D engine Lawn Boy leaks gas while running

[GHLB]

I have a model 7265 that leaks through the air filter while I'm mowing. It only leaks when it is running. I've stored it for an entire week with the fuel shut-off left open and it doesn't leak a drop. But after mowing with it for a while, it begins to drip. I tried adjusting the altitude needle as lean as it would allow and still run well, but that didn't help. Does anyone have experience fixing this problem on one of these D engines?

 

[FuzzyDriver]

I'm thinking it's a float valve issue. Maybe when there's no vibration it can seal, but there's a sticky open spot you hit when there's vibration and movement while mowing. Have you looked inside the carburetor?

 

[GHLB]

Thank you FuzzyDriver for your response. I hadn't thought of the float valve in the same manner that you are. In fact, my thinking was just the opposite of yours. To me, it seemed that if the float valve was the cause, the leak would be more likely to be displayed when not running, and not when the vibration of the running engine would tend to free it. Additionally, I don't understand why any excess fuel doesn't get sucked into the engine with the incoming air rather than go in the opposite direction.
I recall this mower was in rough shape when I bought it about 6 years ago, but I can't remember if I did anything inside the carb bowl. The C clip that holds the recoil together fell off this week (can't figure out why), so it will be a good time to remove the carb while I've got the recoil off. I may not get a chance to do it before we get snow, but will respond again when I do. In the meantime, I'll have to fire up one of my other LB's to do my final mow this year.
The repair manuals indicate that carb cleaner is not appropriate for these plastic carbs. Do you know of an effective cleaner that is safe to use?
Thanks again.

 

[GHLB]

I'm thinking it's a float valve issue. Maybe when there's no vibration it can seal, but there's a sticky open spot you hit when there's vibration and movement while mowing. Have you looked inside the carburetor?

I opened the carb. I carefully looked at everything inside and found all surfaces to be absolutely clean. I examined the tip of the needle with a magnifying glass, and compared it with a picture of a new 681639 float on ebay. I didn't see anything wrong with the tip. After reassembly, I put fuel in the tank, opened the shut-off valve, and left it that way for 6 hours. There was no trace of wetness in the air filter area. I started mowing and it wasn't long before I noticed it was dripping again.
I considered replacing the 681208 float, but haven't located one. I then considered buying a new 681639 float because it looks to be the same, but I'm guessing that different part numbers means there's some small difference between them.
Does anyone have a suggestion (that doesn't involve buying an entire carb)?

 

[bogdaN]

Check reed plate and clearance should be .015 Here is pic from original lawnboy mechanics handbook.

 

[FuzzyDriver]

If you are interested in the service manual for your mower, I keep it available on my website at 1950-2000 Lawn-Boy Service Manual. I found the D-400 Series Carburetor Servicing - Service Buliten with bogdaN's information on page 61. If you download it, be patient: It is 140.9 MBytes and 639 pages.

 

[GHLB]

If you are interested in the service manual for your mower, I keep it available on my website at 1950-2000 Lawn-Boy Service Manual. I found the D-400 Series Carburetor Servicing - Service Buliten with bogdaN's information on page 61. If you download it, be patient: It is 140.9 MBytes and 639 pages.

Thank you. I appreciate your assistance.
I just had to take a look at your site and admire your amps. When I was a teenager, my dad operated a TV and Stereo repair from our basement. I spent a lot of hours operating the tube tester. It's still in Mom's basement, along with some tubes that I didn't sell when Dad passed. But that's a different subject. Thanks again.

 

[GHLB]

Check reed plate and clearance should be .015 Here is pic from original lawnboy mechanics handbook.

The reeds had about .030 clearance. I have a parts engine that I pulled from a large pile of mowers at an auto salvage yard years ago. Fortunately, the carb side of the engine was not damaged when they used a dozer to push those mowers into a pile. Those reeds have about .011 clearance. I put that reed plate assembly into my mower today and mowed a section of my lawn for about 30 minutes. No drips on the deck. Thanks so much for teaching me about the reeds.

 

[FuzzyDriver]

Thank you. I appreciate your assistance.
I just had to take a look at your site and admire your amps. When I was a teenager, my dad operated a TV and Stereo repair from our basement. I spent a lot of hours operating the tube tester. It's still in Mom's basement, along with some tubes that I didn't sell when Dad passed. But that's a different subject. Thanks again.

I'm so sorry to hear of your dad's passing. I began working for the local RCA/Zenith dealer back in 1971, when I was 13. Been seriously into electronics ever since. It seems we lose people who are knowledgeable about tube equipment all the time, and few pick it up. Are you planning on keeping your late-dad's tester and the remaining tubes? Or maybe you are following his footsteps into tube electronics? : )