Confounding problem (1993 CR250R)

[SilverSurfer]

I bought this bike and it was in sad shape. I have completely rebuilt the motor (new crank, wiseco piston, rings, stock reeds, new out of the box 1999 PWJ carb with 175 main, FMF fatty pipe, fmf spark arrestor, new stator, new coil, etc, etc).

Here's the problem. Down low and mid range the bike is excellent. Throttle response is great and it will yank the front wheel up easily.

However, once you get into the upper RPM range the bike just falls flat. There's no over-rev and it doesn't pull very hard at all. Having ridden 250 2 strokes before, usually in the upper rpm band you have to hang on for dear life. Not on this bike. It just has no pull at the upper rpm band.

The 175 main jet seems to be perfect (set the needle at the #3 slot, stock pilot jet, etc).

Checked the compression and it was fine at 190. The head has not been shaved or ported.

The spark is fine, CDI is fine, stator, coil and plug are fine. Bike always starts on the first kick.

The only thing I can think of is it's the FMF fatty but others with the same pipe have said their CR250s pull fine at the top end and have some over-rev. I have ZERO over-rev. The bike won't go past 60mph so I know it's not pulling very hard at all.

Any ideas on what the problem could be. I know it's not the carb, the reeds or anything mechanical. The most logical explanation is the FMF fatty - unless someone else has something I have over-looked

 

[CRazy250]

powervalves not working? bad reeds?

 

[SoFlo]

How about the silencer, is it in good shape, cracks, needs to be repacked, anything like that?

 

[SilverSurfer]

Power valve works perfectly, reeds are brand new. Compression check is perfect. Top end and bottom end completely brand new....

Both the FMF Fatty Exhaust and Silencer are brand new....

 

[Dizzed_Nimrod]

Does it suck in air from anywhere it isn´t supposed to suck in air? What does it sound like when you rev it?

 

[CRazy250]

what kind of reeds did you put in, i know with my boysens i had to lean the main jet down a lil

 

[SilverSurfer]

what kind of reeds did you put in, i know with my boysens i had to lean the main jet down a lil

Stock reeds on a brand new (stock) PWJ carb from a 99 (carb was out of the box brand new, all I did was change the MJ from a 190 to a 175. Ran like crap with the 190).

What about the CDI?! If the CDI was bad would the bike run at all? I have no experinence with CDIs and that's the only part I have not replaced.

 

[SilverSurfer]

Does it suck in air from anywhere it isn´t supposed to suck in air? What does it sound like when you rev it?

Sounds fine when I rev it. Whether I have a load on the engine or not, it revs the same way, strong from low to mid then tails off on the top end. Not really sputtering or anything, just not really revving like a good 2 stroke does. When I back off the throttle it will start to pull a little harder (this is a characteristic of it being a bit fat on the main, but stock is 190 and I am running a 175).

There are no air leaks that I can detect. I've gone through pain staking lengths to check but I have not really checked to see if the airbox has a leak. I guess I could run it without the air filter to see if that makes a difference. It's new and not dirty, that I know. Maybe it's over-oiled?

Basically this is what it runs like.

From low range to mid, it pulls like any other CR250. When you get into the upper RPM band it just tails off the power. No over-rev at all. It stops pulling like a CR250 in the upper rpm range. It's not the exhaust valve, reeds, carb, top end, coil, stator, plug, etc. All those have been checked 100 times over.

It has PERFECT compression (180ish), leakdown is fine.

Only things I can not confirm:

1. Air filter (have to pull it and run it without one)
2. Air box (could have a leak somewhere)
3. CDI (no way to test it?!)
4. FMF Fatty pipe (does it suck or no? Never used one before, could it be that the pipe just won't allow over rev?!)

 

[CRazy250]

well on my 93 cr250 the powervalves where shut and i had a tiny bit bottem end and could pull 4th gear wheelies but once it moves past bottem end it wanted to just die, my peddal bike put out more power than my 250 did at top end

 

[keithb7]

I have a 1993 CR250 with an FMF Fatty pipe and a Core II silencer.
It makes good power all over. I can pull way past 60, and there is lots of power on the top end. I generally ride in the mid's and don't use the top end too much, but is certainly is there if I need it. I love the Fatty pipe. The CDI is programed I believe to curve the timing as the engine RPM's increase. The timing has to advance as the engine rev's. Remember in the old days, car distributors had weights for mechanical advance. Then we went to vaccum advance, then finally to a pointess CDI ignition system. Our dirt-bikes CDI's advance the timing as the PRM's increase. If it does not advance, the power falls flat on it's face.

This could very well be your problem. Do you have access to another CDI to perform a test?

Based on your findings, and new parts, I'd just about bet the farm on the CDI.

 

[SilverSurfer]

I have a 1993 CR250 with an FMF Fatty pipe and a Core II silencer.
It makes good power all over. I can pull way past 60, and there is lots of power on the top end. I generally ride in the mid's and don't use the top end too much, but is certainly is there if I need it. I love the Fatty pipe. The CDI is programed I believe to curve the timing as the engine RPM's increase. The timing has to advance as the engine rev's. Remember in the old days, car distributors had weights for mechanical advance. Then we went to vaccum advance, then finally to a pointess CDI ignition system. Our dirt-bikes CDI's advance the timing as the PRM's increase. If it does not advance, the power falls flat on it's face.

This could very well be your problem. Do you have access to another CDI to perform a test?

Based on your findings, and new parts, I'd just about bet the farm on the CDI.

I think you are right. I don't have a CDI laying around but I will go ahead and start looking for one. Since I can't test for it....any CDI I buy (other than new) is a gamble.....sigh.

Thanks man, you've been extremely helpful!

 

[keithb7]

Silver Surfer where are you located in the USA?

 

[SilverSurfer]

Silver Surfer where are you located in the USA?

Orange County. It's between Los Angeles and San Diego, CA.

 

[keithb7]

Well, I guess you are little to far away to borrow my CDI. I have been to Orange County, it takes about 25hrs to drive there from here. Good luck.

 

[SilverSurfer]

Well, I guess you are little to far away to borrow my CDI. I have been to Orange County, it takes about 25hrs to drive there from here. Good luck.

Heh, thanks. Well, since I've replaced everything else I'll just go ahead and replace the CDI as well. Might as well. If that doesn't do it then I KNOW it's the pipe and will just by a DG stock replacement pipe.

Do you know of any way to test the CDI other than swapping it out?

 

[keithb7]

I don't think there is a way to test a CDI. You can check continuity, but that's not going to tell you what you already know. Continuity will only tell you if it works, like a light switch...On or of. We know it works on or off. We just don't know if it is capable of adjusting the timing as RPM's increase. I don't believe there is a way to test without some crazy priced special tool from the manufcturer, snap-on etc.. I am pretty sure you can find a cheap CDI on E - B A Y.

 

[SilverSurfer]

I don't think there is a way to test a CDI. You can check continuity, but that's not going to tell you what you already know. Continuity will only tell you if it works, like a light switch...On or of. We know it works on or off. We just don't know if it is capable of adjusting the timing as RPM's increase. I don't believe there is a way to test without some crazy priced special tool from the manufcturer, snap-on etc.. I am pretty sure you can find a cheap CDI on E - B A Y.

Yep, I've be scouring flEaBAY. If I can find one cheap I'll get it, otherwise I'll drop the $$ and get a new one.

You'd think the DEALER would have the tools to check a CDI or at least run it through some tests, wouldn't you????

 

[cnielse5]

Uh, dude did you notice that there was an eletrical plug on that carb? did you have any thing to plug into it?

 

[SilverSurfer]

Uh, dude did you notice that there was an eletrical plug on that carb? did you have any thing to plug into it?

For the 99 carb? I didn't notice one. That said, the 99 carb was recommended to me as a superior carb to the 93 and nobody mentioned any electrical connections.

However, the carb DID have better throttle response but had the same performance from 75%-100%, so I am assuming the carb is not the problem....

 

[cnielse5]

If it is a true 99 carb then it will have an electrical connection. starting in 97 the carb has an electrical solenoid that opens another fuel jet in the carb. The solenoid opens from about 1/4 throttle to full throttle.

 

[SilverSurfer]

If it is a true 99 carb then it will have an electrical connection. starting in 97 the carb has an electrical solenoid that opens another fuel jet in the carb. The solenoid opens from about 1/4 throttle to full throttle.

It is. I bought it brand new out of the box. I have to pull the carb to replace the 190 with a 175 so I'll check it. If it does have an electrical connection -- are you saying it's no good for my bike?

 

[2-strokes-4-life]

If it is a true 99 carb then it will have an electrical connection. starting in 97 the carb has an electrical solenoid that opens another fuel jet in the carb. The solenoid opens from about 1/4 throttle to full throttle.

after the 98 model yr,honda went back to a traditional carb on the 250

 

[Faded]

The '99 carb doesn't have any electrical connections, stock or otherwise. It's a Keihin PWK, a better design than the stock Keihin PJ carb. Only the '97 and '98 had electrics up until they put TPS on the '04's.

 

[SilverSurfer]

Never mind....lol

 

[tracetrimble]

Are you sure the power valve is opening? Really sounds like PV to me.