Following on from theconrodkid's thread...

My 150cc lawnmower hunts and rocks along and theres hardly any difference in rpm between the slow and fast bit on the throttle.

Looking at the carb there is a solid rod runs back down to an arm and a very light spring goes forward to the throttle bit..

Heres the arm, does anyone know what it does? It only moves a little bit between closed and wide open...



When the engine is off the butterfly is wide open... and the spring is pulling it open..



When the butterfly is closed the spring going to the mech is stretched trying to open the throttle..



However once its started the arm pushes it closed and it just floats back and forth in the mid position and opening and closing the handle hardly makes any difference..



If I manually operate the butterfly the engine behaves and has a good range and revs its nuts off at fully open..

I'm thinking of replacing that spring with a bit of wire so the throttle handle controls the butterfly directly.

Before that does anyone know what that arm on the bottom of the engine does? Directly underneath theres a hole in the casting...

Steve

on mine (briggs engine) there is an arm conected to the govenor linkage,the spring opens the throttle fully and the arm,by wind / air pressure from the cooling fan closes the throttle.
it is a clever balancing act between air pressure and spring tension .
could be leaves/grass/dead chavs jamming the linkage

Thing is its brand new, its a GPP 150cc V35 engine.

B&Q have the same engine on the Mountfield mowers for £270 upwards and I got mine for less than half that!

http://www.cheapmowers.com/acatalog/Lawnking_EP414G_Petrol_Lawnmower_15in_Cut_.html

I think before I get a high lift cam and a Webber 40 for to I'm going to have that spring go back so it acts against the butterfly and put a piece of wire in its place to control it better.

I'm wondering if that arm is a governor that works off the wind pressure when the blades spinning.

i see the problem,on the makers plate it,s made in China where mine is from the good old US of A,home of the brave and land of the free .
take the cowling off and have a look how it works,might be a stowaway hidden under there ?.

That is the governor arm, same principle as the wind vane type but much more reliable, there is a small set of bob weights inside the crankcase.

From the manual:

ADJUSTMENT OF THE
ACCELERATOR CABLE
If the engine does not reach its maximum rpm
with the throttle control in “FAST” position, this is
likely due to an out-of-phase connection between
the accelerator lever and the governor lever.
To restore the correct phase:
a) Stop the engine, remove the spark plug cap
and wait until the engine has cooled.
6.7 b) Loosen the screw (1) of the clamp (2) so that
the cable casing (3) is free to move.
c) Move the throttle control to “SLOW”.
d) Move governor control lever (4) forward as far
as possible and, by keeping it in this position,
lock the casing (3) full tightening the screw (1)
of the clamp (2).

Cheers
Davie

Cheers Dave, I'll see if that works.