Atc motor jetting.

89 250r guy · Sep 2, 2015

I got a atc motor but dont know what bore it is.
Il look threw the spark plug hole a see if I can tell the piston size
I have to use my stock reed cage and carb I have 165 and a 175 main.
would the 165 be safe to start ?

Swanitalia · Sep 2, 2015

I would go with the 175 1st. You can always jet down if it's to rich, a spark plug is cheaper then a piston.

89 250r guy · Sep 3, 2015

If its to rich why would the piston be at risk ?
I found the stock settings for the main and its 138-148.
Im not saying your wrong but 175 seems high when all I have is a fmf gold fatty pipe.

89 250r guy · Sep 3, 2015

The book said 138 to 145 main-needle 2nd groove
I dont know much on jetting dont know what bore either the guy said 66.50 and all I have is fmf pipe.
My lowest jet is in it now 165 and needle is on the 4th or 5th.
It feels a little slugish.

250rRoostmaster · Sep 3, 2015

66mm is stock bore size. So 66.5 is your 2nd bore most likely.

My motor is a LED performance built 272 4mm stroker and I'm running a 175 main/52 pilot/2nd clip from top at sea level in the Oregon dunes.

Your more than safe starting at the 175 and working your way down.

You say it's sluggish.. Elaborate a bit more? Is it bogging or sputtering? I'm guessing sputtering which is a rich condition but need a little more info. What does the spark plug look like? Do you know of any porting done to the cylinder?

89 250r guy · Sep 3, 2015

Hear let me start over with more info.
I have a 85 act motor.
A 88 trx stock carb and stock reeds.
fmf gold fatty pipe.
Im in Illinois sea level.
Stock bore Im told.
Air box 4 holes drilled in lid K&N air filter with stock snorkel.
Premix pump gas 32:1
I need to know what I should be on -main jet ?-pilot-?and what clip down from top of the needle?
And how many turns out on the air screw.
Thanks guys.

american opel · Sep 3, 2015

do to Duncan racing's site.it will give you all the info you need.jetting from A keyboards is hard.

89 250r guy · Sep 3, 2015

Jetting confuses me ?

Swanitalia · Sep 3, 2015

175 maybe to big, but it's a safer starting point. The K&N filter will require larger jetting and the holes in the lid will allow more air into the engine.

It's better to be rich then lean, my bike runs a little on the rich side at 60 pilot, Custom Needle 4th clip, 220 main.

89 250r guy · Sep 3, 2015

Is it the bigger the main jet the richer ?
The book said 2nd groove on the needle I was on the 5th lol.
I was told on the needle the more clips down the richer Im going to try the 3rd clip.
Im like you want to be safe.

Swanitalia · Sep 3, 2015

Yes the bigger the main jet the more fuel the engine will get (richer). The clip position is 1st clip (lean) is the very top of the needle, and the 5th clip (rich) position is at the bottom towards the taper.

What premix ratio are you running? 32:1?

89 250r guy · Sep 3, 2015

Yes 32:1 .
I moved the needle clip to the 3rd groove little better but it calls for the 2nd groove.

american opel · Sep 4, 2015

I pmed you.

Atc motor jetting.

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