OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines Honda GCV 135

Hi Guys,
I have a JCB SPM4855F mower with what I believe to be a Honda GCV135 powering it.
The engine is running slowly and is 'hunting' [revs fluctuating].
I have removed the carb and cleaned it although I must admit I didn't put a pin through the jets! they did appear clear though.
I have re assembled the carb and have run the mower but the hunting problem persists!! I have change the plug and the fuel!
I am testing it without the air filter attached but, I don't think that should make too much difference should it?
Any ideas as to how to resolve the running problem?

Hunting (recurrent cycling in speed, with a period per cycle of something like 5 seconds) is just about always caused either by lean mixture, or binding in the governor mechanism. If the governor arm will move easily through its full stroke under very light finger pressure, you can be fairly sure the problem is lean mixture. A faulty air cleaner can only make the mixture rich, not lean, so that is not the problem.

Stable, ongoing lean mixture with Hondas is commonly caused by dirt in the fuel system (obstructing the in-tank or in-line filter, or the petrol tap), dirt or gum in the carburetor (obstructing the float chamber needle-and-seat, or the main jet, emulsifier, or idle jet) or a leaky carburetor insulator gasket. You should check all of these, carefully. Split insulator gaskets are very common - many Hondas were built with sticky gaskets that always split when the carburetor was removed, and split gaskets will not seal when reassembled. Remember there is a gasket on each side of the carburetor insulator.

I suggest you begin by checking that the governor linkage is free, then clean the fuel system, then disconnect the fuel hose at the carburetor and check the flow rate of fuel out of the fuel hose into a cup. Then check both of the insulator gaskets to ensure they are not split or leaking.

If you get that far and the problem still exists, it will be time to strip the carburetor and clean it in detail with carburetor cleaner. Refer to this thread:
https://www.outdoorking-forum.com.au/forum/u...p;Words=gcv160&Search=true#Post38602

Please report back, either to confirm success, or for further discussion if necessary.

Thanks for the advice and I did indeed give the fuel system a good clean. I noted that the fuel filter had been put in the wrong way around and dirty and the flow of fuel at the carb end was much slower than at the tank. I also removed and cleaned the carb again.
The mower is running much better now, but only until you pull the choke lever back about half to two thirds way, any further and it seems to lose power and run poorly?
Not to much of a problem as its running well on a two thirds setting but I was wondering if you would have any advice on how to remedy this? I had previously adjusted the screw on the carb right at the governer linkage end? Could thus be the problem? I put it back as near to how it was as I could.
Thanks in advance!!
KB

If the engine runs better with choke than without it, it is running lean. That probably means that either there is an intake air leak at one of the carburetor insulator gaskets, or an obstruction in the carburetor. You did not say that you had taken adequate measures to fix either problem.

I suggest that you take the following specific steps. First, remove the carburetor. Then remove the insulator (the thick plastic part between the carburetor and the engine's intake port) and replace the thin gaskets on both sides of it.

Second, strip the carburetor again, but this time clean it out with a spray can of carburetor cleaner. As an experiment, I once tried to clean the main jet of a GXV140 carburetor without using this cleaner. I washed it repeatedly in petrol, and probed it repeatedly with the standard jet cleaning tool (an oxy torch tip cleaner of the largest size that will pass through the jet). After a fair amount of work, I was able to get a 0.45 mm tool though the jet, though it was a tight fit. Then I sprayed a quick blast of carburetor cleaner through the jet. Instantly, it would freely admit a 0.55 mm tool. The GXV140 suddenly lost all its symptoms of slightly lean mixture.

You can't remove built-up gum from a jet by mechanical cleaning, or by the use of mild chemicals. You need carburetor cleaner. You also may not be able to get the emulsifier out of the carburetor - they are prone to getting stuck in place due to hard gum formation. Whether or not you get it out, in addition to the main hole in the far end (at the carburetor's venturi) it has a dozen tiny (0.35 mm) holes coming out of it crossways, and all of these must be able to pass air freely for the carburetor to give the correct mixture. Unless you keep the carburetor wet with carb cleaner for long enough to soften the hard gum so you can push the emulsifier out, the only way to try to clean those tiny holes is with blasts of carburetor cleaner through the threaded opening where the main jet screws in. Even then, I think your chances of being fully successful are not good unless you actually remove the emulsifier, and clean it in detail.

Did you remove the plug above the idle jet, and clean that jet also? I've explained how to do that in the other thread I referred you to.