Honda 7,5hp (older) problem with idle power/speed

[IvanJ]

My Honda is 7,5hp 149cc version.
I have a problem with idle speed. Usually it's not constant and if the engine doesn't warm up for like 1-2minutes with 1/2 throttle, it fails so I need to start it again.

What's worse, the same happens when driving forward on that (minimal) speed... the engine literally shakes and produces lots of vibration, like it struggles to maintain the power. Driving at that speed for a few minutes usually makes the engine stop by itself.

I managed to increase the idling speed by twisting the screw, so it's better now, but I'm still not satisfied - the engine still produces lots of vibration on the slowest speed and usually fails.
However, it runs fine on the higher speed and opened throttle. What's the problem?

Thanks!

 

[IvanJ]

Re: Honda 7,5hp (older) problem with idle power/speed

I messed with two adjustment screws located at the carb. I did manage to remember their position, so it's reversible.
Since I don't have the manual, can anyone tell me what are they for? One is for idling the throttle speed (that's obvious), but what is the other one...?

Things started to get better once I messed with that other screw... though not entirely.

 

[Nick on the Bad Habit]

Re: Honda 7,5hp (older) problem with idle power/speed

You are correct as far as the idle screw, the other is a fuel mixture screw.
adjust the mixture screw for smoothness and the idle screw for the correct speed. You might be able to squirt some carb cleaner into the the fuel mixture bore to clean it out. You also have a drain screw on the bottom of the float bowl, try opening that while quizzing the primer bulb to force any crud out of the float bowl.
Good luck, Nick

 

[IvanJ]

Re: Honda 7,5hp (older) problem with idle power/speed

Thanks Nick!!
I played with both screws and now my engine is idling like a charm!!

The badly positioned mixture screw was causing the vibrations and failure. Since I didn't know that, I mistakenly increased the idle screw. All I got was much higher idle speed and higher RPM. Luckily, the gears didn't brake at shifting. :redface:

Now I decreased the idle screw for like a half turn and I have a quiet and smooth idling speed!

I already used Motul Engine & Fuel clean. But anyway, I'll open a drain screw and squeeze the bulb to see if any junk comes out.