1986 250r Bogs on top end

[Evan Hagenow]

On my 250r Im having trouble with getting it to run right. It starts right up and idles fine, but when you go to give it throttle it revs fine until half throttle. Any more than half throttle and it bogs down and doesnt go anywhere. It leaves pretty hard but it seems more sluggish that a 250 smoker should be and when you rev it up it doesnt like to idle down right away, its like it takes a second for it to rev down. It currently has a Keihn flatslide carb on it with PJ stamped into it. with a 148 main jet and a 48 pilot jet running through a stock pipe and a motor on its second bore I think with some porting done to it. This is my first 250r and am stumped by what could be causing it. Any help would be appreciated.

[Jmoozy27]

That's definitely lean conditions!!! 148 sounds kind of small for a 250r. I don't own one but I say go up a size or 2 on the main jet. What slot is the needle clip on?

[fabiodriven]

Yup you're lean which is dangerous. Make sure you're not sucking air anywhere else and get to jetting.

[John_Neary]

have you checked the color and surface of your spark plug? what size is your carb? on a 38 PJ i would start with a 165 main for a 250 but that is with a race engine and not a stocker

first thing you need to do when jetting a 2 stoke is inspect the spark plug, dark and wet is rich while light tan and dry is lean...you want it somewhere in the middle on the rich side

[Dirtcrasher]

Yes, just jump the main 2 sizes, see what it does.

Then move the needle a clip up or down, see what it does.

Does it have an airbox cover? does it run better with it on or off. One being rich, one being lean.

One change at a time, write down results.

I just went up 7 sizes on the main on my 200X and it takes off soaring. Struggled with it for years.

EBAY has jets in 10 packs, I'll NEVER quit the sport so I have a ton of jets...

EDIT AGAIN - I just meant to say that mine is a thumper and yours is a pinger, lean is dangerous in your case. The air box lid as well as the plug color will help you see what direction to go in.

When I went down to 11:1 on the piston it was bogging bad. Never really took off...

[Evan Hagenow]

Thanks. Once you hit above half throttle it blows considerable more smoke. and I was running it with just the carb for easy access. Never being ran for more than a minute or two. Ill stop that when I get the jets. I ordered the 10 pack from 150 to 170 so Ill have to wait a week for those.

[John_Neary]

@Evan - excessive smoke when already using a smaller size main jet points to another issue than jetting, are you sure the fuel is fresh and that the engine has the proper amount of compression?

[yaegerb]

First put the airbox back on with lid or pod filter or whatever you are running to restrict the air flow (from your last post I read it as you are running it with nothing on the carb. That sure as hell will lean you out). Then lower your clip one. If it bogs more then raise it two. Change the needle clip before messing with your main.

[fabiodriven]

Yes you will have no idea what's what with that engine just running an open carburetor. You have to put the rest of your intake on and go from there.

[John Tice]

Nobody has mentioned spark timing; a retarded spark may destroy the top end.
Did you give it a leak down & compression check? Have you sprayed soapy water on the engine looking for bubbles?
:wondering

[Evan Hagenow]

well I got a 165 jet from a local shop to try, along with a 52 pilot jet. And after it was all buttoned up with the carb boot on it and air box lid on. It still did the bog. I moved the needle to both the top and the bottom positions, and it was hardly any better at the top then the bottom. Almost no difference at all from when it had the 148 main jet in it. So I pulled off the stator/flywheel cover and it was kinda crusty in there. Im starting to think electrical since stock jetting is 142/42. And no the bigger jets dont help at all. I got a flywheel puller coming so Ill see what the stator and flywheel magnets look like then. Other than that I am completely clueless with this thing. The 200x is so much more simple. Could it be my reeds maybe?

[fabiodriven]

Some might argue that it's actually a lot more simple than your 200X. So you're new to two strokes then. I think most people would have assumed you'd take a peek at your reeds while you were in there but we may have a bit more experience than you. It's very tough to diagnose from the other side of the computer, especially if someone is a little inexperienced. It sounds like you're digging and looking which is a good thing. Keep looking for potential problems and clues, that's how you learn to diagnose. You could have a plugged silencer for all we know (in which case hang it from a tree limb or something with a propane torch aimed into it).

[yaegerb]

x2...in time you will learn that a 2 stroke is much easier than a 4. I own an R and a 200x and I will gladly take apart my R motor than take apart my x (in a helluva lot faster time frame too). Like Fabio said, look at your reeds. Pull them out and shine a light in the open side of the cage. If you see any light come through then replace the reeds as they can warp. If they are warped or damaged, get a good set of boyesen carbon fibers. Clean your electrical components and I would also do a compression test. If you want to get uber fancy, perform a crank case pressure test. All things being equal, with a clean carb, sound reeds and good electricals, it should run perfect on stock jets (even with some porting).

[Evan Hagenow]

Yeah the 200x has just always worked. It used to burn a quart of oil for every tank of gas, but it never missed a beat. original rings and all. And I did pull the reeds out and take a look at them. They seemed fine to me, no major gaps in the pedals, seemed to be closing all the way. Even managed to take some pictures of them.
221455221456

[El Camexican]

I just chased this rabbit on a bike and it darn near drove me to drink. If you really want stop guessing and have a worry free runner you need to do the following:

- A proper (read up on that) compression test (less than 140psi would mean its time for a top end rebuild)
- A leak-down test (engine should hold 6psi for at least 5 minutes, if it drops more than 1psi in 5min start looking for the leak)
- Check the timing (I don't think yours is adjustable)
- Check the reeds (I prefer the suck test regardless of the ribbing it brings from my so called friends)
- Make sure you have the right plug and that it is gapped correctly
- Start with a 165 - 170 main jet, a 45-50 pilot, any 250 will run with these, you can tune later
- Set the needle clip in the middle (Check the # of the needle and search it to make sure no one put something weird in there and make sure it isn't bent or damaged, it must be smooth. You can call Sudco to ask what the standard # is for that carb)
- Start with the air screw 1.5 turns out
- Set the float height to 16mm
- Make sure there is a gasket in the cap of your carb
- Make sure the slide in your carb isn't worn, or has deep scratches in it (they need to be pretty bad before they cause problems)
- Put a clean air filter on it
- Make sure your pipe and silencer aren't obstructed (a large dent or kink would count as an obstruction)
- If you have a power valve make sure it's clean and moves freely
IF YOU DO HAVE LOW COMPRESSION DON'T BOTHER REBUILDING THE TOP END BEFORE YOU DO THE LEAKDOWN AS YOU MAY END UP OPENING THE ENGINE TWICE AND ALWAYS DO A LEAKDOWN TEST AFTER A REBUILD.

If all this checks out the only other thing I can think of that could cause a bog only at the top is if someone ported the cylinder and messed it up.

Good luck!:beer

[bkm]

I'm going to go with worn out 30 year old carb syndrome

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[onformula1]

I'm going to go with worn out 30 year old carb syndrome

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I never heard of that one. :lol:

[atc300r]

Have you tried a new or different coil.