AF18e Engine Won't Idle

[scooter.boi]

I need some help on my DIO AF18e engine. I've replaced the piston and rings recently (no re-bore done). I have to say I am convinced the compression is below what I want from it. Now the problem is it won't idle. It runs great but when I let go of the throttle it dies.





Does it have something to do with compression? Is it a carb problem? Will re-boring it to a larger size solve the idle issue? I saw some scratches in the cylinder the last time I opened it.
Any suggestion will be appreciated. Thank you everyone.

[swflcarl]

Sound like your pilot jet is clogged.... this is typically the 1st orifice to be impeded - as it is the smallest.

It is the small metal tube (copper looking) adjacent to the main jet. It has a common passage to the idle screw (hole in the tube at the intersection). If it is not clear you will have idle problems.

I like to get a high intensity LED flashlight and flip the carb upside down and shine a light up the where the throttle slide to verify the circuit is clear.

Here is an example... best of luck my friend.

https://www.youtube.com/watch?v=KbNzbwbuqL8

[scooter.boi]

Sound like your pilot jet is clogged.... this is typically the 1st orifice to be impeded - as it is the smallest.

It is the small metal tube (copper looking) adjacent to the main jet. It has a common passage to the idle screw (hole in the tube at the intersection). If it is not clear you will have idle problems.

I like to get a high intensity LED flashlight and flip the carb upside down and shine a light up the where the throttle slide to verify the circuit is clear.

Here is an example... best of luck my friend.

https://www.youtube.com/watch?v=KbNzbwbuqL8

Good video right there. It's worth checking, thank you very much.
By the way, I forgot to mention the bystarter circuit on my carb is no longer working so I plugged the hole with rubber and then silicon gasket maker to make sure its air tight. Can that be the problem too?

[swflcarl]

You can find knock-offs for the by-starter on fleabay. This bystarter circuit allows additional gas to flow during a cold start. The circuit gets blocked when the bystarter starts to receive current when the motor runs / stator. If you have effectively blocked the bystarter tube from the carb bowl... you should be fine. This will make starting a biotch... as you have no priming circuit, but you should be fine once running.

Mousewheels has plenty of write-ups on this topic if you search this site.

I recommending getting this working... that is my 2 cents. Best of luck.

[patthesoundguy]

Did you check the compression with a tester? I agree with the boys, I think you Have pilot issues. Did you set the idle air mixture and idle speed to the spec? Also did you de- glaze the clyinder with a hone? The new rings will have a hard time seating if you dont. And if the bore is shiny as hec you will have weird issues. No cross hatch in the bore means no place for the oil to live between piston rings and cylinder walls and the piston and the cyl walls. It will be fine when its cold and the longer you drive on a run the worse its going to run.

[Johnniespeed]

Teflon tape and silicone cause more problems than they fix. Teflon tape should never be used anywhere and silicone should never be used on carbs or fuel pumps.
I agree with everyone else, that the idle circuit needs attention, but I also feel strongly that the bystarter needs to be in place and functioning correctly.
Now onto your compression concerns, here is a little story that is related.
My Gyro, when I bought it, had a perfect brand new piston and rings, but yet, it would barely start and refused to idle. While the previous owner did a great job of installing the perfect piston and rings, he neglected to measure the cylinder for out of round. Once the cylinder was bored and an oversize piston installed, it starts easily and ides smoothly. The Gyro taught me that the cylinder is not tolerant of imperfection.

[patthesoundguy]

The bystarter totally needs to be there for it idle and run properly. Plugging the hole may work but there is only one way to fix it right and thats a by starter in the hole. Some have blocked the hole with varying success. I'd do a search and see what you can come up with. What I would do if you ate having trouble getting a by starter is to look up the vacuum test for the bystarter in the manual. The passages will pass air according to whether the bustarter is cold or hot. You may be able to confirm whether you have blocked the passage well enough with that test. The idle air mixture and the idle speed are key for it to idle and start. Just the idle speed being a tad below normal will cause it not to idle. When I first got my spree the idle air settings were off just a fraction and it would stall in off throttle all the time. I think part of the issue here is you have a few variables so it might not be any one thing causing the problem it could be a combination of many. Start with the cylinder check the spark plug gap and compression and go from there. lousy compression can't fixed with carb adjustments.

[Wheelman-111]

Greetings:

I noticed that there is no left cooling shroud in the pic. Does the AF18 not normally have one? Are you running it that way? If so consider the effect of overheating and piston damage, decreasing compression along with carb issues. Perform a compression test to confirm.

[patthesoundguy]

Af18e does have a shroud, I just bought one for my af18 from honda it arrived a couple days ago. I agree it should be there to avoid possible overheating.

[scooter.boi]

Thank you for all the inputs.
@Wheelman sir, I have both sides of the shrouds. I just bought the engine from a friend a few weeks back to replace the AF05e engine on that Aero/Vision. Haven't actually gone for a long spin.
So low compression could cause it not to idle properly? I need something to start from. I can re-bore if necessary.
Thank you.

[Johnniespeed]

Of course the carb needs to be fixed, by why not check the compression and post the results here ?
Pay attention to the first hit ( compression stroke ) what the needle rises to, and how many compression hits it takes to arrive at max compression.
In the case of the Gyro issue, the first hit of compression was under 30psi and it took fifteen engine revolutions to get to 115 PSI. This was way too low on the first hit and way too many hits to arrive at maximum for my Gyro.

Max compression should be attained by five or six revolutions ( hits ).

[patthesoundguy]

Of course the carb needs to be fixed, by why not check the compression and post the results here ?
Pay attention to the first hit ( compression stroke ) what the needle rises to, and how many compression hits it takes to arrive at max compression.
In the case of the Gyro issue, the first hit of compression was under 30psi and it took fifteen engine revolutions to get to 115 PSI. This was way too low on the first hit and way too many hits to arrive at maximum for my Gyro.

Max compression should be attained by five or six revolutions ( hits ).

I love this post those are the kind of details and tricks that make one a master at diagnosing problems. I always pay attention to those kinds of things because of my audio background, same kind of thing and it pays off. The more aware you are the more you will notice even more stuff like that.

[Wheelman-111]

Greetings:

Another thing that will make an engine perform decently at upper revs but fail to hold idle is a leaky reed valve.

[patthesoundguy]

Greetings:

Another thing that will make an engine perform decently at upper revs but fail to hold idle is a leaky reed valve.

Ive had this happen. it was very hard to diagnose

[scooter.boi]

So reopened the carb and made sure to see light through all the passages specially the pilot hole. Still no good idle. I suspect its really the bad compression(???)