Your Problem Will Likely Be Loose Battery Connections, Flat/Faulty Battery Or Faulty Starter Solenoid.

Briggs Stratton Plastic Intake Manifold

As you may already know, in the majority of cases the carburetor to fuel tank gasket is the main cause of surging.

Surging symptoms include:

  • Surging
  • Misfiring
  • Running hot
  • No start
  • Cold start problems
  • Running rough

The Briggs classic 450/500/550 engines are fitted with a plastic intake manifold, it lives right above the cylinder head and as you can imagine it gets very hot. It's not very common for them to fail, but when they do, it causes a vacuum leak (surging).

 

The manifold which is basically a tube that carries the fuel/air mixture from the carburetor across the engine to the intake valve, and can be replaced without much difficulty.

If you need video help, check out "Mower surging" in the repair video library. It walks you through the process step by step - removing the carburetor, armature, manifold and refitting including setting the armature air gap.

Fitting Intake Manifold Tips

Fitting the new manifold will mean removing the carburetor, engine cover and flywheel housing (pull cord assembly) and armature/coil. None of these components require special tools, however a feeler gauge set would be useful.

 

A good socket set, pliers and screwdrivers will do the job.

When you're fitting the armature/coil, you'll need to maintain an air gap between the coil and flywheel, it's simple and all covered in the guide below.

 

Often the gasket is really stuck firmly to the engine after you've removed the manifold, the Briggs manual will of course tell you to remove it, but I don't unless it's damaged, does that make me a bad mechanic?

 

Anyway, if you decide to remove the gasket, be sure to use a plastic scraper otherwise you'll run the risk of scoring the face of the seat. You'll also need to stuff a piece of clean rag in to the cylinder head manifold port to prevent debris dropping in on top of the valve.

 

You might find this page useful, "B&S surging repair tools and parts". I have listed all the parts and tools you'll need to complete the task of replacing the manifold, the pictures link to Amazon where you can check prices and availability.

mower manifold

Order

Manifold pipe has a few variations, so remove your old one to match it against the new before ordering.
mower engine cover mower manifold damage

Remove

To gain access to the manifold, we will remove the pull assembly, coil and fuel tank.

Crack seen here in the wall of the intake manifold pipe. I have also seen the metal pull assembly come loose and wear through the top of the manifold pipe.

This damage will cause surging, the fix - replace manifold pipe.

Carburetor removed as per guide.

Mower engine cover bolt Mower pull assembly

Remove

Remove bolt at the front and two at rear either side of the metal pull assembly cover.

Pull assembly pulls straight up, and dipstick comes with it.

No need to remove the cable attached to the front of the cover, just place the assembly out of your way.

mower engine coil mower governor mower manifold

Remove

Remove the coil and governor flap by removing these two bolts. No need to remove the control wire attached, just set the whole unit to the side.

Blow away any dirt from the manifold.  Remove both bolts from intake manifold.

Remove manifold and gasket. There are a few different types of manifold fitted to this engine. Use your engine number to order the correct manifold, or remove yours and match it against the new part online.

mower manifold mower coil fitting

Now rebuild in reverse order. The coil air gap will need to be set, a business card does the job. Check out "Guide to fitting a coil" which includes pictures.

That's it, your Golden!

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Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.