing swollen shut. The only thing I did just consider is something clogging the outlet of the tank. The line is new from the tank, through the shut off valve and to the carb. The little primer is new with new line as well. I tend to think it's getting enough gas as it will run at idle for a good long time after you shut the valve off at the tank. I'm not sure what kind of flow it should be getting, but I could take the bowl off, open the valve and just see how fast it flows.

Yes it has both high speed and idle mixture, it's not a later fixed jet carb.

Thanks
 
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Old 03-13-17, 12:09 AM
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The surging is it running out of fuel. It going full throttle as it dies is a result of the governor trying to give it more fuel to maintain speed, but it's only getting more air, not fuel. The main jet has picked up something or something is clogged/restricted. Does the carb have holes for an air intake box or filter housing? Is it in place? Some of these carbs will pull air through those holes if the bolts are not in them.
 
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Old 03-13-17, 05:34 AM
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I was thinking about it last night, what about the seal of the bowl itself to the carb? I was struggling a bit with that. Could it be pulling air in their, lowering vac pressure? Not sure if that's a thing or not.
 
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Old 03-13-17, 10:43 AM
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No, that won't cause a running issue. It would keep the primer from working right though.
 
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Old 03-13-17, 09:09 PM
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It runs. It was the metal screen at the bottom of the tank. Cleaned it all out and it's running decent. It's popping and spitting a tiny bit. but I did three passes through the yard (much to my neighbors amusement) and it pulled with no surging and no clogging. Tomorrow will be the big test! It will need a new tank, belts and some other things. But I'm not going to put any more money into it until I see how it performs. It's a 2 stage 28" Simplicity with an 8HP motor. I'd think that's a bit under powered for that size but I don't know. I will also need to verify the RPM at some point. But for now, let's just hope it gets through tomorrow!

Thanks
 
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Old 03-14-17, 12:31 PM
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Well it ran like a beast for over an hour. Then started running lean and coughing again. More dirt I'm sure. It ran like that for another 1/2 hour where it would cough for a bit then come back strong. now I'm seeing the bowl is dripping a bit too. Having' looked from where. Side effects of bringing back a machine that should have been dead. For that hour though it ran strong. I need to get something so I can measure RPM. No load sounds about right but under heavy load it seemed to be looking for more. I'm assuming that would be a minor governor adjustment. But again, without a way to measure RPM I'm just guessing.
 
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Old 03-14-17, 03:31 PM
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The fuel restriction would cause it to want for more under a load. SOunds like you need to do some more cleaning and put a good filter in between the tank and carb because the float bowl dripping is most likely due to trash getting in the inlet needle/seat area.
 
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Old 03-14-17, 05:10 PM
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The tank is toast and the cause of the dirt, but I agree on inline filter regardless. Float I don't know, it may just be I didn't tighten it enough and it vibrated loose. I don't really have any experience to compare it with anything else. But this was a good 12" of heavy wet crap for over an hour and it was tossing it at least 10'. Even passing through drifts that were taller than the scoop it pushed right through.
 
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