Honda 10 hp won't idle

I just acquired a used Honda 10 hp 4 stroke motor. I have gone through the carburetor and it looks great. The motor has 105 psi compression on both cylinders and the spark appears to be strong on both cylinders. The motor will start and run just fine at a higher RPM range, but as soon as it drops below fast, it just dies, no matter what adjustments I make. The motor is very clean and worth fixing, can you help me figure out why it won't idle?

Thanks,

Troy

What is the serial number? There are at least three versions of the 10 HP (9.9). Most likely you still have clogged idle passages in the carburetor. Compression seems low, but if you measured compression without putting the carburetor in full wide open throttle, the measurement will be low. The compression will vary dependent upon the vintage of the motor.

Mike

I can't seem to find the serial number, The tag on the midsection is painted over and damaged beyond being able to read it. I can describe the engine as having a blue lower section with a white top with honda written in black and red on the cowl. I did not check the compression with the carburetor in wide open throttle. I will do that. I was thinking clogged idle passage too, but when I took it apart, it seemed to be very clean inside and I could spray carb cleaner through the idle screw adjustment hole into tow different areas. The only one I questioned was a brass fitting at the bottom of the hole that does not have any clear passages. It appears to be glazed over, but i can't tell if it is supposed to be that way or not. I am not talking about the main high speed jet, it is clean, but inside the screw you can remove from the top of the carb there is a brass fitting or something in the bottom.

There should be a "slow jet" that can be unscrewed on top of the main body. It has an orifice in the end. Is that what you are talking about? The orifice does get plugged and if it's solid, you need to be careful not to enlarge the orifice by probing too hard.

In addition to that, and what can contribute to a no idle problem, is a "slow air jet". It is internal to the main body...not removable... and is a place that easily gets "overlooked" by anyone that doesn't possess the HONDA CARBURETOR MANUAL. With all the intake ducting removed or the carburetor on a bench, look at the front of the carburetor "throat" or barrel. DEAD CENTER and above the opening, is a small hole. That is the entrance to the slow air jet. Make sure any gasket that may be used allows for air to enter that passage.

You can spray the piss out of it with a carb spray can and straw and probe it with a small wire. That should clear it out. Just don't dig around in there with anything solid or you could ruin the carb for good.

Hope this helps.

Excellent information! I will try these two solutions. I am just not that familiar with Honda motors. It definitely sounds like one of these is plugged.

The sad thing...might be,,,,what hondadude alluded to. Your compression is pretty low. It has been my experience that they will run and perform with compression in the 120's but I just don't know about lower. If your revised compression test yields equally low results then, I'm afraid you're looking at having to seal the engine. The good news is that these are easy to work on and parts are still available at reasonable prices. That is unless your cylinder barrel is worn oversize. Then it can be curtains!

I hope the extra carb clean up does the trick.

The sad thing...might be,,,,what hondadude alluded to. Your compression is pretty low. It has been my experience that they will run and perform with compression in the 120's but I just don't know about lower. If your revised compression test yields equally low results then, I'm afraid you're looking at having to seal the engine. The good news is that these are easy to work on and parts are still available at reasonable prices. That is unless your cylinder barrel is worn oversize. Then it can be curtains!

I hope the extra carb clean up does the trick.

Ok, I finally got back to where the Honda was located and was able to pull the carb off again and try to clean it. Everything looked perfect except for the tiny port in the idle circuit going down to the pickup area. The tiny jet was clogged solid. I had to find an super thin piece of copper wire and it went right through so I could clean it out. Now the motor idles perfectly. Problem solved. Thanks for your help everyone

Fantastic! It's good to hear that another one O them old girls is still GiTTIN' IT DONE!
Thanks for the update!