Honda lawn mower

[jjb1333]

Hi all
I have a Honda HR216 Petrol lawn mower which was running a bit rough, took it to my local dealer who looked at it and said it needed a new carburettor
I bought a carburettor on line fitted it replaced the spark plug and it is still pretty much the same
It starts first time on full choke but when i move the throttle to normal operation speed it backfires violently (You can see the flame coming out of the exhaust) when i move it to idle the revs go up and down (i think the technical term is the engine is hunting)
I can cut the grass on full choke as it works fine but soon as i take it off choke
the above happens and then it eventually cuts out
Any help appreciated.as i dont really trust my local dealer after he mis diagnosed my problem in the first place

 

[Mursal]

The carburetors give trouble on those, especially flooding the engine with petrol, probably why the dealer punted for a new one.

Try it without the air filter

If still the same try new/different fuel

Pull the exhaust off and try it (may be clogged)

If still the same it may well be the air screw on the carburetor needs adjusting, BUT do not touch this until you are absolutely sure everything else is OK. They can be hard to adjust if disturbed, so note where it was before you start. Best way is to adjust in by half a turn at a time then try it.

You may have a value tight in the head (just needs adjusting, hopefully), but do all the easy stuff first.

Let us know how you get on?


PS As you know petrol is highly flammable, do not start the engine in a confined space when it is backfiring, just say'in

 

[Burnerman]

Flames from the exhaust indicate that the fuel isn't being burnt in the cylinder, so pop a new plug in....I think NGK BPR6ES is the one for these.
John

 

[jjb1333]

Thanx
As i say i did get a new spark plug
Which one is the air screw ?

 

[Burnerman]

There's actually no air screw on these.....the carb has two adjustments.
1) The idle speed screw, that is spring loaded and works against the throttle mechanism (in effect it keeps the throttle open a little)
2) The idle speed mixture screw which is usually on the top of the carb (it may be hidden under a plastic cover which prevents you turning it too much). Its often practice to snap the plastic cover off and adjust the screw manually - about one turn out from fully in.
Just reading your post a little more carefully....its a new carb and plug, yet the engine is running crazily weak. Does fuel flow freely from the tank (there's a lint filter within), is the fuel tap (if fitted) fully open, and are the gaskets between the carb / manifold and manifold / cylinder head in good condition?
John

 

[jjb1333]

yes i have replaced the gaskets as well
i notice that there is a black plastic screw on the front edge of the carb is this the mixture one ?
I can also see a small brass screw which did have a plastic cover over it which i removed when i unpacked the carb from the box.
thanks.

 

[Burnerman]

The idle speed adjustment screw is external to the carb, and mechanically (by contact) holds the butterfly open in the internal venturi. These were sometimes made from black plastic, and often snapped off.
The pilot mixture screw will have its end screwed into the carb body itself.
Post a pic if you can!
John

 

[jjb1333]

The black plastic screw is large and is just below the throttle linkage
The brass small screw is next to where the carb fits onto the cylinder block
Unfortunately i dont know how to post a picture, if u could give me an email address i can send a picture to that.. Thanx

 

[jjb1333]

I have just completed the valve clearance adjustment and started it up and its stilll acting as before, backfiring and then cutting out....

 

[jjb1333]

I have also noticed that when the engine hunts the throttle linkage on the carb is moving back and forth as if someone is revving the engine............

 

[Mursal]

Yes, the governor will be trying its best to keep the engine going at a steady speed. Its an air flap that get the air blast coming from the flywheel blades on top of the engine. The faster the engine turns the higher the volume of air that hits the flap pulling the revs back. This ensures the engine does not over rev.

Did you try it without the air filter?

 

[jjb1333]

yes i tried it without the air filter
i emptied the tank and replaced with fresh fuel
I removed the exhaust and checked for blockages
i have done the valve clearance gaps
ive replaced the spark plug and carburettor
I cant think of what else it could be..;;;
Thanks...............

 

[Burnerman]

The machine still works well on full choke....is this correct?
If this is the case, we needn't suspect a sheared flywheel key, but the igniter coil itself does become a suspect - though they don't usually fail like this.
The governor is trying to keep the engine running, hence the linkage jumping about (its a centrifugal governor inside the crank case I think on these, not an air vane type).
They are prone to failing plugs....is the replacement new or a second hand one?
Disconnect the fuel pipe from the carb....does petrol pour out? If there is a fuel tap, does this interfere with the flow?
Undo the nut on the side of the float bowl. (Not the bottom one). Does petrol flood out from there?
John

 

[jjb1333]

Yes its a new plug the one you advised bpr6es
the fuel does run out of the carb bowl ok
I drained the old fuel out of the tank and it runs well out of the pipe
and yes it starts first pull on the choke but as soon as i move the lever onto normal operating speed thats when the hunting starts.

 

[Mursal]

Inspiration:

http://www.youtube.com/watch?v=1nYiQghmCF4


Were the valves tight?

Disconnect the breather pipe coming from the oil sump into the air-box pipe?