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View Full Version : 85 ATC250R Need Jetting Help!



Eraginal
02-18-2018, 02:04 PM
I just rebuilt the engine, bored .40 over, new Boysen pro reeds, and a eBay carb kit, fmf fatty gold series and fmf powercore. Choke kills the bike, idle screw is all the way in to make it idle, fuel air is about 1 1/2 turns out, needle on second clip. No bottom end just half throttle or more to make her wheelie. Also running 32:1 91 octane Motul Premix.
Another question I replaced my kill switch and light switch because the old one didn’t work and the new one doesn’t work either. Any help bad CDI?250341

yaegerb
02-18-2018, 02:54 PM
Could be bad Cdi.
What size carb?
What size jets?
Are you running an airbox with lid?

Eraginal
02-19-2018, 02:20 AM
Whatever stock carb is and jets air box does have a lid on it I had it off when I didn’t have my shrouds on what do you recommend, I’m thinking pilot jet needs to go smaller to give it more rpm and torque at bottom.

yaegerb
02-19-2018, 01:10 PM
I need an actual number off the carb and jets. You can’t guess at this. Assuming you have a stock carb and jets is ok until you find they aren’t. Leave lid on and run a well oiled uni filter.

Eraginal
02-19-2018, 11:50 PM
I’ve got a 3YAHYC7 off the carb, lid is on the air box and have a non oiled K&N round filter. Carb is round slide not flat. 142 main and 52 pilot.

Eraginal
02-19-2018, 11:58 PM
250477
Here’s a picture of the carb is that helps

Eraginal
02-20-2018, 12:17 AM
Keihin PE 34mm is the size of the carburetor lol that’s small for a bore, carbon reeds and pipe and silencer. What do you think?

yaegerb
02-21-2018, 12:40 AM
Try 2 turns out on air screw. All things being equal, other than 2 turns out that carb is jetted spot on. What kind of jets came in the carb kit? Were they genuine Keihin jets with numbers in the side? Sometimes the knockoffs have different orifices than the genuine jet.

Eraginal
02-21-2018, 08:39 PM
2 turns runs like crap, numbers on the top of the jets, where should the needle clip be mines at 2. Also does solve my idle issue and choke killing the engine.

yaegerb
02-21-2018, 09:30 PM
Needle clip should be 2 from the top. Do you have any air leaks around the carb? Have you performed a pressure test? If those two things check out then it could be electrical.

jeswinehart
02-21-2018, 09:34 PM
http://www.3wheelerworld.com/showthread.php/55086-Carb-Jetting-101-Terms-Tips-and-Jetting-Theory

Eraginal
02-22-2018, 12:49 AM
Possible electric I have a new cdi box coming this week, I was thinking it would be my pilot jet that needs to be changed to bring up the idle rpm