1985 ATC250r jetting help

[Ndog]

Hey guys I need your help. I have a 135 main jet in my trike and it still seems to be running rich. The manual recommends main jets from 138-148 so I am already a bit below what is recommends. I am in Indiana so I am at sea level and it is even cold out now so it should be running lean anyway. The needle clip is right in the middle so that is correct. I also have a new air filter too. I am just concerned that i am missing out on power if i cant even run a 135 without being rich. The only thing I can think of is that my stock exhaust has excess carbon buildup inside it which would make the sytem not flow enough air to match the fuel. Should I just start looking for aftermarket pipe? If so which ones are good for a stronger powerband? I have heard alot of them just add low end torque. Do the pipes add quite a bit of power? The PT hi-rev says it adds like 20% more power. Sorry for the length of this post but please help me. Thanks a ton guys!!

[RideRed250R]

go one down in the clip position and to to a 37 pilot.... i would even possibly put a whole new carb rebuild kit in it... take the exhaust off it.. go to a quater car was....stick nozzle in the big side... hold on tight and watch the crap come out... if its still rich then it could be crap... tiem for a new top end...
Adam

[Dammit!]

go one down in the clip position and to to a 37 pilot.... i would even possibly put a whole new carb rebuild kit in it... take the exhaust off it.. go to a quater car was....stick nozzle in the big side... hold on tight and watch the crap come out... if its still rich then it could be crap... tiem for a new top end...
Adam

What works for you in the California desert isn't what's going to work in Indiana. Your bikes and location have next to nothing in common.

My advice,

Clean out the pipe. Adam's method will work. Replace the baffle packing too.

Check your air filter and air intake (if you're running with the airbox lid on). You can clean out the air intake the same way as the pipe. They can get clogged up full of all kinds of crap.

Clean out the carb paying special attention to the jets. They can get clogged as well. Check the float adjustment and seat.

Now,

How do you know it's running rich? Are you doing proper plug chops? You're not giving enough information. The only way to check the main jet is by testing it at wide open throttle. Use a clean spark plug. Get it wide open, hold it there for a few seconds and in one motion pull in the clutch and kill the engine and coast to a stop. If it's wet and black, it's too rich. If it's tan you're right on. If it's light gray or white you're lean. You can also tell by how it's running to confirm what the plug is telling you. If it's sputtering kind of rapidly at wide open throttle, it's rich. Too much gas for it to burn effectively. Unfortunately, it's possible to run lean with no outward symptoms which is why you need to do plug chops instead of just going by the way it's running alone. A lean condition that doesn't manifest itself in performance can still fry your top end.

Do that first. The main jet effects everything past 1/4 throttle to at least some extent so it's important to figure out which main to run before doing anything else.

After you get the main dialed in, you can do some half throttle plug chops but you can really tune it by ear at that point. Do both until you're comfortable. It's possible to have your main jet the perfect size and still run way too rich or lean at anything less than wide open throttle. Needle clip position and air screw are going to be the two circuits that have the most impact on how it runs at anything less than full throttle. The stock pilot jet will most likely be fine (it works in conjunction with the air screw so you can fine tune it that way instead of changing the jet unless it's way the hell off). Remember, tightening the air screw will restrict air flow which makes it richer and vice versa.

It's hard to tell the difference between a bog (lean) and a sputter (rich) until you run into both. I screwed up at the dunes and went the wrong way with my adjustments. I was feeling it cut out around mid throttle and just assumed it was rich because it feels similar to a main jet that's too rich. You have to listen to it. A bog sounds like the way it does when it's running out of gas. A sputter is a little bit different but you have to get pretty far off before it's obvious what's wrong. Mine was bogging at mid throttle so I needed to richen it up with the needle clip. I was goofing it up until Kasey pointed out my error.

Bottom line is, nobody on here can tell you exactly what you need to set your jetting/needle/pilot/airscrew at. Every trike is going to be a little different due to different mods and location/atmospheric conditions. What you need to do is understand exactly how it works and then just figure out what your trike needs. Takes a little practice and trial and error. I understand it fine but still screw up in my applications sometimes.

Sorry for the novel.

[TeamGeek6]

I have a 135 main jet in my trike and it still seems to be running rich. !

It is, and may have nothing to do with jets.

First problem - float. Those carbs tend to run very rich from float problems. I had to greatly lower my fuel level and run a 132 main.

second problem, it can be rich on idle, transfer, midrange or wide-open. Which one or ones are you having trouble with? The main jet affects 3/4 - full throttle.

[Ndog]

It is, and may have nothing to do with jets.

First problem - float. Those carbs tend to run very rich from float problems. I had to greatly lower my fuel level and run a 132 main.

second problem, it can be rich on idle, transfer, midrange or wide-open. Which one or ones are you having trouble with? The main jet affects 3/4 - full throttle.

First of all let me tell all of you guys I really appreciate your help. I took off my pipe (it had like a quarter inch of buildup) and sandblasted the inside and got all the crap out. Then I repacked my muffler (it didnt even have hardly any packing left!). I scraped the buildup out around my exhaust manifold too. Then I removed my airbox lid and dropped my needle one position (it is now on clip number 2 from the top). I took it out and it ran like a completely different machine. I almost flipped over in 4th! However down low it is still rich and the plug looks wet and black off idle and 1/4 throttle. The response is not good off idle. My air screw is out 2 1/2 by the way. I couldnt believe I was still that rich down low so for the hell of it I did a compression test (yes with wide open throttle and cold) and got 170 psi max every time. The guy I bought it off of said it was bored 10 over fairly recently. Do you think this is ok compression or are tired rings causing my low rpm problems?
Finally, should I go ahead and drop the clip to its lowest setting? YOU GUYS ARE AWESOME!!!!

[TeamGeek6]

I took it out and it ran like a completely different machine. I almost flipped over in 4th! !

You aint seen nothin yet. Wait till you get the low end fixed and it tries to flip you over backwards in other gears too. ITs tuned right when youre a little scared to hit the gas.

Welcoem to the world of NASTY 2 STROKES!!!

Theres a reason 2 stroke riders put up with all that smoke.:lol:

[whyzee]

You aint seen nothin yet. Wait till you get the low end fixed and it tries to flip you over backwards in other gears too. ITs tuned right when youre a little scared to hit the gas.

Welcoem to the world of NASTY 2 STROKES!!!

Theres a reason 2 stroke riders put up with all that smoke.:lol:

:lol: ain't that the truth !!!!

[Racerguy381]

lol I had the same issues with my R and the stock carb.... So I put a 39PWK on it and BAM! problem solved. It works so much better crisp clean throttle response spot on jetting. If you can find one cheap buy it! One of the best investments you can make even with a stock pipe. All the modern 250's came with those bigger PWK carbs. A 38 would even work, otherwise your going to be chasing this jetting all over the place. Mine used to gurgle down low until you had it about half throttle then clean out. Find a better carb and you will be happy.

[FastZ28]

I took it out and it ran like a completely different machine. I almost flipped over in 4th! However down low it is still rich and the plug looks wet and black off idle and 1/4 throttle. The response is not good off idle. My air screw is out 2 1/2 by the way. I couldnt believe I was still that rich down low so for the hell of it I did a compression test (yes with wide open throttle and cold) and got 170 psi max every time. The guy I bought it off of said it was bored 10 over fairly recently. Do you think this is ok compression or are tired rings causing my low rpm problems?
Finally, should I go ahead and drop the clip to its lowest setting? YOU GUYS ARE AWESOME!!!!

When all else fails return to stock regardless of mods. It will get you in the ballpark. Have you inspected the reeds and reed block, bad reeds can cause a rich condition down low if they are not seating. I had pretty much the same issue with my 85 R, I inspected the reeds and they were well beyond worn. My R had a boyesen rad valve and the reeds were not seating, I replaced it with a V-force 3 and it is super crisp thoughout now. I used the same jetting and needle position with both. Its got the stock #52 pilot and a #145 main and middle clip position, and its actually a tad lean at WOT, but since I mx and don't see alot of WOT I am fine with it. If your reeds check out ok I wouldn't hesitate to move the needle clip, its all part of diagnosing the problem for a solution. Thats part of the fun of the hobby.:TrikesOwn

[whyzee]

lots of great info in this thread!

[poppanitrous]

own a 1985 atc 250r-Im trying to dial in my carb KEIHIN 36 (modified bootto fit) PE Carburetor (#PE 40AASJ7)with Jetting as follows : 16O main , 75 idle , 3.5 slide and 28A needle.
aftermarket pipe and dg type2 silencer with no packing-K&N air filter-v-force reed cage.
Has no bottom end hit, seems like it needs to get warmed up and hot before it runs good at 3/4 throttle. You can blip it to wheelie like with the stock POS carb. It lost all bottom end, i pulled the plug and it is showing rich condition. I live in florida and i dont believe i need to go leaner at sea level. i use quicksilver synthetic or amsoil 50:1..i live in Florida so sea level.
I need someone who uses this exact carb and see what clip position its in and what ide and main and air screw how many turns out from seated to make it easy for me. I hate taking carb off in humid 100 degree weather when i can get a great baseline on this forum.
It is not snappy at all on the bottom end and even seems to stutter on the top end as wel.
thanks
poppanitrous

[Mosh]

I am running a PJ series 36 mm from a cr 250 dirtbike on my wife's 85 R.
I always had a hell of a time jetting it for the low end circuit. I finally got it pretty decent.
I believe I am down to a 42 on the pilot and 160 on the main.
No lid above 70 degrees, needle in the middle.
She is 20 over with a CR headgasket and ESR pipe.
It is a little lean when it is warming up for about the first 2 minutes, then it is fine. I had to get her as lean as possible so she would not foul plugs at low speeds in tight trails.
I could go richer, but it would load up after 10 minutes of 2nd gear riding. She never goes WOT for anything longer than a few seconds, so she is safe on being to lean up top.

IMO you may want to try leaning out the pilot. 75 seems way to rich.

[poppanitrous]

Float pods were molded on upside down from factory it was a common issue.i bought one new in 1985 and it fouled plugs constantly so i went back to dealer and found the float pods are upside down and you can jet it all you want,you have to set float height properly or replace carb with keihin air stryker or mikuni flat slide.

[badandy]

What works for you in the California desert isn't what's going to work in Indiana. Your bikes and location have next to nothing in common.

My advice,

Clean out the pipe. Adam's method will work. Replace the baffle packing too.

Check your air filter and air intake (if you're running with the airbox lid on). You can clean out the air intake the same way as the pipe. They can get clogged up full of all kinds of crap.

Clean out the carb paying special attention to the jets. They can get clogged as well. Check the float adjustment and seat.

Now,

How do you know it's running rich? Are you doing proper plug chops? You're not giving enough information. The only way to check the main jet is by testing it at wide open throttle. Use a clean spark plug. Get it wide open, hold it there for a few seconds and in one motion pull in the clutch and kill the engine and coast to a stop. If it's wet and black, it's too rich. If it's tan you're right on. If it's light gray or white you're lean. You can also tell by how it's running to confirm what the plug is telling you. If it's sputtering kind of rapidly at wide open throttle, it's rich. Too much gas for it to burn effectively. Unfortunately, it's possible to run lean with no outward symptoms which is why you need to do plug chops instead of just going by the way it's running alone. A lean condition that doesn't manifest itself in performance can still fry your top end.

Do that first. The main jet effects everything past 1/4 throttle to at least some extent so it's important to figure out which main to run before doing anything else.

After you get the main dialed in, you can do some half throttle plug chops but you can really tune it by ear at that point. Do both until you're comfortable. It's possible to have your main jet the perfect size and still run way too rich or lean at anything less than wide open throttle. Needle clip position and air screw are going to be the two circuits that have the most impact on how it runs at anything less than full throttle. The stock pilot jet will most likely be fine (it works in conjunction with the air screw so you can fine tune it that way instead of changing the jet unless it's way the hell off). Remember, tightening the air screw will restrict air flow which makes it richer and vice versa.

It's hard to tell the difference between a bog (lean) and a sputter (rich) until you run into both. I screwed up at the dunes and went the wrong way with my adjustments. I was feeling it cut out around mid throttle and just assumed it was rich because it feels similar to a main jet that's too rich. You have to listen to it. A bog sounds like the way it does when it's running out of gas. A sputter is a little bit different but you have to get pretty far off before it's obvious what's wrong. Mine was bogging at mid throttle so I needed to richen it up with the needle clip. I was goofing it up until Kasey pointed out my error.

Bottom line is, nobody on here can tell you exactly what you need to set your jetting/needle/pilot/airscrew at. Every trike is going to be a little different due to different mods and location/atmospheric conditions. What you need to do is understand exactly how it works and then just figure out what your trike needs. Takes a little practice and trial and error. I understand it fine but still screw up in my applications sometimes.

Sorry for the novel.

Good Info, but can someone please confirm this, in red... I was always taught the fuel/air screw,metered fuel, not air... in=lean, out= rich.
If the above is true, then I know what I've done wrong....