Hard starting Briggs & Stratton 3.0 hp lawnmower engine

Some libraries have some good books about lawn mower repair. cuhulin

I've worked on a lot of standby generators with small engines and one of the problems with older engines that have accumulated a lot of hours is valve seat wear. The valve recedes into the head decreasing clearance at the end of the valve stem. You can actually heat up such an engine with a propane torch and the expansion of the metal parts will allow it to start easily. If you can adjust the valve clearance, I do believe your engine will start easily again.

TDD

Put some "sea foam" in the tank to clear out the jets and see what happens. If it has adjustable jets try setting 1/4 turn richer to see if it helps. Definitely sounds like it is starting too lean.

Removing the head on those little air cooled engines is a piece of cake.You don't even need a torque wrench to replace the head bolts. cuhulin

I never heard that one, I have had a 2 stroke spark arrestor clog up.

muzician21 wrote in news: snipped-for-privacy@a7g2000yqk.googlegroups.com:

Try this: it won't cost you anything and it worked it my case. In fact I have to do it every year due to poor quality gas.

First drain the gas tank completely along with the hose to the carborator. Next either *temporarily* plug or otherwise stop any ability for liquid to come out of the hose. Vice grips on the end works fine if placed right. Leave the hose attached to the tank however and remove the tank from the mower. Put about 1 cup of Varsol into the gas tank. Screw on the lid for the gas tank so it won't leak. Shake the tank vigoursly for about a minute or so. Drain the fluid from both ends - the tank and the hose.

After a years mowing the filter at the bottom of my gas tank gets so clogged with gunk that it changes colour from silver to black. You can check by draining the tank and looking at it carefully if it's visible.

I went for two years having to start it with ether the first time every year. Even took it in for service with no improvement before I figured this out. Now it will start on choke first pull when it's 45 degrees F. Every time.

If its a 70s mower with a 10-year-newer B&S engine, that would mean its an 80s-vintage B&S. That would be about the lowest point in the armpit of quality of B&S carburetors, and it agrees with your symptoms. The "pulsa-jet" carbs of that era used the vacuum pulses of the intake runner to operate a diaphragm that pumped fuel up from the tank to the carb. They also had a vacuum-operated choke that had a tendency to not choke enough when cold and choke too much when hot. They tended to work fine once you got them running, but they were HARD to get going the first time because there just isn't enough vacuum pulse to pump the fuel while you're yanking the rope. Especially when they aged a little and the pump diaphragm got a little stiff You could try a carb rebuild kit, but frankly the only way I ever made an 80s Briggs run truly great was to scavenge the carb (and fuel tank) off an older (70s or even late 60s) engine.

I tried pouring about a tablespoon or so of gas in the carb before starting and it fired up immediately, much easier to pull than I ever recall it being. Couldn't believe how silky smooth it started. Apparently not a thing wrong with the solid state ignition. Apparently it's the cold fuel delivery issue. Looking into a replacement diaphragm for it.

Anyone have a suggestion for online parts houses for older B&S stuff?

The model on this carb is 092908 0571 01. One of the local places that carries Snapper had a listing for 092908 0571 99 which going by the exploded line drawings on his system looks to be the same carb.

There are lots of parts for the pulsa jets on ebay.

Your problem is the cold starting mechanism and that is what you should be looking at. What does your carb have? Does it have a primer bulb or a choke? If it has a choke what kind of choke?

-jim

I got a new diaphragm, but looking at the old diaphragm, it looks to be intact and in good shape. The material still seems pliable, I held it up to a light and can't find any breaks in it, including where the choke plate rod is attached.

The longer of the two pickup tubes had a fair amount of crud on the screen, which I've cleaned off. Gonna put it back together with the old diaphragm and see if it starts any easier with that pickup cleaned off. If it does, I'll store the new diaphragm in the refrigerator for future use.

And why are there two pickup tubes and why are they different lengths?

##### Look... When this sort of thing happens, most of us want to fix it, not to analyze it. I have had it happen lots of times over the years, and it is usually because of crud buildup in the fuel and/or the diaphragm. I have found that you save time by cleaning out the tank, cleaning the carb, and replacing the diaphragm. You can do this in a half hour in most cases. The diaphragm, IIRC, is not a ballbuster in price.

##### And this is also not unusual, especially when one has starting problems.

#### You must like to work on these engines. I normally keep one or two of the diaphragms around. But I wouldnt put an old one back in for anything. It is a waste of time to fiddlefart with this unless you have a lot more expensive diaphragm that I am accustomed to buying. Or have a lot of time on your hands

The diaphragm was always good. You never had any symptoms that indicated a bad diaphragm.

When you fill the tank all the way to the top the diaphragm isn't even needed because on this style carb it is only really needed when the fuel starts to drop below full.

Your problem is the choke is not closing. There is a spring that closes the choke. The spring may be broken or missing. The diaphragm pulls the choke open once the engine is running. If you had holes in the diaphragm your symptoms would be the opposite - you would be getting too much gas as it would be sucking gas in thru the holes.

One tube (the longer) goes down to the bottom of the tank the other goes in a small reservoir. Part of the diaphragm is the fuel pump that pumps gas up into this reservoir (there are two flaps that act as pump valves). the gas in the reservoir stays at a constant level because what ever extra is pumped in just overflows and runs back into the tank. When the tank is full then the reservoir is also full so no pumping is needed until the fuel level drops down. The small tube feeds the main jet which controls the air fuel mixture. That mixture is adjustable with the threaded needle valve.

-jim

I wouldn't think the two would be mutually exclusive.

To me there's a recreational aspect to it, absolutely.

I don't like tossing out perfectly good parts and if I can get more lifespan out of a part I'm all for it. Learning something and troubleshooting are also part of the goal. If I just slap a bunch of pieces on, even if it works I don't really learn what was causing the problem.

There ARE no "perfectly good parts" on an 80s vintage Pulsa-Jet carburetor :-/

The old Vacu-Jet worked a lot better, but didn't have the "automatic" (automatically applies exactly the wrong amount of choke every time) choke feature I guess.

A diaphragm that has been in service for some considerable time, then is taken out and allowed to dry, might work a while longer, but.... if you want to mow the yard or till the garden, it is foolish to go in and clean the carburetor and not install new elastomer parts, IMHO>

Rubber parts fail. If you have the carb apart anyway, replace every damn rubber part in it... seals and washers, diaphragm and everything. B&S will sell you a "rebuild kit" that has everything in it. If there are any rubber parts in the thing that haven't failed yet, they are on their way to failing anyway so just change it beforehand.

And keep the old diode as a spare!

--scott

I don't know what the part cost, but it should not have been more than a few dollars. Chances are if the new part was put in it would be good for life. If I had gone that far I would not worry about an inexpensive part. Even if it had been an expensive part I would use the new one and maybe save the old one.

Reminds me of what hapened at work. We had a large varitable speed moror drive to go out. Called in a factory man to work on it. He found two bad diodes. There was a third diode (three phase circuit) and I asked him to replace it also. He said it was $ 200. I told him to go ahead. If it went out that $ 200 was nothing to what it would cost to get him back in and the ammount of downtime on the equipment.

Same same as carburetor rebuild kits for cars/trucks/whatever.Use the new parts and keep the old parts,,, if you want to keep them.I don't keep the old parts. cuhulin