Confounding problem (1993 CR250R)

[jason33]

check the ignition timing . mabe you can advance /or retard it a little
sounds like a timing issue ,not reving high enough
cdi is workin or it wouldnt run
has there been any port work done???
pipe and silencer make a big difference ,what is your pipe specified for?
why go dg?
fmf are great pipes

 

[kx125412]

What gearing are you running on your bike?

 

[SilverSurfer]

What gearing are you running on your bike?

Completely stock gearing.

 

[SilverSurfer]

check the ignition timing . mabe you can advance /or retard it a little
sounds like a timing issue ,not reving high enough
cdi is workin or it wouldnt run
has there been any port work done???
pipe and silencer make a big difference ,what is your pipe specified for?
why go dg?
fmf are great pipes

How do I adjust the timing. The plates pretty much make the timing non-adjustable. What if the CDI would let it run but doesn't advance the timing like it's supposed to do?

No port work done. It's a FMF Fatty with Power Core spark arrestor. Other than that and the 99 carb, everything is stock.

 

[SilverSurfer]

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

Yes, I watched it through the port on the left hand side. It moves counter clockwise as it's supposed to when the bike is revved....

 

[ssomerville]

Maybe kinked fuel line from petcock to the carb? Or dirt clogging the petcock from the inside of the tank? The fact that it doesn't over rev is maybe not enough fuel getting into the carb at high rpm? Also, known problem on the '93 was the gasket sealing the carb boot to the airbox. Maybe remove the four fasteners and add silicone RTV to ensure a good seal. But it sounds like not enough fuel or too much air only at a high rpm.

When mine runs as you describe it's PowerPort cleaning time, but said you checked that already.

Good luck!

 

[SilverSurfer]

I'll check for that and order a new fuel line just to be safe. When I tore the top end down I cleaned and rebuilt the power port.

What I don't understand is how to TIME the bike and whether the CDI can allow the bike to start but not advance the timing?

 

[SilverSurfer]

Anyone know how to set the timing?

 

[motometal]

I realize everyone is just trying to help but we should be able to rule out a few things here.

air leak-If it ran better on top with a leaner main, then an air leak is not what is causing flat top end performance. An air leak between the carb and the cylinder, or at the cylinder base gasket would lean the mixture, having somewhat the same effect as leaner jetting although it would probably be most noticeable at lower rpms and idle where there is the most vacuum. An air leak around the boot to the airbox won't make the bike run much different, it will just suck in dirt and hurt the motor.

air filter-you would have to really have it overoiled to cause this problem, but just for the heck of it you could re-do the air filter, after cleaning out the existing oil, and right after you oil it (before the oil has a chance to get tacky) take paper towels and blot as much oil as possible from the filter element. This will still leave behind plenty of oil to do the job, and should rule out too much oil on the filter.

gearing-this wouldn't make a difference.

timing-I can't remember if this is adjustable on that bike, but if it is there should be marks to line up, and that's where you want it.

carb-i've become less enthused about the idea of switching carbs to a newer/"better" model/design after having some frustrating, inexplainable experiences with a bike simply not being compatible with a non-stock carb for no rational reason. I suggest if possible putting the stock carb back on as a "dummy check" just to make sure that isn't it. I had a '93 CR250 and thought it had an absolutely awesome motor, personally I can't see a problem with the stock carb and feel changing it out could do more harm (or frustration) than good.

reeds-if they are bad usually it won't start well or will run funky on the low end.

exhuast-are you sure there couldn't be something obstructing the exhaust? Could something have built a nest in there while it was apart?

 

[john3_16]

SS, Motometal's has some good info there...He's correct on all his points and it would save you alot of trouble following his input.

FMF's are good pipes but I've heard (no actual first hand experience with it) the fatty is not the best pipe for top end...My buddy tried one on his CR and raced one moto with it and he says he couldn't get that thing off fast enough because it killed the top end..Of course his bike is an 04' plus his is ported....How it affects the 93' I don't know but I do know (from what I've heard) that the fatty is an exhaust that enhances the lower rpms more so than the top...

The 93' CR250 was probably one of the best stock 250cc motors ever...I've ridden one and it's been a while (since about 93' actually) since I've ridden one..But wow, that was a meaty motor...Sounds like you've got a nice bike there being that the motor is comepletely rebuilt..Should be really fun once you get the top end sorted out..

Have fun!

 

[SilverSurfer]

I realize everyone is just trying to help but we should be able to rule out a few things here.

air leak-If it ran better on top with a leaner main, then you don't have an air leak problem. The air leak would have the same effect, which would have actually have made it run better, not worse. An air leak around the boot to the airbox won't make the bike run different anyway, it will just suck in dirt and hurt the motor.

air filter-you would have to really have it overoiled to cause this problem, but just for the heck of it you could re-do the air filter, right after you oil it before the oil has a chance to get tacky take paper towels and blot as much oil as possible from the filter element. This will still leave behind plenty of oil to do the job, and should rule out too much oil on the filter.

gearing-this wouldn't make a difference.

timing-I can't remember if this is adjustable on that bike, but if it is there should be marks to line up, and that's where you want it.

carb-i've become less enthused about the idea of switching carbs to a newer/"better" model/design after having some frustrating, inexplainable experiences with a bike simply not being compatible with a non-stock carb for no rational reason. I suggest if possible putting the stock carb back on as a "dummy check" just to make sure that isn't it. I had a '93 CR250 and thought it had an absolutely awesome motor, personally I can't see a problem with the stock carb and feel changing it out could do more harm (or frustration) than good.

reeds-if they are bad usually it won't start well or will run funky on the low end.

exhuast-are you sure there couldn't be something obstructing the exhaust? Could something have built a nest in there while it was apart?

No the exhaust is clear, I checked it myself.

Given your rundown, I would say that I have addressed everything you have listed here in addition to replacing the coil and stator and insuring the power valve is working correctly.

The only part I have yet to replace is the CDI which if the theory is correct, it *could* be working enough to allow it to run but not advancing the timing.

I couldn't find any markings on the stator but the bike fires up on the first kick pretty easily.

 

[BSWIFT]

I've got a used, dinged up pipe that might fit. I'll send it to you for the shipping costs. I'll have to check tomorrow but I "think" it is an FMF SST. The Fatty does improve bottom-mid power and the SST improves mid-top power. I still think you jetting is the problem. You could try the stator swap but several jets and some patience could solve your problem cheap.

 

[motometal]

I edited my post a bit for clarity. Good advice Bswift, and regarding leaning the main jet (which could help...after all it helped when you leaned it last time), there are a few things you should do when leaning out your carburetion:

1. Run at least a 50/50 mix of race fuel for safety (I recommend this regardless, and stick to the same mix once established)
2. Keep an eye on the spark plug (start with a fresh one)
3. If you lean the jetting and it doesn't run better, don't ride it anymore until you richen it back to where it was
4. keep in mind that if you get it where you like it and the weather cools off considerably, you will need to richen it

 

[drew9184]

motometal is right about the jetting being your problem. if it was your cdi your bike wouldnt run or hardly at all and it would only start by dragging it behind a car or running it down a hill.
i had the exact problem with my 1992 cr250 you have. i also went for the newer carb one off a 2000 its called the airstryker very good carb lots of people use them on these bikes i dont know why you would have got a 1999 carb when the 2000 cr250s came stock with the best carb you can get in my opinion. just lean your main jet by 1 or 2 jet sizes at a time and keep a close eye on your plug. it cleaned my bike right up. hope you figure it out youve got yourself a sweet bike.
the timing is non adjustable dont mess with it youll regret it. could burn a hole in your piston in under a minute.

 

[85YZRacer]

i'm no expert but it wouldn't hurt to check your timing. it sounds like your timing is advanced. maybe try to retard the timing so you can get more over rev and more top end power or maybe its your gearing set up. it sounds like you have small gearing for more bottom end torque. if everything else is brand new, i can't imagine what it could be. good luck!

 

[Faded]

i dont know why you would have got a 1999 carb when the 2000 cr250s came stock with the best carb you can get in my opinion...

Because the 1999 is the exact same carb as the one on the 2000 (38mm PWK Airstriker), the only difference is the needle which has a better profile to start with than the goofy 2000 needle. :nod:

 

[Faded]

SilverSurfer,

You can dynamically check to see if the CDI is working if you have an inductive timing light. Eric Gorr outlines the procedure in his book. Also, the factory Honda manual recommends rechecking/resetting the base timing when replacing ignition related components like what you have done. IMHO this sounds like an exhaust valve problem to me, just curious if you've taken the steps to insure that the exhaust valve is installed and adjusted properly, and is opening fully. The exhaust valve rod that slips into the cases is a splined shaft and may have been installed improperly which limits the travel of the exhaust valve. These are not assumptions, just ideas on things to recheck.

Checking Base Timing per the Honda Manual:

Remove the left side (igintion) cover. Look for three different timing marks, one on the bottom of the case (triangle), one on the stator plate (index mark, looks like '|') and the 'F' mark on the flywheel (looks like '||'). Start the bike and allow it to idle. With the timing light focused on the 'F' mark rev the engine to 3000 rpm. The index mark ('|') on the stator plate should line up in between the 'F' mark ('||') on the flywheel. If it does not, scribe a new index mark on the stator plate. Shut the bike down and adjust the stator plate until the newly scribed index mark lines up with the timing mark on the case (triangle).


Checking the CDI dynamically per Eric Gorr:

Remove the left side (igintion) cover and hook-up your inductive timing light. Start the bike and allow it to idle. At idle note the relationship between the index mark on the stator plate and the 'F' mark on the flywheel. When the bike is revved to mid throttle (the RPM at which peak torque is made) you should see some advance. As the bike is revved higher the timing mark should jump back to about the same location as it is found at idle.

These of course are the short/condensed versions since typing pages of info isn't something I enjoy doing...but it should be enough to get you going in the right direction. Good luck.

 

[motometal]

good stuff there Faded...still though, wouldn't you be really surprised if the stock timing was significantly off? Good advice regarding the powervalve, that could be it...

 

[Faded]

...still though, wouldn't you be really surprised if the stock timing was significantly off?...

Yes, I would be suprised if it was really off, but I'm just trying to help him eliminate some more possibilities. I'm still betting on the exhaust valve... :cool:

 

[bruno670]

One thing that is greatly overlooked, not to say this is it. I am not sure if this is adjustable, but you may want to check the timing impulse coil gap. If the gap is wrong you will get a false reading especially on higher RPMs. Your local honda dealer should be able to get this information for you. I think that there is a collar that aligns it up but there is that remote possibility that it could have slipped. This is a no cost fix if I am correct. Good Luck

 

[PEace]

I took a couple of pictures of the timing procedure layed out in the service manual. Give me your email address and I can send them to you if you like.