Tecumseh H50 Idle Speed

#1
What is typical idle setpoint for a vintage 1980 H50 (adj. carburetor)? Minibike Service Manual indicates 1800rpm for float-type carbs. This seems extremely high. Just looking for what others have had good luck with.
 
#5
Idle speed is a blend of the main jet, low jet and the plate screw. You just have to play with all three to get it down. Best advice is to set the carb and governor up as described in a TEC manual, then adjust from there. You won't really have it right until the bike is assembled so the engine can be under a slight load at idle. Even then you'll be playing with the carb because something won't be right at throttle the first time you take the bike out. Patience is a virtue.
 
#8
I was looking more for an empirical number. I'm currently set at 800rpm. Not really close to the "book" value specified...
Which book value are you referring to? There are some numbers on microfiche #30 which maybe Johnny Tillotson has, but I doubt any of the equipment listed on it will be "mini bike."

I never use a tach on these vintage engines. I adjust the idle until it is low enough to not engage the clutch. I don't want any clutch expansion what-so-ever, as it wears out clutches and burns up the lubrication on the bushing.

But I don't turn the RPM down so low that the slinger isn't lubricating the bottom end either. Also, in hot weather, or on slow or stationary equipment, you need enough RPM to cool the engine with the fan.

Sorry if this is not the level of detail you are looking for, but it's how I do it. I'll assume you know the idle adjustment procedures on non-emission engines with adjustable jets, but because I was there, I cut and pasted the book procedures below.

And a correction for a comment made above. The main jet does not come in to play on "this" carburetor at idle. If it is drawing off of the idle transfer passage at idle. If it is drawing off the main jet, it is idling too high. However, the idle setting is additive when transitioning to high RPM and at WOT. Not the other way around. Pretty common method of idle feed on bowl type carburetors.

FINAL ADJUSTMENTS (NON EMISSION ENGINES)
Start the engine and allow it to warm up to normal operating temperature (3 - 5 minutes). Set the speed control to the HIGH or FAST position. From the recommended preset position, turn the main mixture adjustment screw in (clockwise) slowly until the engine begins to run erratic (lean). Note the position of the screw. Now, turn the screw out (counterclockwise) until the engine begins to run erratic (rich). Turn the screw in (clockwise) midway between these two positions. This will be the best setting. (diag. 21, 22 & 23). Set the speed control to the IDLE or SLOW position. Adjust the idle mixture screw following the same procedure used to adjust the main mixture adjustment screw.

If further adjustment is required, the main adjustment should be made under a loaded condition. If the engine stops or hesitates while engaging the load (lean), turn the main mixture adjusting screw out (counterclockwise) 1/8 turn at a time, testing each setting with the equipment under load, until this condition is corrected.
If the engine smokes excessively (rich), turn the main adjusting screw in (clockwise) 1/8 turn at a time, testing each setting with the equipment under load, until this condition is corrected. After the main mixture screw is set, move the speed control to the IDLE or SLOW position. If the engine does not idle smoothly, turn the idle mixture screw 1/8 turn either in (clockwise) or out (counterclockwise) until engine idles smoothly.
Recheck the high and low R.P.M. setting and adjust as necessary.
 
#9
^Thank you for this excellent response. The book I'm using may not be too terrible "correct"- "Minibike Service Manual" (second edition). Sections for Gilson, Wards, AC and the Tecumseh engine section which is what I'm using. I don't think 800 is going to benefit lubrication...

The above procedure is what I read in my book as well. I have noticed that there are extremely tight windows of acceptability for both MAIN and IDLE adjustments. The balance between lean stumble (on load) and smoking is less than an 1/8 turn on the MAIN for my engine.
 
#12
Scroll up ^^^ to the second "Sticky" entitled "Tecumseh Flathead Service Manual" and click on the link/pdf. That will get you started for FREE. As for me, I'm "old school" (and OLD!) and prefer to hold/read a paper manual.
Michael
 
#13
I hear you. I like a hardcopy for the top drawer of the tool box. I have a fiche reader in the garage so I wish I could lay hands on #30. That seems to be the only place with possibly an actual number for idle speed.

For me, it merely boils down to clutch engagement and proper lubrication. The only complaint I might have is that 1000+ rpm tends to shake the machine a bit besides being loud. The positive with that setting is it is not far from torque converter belt hook-up point.
 
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