2002 cr250 surging?

[dodgeaspen]

Welcome to my nightmare!! I am running rather rich but remember I'm riding in 25 degrees and below. I bought that needle (30-71 is correct) on purpose to help a cold temp, off idle knock and I also hoped it would help this surging problem...it fixed the knock but not the surging. The reeds (V-force) look fine and I totally agree it seems like an air leak but I can't find one. I'll have to build your leak tester to prove that though. I did order an ignition side crank seal and I'll install that just to see what happens. I know there a a few people out there with the same problem and I'm curious what nmitcheff (stater of this thread) comes up with.

[Faded]

Originally posted by dodgeaspen
Welcome to my nightmare!!

I hear you brother, I have been there believe me. Sorry to doubt you on the needle, I checked my notes last night (I’ve owned every optional needle) and you are correct, there is the optional 6BEY30-71 Needle. This is the largest (richest) straight section needle you can get. I know because I tried getting a 30-70 at one time and despite calls to Honda, Mikuni, and several dealers it simply was not an option.

Just to clarify I'm going to round up all your info and type it here:

• Elevation = 700ft
• Temps = 25 degrees
• Fuel/Premix = 92 Pump, Yamalube R @ 40:1
• Float Level @ 15mm
• Pilot Jet = #35
• Air Screw = 1.25 turns out
• Needle = 6BEY30-71
• Needle Clip Position = 3rd
• Needle Jet (Nozzle) = S-8
• Main Jet = 430

And now a list of your problems:

Originally posted by dodgeaspen

1. The reason I say jetting is that the surging gets worse with colder temperatures. But on the other side of the coin the surging doesn't happen until the enging gets warm?????
   
2. I'm pretty sure that the problem would go away if I changed the pilot to a 37.5 but then closed throttle would load up rather fast.
   
3. I bought that needle (30-71 is correct) on purpose to help a cold temp, off idle knock and I also hoped it would help this surging problem...it fixed the knock but not the surging.

Okay, now that we have all the info we can attempt to solve the remaining problems.

1. Obviously lean here as stated in the past. The colder temps will require richer jetting and the colder it gets the more aggravated the problem will be. Since you mention that it doesn’t do it until the engine is up to operating temp then this could tell us something. Remember that engines are made of metal and metal expands under heat, especially considering the temperature extremes you’re experiencing. These expansion/contraction cycles could be the cause of the problem, but not necessarily the problem itself. I still think it’s an air leak and given this information I wouldn’t rule out a bad case halve gasket or a cylinder base gasket.
   
2. If the problem can be fixed with a larger pilot (due to jetting circuit overlap) but loads up at idle then this, to me, points to an air leak as well. Churning along at a slow idle your vacuum will be rather low, but at a crack of the throttle the demand for a larger intake charge really goes up. If an air leak is present then this will supplement the intake charge during this off idle transition. Trying to richen the jetting to cure the problem only makes matters worse during idle.
   
3. These bikes are great at pronouncing lean conditions via knock (especially on pump gas). I will almost guarantee (99% sure here) that if you’re have an off idle knock with that needle, even @ 700ft and 25 degrees, then you’re sucking air from somewhere. I know that knock all to well, trust me. I have been around the world with this bike and carb. I have ridden from 1600ft to 7000ft with temps between 20 and 105 degrees. When I look at your jetting from 0 to ¼ throttle I cannot believe how rich you are. I could see you running a 35 pilot due to temps, but with the stock needle, not one that is 2-3 steps richer. I really, really think that you’re facing a mechanical malfunction of some sort and not just jetting woes alone. I know what you are going through; trust me I’ve been there. I’m not trying to second guess you, these are simply my humble thoughts and I’m only trying to help. Please don’t take offense to these comments, they are not submitted with that intent.

Other things to consider:

The V-Force cage is prone to leakage. This could be another problem spot with regards to an air leak. Make sure your gasket is mint and I would strongly advise the use of a sealant such as Hondabond or something similar that is impervious to gasoline vapors.

Did these problems start occurring after a recent top end? A torn or otherwise flawed base gasket could be leaking. Definitely check for leakage here. FWIW, I use the spray-on copper gasket adhesive on all my gaskets when doing any R&R work. Also, check the torque on your cylinder nuts, it’s a long shot but maybe they’ve come loose for some unknown reason.

Let me know what you think, I only hope that you’re able to find the problem. Good luck.

Thanks,
Andrew

[dodgeaspen]

Andrew,

First off, thanks a lot for taking the time to help me out..this is a real pain! I think my next step is to build your leak tester and see what happens. I know all things point to an air leak but I cant seem to find it using a "spray method". When I get done screwing with the bike I'm 100% sure that it's not an air leak but then when I sit back and think about it I'm convinced that it can't be anything but an air leak. My problem may be that I'm not checking for an air leak at the correct time. The surging only happens after running the engine hard at high revs...possibly getting the engine very hot and it leaks only at this point of extreme heat. This fact alone says it has to be an air leak because it seems impossible that the engine would crave more fuel as it gets hot. I'll try the leak test this weekend but I'm not sure if it will be valid unless I get the engine hot. I guess I could also try the spray test after getting the engine up to the "surging temp". One other thought- could there be any sort of air leak coming from the tranny/clutch area that would not suck in enough oil so that I would be able to see smoke or smell the burning oil??

Thanks Again for your help!,

Eric

[Faded]

Originally posted by dodgeaspen
One other thought- could there be any sort of air leak coming from the tranny/clutch area that would not suck in enough oil so that I would be able to see smoke or smell the burning oil??

Eric,

I doubt it, if the right side crank seal is at fault then it would suck trans oil. You can check for excessive spooge and smoke as indicators. You could even fill your trans up (write down how much you put in) and run it for a couple days and measure what comes out when you drain it. If it's leaking there will be a substantial difference between your fill amount and your drained amount. Good luck with the tester. If I think of anything I'll be sure to come back to this thread. If you get it figured out please post back what you find as I am interested in the result. If you have any more problems or questions let me know.

Take care,
Andrew

[dodgeaspen]

Andrew,

Did that pipe pressure gauge in you leak tester come with the air inflation valve on the end or did you rig that up?

Thanks,

Eric

[Faded]

I got mine at Home Depot. It came with the Schrader valve on the end.


30lb Gas Test Gauge by Prairie Home Product
Item # 51803
SKU # 7 39236 51803 3
$12.98/ea.


I guess they make a 15 psi gauge to but my local Home Depot didn't carry the 15 psi one. When you pressurize your motor you only want about 6 psi in there and it shouldn't lose more than 1 psi over about a 5 minute span. Once pressurized you can start spraying soapy wayter, WD40 or whatever you like on suspect problem areas. Good luck.

[Yardpro393]

good info faded, you are an invaluable resource for this site.

thanks

[Faded]

Originally posted by Yardpro393
good info faded, you are an invaluable resource for this site.

thanks

Thank you!

[dodgeaspen]

I finally got my leak tester together and did my "leak down" test today. I found nothing at all to be leaking. My bike lost 1# in 3.5 minutes from an initial 6# charge. I went over everthing with soapy water and nothing was leaking. The main flaw with this test is that the surging happens only when the engine is hot. I decided to change the mag side crank seal anyway to see what happens but no luck. The bike still surges before it settles to an idle after winding out the engine. I'm at a total loss- I've done a leak check with the engine cold and I've sprayed the entire engine with (engine killing) carb cleaner while hot to try to find a leak with no luck. I guess it must be jetting or somthing else screwey..

[FFRacing11x]

Just my 2cents worth here...
An often overlooked area when trying to fix a lean spot is the exhaust junction. CR80s were nortorious for this. It is a possibility that if the exhaust is not sealing properly at the cylinder, it could be sucking air on the reversion. Just a thought. Tdub

[tomnelsonii]

Hi Guys... Ok, probably should have posted this a while I ago. I sold the Honda and bought a KTM, but I did get the Honda jetted spot on before I sold it. First, I put new ORIGINAL HONDA gaskets on eash side of the reed cage. I think the ones that came with the V-Force were cheap. They seemed to attract dust like they were saturating from the inside out with fuel/oil. Anyhow, I wouldn't have believed this if I didn't experience it first hand! I jetted my bike from the stock 380 main to a 410 for winter riding. When I got my bike out in the spring I forgot to re-jet. The bike ran way better w/ the 410 than the stock 380, and we were in muggy Florida heat. I ended up putting in a 400 main and playing w/ the pilot. I also tried a different nozzle, needle, and clip settings. Sorry, don't remember what combo I ended up going with! Anyhow, this is important... make ONE, and only ONE SMALL CHANGE at a time and see how it works. I believe I ended up with 400 main, 1 larger on the pilot than stock, and the S2 nozzle. My bike ran great for a whole season with that jetting. I would not have expected my bike to come that lean from the factory. Anyhow, I hope this helps somebody out!

Regards,
Tom

[Faded]

Originally Posted by FFRacing11x

An often overlooked area when trying to fix a lean spot is the exhaust junction. CR80s were nortorious for this. It is a possibility that if the exhaust is not sealing properly at the cylinder, it could be sucking air on the reversion.

I agree with T-dub and have noticed that many struggle with getting a good seal. The best fix I've found (again, T-dub's info that he's passed on to me) is using Permatex Ultra Copper sealer. Read the application instructions and allow plenty of time to cure and you'll be in business. Better than rubber O-rings, better than Chamber Seal, etc. Get some...