Posts
181
Joined
12/15/2015
Location
Phoenix, AZ
US
Edited Date/Time
3/3/2020 8:24pm
Had a question about this spark plug reading.
Yz 250 with mild porting and head milled for 110. Carb is bored a little and has rifling done to it.
Running straight c12 with k2 at 32:1 track riding. Fmf fatty with power core 2. Boyesen rad valve with brand new reeds and no spacer.
Has a bog/hesitation on the bottom then it’s a light switch. Absolutely no bottom end.
Current jetting is:
JD Blue needle 2nd clip position
180 main
50 Pilot
Richening the needle to the blue needle in the 3rd position gave me a big at half-ish throttle bog. I thought this was a lean bog but richening seems to make it worse.
Half the plug is a light brown and the other half is black after 20 minute moto. Is this a timing issue I am battling?
Yz 250 with mild porting and head milled for 110. Carb is bored a little and has rifling done to it.
Running straight c12 with k2 at 32:1 track riding. Fmf fatty with power core 2. Boyesen rad valve with brand new reeds and no spacer.
Has a bog/hesitation on the bottom then it’s a light switch. Absolutely no bottom end.
Current jetting is:
JD Blue needle 2nd clip position
180 main
50 Pilot
Richening the needle to the blue needle in the 3rd position gave me a big at half-ish throttle bog. I thought this was a lean bog but richening seems to make it worse.
Half the plug is a light brown and the other half is black after 20 minute moto. Is this a timing issue I am battling?
Overall the plug looks a bit dark indicating it is rich, but is it oil or fuel rich?
Keep in mind that race fuel burns slower and thus can make the plug reading show rich as a result.
Paw Paw
I ran my previous motor at 40:1 with a head that was milled for pump gas riding motocross and it ran perfect. I haven’t had to run race gas before and the previous owner said to run it straight and they ran 32:1 so I went with that route so this is all new to me as well as chasing jetting haha.
The only thing that I changed since I got the motor was adding the JD needle from the stock N3EW needle but I left the same 180 main and haven’t touched the pilot. (I will check what size the pilot is tomorrow).
I pulled off the head to replace the o rings on the cylinder and the power valve functioned at the linkage but I am not sure if that is enough to tell if it is functioning properly.
The motor that ran fine before was the motor that came in the bike but that turned into a basket case.
The Shop
Also used a butane torch around the intake area to check for an air leak and didn’t hear any change in idle.
Not sure how to check main seals for leaks.
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