86' ATC 250R Running not just right

[Merge_88]

So I've had a pretty clean ATC250R for the last six months and have not yet to get the thing to run like i think it should. I used to have an 85' with low compression and I swear that it had more power than this thing does. When I got the bike, the owner had just put a new FMF Fatty pipe on it. The bike seemed like it was starving for fuel on the top end and had a dead spot on the low end. I put a fatter main (150) in it than the FMF specs and it still ran the same. I put a fresh set of rings and hone job not long after just to be sure it wasnt any type of compression issue. I still have the same problem. I then decided to play with the needle by moving it up and down in the grooves with little success. Today, I put a 140 in it and it really seems like it made little difference as well. I'm confused as what to do next. Maybe I should put a new set of reeds with a spacer plate? I'm tempted to go back to the stock pipe and see what results I get (thats what my 85 had, stock pipe/silencer and I liked its power). I dont know, maybe Im spoiled by the low-end my TRI-Z and Tecate have compared to the R. The thing is, I like the braking, handling, and suspension MUCH more than the othere two. If I can get it running similar to the other two with some low end power then I'm sure the R will be my favorite and daily rider. A lot of guys told me to just go with the 310 kit and Ill have all the low-end I need. What to do?

By the way, Ive also messed with the air box lid on and off along with the snorkel on and off, but still it isnt as crisp as it should be. When I pin the throttle, the R never sounds like it clears out, maybe this is a sign of something else? Almost making it sound like a rev limiter if that makes any sense. Thanks

[NINJA]

I know you said you rebuilt the topend, but it sounds to me like it's low on compression.

[Merge_88]

About how much psi should I have with the stock bore with fresh rings and a hone? If memory serves me right, a true reading comes after about 10 kicks and then check the compression gauge?

[Mosh]

First of all,I would dump that stock 85 round slide carb.
I rejetted her bike 10 times, all over the place,and could never get it just right.
I would go for a 86 ATC or trx carb.They have a flat slide set-up,and breath much better.Also check your air filter,and make sure it is good,and not over oiled.

Next,if your reeds are stock,or older than 1 year,dump some good Boyeson power reeds in it.Then get your jetting dialed in.Check your gearing.Make sure you are at least stock on the chain and sprockets.
If you want more low end torque,drop down to a 12 tooth front sprocket.

But seriusly,you will mess with that 85 carb forever,and never be happy with it.IMO.

You can round up the carb and new reeds for less than 100 bucks on Ebay.

[Merge_88]

Hey Mosh, thanks for the advice but it IS an 86 ATC 250R, I mentioned how much better my 85 ran than this 86, I think thats where the confusion came in at. Thanks though! I think I am going to run a compression check to see what is going on and throw a new set of Boysen reeds in.

[Mosh]

Sorry my bad for not paying more attention.Check the air filter,and have you tried a new plug?

The FMF pipe is not a real high revver vs other pipes.If you were lean it would rev out clean,but lack power.

If it is bogging and wont clear out on the top,either you filter is dirty,the plug is bad,or you might be too rich.

[Merge_88]

Would the reeds for an 86TRX be the same for an 86ATC??? Bikebandit doesnt show an 86ATC for power reeds or any reeds in that matter from Boyesen, but they do for an 85ATC and an 86TRX.

[Merge_88]

Nevermind, answered my question.

[NINJA]

Found out what the issue is yet?

[Merge_88]

I am waiting for my Power Reeds to come in the mail, should be here tomorrow. By the way, what psi compression should I have?

[DeePa]

160-180 ish

[Blown 331]

What's up man. Let me know what you find out. My 1984 250R is having a similar problem. I know I need to lean it out but I'm thinking my silencer might be clogged (haven't checked yet). I put a standard bore Wiseco in it and new Boysen power reeds. Runs MUCH better but I still don't think it's right, I know it's a little rich on the main but I still think it's more than that. Just like you are saying, it doesn't seem as crisp as it should. I'll check the compression. Ever ride a Polaris 250 2-stroke? Even though they are 2-stroke it's amost like they run like a 4-stroke. No real noticable power band and kinda doggy. That the best comparison I have to my 84. It is much better than it was, it was mostly reeds but it's nothing like my buddys 82.
A buddy of mine came over with his 82 250R yesterday and it does have a super nice pipe on it but this thing runs unbeleivable.
We also got my 85 250R out and I think thats a little rich on the main also but this thing is insane. I'm running a rad valve, ESR pipe, 36mm flat side, Fresh Wiseco and just one thin layer of the head gasket for some compression. My buddy with the 82 rode it, came back and all he said is that thing is rediculous and he wants one. lol.
Good luck and keep us posted!