Honda GCV 160 surging when hot

nicebutdim1 · 22 Jul 2017

Hey guys,
Got a problem which I don't see covered elsewhere.
My stiga mulcher of 12 years has started to surge after a few minutes of perfectly fine operation.
Fresh fuel, clean lines, new carb and gaskets etc etc.
Every attempt to sort the problem produces exactly the same effect.
It always starts first time and runs at a nice 3100 revs before beginning to surge.
Any ideas before I replace the engine?
cheers

r896neo · 22 Jul 2017

Fuel tank vent blocked? Does it improve when you loosen the fuel cap while its running? This usually causes it to die when hot though rather than hunt/surge. It really sounds like a fuel/carb issue.

nicebutdim1 · 22 Jul 2017

thanks for replying.
tried the fuel cap already ☹
I think I've tried every trick now.
I have another gcv160 mower, so swapped a few things out with no success, too.

r896neo · 23 Jul 2017

John aka 'burnerman' will no doubt be along soon and he is the resident machinery expert.

If you replaced the carb, fuel, and are sure there are no leaks in your air lines and vents I cant help anymore.

Good luck

lostinthelight · 23 Jul 2017

Will it smooth out if you take throttle past max to bring choke on slightly ?
litl

nicebutdim1 · 23 Jul 2017

nope. Still hunts lol.

lostinthelight · 23 Jul 2017

nicebutdim1 said:
thanks for replying.
tried the fuel cap already ☹
I think I've tried every trick now.
I have another gcv160 mower, so swapped a few things out with no success, too.

Diagnosis by substitution then ? is the other engine running ok ,what have you swapped?
I take it You've looked at things that can alter with heat like swapping coil and setting air gap, change spark plug, adjust valve gap
Edit : and assuming because you have a tacho? ,if the replacement carb was not new, you cleaned the emulsion tube above the main jet, throttle shaft isn't worn carb flange is not distorted so gaskets don't seal
litl

Burnerman · 24 Jul 2017

When the engine is surging, can you see the governor rod starting to move, as it tries to accommodate the loss of RPM?
I think you have fuel starvation, as has been said but if the carb is new, can you check for a deluge of fuel flowing from the tank?
Also try running the motor without the air filter just to see if things change.
John

nicebutdim1 · 24 Jul 2017

hi, the hunting did stop surging with the filter off. I assumed it was a leak from a poorly seated gasket, so replaced them. Now the surging occurs with the filter off too lol.
the governor arm does move with the surging.
I'm nearing my threshold and may just replace the motor with a gxv 160.
I did think of a fuelling problem, but all the lines are clean, as is the tank.
thanks for the help and the suggestions

Burnerman · 24 Jul 2017

Just a thought.....the usual Honda carburettor has an adjustable pilot mixture screw. Normally, these can only be adjusted through 30 degrees or so, due to an anti tamper head on the mixture screw.
It's impossible to clean out the pilot jet with compressed air unless this mixture screw can be removed - which can't be done unless the lug on the mixture screw is sawn off, allowing it to be unscrewed completely.
Is your replacement carb new, or second hand?
Unless your existing engine is smoking, replacement isn't usually necessary!
John

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Honda GCV 160 surging when hot

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