3hp Briggs will run without air filter but carb covered but wont run with air filter

[webby]

Hello

I have a 3hp Brigs and Stratton engine on my rotavator/tiller and it has trouble running. It seems like it wants to start but it will not keep a steady tick over as it keeps cutting out after a few seconds. We took the air filter off the carb and I covered the carb with a gloved hand and to my amazement it started and ran quite smoothly. So I left it running to warm the engine whilst my hand was covering the carb after a few minutes I removed my hand and the engine died. I tried to start it again but it would not fire or start with the air filter in place or removed so I put my hand over the carb with the filter top removed and it started fine and ran ok until I removed my hand.

The question is what could be causing this strange problem? We have never encountered this before and although it has always been a problem to start the engine with a little prime with fuel it has normally started then ticked over without any problems.

Thanks in advance.

 

[reynoldston]

Yes I know what you are talking about because this pass summer I had one that did that same thing. But for the life of me I can't remember what it was. It almost seems like it was a very simple thing like the air cleaner stud was shorting out the engine. Check the stud that holds the air cleaner on and you might see the problem and all around the air cleaner. Sorry old age and many jobs the memory isn't that good anymore. And yes it seem like it was a small Briggs on a tiller.

 

[bertsmobile1]

Hello

I have a 3hp Brigs and Stratton engine on my rotavator/tiller and it has trouble running. It seems like it wants to start but it will not keep a steady tick over as it keeps cutting out after a few seconds. We took the air filter off the carb and I covered the carb with a gloved hand and to my amazement it started and ran quite smoothly. So I left it running to warm the engine whilst my hand was covering the carb after a few minutes I removed my hand and the engine died. I tried to start it again but it would not fire or start with the air filter in place or removed so I put my hand over the carb with the filter top removed and it started fine and ran ok until I removed my hand.

The question is what could be causing this strange problem? We have never encountered this before and although it has always been a problem to start the engine with a little prime with fuel it has normally started then ticked over without any problems.

Thanks in advance.

If the engine will run with your hand blocking off the air inlet to the carb then there is a massive air leak between the carb and the engine .

With the normal air intake ( no hand ) plus the air leak the air : fuel ratio is far too weak to start the engine.
At start up you need SFA air so a tiny leak like around a worn throttle or choke shaft will be enough to prvent normal starting.
Finding the leak can be a big problem if you cannot get it to run without your hand there.
See if you can get it to run at about 1/2 full speed.
Using a trigger pack NOT A PRESSURE PACK CAN , spray some thing like WD40 all over the carb then all the way along the inlet tract till you get a rich running reaction from the engine and you have found the air leak.
You can substitute the WD 40 with water , which is a lot safer, if you like but that will usually wet the plug so you will need to have a few plugs on hand.
Naturally you need to be very close and spray lightly so you can see exactly where he spray is landing when the engine starts to cough & blow black smoke.

 

[Rivets]

You don't really tell us exactly which engine or carb you have, so I'm guess it is a horizontal crankshaft and a tank mounted pulsa-jet or vacu-jet carb. The common problem with these carbs is a leak between the carb and tank. I would start by replacing the gasket between the tank and carb. If you have the pulsa-jet carb, I would also replace the pump diaphragm. This manual may help you, section 3.

http://evanosaurus.com/ebooks/270962 Single Cylinder L-Head BRIGGS & STRATTON.pdf

 

[bertsmobile1]

Did they make a horizontal shaft with a under carb tank ?
I thought all of them had an overhead tank & gravity feed.
And it was on that assumption that the response was given.

 

[Rivets]

The 80000 series engines used this style for many years. Most of the old small HP engines used them, most commonly on tillers and edgers.

 

[bertsmobile1]

There you go .
Down here being a loyal part of the empire ( Play rule Brittania in head )
most of that small stuff got Pommie engines which universally had either a cowel mounted tank or no tank.
BSA was the biggest till they sold the small engine division to Villiers in the late 60's.