The valve springs on Honda Gx160 & GX200 are designed to be ran on an engine with the standard factory govenor set up.When removing the govenor to get the engine to run harder there are a few things that will need attention. The standard valve springs dont have enough tension or open pressure to be run up to 5000 rpm. The standard cast iron can also fail when the engine is pushed to higher RPMs. If you are going to modify your Honda engine it is very important as a safety issue to replace the flywheel with a billet flywheel that can with stand higher RPM & engine load.There are many after market valve springs available & a good choice is the factory Gx140 Honda valve springs. The Honda GX140 valve springs are used in many modified Honda engines,Another problem when valve springs loose tension is that at any RPM the valve can float & the whip that can occur with valve float can cause the valve to pop out of the retainer & the valve drops straight into the cylinder. Always check valve springs & retainers for signs of wear.Check the pushrod ends & if there is any signs of wear replace them.
The Honda GX Rocker arm is a good strong design & do not cause many problems.
valve clearances on the GX Honda engines are to .004" inlet and .008" exhaust when the engine is cold.
with a .004" feeler guage you should be able to slide the feeler in and out with slight resistance. take the time to set rocker clearance correctly as it will pay off at higher RPM
The exhaust valve clearance is set wider than the inlet valve due to the heat of the exhaust gases as the expansion is greater on the exhaust valve than the inlet valve.
When the valve clearances are set cold it is a good idea to run the engine to operating temperature if you recheck the clearances you will notice that the clearance is greater than when they were set cold. Let the engine cool then recheck the clearances to the original settings.
Changes in emission law & regulations in the USA have required continual upgrades & modification to the Honda GX platform engines, Honda GX120,GX160 & GX200 Honda engines the Quarter Midget Association in the USA is now allowing the use of the Briggs & Stratton Animal into Quarter midget racing. The Briggs & Stratton Junior Animal is replacing the Honda Jr. GX120 Honda classes.
AussieSpeed Small Engine Performance have spent many hours on the flow bench testing & finding better port & manifold shapes & sizes to increase performance on many different cylinder heads.Our research goes as far as testing carburettor bore sizes with & without air cleaners.With the hours spent it allows us to understand what works best with different camshaft profiles & maximum valve lift on certain engine combonations.We try to increase velocity & flow at low lift & also get the benifit of maximum flow at high lift.