84 250r running lean

[BrandonRadtke]

So I have a 84 250r and I just rebuilt the top end now it leans out when I’m running wide open. The motor revs itself so I have to use the brake to bring it back down to idle. My question is if it didn’t do it before the rebuild it shouldn’t be crank seals right? Would you guys just think it’s main jet? It idles good and plug is dark brown. Just want to know where you guys would start? I will pull stator cover tomorrow to see if there is any oil residue and it doesn’t smoke like it would if the clutch side were bad.

[Atc 200x 1985]

Check your float level before you start messing with jets there is a lot of things that will make your engine lean. Another thing is rev it up at idle if it goes back slowly then you will need to turn your screw that moves the slide up and down bring out I’ve had that problem before I done that and that fixed it but it won’t idle so it could be that and the float but try the screw trick first before you tear your carb apart.

[BrandonRadtke]

It doesn’t have an inline filter so it’s very possible that it got something in the carb. I will clean the carb tomorrow also and take notes of jet sizes just in case it still does it. I don’t want to run it much in fear of blowing it up. lol

[Atc 200x 1985]

Yeah I would be careful about it running lean especially since it’s a 2 stroke. And yes look into the air filter cause that would open up more air into the engine.

[BrandonRadtke]

I meant inline fuel filter and I plan on changing air filter too.

[yaegerb]

So I have a 84 250r and I just rebuilt the top end now it leans out when I’m running wide open. The motor revs itself so I have to use the brake to bring it back down to idle. My question is if it didn’t do it before the rebuild it shouldn’t be crank seals right? Would you guys just think it’s main jet? It idles good and plug is dark brown. Just want to know where you guys would start? I will pull stator cover tomorrow to see if there is any oil residue and it doesn’t smoke like it would if the clutch side were bad.

I don't know what you mean by "motor rev's itself".....

If you just rebuilt the top end but didn't pressure test the motor post rebuild, you have done yourself a disservice. I would start by pressure testing the motor (this is not a leak down test, this is a crank case pressure test). There are many how-to articles, a few I have written myself on the subject that you can find on this site.

A dark brown plug after idling and riding will tell you nothing. The plug could be brown from the idle circuit or the needle circuit or the main circuit. Once you have the motor pressure tested and it passed (needs to at least hold 6lbs for 6minutes) then move on to the carb. A thorough cleaning would help along with identifying the jets you are currently running. On idle circuit your air screw should be turned out 1.5 turns and your engine should rev fast and then quickly come back to idle. If this is not the case then your pilot is wrong.

Start on the pressure test and then move to the carb cleaning and then to the idle circuit and report back.

[BrandonRadtke]

It was so lean the motor was revving out by itself. The only way I brought it down was to hit the breaks in gear. And I will try to get a pressure tester and test it. I just thought it would be okay since it was running perfect then I had it bored and a new piston. It revs fine comes down fast and is super snappy. It’s just when it gets to 5th on the road it leans almost as if it’s not getting enough gas.

[christph]

Sounds like your needle jet is too lean. The needle jet controls fuel delivery from about 1/3 to 2/3 throttle, and then your main jet for the final 3rd. Drop the needle jet c-clip down by one slot.

[BrandonRadtke]

The thing is it runs great for a few passes and it doesn’t do it but I would say like 5-10 minutes of harder riding it will start to rev without throttle. I had an old 2 stroke tri moto and the fuel filter plugged and it leaned out of fuel and revved uncontrollably. Same way this one is revving out. It’s like I’m using fuel faster than the bowl fills. I ordered a pressure tester online so I will test that next week sometime.

[Atc 200x 1985]

Oh I thought you met a air filter sorry. If it’s getting warm then doing it that means it is most likely pressure or the needle move it Down one spot from where it is now that would richen it up when you give it throttle.

[atc300r]

Check your gas cap vent you should beable to blow through it.

[BrandonRadtke]

Sorry for the late reply but I did the pressure test and it held 6 lbs for 6 minutes. I actually forgot about it and looked back 10 minutes later and it was still at 6 lbs. I cleaned the carb today and it doesn’t rev itself out anymore but it hangs before returning to idle. Jets are 50 pilot and 130 main. I think the main sounds a bit small at 130 because my 350x has 142 main and a 42 pilot but I realize comparing the 2 is like apples and oranges. I’m just wondering if the 130 main is small and if there is something else I should look for as an issue?

[BrandonRadtke]

Another thing to note is it has no air box with a uni filter. And also an aftermarket exhaust. I found online stock main jet size was 130 but what would be a good starting point like mid 130s or 140?

[350for350]

If the stock main jet is a 130 and you're running that with a pod filter and an aftermarket exhaust, that's way too small on the main. If I was to guess, I'd start with no smaller than a 140 and don't only buy that one size. I'd guess that you'll be going up a ways from there. As an example, my AutoX is running a 140 main and the stock for a 200X is a 108 (I think). It has a higher lift cam, a pod filter, and a custom made pipe and muffler (in name only) on it. Yes, apples to oranges, like you said, but that's an idea of how much your jetting can change with better air flow through your engine. This 200 four stroke engine puts out way less power and uses way less fuel than your 250R does.

[BrandonRadtke]

I was thinking about ordering all from 140-150 just to start. Also thinking about bumping the pilot up too

[yaegerb]

I can’t throw out jet sizes until I know what carb you have. Is it Stock or not? The oem carb was a 30mm keihin PE30A.

[BrandonRadtke]

It’s a stock carb PE30A

[yaegerb]

50 pilot and 130 main are stock. That’s what you should be running unless you are using an aftermarket pipe or an aftermarket set of reeds. Float should be set at 20mm and air screw turned out 1.5 turns from seated. You need to put you air box back on.

[BrandonRadtke]

I don’t have the factory air box it came with a trash air filter so I put one of my uni pods on it. It does have some sort of aftermarket pipe I’m going to change the silencer tho because it’s way too loud.

[yaegerb]

I don’t have the factory air box it came with a trash air filter so I put one of my uni pods on it. It does have some sort of aftermarket pipe I’m going to change the silencer tho because it’s way too loud.

Here you go. Buy this and put it on. https://www.ebay.com/itm/1983-Honda-ATC-250R-Air-box-W-Lid-OEM-filter-cage-NO-CRACKS-ATC250R-83/274045695738?hash=item3fce6576fa:g:-oAAAOSwGrBdnlAs

The air box not only acts as a guard against dirt but also acts as a resonator for your carb and right now your air signal is screwed up because you are running a straight pod. You can either keep screwing with your carb and jetting or you can buy the box and see if that clears it up.

[BrandonRadtke]

For people reading this in the future yaegerb is right. I ended up buying an air box and with my cylinder bored .020 over running no lid aftermarket silencer and some porting done I’m running a 52 pilot and a 140 main and it runs perfect.