Initially Lawn Mower Won't Start - After it starts it runs perfect.

[ballpark]

HI, I am fixing a Toro Super Recycler (20043) for a friend. It's has a 6hp Briggs engine. It has no throttle (auto throttle?). I have replaced the plug, fuel line, and air filter. I also rebuilt the carb including new gaskets. I cannot get the mower to start. If I add a few drops of gas into the cylinder then it starts right up and runs like a champ. I can even shut the mower down and it will start right up again. But if you let it sit for a day, it will not start again.

Its a primer system but its an odd setup as the primer bulb is on the air filter.

The throttle / governor seems odd to me also. A spring pulls in one direction holding the throttle open while a air vane on the engine pulls the throttle closed. So while running the throttle is in equilibrium between the two. The odd thing about the setup is that when you are starting the engine, the throttle is wide open.

Any suggestions?

Thanks in advance.

[Brad]

The governor is typical for many small engines that run at one speed. It sounds like this engine is not getting the extra fuel it needs to start. Check if there is a choke that is not working. If there is no choke then the primer is the only means of adding the extra fuel, be sure the primer is delivering fuel. A small crack in the primer bulb can really limit the fuel delivered. Brad

[ballpark]

The bulb is fairly new. It does have a small hole in the center though. (It's supposed to be there.) When you push the primer bulb, air is pushed though some channels in the back of the air filter between the air filter and a gasket. The gasket is new. I think the air then blows into a small hole slightly pressurizing the fuel and pushing vapor out of an even smaller hole into the intake. (or maybe using the venturi effect)

That makes sense though that something is not quite working in that area. I know the holes in the carb are clean, but I think I could clean up the primer system a little better.

Quick question: Do I need to oil that gasket? it seems like it would make it more air tight and increase the amount of air getting to the carb? I will post tonight on what I find out.

Thanks for the help.

[ds549]

look in the carb while yo push the primer ,you should see a spirt of gas ,if not,primer isnt working right.

[Jeff Wisnia]

As others have already said, that air pressure should be causing some fuel to squirt into the carb's intake passage.

I haven't personally encountered a primer bulb with a hole in it, but probably it's covered by your thumb when pushing it and is there to let things equalize when you're not.

My best guess is that maybe there's a tiny valve ball or sumpin' like that in the carb which might be stuck closed, or maybe even fell out unoticed when you rebuilt the carb.

Might be you're going to have to open up that carb up again and compare things with an accurate exploded view of all its parts to figger out why the primer isn't having its expected orgasm when you push on its bulb.

Jeff

[Mech_Tech]

What is the engine model & type number? Date code would help also because some engines were slightly different over the years.

One of the easiest checks is to remove the air filter cover and filter, prime the carb and see if there is any fuel in the carb throat. If there is fuel, then you have a problem with either a gasket leak or compression and/or valve problem. One way to check that is to do the same as before but start the engine. As the engine is running, slide a finger over the carb a small bit at time so that you are creating a choke effect. If the engine starts to stall, then you can rule out a fuel problem or gasket leak. If the opposite is true, then look at those. This is also a trick used for other types of engines too.

One thing that most people miss when servicing small 4 cycle engines are the valves. The exhaust one being a culprit alot of times because of the heat that passes by the valve face and either burning it or causing carbon build-up. I'm not saying that is your engine problem but keep it mind if everything else checks out ok. Many times Techs will change both valves plus the headgasket when an engine hasn't been serviced for quite a while. One bad habit that many people have is leaving an engine in a damp place with one valve open. The valve stem may corrode enough to stick it open a little and cause backfire as I've seen that many times.

Not that it makes a whole lot of difference, but I'm a Tech and if you need any other info, I'll try to reply if possible.

Mech_Tech

[mm]

I have that with one of my lawn mowers. I use starter fluid in an aerosol can. That might be more convenient for you. No need to take off the air clearer, if you do that.

It's good for a couple hours of not running after I've run it. Not sure how much longer before it won't start again.

That's standard. AFAIK they all have a choke that closes when the throtlle is in the start position, but you don't have a throttle. I have two lawn mowers that also don't have one. I don't like it. Maybe that means you and I don't have chokes????

When the grass isn't heavy, I want to slow the engine so it doesn't make so much noise, and these mowers don't provide for it.

The noise drives me crazy. It's a push mower. Why do people put up with it.

One of them has a place where I could probably mount a throttle -- should I? -- but the other has no place at all.

Remove NOPSAM to email me. Please let me know if you have posted also.

[ballpark]

Hi,

Cleaned the primer system tonight. Everything went back together very good. I removed the air filter and tried to see if fuel would appear if I primed the carb. I didn't see any fuel at all. Later, after I pulled on the start cord there was gas in there, but it just sat on the bottom of the carb.

Couldn't get it started so I used some started fluid to get the engine going. I could definately see the fuel comming out of the jet at that point. I also did the test of starting to cover the intake and the engine would almost stall and even made a quick puff of dark smoke.

Once its going it runs forever.

Here is a web page of some pictures of the intake, mower, governer, and model numbers. Maybe it will help.

Thanks for all the help. I do think its not getting enough fuel though priming. As to the next step I am unsure.

[Mech_Tech]

I should mention that the advice I'm giving you is from my experience servicing small engines of kinds. However, it is really hard at times to explain all aspects of repairing if I don't have the engine in front of me to examine. I can give just general idea of what may be wrong and how to repair it, but that's about all.

It sounds like you may have a plugged passage or leak in the primer circuit. You didn't say how you cleaned the carb and related parts so I'm guessing at what is happening, which I absolutely hate doing. Anyway, it's most likely there is a leak because of the way this circuit works. It's the rapid push of air through the carb that forces fuel into the carb throat (venturi). You will have to take off the air filter base plate and look for anything that maybe causing a leak between the plate and carb. If ok, follow the circuit from the primer bulb through to the venturi. The more a person understands in how it works the easier it is to diagnose the problem. I've found that most of the time, engine problems are caused by something quite simple but frequently hard to spot.

If everything looks ok, then you will have to take out the primer bulb and see if there is anything plugging the passage behind it. The primer bulbs themselves can be a problem because the rubber they are made of does not like unleaded gasoline. They have a tendency to turn into mush after a while or get rips in them. The ring that holds the bulb in can be a pain in the butt taking out so try not to damage if possible. If you have any doubts of how good the bulb is, just replace it because they are not very expensive.

Try these ideas and post your results.

[ballpark]

Hi,

I will try to explain the priming system up to the point where I am not sure what it does anymore. The bulb is located on the side of the air filter mounting plate. When you push it the air moves down a cone and then runs though a small channel around the top of the carb inlet. The channel is half made by a groove in the air filter, and it is enclosed by the gasket that fits between the air filter mount and the carb. Then the air comes out a small hole, and goes into a small hole with about a 1mm diameter in the side wall of the carb intake mount. Here is where I get lost. It's hard to follow the internal channels of the carb. There are 2 holes pointing back at the air filter that I think have something to do with it. One is large at about 3mm diameter and the other is very small, closer to .001 of an inch.

When I cleaned the carb I disassembled every thing I could and actually washed it in a water/soap bath. I used an old toothbrush to clean all the crevices. I also used a small wire and ran it though all the passages I could find. I didn't really see any crud come out. I would also note the the carb, before I cleaned it looked fairly clean. I then rebuilt the carb using new o-rings and gaskets. Everything was clean and dry when i put it back together. One thing I didn't remove was the half circle plug on the underside of the carb. I didn't know its purpose and didn't want to mess it up.

As for the intake, its all plastic. I removed the bulb and thoroughly cleaned the channel.

The bulb itself appears to be blowing the appropriate amount of air. I think that I can also feel air come out of the 2 small holes I earlier described. It's like it just not picking up any gas.

I think if I understood the theory on how the primer was suposed to work, then that would help. Like, when priming, what hole should the gas come out of? Are there any ball valves that could be missing? Thanks again

-Brian

[Jeff Wisnia]

Serendipitously, on another newsgroup I haunt (rec.crafts.metalworking) the same question came up and I'll paste the poster's explanation of how the primer bulb system works here:

*******************************************

The float controls the level of gas in the float bowl, most carbs have a small air inlet to keep it from air locking. On the primer bulb models, this air inlet is hooked to the primer bulb. When you squeeze the bulb the air pressure forces the gas down in the float bowl, and up into the main needle, dumps raw gas into the carb throat. As soon as you remove the pressure, the float needle opens a bit to replace the gas that was pushed out. Radically simple.

******************************************

Now, that makes elegant sense to me on a carburetor with a float bowl, and that hole you mentioned in the center of the bulb may well provide the bowl vent.

So, take off from that point and see if you can figure out why the primer isn't doing it's thing. If it's supposed to work on the principle described above, then I'd have to assume that there's a leak from the carb bowl to atmosphere preventing pressure from building up and pushing gas out the main needle valve. Try

But some carbs which mount right onto the fuel tank also use primer bulbs, and those must work on some other system. Maybe there's just a couple of little ball check valves which facilitate the pumping action.

Jeff

[WM]

I had a mower that would start and then quit after 5 minutes. Wait

10 minutes and it would start fine.

The problem was the gas cap. It had a washer and rubber gasket in it and a tiny hole in the washer. The gasket was deteriorated and stopping air from entering the gas tank. We just loosened the cap and problem disappeared.

There is a possibility you have a vacuum in your gas tank. Once running, the vibration cures the problem.

[ballpark]

Its fixed! Here is what I found. When I described the primer system I talked about a channel running around the intake, and puffing air into a small hole. Well I was watching the primer last night and put a little water around the orfices to see where air was blowing. It was actually leaking from that channel, and never making it to the carb. Its a plastic air filter mount and didn't make a tight fit. I took some gasket maker and used it to attach the gasket to the channel and used some to build up some volume so that the intake would fit snuggly against the air filter mount. After letting it cure over night, I pushed the primer bulb and gas spilled out! It came from the main jet. It runs like a champ now! Thanks for all your help.

[Jeff Wisnia]

It's feels nice when things work out, doesn't it?

Have a nice weekend....

Jeff