Hey all. My 10552 started running terribly today, wouldn't rev, would just putt at low rpm and couldn't really mow with it. 'Felt' like a carb issue - it would gain revs on choke slowly and then sound like it was fighting the choke, turn choke off and slowly it loses revs, regardless of throttle position. So I took the carb off and all seemed more or less ok (inside was clean, jet not clogged, float seemed to be ok...) But I noticed this jet on the outside left side of the carb, which I've never noticed before. Took it out and it looks like a pilot jet of sorts, but it must be air right? It was covered with oily dirt/grass like everything else around there. I cleaned it off and it runs better now but still not right. I looked at parts diagrams and they don't show this jet separate from the carb body. Pic is looking at the left side of the carb with everything fully installed.
So...... Am I missing a cover or something? No way can a jet be exposed to such a dirty area on purpose.
Thanks!
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#2
dougmacm
Yes, that is the Pilot Jet and it is NOT connected to atmosphere, it is an internal fuel orifice. Pull it out again and you will see the orifice goes nose to side and not to the outside. It is a very small orifice and if plugged will cause running issues.
Stock pilot jet was:
Toro / L-B # 475-8452 and is stamped "37.5" size (= 0.375 MM)
Alternate ones that were available that could make mower run better:
Toro / Suzuki # 81-1030 "40" size (0.400 MM)
Toro / B&S # 801308 "42.5" size (0.425 MM)
You can also drill out the stock jet if you have a set of micro drill bits and a pin vice:
#78 drill = 0.406 MM
#77 drill = 0.457 MM
Sorry but I don't understand. Should there be a cover over the jet? Right now it's just like in the picture, nothing at all covering it and of course in that area it gets filthy quick. It seems like something is missing on that side of the carb?
#4
dougmacm
When the mower was new, Lawn-Boy put a black sticker over the orifice. The reasoning was more for stealth, in that they wanted to HIDE the orifice to avoid tampering.
As I said before (and sorry if I was not clear enough), the orifice is "internal" on this small brass part, the hole you see in the middle on the outside is a DEAD END / does not actually connect internally. So it could be completely caked with dirt and it would have no effect whatsoever.
Ah, now I get it. Thank you for the explanation, I'm going to clean it real well again and drill it out if it's generally accepted that these run better that way. And now I know not to drill it all the way through!
#6
dougmacm
You can get a set of the 61-80 micro drill bits & pin vice off of ebay for under $10. I bought mine back in 2005 when I was experimenting with jet sizes on my Duraforce mowers.
As the stock orifice is 0.375 MM / 0.0147", the #79 drill / 0.0145" (2nd smallest in set), is just a hair smaller so it is good for cleaning jet out / checking that it is clear.
And make sure you get a pin vice (micro bit holder) with the set as it is the only way to hold these small drills !!
The #40 Suzuki Pilot Jet was typically the ideal pilot jet size and the # 78 drill is just slightly larger. There is one on ebay right now for $18.37 shipped, which is almost double the cost of the drill bit set & pin vice.
Thanks Doug. I have a set of those drill bits already (motorcycle carb work) and I've had luck putting the bit into my vise to hold it securely and then turning the jet manually on the drill bit to drill it out, since you're hardly taking any brass off with the drill. I'll get after it today, thanks again!
I drilled out the jet with the 78 drill bit which definitely took off a little brass. Cleaned it all out and it seems to run good again. One more question: it hasn't ever seemed to rev very high, like a 4 stroke does. Is that normal for these 2 strokes? The governor seems to be allowing the throttle plate to open fully but it's hard to tell.
Thanks again for the help, you saved me a lot of head scratching!
#9
dougmacm
If you have a tach, the Lawn-Boy Duraforce spec for operating speed is 2900 RPM +/- 300 RPM.
To adjust RPM, you just turn the toothed collar below the air vane (can be seen in the pic you posted).
Turn CW to raise the RPM / CCW to lower.
You should see about 50-75 RPM change per click on the adjustment collar.
You typically do need to tweak this after messing with the orifice(s).
The Lawn-Boy Duraforce "TORO E Engine Service Manual" is a handy thing to have if you don't already have a copy.
Not sure if this is still available for download on the Toro web site or not. If you can't find it, I could email you a copy.
Thanks Doug, I downloaded it. The mower is running well right now, I put the tach on it and it's at 3200rpm. Sounds a lot better than it did previously when it was revving low.
