ATC250r Jetting Procedure

[jchale]

Hey guys,

Anyone in this forum familiar with how to properly set the pilot, needle and main jetting for certain altitude and temp? I live in Winnipeg Manitoba and purchased a 1985 ATC250r. I'm at approximately 763ft and temps between 5c to 30c. Just bought a new fmf pipe and silencer. FMF says to use stock but I want to fine tune. I'm a casual rider, not a racer. I will run 20:1 mixer as I'm a believe 2stokers like oil. I did read to set jetting (on the rich side). Bring to operating temp, have it in 5th gear under load at high throttle, pull in clutch and hit kill switch. Check plug to see how it is running. I think there are topics on this issue in other forums although I'm a newbie and can start or reply yet. I need to hit 2 months of registration and 10 posts.

Thanks in advance for the replies.

J

[barnett468]

hello;


is your cylinder ported?

is this the only change you made?

how did it run before the new pipe?

have you ridden it with the new pipe and if so how does it run?

exactly what carb is on it?

look at the plug and tell us the color.

white/lite gray n= lean

lite tan = slightly lean

medium tsan = ideal

dark tan = slightly rich

dry black = rich

moist goey black = butning oil and possibly rich.


start test with a new or lite colored plug.

it might btake around 30 minutes of average riding to get good color on it.

i would not do a high speed plug chop yet.


if it burbles/sputters when opening the throttle it is rich.

if it simply fails to accelerate [hesitate/bogs] like it is out of gas it is lean.

[barnett468]

If it ran perfectly before and it had a stock pipe AND muffler, I would start with a 2 size larger main.

Exactly what model is the pipe ie., "fatty" or an "rpm" type etc.?

You mentioned running a 20:1 ratio, is this what you have been running with your old pipe and jetting?



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Hi, I’ll be a cute little baby fur seal for around 2 more weeks when hunting season starts.

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[DohcBikes]

I heard somewhere on the internet that if you simply change to a 40:1 mix you should gain some serious power.....:D:lol::wondering



Sorry jchale I just had to do it:lol: Disregard my previous info. Fine tuning the jetting is best done ONE THING AT A TIME. Read the plug. RECORD THE RESULTS. Ask for help when you need it!!

Happy tuning:beer

[barnett468]

I heard somewhere on the internet that if you simply change to a 40:1 mix you should gain some serious power.....:D:lol::wonderingHey Dohc, I saw that too. I guess if going from 25:1 to 35:1 to 40:1 is good then I should be able to do around 8 seconds in the quarter mile with around 200:1.

I also read somewhere that it is beneficial to run oil that has Prefabulated Amulite anti wear additive.

They say that Prefabulated Amulite is one of the best anti wear additives available.


Hey Bevis…get a load of these clowns.

Yeah b head…they make us look like rocket scientists.

Well duh...that shouldn't be to hard to do.

http://media0.giphy.com/media/dxwYVGx3Q94pa/200_s.gif

[jchale]

I have recorded and printed this info. I will have the bike hopefully this week and will begin to tear down and redo bearing etc. I will go through the entire bike so will have all information and will be able to start communicating. Wont be riding for a bit as there is probably 3-4 feet of snow left on the ground............. Gives me time to make things perfect.

Thanks a bunch for the replies. I would never forgive myself if I popped a piston because not researching and learning.

Will be in touch.

Jay