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I have a 19" D-series mower that I saved from a friends house. I've been a life-long Lawn Boy user and picked this one up for my wife to use...it's a 1976 5274.

It ran fine for the first few uses...but started to stall like it was starving for fuel a few days ago. I can start it and get it to run by hitting the primer, and keep it running if I increase the engine speed with my hand on the throttle...but it won't stay running on it's own.

I don't have diagnostic experience...I did the typical carb cleaning, new gas, air filter cleaning, spark plug.

I cleaned the exhaust ports a few years ago for my friend and I don't know how much it's been used since then...but I don't think this is an exhaust port issue?

Any tips or direction to search it out? Worn governor? Carb problem? Something simpler?

You probably just need to completely disassemble the carb, thoroughly clean all passages, and make sure the float & needle aren't worn.

Any diagnostic tips to help me determine it IS in the carb?

If I need to do a rebuilt, I will...but I don't want to do it if I can't tell it's my problem.

TJM_70 said:

Any diagnostic tips to help me determine it IS in the carb?

If I need to do a rebuilt, I will...but I don't want to do it if I can't tell it's my problem.

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You kinda described all the symptoms that would point me to the carb. It's a very common thing you have to do in order to keep any old lawn boy going. Very simple to fix, and parts are inexpensive.

Fireman's got you on the right track. Rebuild the carb.

You might also while rebuilding the Carb make sure to check the reeds, they should be flat against the plate sometimes they tend to gain space and quit working g as efficiantly seen it several time easily fixed by removing them and flipping them. There should be no clearance between them Ann's the mounting plate if there is.it should.not exceed 11 thousandths of an inch. You would be surprised at how.many I've worked on running the same.way and it was all on the Reed valves!!!

Thanks guys...I appreciate the advice. I suspected carb but it's nice to have some backup before tearing into something. I'm a good technician but a poor diagnostician.

My father is still using a 1972 19" to do the trimming every week at his house. When my brother and I were kids we mowed 30+ lawns a week with our two Lawn Boys - the 19" my dad uses and a 21" that has gone to the graveyard already.

I had a '96 Duraforce until the wife hit a rock while mowing and trashed it. I scrapped it and the cash from the junkyard bought went toward an early 80's 21" to replace the Duraforce. Craigslist - $50!

The 19" in this post was given to me by a friend who moved into a personal care home. The wife has her own vintage LB and seems to appreciate it. I'll post back once I have it running again.

Disassembled and cleaned the carb tonight...no improvement.

It will still start but the idle seems like it's too slow to keep it running. If I start it and just touch up the throttle an eighth of an inch, it runs strong and steady.

I tried to check the rpms tonight but couldn't get my automotive meter to work on the 1 cyl. Any way to do this?

If it was my chain saw, I'd adjust the idle up a little and go back to work.

Any other thoughts? How can I get the idle speed higher and what would be the cause of slow / low running speed?

I'm assuming the hi / low speed knob is intact? It should be located below the rear side of the shroud / fuel tank. If it is, and functioning, the next thing I'd do is remove the flywheel, and check the governor assembly. I highly recommend finding an old lawn boy mechanic's handbook to help with this procedure as there's several parts to the gov assembly.

Have you tried loosening the governor spring. You may have set it to tight when you rebuilt the carb.

Here are a few pictures. Hope it helps.

And as I stated before check the reeds!!p

I will check the reeds...

and the hi / low knob is intact...when I manually up the rpms it works as it should...if I hold the rpms steady and switch between hi and low the engine drops as it should.

I appreciate all the advice and will track down the help I can get.

I have the online manual...seems to have everything I need. After having the carb apart tonight, the illustrations make a little more sense.

Lawn-Boy Service Manual 1950-88 Complete

TJM_70 said:

I will check the reeds...

and the hi / low knob is intact...when I manually up the rpms it works as it should...if I hold the rpms steady and switch between hi and low the engine drops as it should.

I appreciate all the advice and will track down the help I can get.

I have the online manual...seems to have everything I need. After having the carb apart tonight, the illustrations make a little more sense.

Lawn-Boy Service Manual 1950-88 Complete

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hey if i were too send you a blank disc could you copy that lawnboy manual you listed in this thread for me, i have only library and cell phone use for net and the library won't allow me to go to the sight to download it and my phone won't download it?? thanks for you time robin barnard

Robin - I am not a member of the site so I don't have download privileges - only viewing...so I can't help you out with a copy. From what I understand, Toro also makes the manual available on their web site.

Well...I've learned on many other projects to never overlook the simple things. And my problem was a simple thing.

I got the mower working today after discovering that the throttle spring was not hooked into the notch on the carb...thus, the throttle had no force lifting it upward.

I connected it wrong the first time - force was going toward the deck...but then got it right and now have a fine running mower (again).

It probably didn't hurt to take the carb apart and clean it and re-adjust the altitude screw. Plus I learned a bit about the modular carbs.

In the service manual, there is no real discussion of the spring tension or connection in the D-600 fuel system section. It must not have been written for guys like me starting out with no advance knowledge. I finally read the D-400 section and found a passing mention of the tension and connection of the throttle rod spring.

I appreciate your help & plan to continue to check in now and then to this great forum about the world's best lawn mowers.

TJM_70 said:

Disassembled and cleaned the carb tonight...no improvement.

It will still start but the idle seems like it's too slow to keep it running. If I start it and just touch up the throttle an eighth of an inch, it runs strong and steady.

I tried to check the rpms tonight but couldn't get my automotive meter to work on the 1 cyl. Any way to do this?

If it was my chain saw, I'd adjust the idle up a little and go back to work.

Any other thoughts? How can I get the idle speed higher and what would be the cause of slow / low running speed?

Click to expand...

A lot of fellows seem to be interested in knowing more about how to check the rpm's. Replies about this can be found on Forum>Brand specific Forums>Lawn Boy forum > Tiitle / Thread Starter> "How are rpm's measured on a two cycle Lawn Boy?" started by Gene123 on 4/4/2012. Good luck. There are good guys on the forum helping.

Thanks for the RPM tip. I have found niche forums like this one to be filled with some of the most helpful and knowledgeable people around.