A carb swap may solve your problem if off a similair 3.5 engine--too much work though. You mentioned your throttle adjustment was frozen--you might try advancing the control wire (pliers might help) toward a faster run postion to get away from slow idle.
If this doesn't work--carb cleaner would be my next attempt at solving the problem. Squirt it every where (in and around the carb.)
Lastly, as your time and parts cost creep higher and higher--don't forget a new 3.5HP mower is only $99. ;-))
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There are practical limits to fun--the grass keeps growing and the wife doesn't like it long. Remember that microwave I was trying to fix--"Sharp powers down after 40 seconds"--couldn't get parts so bought a new one. The wife is very happy now--should have bought a new one earlier--good note is that my parts box is now full of used microwave items--maybe I can use some of them before I die--probably not though.;-))
It's the carbuerator diaphram, worn out most likely. Yours is the plastic bodied carburator with the black or red primer bulb yes? If so you'll need to purchase a new diaphram and gasket for the carb, about 4 bucks or so at a lawnmower parts shop. The carb is secured with 5 philllips head screws. Take those out and gently pry the plastic carb off the fuel tank. Take care not to lose the diaphram spring( it'll be on the bottom side of the carb.) or the mesh filter screen on the main fuel intake port. Note whether the fiber gasket is on the carb side or the tank side( varies with each model.) of the rubber diaphram. Replace new ones in that order. Take care not to crease or wrinkle the rubber diaphram whille tightening the screws down and you should be good as new. While apart use a good aerosol carb spray to clean out the carb and tank resevoirs.(just about any brand but Gumout will do, I use Super Tech brand found at Wal-mart. Autozone brand of carb spray is good as well.) Spray through the intake port(under mesh screen) to back flush the supply pipe and the main port in the carb throat as well. blow off any excess cleaner or allow to dry before replacing rubber diaphram.(cleaner will attack the rubber shortening it's life.) Any questions in particular just post back. One of my many skills is small engine mechanic and I have years of experience with lawnmowers.
Oh, I definitely agree when it comes to strange problems like the one you had. But unstable idle on a lawnmower engine isn't rocket science or something that's likely to stump everyone.
And there's my "fix once rule": I don't mind repairing something I picked up on eBay cheap (replaces garage sales!) or what I might have bought new many years ago. But I don't want to have to deal with it more than once! :)
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One last thought--check the plug for soot (running rich)--clogged air filter causes lower Air/Fuel ratios--leads to poor burn, soot and suttle misfires--leading to rpm searching.
I took the carb off and found that rubber O-ring was broken. I assume that was the culpret. I hosed down the carb with wd-40 and she started up with no idle problem. However now the idle is too low. I probably stretched the spring or something but atleast it mows the lawn! Thanks for all the help!
On a different subject; the last time I had occasion to check the Repair FAQ regarding a lawnmower issue, (I had a shear key problem which was easily fixed with the info contained there. Thanks, Sam) I noticed a very interesting dialogue concerning the relative merits of Briggs and Tecumseh small engines.
Being how it's much too late (probably) to get my $.02 in the FAQ, I thought I'd post my opinion here:
IME, Briggs motors are much more 'finicky' for starting and maintenance, but they last longer and use much less gas and oil.
The Tecumsehs (I have two of those, and one Briggs & Stratton) start much easier, although that's probably due to the priming bulb which my Briggs does not have. They start using oil right out of the box, however. I have to check and add oil on almost every use. My Eager1 uses almost twice as much fuel to mow the same yard as my older Briggs of the same horsepower and cut width. I almost never have to add oil to the Briggs in an entire season.
Given the greater oil and gas consumption, I assume that the Tecumsehs are emitting considerably more pollutants per hour of use. The consumables only add a negligible amount to my lawn-care costs every year; but multiplied by (however many millions) of them out there.....
Well it's hard to say these days, back when I was tinkering with this stuff a lot I was dealing with engines made mostly in the 1970's and the Briggs motors were very noticeably better made and easier to work on. The Tecumsehs' were nothing but a pain in the ass, carb problems, ignition problems, a few common models would regularly throw rods. It was no shock since they were always about 40% cheaper than a comparable B&S. Now days I don't really know, the Tecumseh engines seem to have improved somewhat, while the Briggs engines have gotten *very* noticeably poorer. Somebody said they're now made in Asia so perhaps that's when the quality took a dive. BTW the new ones do have a primer bulb, haven't tried starting one though. My mom has an old mower with a Tecumseh and it does actually start quite easily though I have to take apart the carb and clean out the banjo bolt on the float bowl every year, never had to do that with an old Briggs. Unfortunatly I never compared fuel consumption but I don't recall oil usage problems on either.
On Tue, 17 May 2005 03:18:06 GMT, "James Sweet" wrote:
Yes, there was a time when Briggs were better engines. Not so anymore. B&S has gotten into the parts game. They make nearly as much profit on parts and service as they do intial sale. Techumseh had to rethink their whole market strategy in the late 70's and refocused on building better quality engines that were certainly more standardized. On virtually every Techumseh vertical shaft engine the carbs and coils are interchangeable, unlike Briggs where every engine requires a particular model coil or carbuerator-setup.
Odd that your eager-1(Sears) mower uses so much oil. I'd say it might be just the particular engine as virtually none of the ones I've used or serviced ever developed this problem during their useful life.(Cast iron sleeves and 2 oil rings unlike the single ring in Briggs and the cheap alloys used in both the sleeve and ring.) The poorer, cheap design in the Briggs carbs make for a much worse problem in regards to polution as they tend to run rich with just a little age.(I've seen some come into my shop that are runnign so rich that they actually wash the cylinder. This results in excessive wear on the sleeve and rings, allowing bypass into the crankcase. Once the oil is broken down by the gas it'll bypass the rings and the result is a smoking engine.(great if you want to fog your yard as you cut it.) Techuseh carbs are actually easy to operate and care for once you learn some basics. They're float style carbs and as such you can't just run 'em and forget 'em. leaving gas in the carb and tank off season is the worst thing you can do. (Most people don't realize that gasoline actually goes bad with time and actually expect a mower that's sat unused for six months to just crank up on the first pull.) Run the tank dry at the last cutting of the season then loosen the Bowl nut and drain the gas out of the float bowl.(It's easy, all it takes is a 1/2 inch socket to loosen it.) Then leave it dry for the winter, DON'T put any type of winterizer in it. Worst stuff in the world. Just ensures you'll be taking it in for a carb job as the stuff just turns to jelly and will make a real mess of your carb and tank. There's just no way to "preserve" gas, use it or lose it.
If you want proof as to Techumseh's quality over Briggs just look at how Briggs has copied Techumseh design. Techumseh has the best design in a starter recoil mechanism hands down, Briggs finally gave up using their ball bearing starter clutch mechanism on all their 5hp or larger engines and copied the Techumseh design out right.(stilll not as good.) They went to a float style carb but picked what is in my opinion one of the worst makes, Walbro. I tell all my customers if they insist on a Briggs just get one of the Sprints, either a 3.5 or 4hp model and don't expect much more than 2 years of use out of it. I have some customers still using the same Craftsmans mower with a Techumseh engine for 10 years or longer. I gave my inlaws one of my personal Craftsmans that I purchased back in 82 and it's still going strong, with NO major engine work at all.
You can get a new o-ring at you local harware store for about 50 cents. It's usually size 42 on the chart in the o-ring boxes. I can look it up for you if you can't get a match.
I've not had to pull the carb on either of my Tec's, but the Briggs (bought new in the early 90's) is laid up until I can pull the carb and determine if it's the cause of the hard starting. Both Tec's have worked reliably since I aquired them, except for the shear pin, which was result of operator error, of course. This morning I pulled out one of them and oil was below the dipstick. (5.5 hp, self propelled pusher...I ran two+ tanks of gas through it last session, and oil was full when I started...need to check more often!)
However, both of them were aquired used, as opposed to the Briggs. I wonder if they were abused in an earlier life. I had one other many years ago, and it 'used' oil/gas as well. It might have been old enough to have been made in the 70's...thrift store find.
I'm glad to hear Tecumseh quality is going up. Except for needing to keep a close watch on the oil, and seemingly needing to fill gas more often, both of these mowers have been relatively flawless.
It's also a shame about Briggs & Stratton. The first engine I ever worked on was a horizontal shaft Briggs which came off my dads old reel-type power mower from the 50's. I pulled it off the mower some time in the mid-60's, used a pipe wrench to break the rings free and mounted it on a go-cart. It was too small for the application at a (maybe two, it's been a long time) horse and a half, but it ran well.
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Yes the earlier Techumsehs did have a problem regards to burning oil. They were built terribly cheap way back. And yep, the earlier B&S engines were built like a tank. The problem with using the older Briggs horizontal shaft motors for go-carts or minibikes was they had low rpms and not much torque. The ones they marketed specifically for that purpose were setup tp spin a bit faster and had higher compression. You could fudge a bit with some of the 3hp models by resetting the mean idle on the govenor springs and either rejetting the carb for quicker response or replacing it with a bigger throated one so the engine could breath a bit better. Using a low hp engine like a 2 or a 2 and a half you'd have had to change out the drive sprocket for a much larger one to make it an easy pull. Which of course would have made it as slow as a turtle.
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