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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 26293
Experience:  Service manager and technician for all brands of engines with 40 + years of experience.
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Small Engine

I have a Countax C38H garden tractor, fitted with a Honda 13hp

engine. It is running rough... Show More
engine. It is running rough. How do I tune the carburretor, because the manual is not helpful?
Submitted: 1 year ago.
Category: Small Engine
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Curtis B., Technician
Satisfied Customers: 26293
Experience: Service manager and technician for all brands of engines with 40 + years of experience.
replied 1 year ago.

I doubt tuning carburetor will help! The carburetor has little adjustment, only an idle speed screw. If it were mine, I would try replacing the spark plug, and clean the carburetor bowl , as it may be gummed up or have water or debris in the bowl. This keeps the float and needle valve from working properly. And replace the fuel filter.

Customer reply replied 1 year ago.

Thanks for your advice, and I apologise for the delay in getting back to you, but have been away.

I have today fitted a new spark plug as suggested (having already checked the carb bowl and in-line fuel filter which were OK), and the misfire is now sorted. However I bought the tractor second-hand recently, so is new to me, but the maximum engine speed (before the choke engages) seems perhaps rather slow, though it does operate the cutter deck OK.. Do you think there is a problem here, or is this Honda 13hp motor a relatively slow running unit anyway?

When we've finished I will be happy to give you an excellent report!

Curtis B., Technician replied 1 year ago.
No, engine is not slow running! Should run 3300/3400 rpm! Valve lash could be something that needs to be done, if the engine is over two years old. If valves are not set, it can cause misfire.
Customer reply replied 1 year ago.

Thanks for that. Is "setting" the valves a major job? In the past I have on many occasions adjusted the tappets on OHV car engines, but never on a single cylinder unit such as this, and I have no workshop manual for this engine to guide me.

Would you say this a job for a suitably qualified workshop, not an amateur like me? And is it a major job, so expensive?

Curtis B., Technician replied 1 year ago.
Setting the valves on the Honda is easier than setting tappets! Just need the feeler gage and wrench to fit the adjuster. Get the numbers off the engine, and we can find the correct settings. Usually around .20 MM or .008 inch. Turn one valve till it is down (open) and set the one up, (closed), then when it is set, turn it down, and set the second one. Twin cylinder would set same way!
Customer reply replied 1 year ago.

Hi Curtis

Again, thanks.

I've just has a lookat the engine, but can't see anynumberson the block, though admittedly most of the engine is covered or shielded by fittings of one sort or another. Any clues as to where I might find the numbers before I start to dismantle the engine just to look for them?!

And when I have got back to you with the numbers, how do I then get at the valves in order to adjust them?

Curtis B., Technician replied 1 year ago.
I assume this is overhead valve engine, there will be a valve cover that needs to be removed, any numbers would be on the outer covers on the engine, example Honda GX570.
Customer reply replied 1 year ago.

Hi Curtis

I've looked again at the engine, and short of removing heat shields, the alternator, etc, I can find no model number stamped or fixed to any part of the block or elsewhere. All I can see are the words "Honda 13.0 OHV" on a label on the top of the engine.

However, I have been online and the only13hp engine I can see produced by Honda is the GX390 (horizontal) or GXV390 (vertical). Apart from the way they are modified to be mounted I assume they are the same 4-stroke single cylinder engine, and on one of the websites I visited theyare stated to be commonly fitted to ride-on mowers, etc.

So on the assumption that it is this engine, what should be the valve settings, please, where on the engine is the valve cover, and what needs to be removed from the engine to get at it?

These should be my last questions, and as I've already said, I'll then give you an excellent rating. Thanks for your advice and patience.

Curtis B., Technician replied 1 year ago.
GX390K1 0.15 +/- 0.02mm ( 0.006 +/- 0.001in ) 0.20 +/- 0.02mm ( 0.008 +/- 0.001in ) .006 inch on intake and .008 on exhaust. The valve cover is the cover over the cylinder head, where the spark plug goes.
Customer reply replied 1 year ago.

That seems clear - 6 thou intake, 8 thou exhaust. Remind me how I tell which is which. That's the very last question, I promise.

Curtis B., Technician replied 1 year ago.
Intake will be on the carburetor side, exhaust will be near exhaust pipe.

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