Got my ATAC cylinder installed on my 85 250R

[dansvan]

Got my 85 ATAC cylinder on and running. Holy cow does it fly! Made an adapter for the exhaust flange, blended it in, opened the boost ports very slightly, removed the rough edges and casting flash. Had it bored the first size over. Wiesco piston. Thin headgasket from the three piece type. 38mm Carb, dial a jet, MSD ignition, lightened flywheel. Paul Turner pipe, 100LL gas with Torco Accelerator and Amsoil synthetic oil. Thing is an absolute beast. Rip your arms off midrange and eye watering top end. I can putt around at slow speeds ( my 4 year old rode in front on the beach this weeekend) all day, rip the throttle and "hold her Luke she's headed for the barn!" Can't wait to get her even more dialed in.

http://www.supermotors.net/getfile/650445/fullsize/p1010409.jpg
Gratuitous waterfall shot. Clam Gulch, Alaska.

http://www.supermotors.net/getfile/650446/fullsize/p1010427.jpg
Man saltwater does a number on things.

http://www.supermotors.net/getfile/650447/fullsize/p1010426.jpg
Nice and stealthy looking. This winter when it gets a full cosmetic makeover I'll grind and fill the rack hole and unless people know what to look for and where, it'll be just another 250R.

http://www.supermotors.net/getfile/650450/fullsize/p1010425.jpg

http://www.supermotors.net/getfile/650451/fullsize/p1010424.jpg
Shot of my modded TRX airbox.

http://www.supermotors.net/getfile/650453/fullsize/p1010423.jpg
MSD control box and battery mounted out of site.

[J.D.]

What's an ATAC cylinder?

[Duner]

Looks good, although I have no idea what ATAC cylinder is (Automatic Torque Amplification Chamber)???? which was used on the CR bikes???...:headbang:

and how did you lighten your flywheel? The 85 is the lightest to begin with....

What main and pilot are you at for the elevation your running?

[dansvan]

The cylinder is from a 1985 Cr250R. It had a removable power valve that bolted on the cylinder and was actuated internally. They make a good upgrade over the stock ATC cylinder as it has more agressive port timing and additional cooling on the exhaust side of things.

Not sure what year flywheel. I had three of them laying around, from 85/86 bikes and my cousin turned it down on his lathe. I did not weigh it before and after but compared to stock it's been turned down below the ridge.

Jetting I honestly dont remember. I left it alone from the prior build. Stock cylinder/piston, same carb, FMF pipe, stock ignition, old reeds. I figured with the dial a jet it would be ok. I had literally 45 seconds of run time on this engine before we left. I was gentle with it for the first several runs, checking the plug constantly. I put the MSD at full retard, went the richest the dial a jet could go and it liked it alot. I will be installing the EGT guage next and doing the fine tuning.

[Mr. Richard]

85 cr is the only true bolt on cr cylinder for the atc 250r,, they do make alot of difference too,,, heres mine,,





http://i29.tinypic.com/hvt9hg.jpg

[Duner]

The cylinder is from a 1985 Cr250R. It had a removable power valve that bolted on the cylinder and was actuated internally. They make a good upgrade over the stock ATC cylinder as it has more agressive port timing and additional cooling on the exhaust side of things.

Not sure what year flywheel. I had three of them laying around, from 85/86 bikes and my cousin turned it down on his lathe. I did not weigh it before and after but compared to stock it's been turned down below the ridge.

Jetting I honestly dont remember. I left it alone from the prior build. Stock cylinder/piston, same carb, FMF pipe, stock ignition, old reeds. I figured with the dial a jet it would be ok. I had literally 45 seconds of run time on this engine before we left. I was gentle with it for the first several runs, checking the plug constantly. I put the MSD at full retard, went the richest the dial a jet could go and it liked it alot. I will be installing the EGT guage next and doing the fine tuning.


The lathe soaking is the best method for reducing the flywheel, but if your using an '85 to start, they are light and taking much more down would concern me if/when you start making good power (60+).

Did you get CR ignition when you got the motor?

Where did you plumb your pipe for the EGT sensor at?

Kasey, you run that motor yet, or is that the one going in the 70:D

[dansvan]

No CR ignition, just bought the cylinder off of ebay.

I haven't installed it yet. Some time this week. I'll post pics.

[Mr. Richard]

Kasey, you run that motor yet, or is that the one going in the 70


nope i sold that cylinder. i bought another 250r with a good bottomend,, i am putting the 310 on that bottomend,,, and that will probably be the one i will use,,,,,,,