Briggs Stratton Plastic Intake Manifold

This post is a follow on from the surging mower post where we replaced carburetor gaskets on the Briggs & Stratton classic engine (common fault). If you missed it, you can check it out here “Lawn mower engine surging”.

This post covers the replacement of the Briggs & Stratton cross over manifold pipe. The pipe is prone to cracking and is also a cause of surging, although not as common a cause of surging as the tank gasket which we covered in part one.

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.

Manifold pipe

Order – Manifold pipe has a few variations, remove your old one to match it against the new, before ordering.

Cracked manifold pipe

Crack – Damage 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.

Engine cover

Remove – To gain access to the manifold, we will remove the engine cover, blower & pull assembly, coil and fuel tank.

Carburetor removal shown in here or you can check out the video here.

Blower housing

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

Assembly pulls straight up, 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.

Coil removal

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.

Manifold pipe

Clean – Blow away any dirt from the manifold.┬áRemove both bolts from intake manifold.

Ideally the gasket should be replaced, however they can be difficult to remove. In many cases, there’s no need to replace the gasket unless it damaged.

new manifold

Fit New Manifold – Snug the new manifold into place, it’s plastic so careful not to overdo the tightening.

Coil fitting

Refit Coil – The coils (also known as an armature) air gap will need to be set, a business card does the job.

Check out guide to fitting a coil which includes pictures or see the video here.

That’s it, you’re Golden!