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Discussion Starter #1
Engine is a Tecumseh HM-80. I rebuilt the carburetor and set both the idle and main needles 1.5 turns out. I adjusted the governor to the right spot when I reinstalled the carb.

I started it up and got the idle needle adjusted no problem.

When I back the main needle out, it's about 2.75 turns out when it starts to die. If I turn it in 1/4 turn at a time, it smooths out at about 2 turns out. From what I've read, I want to keep turning it in until it runs bad again, then set it midway between that point and 2 turns out.

My problem is that I can turn the main needle in all the way without it running any worse. I noticed my muffler starting to turn red so I shut it down and backed it back out to 2 turns.

For lack of any other ideas, when I started it back up, I sprayed carb cleaner all over the place trying to see if there was an air leak but didn't find anything.

What does this mean?
 

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Safety note, Please don't spray carb cleaner on a hot / running engine. Could ignite off the muffler.


The muffler glowing red was from a lean fuel condition. By turning in the main jet at wide open throttle you starved the engine of fuel, driving heat up in the cylinder. Result a red hot muffler. I've found TEC. engines to be fussy with adjustments like your describing. Back it out until it runs bad and bring it back until it just runs good and leave it. If your using fuel w/ methenol it will need to run a bit richer on the main.
 

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Discussion Starter #5
That's pretty much what I have done, but I'm still trying to understand what's going on.

If I gradually lean out the mixture, what stage comes first, a red hot muffler or the engine starting to run rough? I ask because I've adjusted a few others and turned the screw in until it was running rough before backing it out. Was I past red-hot muffler stage and didn't notice?
 

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Discussion Starter #6
While I'm asking carb related questions.... Where does the float level fit into this all? I've read that too low makes it run lean and too high makes it run rich.

With properly adjusted mixture screws, would a slightly high or low float level make a difference? Would it only make a difference if I ran out of adjustment on the screw?
 

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Factory float level (usually float parallel to carb casting) shouldn't cause a problem. E10 gas is gonna lean you out some & it also absorbs humidity (hygroscopic is the term & it's why you're supposed to change brake fluid periodically). I set the high speed @ high speed & under a load (when I can). Hunting a vacuum leak was a good idea, but they generally have a greater effect at low throttle settings (higher vacuum then, & WD-40 is my choice of aerosol ). Leaky valves could be causing a blow-torch effect at the muffler, but an old rust-thinned muffler might too. I wouldn't guess that HM 80 as being a spring chicken, right? An additive like Sea-Foam to insure carb cleanliness & maybe a top-end oil like Marvel Mystery Oil periodically should help a mite, but be ready to 'touch-up' the mixture when you do. Do a little research on the web & maybe with some local shops about the lean-out & deposit forming ills of the E-gas. I think you'll find it surprising. Local stations have aired pieces on mowers being scrapped at a record pace due to the effects of the 'improved' gas. Good luck to us all, with all this progress!
 

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Tecumseh carbs a pain in the but. I have a generator with a HM100. I soaked the crab out of the carb, got, what I thought was pretty clean. And it won't run without the choke on. Took the carb back off, tried cleaning it again, still same problem. So I broke down and ordered an Oregon Products replacement card. Also have a snowblower 5.5hp snow king, with same senario, clean real good, and still won't run right. had to order a replacement for it, also. Oregon is going to make some good money selling carbs fro Tecumseh's It seems, the best thing to do with Tecumseh's is drain the gas out, when your not using it.
 

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tecumseh's have that little hole that has to be cleaned and can be missed. took me a while to get one running good again
 

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Aren't Tecs the ones with the welch plug covering access to the (plastic?) discharge nozzle in the carb throat? I don't retain like I once did, but seems that a member fixed one of these by pulling the plug & replacing an 'O' ring which sealed that nozzle, restoring the vacuum signal. Seems that there are different rated nozzles with different colors too.
 

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The nozzle is up above the high speed jet (the nut that holds the fuel bowl on). You can push it out with a small screwdriver or pick, thru the carb throat. I replaced the O rings and haven't helped my 2 carbs at all.
 
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