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post #1 of 13 Old 06-03-2019, 03:27 PM Thread Starter
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D-600 Altitude Screw

This hasn't been my week for my Lawn Boys.

I was mowing a neighbors lawn and I believe I adjusted the carburetor wrong on my 5273 when I rebuilt it last year. The engine starts and runs okay but it seems too smoky under load and like it's bogging. The "power hum" the mower gives when under heavy load seems very low and weak. I have the screw turned out to 1 1/4 turns. Is that too rich? Unlike the F series this adjustment seems way more tedious. I think I'm starting to understand why some people don't like Lawn Boys. Any help is again deeply appreciated

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)

Last edited by LawnBoy90; 06-03-2019 at 03:38 PM.
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post #2 of 13 Old 06-03-2019, 04:48 PM
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Talking Re: D-600 Altitude Screw

Actually that has much less adjustment because that has an atmospheric adjustment because it is a fixed jet. Preset is 1 1/2 turns and then tune from there. Turn in a little at a time until it starts to falter and then back out 1/4 to 1/2 turn. I have a 5273 and it runs well with no extra adjustments and little to no smoking. Obvious question would be how are the ports? Clean? Pretty hard to clog up that big dinner plate muffler unless something would be in the round outlet. May be some other issue if it is running rich. Try manually lifting the throttle rod to speed up the engine and see what kind of power it has. Don't over rev it but it should speed up pretty well and have a lot of pep. If not, check ports. Any chance the needle is not seating after the cleaning and it is flooding out? And for the record, I personally love the Lawnboys, especially the older ones due to their simplicity and ease of operation and repair. Don't give up yet. Bill

1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

Where there's a will, there's Mr. Bill!***They don't call me MacGyver for nothing!***I have LBAD and DCAD!
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post #3 of 13 Old 06-03-2019, 08:13 PM Thread Starter
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Re: D-600 Altitude Screw

I had the adjustment at 1 1/2 turns but it didn't seem like it wanted to falter at any point even when I got close to closing the needle. That's where I'm stuck scratching my head. I allowed time for adjustments to stabilize. My ports are clear and throttle response is normal. The float was terribly loose before and I crimped the little hinge clip on the float to tighten it up a little. Needle and seat made a little clicking noise when opening and closing indicating they were working. Could the float still be at fault?

I love the old LBs the D400s are great reliable machines but the D600 seems to be finicky to adjustment.

Sent from my XT1710-02 using Tapatalk

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #4 of 13 Old 06-03-2019, 09:43 PM Thread Starter
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Re: D-600 Altitude Screw

Update: I turned the needle adjustment out a little more after letting it sit a while and it starts good cold. Adjustment is maybe about 1 1/8 turns to but it doesn't seem to smoke bad anymore. It burbles and seems to tackle long grass okay. Thanks for the help!

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #5 of 13 Old 06-04-2019, 01:38 PM Thread Starter
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Re: D-600 Altitude Screw

Another update: Turns out the oil seal is indeed leaking. The muffler was sealing correctly and had no blockages but I had a nasty oily film around the part where the crankshaft is. Guess that's why the mower wasn't responding to adjustment very well and running really rich at 1 1/2 turns out. Will pull the engine and give it a metal oil seal instead of the rubber one.

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #6 of 13 Old 06-19-2019, 04:28 PM Thread Starter
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Re: D-600 Altitude Screw

Okay finally have an update. I've since replaced the seals and adjusted the altitude screw until the engine sounded okay. It still smokes but that's probably from all the oil residue in the muffler. What's a good area to have needle out? Is between 3/4 and 1 turn good for the metal D-601 car or is it too lean?

It seems any more than 1 turn will cause it to smoke more and rpms drop and the mower bogs in a load. Around the one turn spot it sounds like it gets up a little in RPM and burbles.

Sent from my XT1710-02 using Tapatalk

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
LawnBoy90 is online now  
post #7 of 13 Old 06-19-2019, 08:09 PM Thread Starter
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Re: D-600 Altitude Screw

Anyone?

Sent from my XT1710-02 using Tapatalk

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
LawnBoy90 is online now  
post #8 of 13 Old 06-19-2019, 08:13 PM
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Re: D-600 Altitude Screw

Please re read post #2. Bill

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1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

Where there's a will, there's Mr. Bill!***They don't call me MacGyver for nothing!***I have LBAD and DCAD!
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post #9 of 13 Old 06-19-2019, 08:32 PM Thread Starter
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Re: D-600 Altitude Screw

Everything checks out on this mower. Clean ports, new spark plug, new gaskets and seals. New needle and seat. Still runs like a dog. Adjustment seems to work but no faltering or hunting or surging. I was asking for general ballpark of where the needle rests after adjustment. My engine seems to run okay between 3/4 to 1 turn but I'm thinking that's lean. It runs rough still at 1 1/2.

Sent from my XT1710-02 using Tapatalk

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
LawnBoy90 is online now  
post #10 of 13 Old 06-19-2019, 11:06 PM
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Talking Re: D-600 Altitude Screw

Okay a couple of points. According to the Lawnboy Service Manual, adjustments to the atmospheric needle are rarely needed unless the mower is operated at extremely high or low altitude so with the pre set at 1 1/2 it should run pretty well with minimal tweaking. Also, when the atmospheric needle is completely closed there will be no air flow through the carb vent passage therefore the float bowl pressure will have been eliminated and the fuel supply to the carb venturi will be cut off. Just curious, have you tried turning the needle all the way in and lightly seat it to see it the engine stops running? There shouldn't be any air flow if the needle is all the way in. Just looking for something out of the ordinary here. Bill

1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

Where there's a will, there's Mr. Bill!***They don't call me MacGyver for nothing!***I have LBAD and DCAD!
Yard Nazi is online now  
post #11 of 13 Old 06-20-2019, 12:27 AM Thread Starter
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Re: D-600 Altitude Screw

Quote:
Originally Posted by Yard Nazi View Post
Okay a couple of points. According to the Lawnboy Service Manual, adjustments to the atmospheric needle are rarely needed unless the mower is operated at extremely high or low altitude so with the pre set at 1 1/2 it should run pretty well with minimal tweaking. Also, when the atmospheric needle is completely closed there will be no air flow through the carb vent passage therefore the float bowl pressure will have been eliminated and the fuel supply to the carb venturi will be cut off. Just curious, have you tried turning the needle all the way in and lightly seat it to see it the engine stops running? There shouldn't be any air flow if the needle is all the way in. Just looking for something out of the ordinary here. Bill
Thanks for the insight on this! I checked and the engine does die at closed. I didn't run it long like that this time but usually around a minute the engine quits.. It seems to respond to 1/4 turn increments from preset. Is it best to adjust at high speed or light speed? The service manual states to test both speeds. I usually just adjust at top speed.

I forgot to factor I am actually fairly low elevation for Indiana.

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)

Last edited by LawnBoy90; 06-20-2019 at 12:32 AM.
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post #12 of 13 Old 06-21-2019, 02:38 AM
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Talking Re: D-600 Altitude Screw

I never run my 2 speed Lawnboys on low but the manual does say to check ease of restarting on both high and low. If it restarts well on high then I wouldn't worry about it. Bill

1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

Where there's a will, there's Mr. Bill!***They don't call me MacGyver for nothing!***I have LBAD and DCAD!
Yard Nazi is online now  
post #13 of 13 Old 06-21-2019, 03:53 PM Thread Starter
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Re: D-600 Altitude Screw

Will keep in mind for future tuning on my mowers! I unfortunately have come with bad news. I've had a sneaking suspicion that the bottom bushing in the crankcase was worn out of spec judging by the oil seal failure on both ends of the engine. I checked the bottom seal again today and once again seal failure. Found lots of play on the bottom end so I think that means the engine is toast. I don't really want to dump money on a new crankcase either so I don't know what's going to happen to the mower.

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
LawnBoy90 is online now  
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