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post #1 of 14 Old 08-21-2019, 03:46 PM Thread Starter
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Lawn Boy 7260B No Running properly

Hi all,

I've been working on this 1973 7260B for weeks now and just got it back together. I've rebuilt the engine with a good piston, NOS rings, NOS gasket set, new carburetor rebuild kit, cleaned and adjusted the points, and new oil seals yet it runs very low and smokey at the preset of two turns on the needle valve. With all these new parts I'm at my wits end with this machine. It'll run and sound normal if I lean out the adjustment but something tells me that's not right. Most of my 400s run between 2-2 1/2 turns out on the needle valve. But this mower is running too rich. I've heard of coil failure but it can't be I get a really good spark and it's been gapped correctly as well as the plug. I just don't know what's wrong. I'm very close to sending it off to the local scrap guy because I don't want to deal with it anymore. Any help and suggestions are greatly appreciated

Thanks,
LB90

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 #2 of 14 Old 08-21-2019, 04:37 PM
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Re: Lawn Boy 7260B No Running properly

Lean out the carburetor and leave it alone. Someone before you owned it may have drilled the jet and the only way to get it right is at the leaner setting. If you want to scrap it and will bring it to southern WI I will deal with it for you. The books are not always right for a given engine. Roger
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post #3 of 14 Old 08-21-2019, 06:20 PM Thread Starter
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Re: Lawn Boy 7260B No Running properly

The engine did start to respond well and the throttle plate moved like normal when I did lean it out so I think you are right. Throttle response is normal as well. I really don't want to scrap it but its been a headache ever since I got it together. It's been in heavy loads a good few times and the cylinder walls and piston look good so I don't think the leaner setting is hurting it.

Good point on the manual. It's put me into more stress than confidence. I think all our machines have so much age on them they're gonna be more finicky compared to when they were younger. Thanks!

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 14 Old 08-21-2019, 08:13 PM
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Re: Lawn Boy 7260B No Running properly

Almost has to be getting itís extra fuel through the primer circuit. Typical for these carbs. Need a primer kit, new would be better, if itís new, but sat on the shelf for 40 years there is no guarantee that itís going to be good.
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post #5 of 14 Old 08-21-2019, 08:58 PM
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Re: Lawn Boy 7260B No Running properly

hello Seth
do not give up yet Scott here to help you out sometimes when work on them i find
that the adjustment side of points you can bend to set right to ask you can you send
a picture of points condenser would like to see the wiring how you placed it to share
the wiring place coil wire on condenser post first then shut off wire that would help see
how it looks thanks pm the picture to me
your lawn-boy friend Scott
points are set for your engine is .020
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post #6 of 14 Old 08-21-2019, 09:43 PM Thread Starter
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Re: Lawn Boy 7260B No Running properly

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Originally Posted by Lawnboy77 View Post
Almost has to be getting itís extra fuel through the primer circuit. Typical for these carbs. Need a primer kit, new would be better, if itís new, but sat on the shelf for 40 years there is no guarantee that itís going to be good.
Primer assembly is new and seems to work okay. I don't think it's that old the rubber components still appeared good. When this engine was malfunctioning the first time I replaced the assembly when I redid the carb. Do you think the air filter box gasket could be a culprit? I think I have the one meant for the 600 carburetor on there. Didn't think there was a difference but it seems the one for the 400 series mowers has smaller holes on it.

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 #7 of 14 Old 08-21-2019, 10:06 PM
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Re: Lawn Boy 7260B No Running properly

good evening Seth
do check that gasket under the air cleaner i have had that problem to
and changed and did the trick is was on a 7261 carburetor so try that
please let me know how it goes
your lawn-boy friend Scott
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post #8 of 14 Old 08-21-2019, 10:31 PM Thread Starter
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Re: Lawn Boy 7260B No Running properly

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Originally Posted by lbuser64 View Post
good evening Seth
do check that gasket under the air cleaner i have had that problem to
and changed and did the trick is was on a 7261 carburetor so try that
please let me know how it goes
your lawn-boy friend Scott

Well just got back from the shed. The smell of gas was in the air and the mower was dripping fuel from the air box. I forgot to turn the fuel off. So, can a faulty needle and seat cause over rich running? The gasket was the correct one to my surprise since I swore I put the one with larger holes on. Float is still good I think so that may narrow it down. Also it ran okay with the air cleaner off does that point anywhere?

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 #9 of 14 Old 08-22-2019, 02:11 PM Thread Starter
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Re: Lawn Boy 7260B No Running properly

Pulled the carb off today and checked everything. The float was leaning more towards 1/2" rather than the standard 15/32" setting so I corrected that. The washer for the needle and seat was pretty squashed so I think I found the flooding problem. Replaced the washer, new gaskets and a reed flip later it started but did the same thing. This time I only had to turn it about a third turn in and it ran rich but with only a hint of smoke. Ran it in some heavy grass out back and it seemed to respond okay. Smoothed out like it should and got smokey under heavy load. If it blows up it blows up. All the wiring under the points chamber was correct as per the manual.

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 #10 of 14 Old 08-24-2019, 04:57 PM Thread Starter
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Re: Lawn Boy 7260B No Running properly

Today was a success! Turns out the spark plug was the culprit. After all the over rich running it was fouled past the point of cleaning. I threw in a good plug that was laying around and my RPMs went up and now the engine runs like a top with some smoke under heavy load..just right. Lesson learned: Never doubt your ignition for causing issues! I think I'm going to switch plug brands though since this hasn't been the first time a spark plug was bad.

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 #11 of 14 Old 08-24-2019, 05:07 PM
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Re: Lawn Boy 7260B No Running properly

Don't leave me hanging... Which brand has been bad for you??
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post #12 of 14 Old 08-24-2019, 07:49 PM Thread Starter
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Re: Lawn Boy 7260B No Running properly

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Originally Posted by TheSteelGator View Post
Don't leave me hanging... Which brand has been bad for you??
Champion. I've been burned a good number of times with faulty plugs. I used to use them religiously since LB/OMC said so but it seems in recent years folks have been having issues with them. Most of the places around me sell ones made in Mexico and that could be why. No worries I'll just upgrade to Denso or NGK.

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 #13 of 14 Old 08-24-2019, 08:37 PM
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Re: Lawn Boy 7260B No Running properly

Good call. NGK have never given me problems in Toyotas, Subrarus or Lawn-Boys.
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post #14 of 14 Old 08-24-2019, 11:47 PM Thread Starter
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Re: Lawn Boy 7260B No Running properly

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Originally Posted by TheSteelGator View Post
Good call. NGK have never given me problems in Toyotas, Subrarus or Lawn-Boys.
I recall NGK's being my father's Honda mowers and if a brand like Honda uses them they have to be very good. I've had good experience with a Denso in my two cycle Mantis tiller. It does seem to run with a little more "up and go" compared to the new Champion that was in it. May be a little more but hey I want my stuff running the best!

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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