Yes, I know. Ghost riding this thing off a cliff would be an improvement lol.
A few years ago I bought this bike for my son. After a couple summers on it, he wrecked and, lost interest.
It’s been sitting in my garage for awhile and, I figured screw It. I have time to go through this thing while I’m stuck at home licking my own wounds.
I have a few questions and, any replies are appreciated. I know this was a one year model with a POS servo powered RC valve. Not to mention it ran like there was a rag in the air box.
A couple weeks ago, I took this thing down to the frame. I’m now in the process of putting it back together and, was hoping for a little direction before going any further.
Jetting on this thing was garbage. Even after following the Pro Circuit recommendations it blubbers and, has a serious case of blahs up to 1/4 throttle, After that it revs fairly cleanly though it’s about as fast as a snail finding its way out of a salt shaker. I just want to get it running decent.
Current jetting
Pilot 40. I tried a 35 and, it still blubbered
Main 390
Needle 6DGY26-69
AS 2
Has anyone found jetting for sea level - 1000’ elevation?
I also noticed the reeds need replaced. Slightly frayed on the edges. No biggie.
Is there a huge difference between just installing a set of Boyesen reeds and, Rad Valve? If I can save $120 and, use it elsewhere on the bike, I won’t complain. I also noticed a white plastic block in the stock reed valve assembly. It’s the first time I’ve seen it. Since the bike runs like there’s a rag in the air box, would it be beneficial to remove it? Here’s a pic.
Next question is, what is this screw? It’s missing and, NLA on every parts house I’ve looked at online.
It goes into the area below the rubber seal for part of the power valve assembly. I feel like a dumb ass having to ask. Seems like it goes nowhere but, if it’s there, it obviously goes somewhere.
I took the time to research setting up the RC valve correctly and, cable adjustment. Getting the jetting sorted is a pain from everything I’ve read and, dealt with. The only aftermarket parts on this bike is a FMF pipe and, spark arrester. Though I do have a PC shorty as well for it.
I’m hoping to have this bike back together within a few weeks. Maybe getting this thing freshened up will get my son interested again. If not, it’ll be something else for me to play with. If there’s any bolt on items I should get that’ll help, let me know.
Thanks for taking the time to read through this. I appreciate it. The last 125 I had was an 87. I’m a bit lost dealing with all these quirks of this cable ridden turtle.
I don't have any experience with the 125, but do have experience with last generation 250.
If you've split the cases, face the crankcases, they are vulnerable to leakage between the intake and gearbox...
I'd do a leakdown/pressure test, if you've got an air leak jetting will be problematic.
The white plastic is a flow guide, it will run poorly without it, if you buy a Boyseen Rad Valve it will have it's own flow guide and rubber insulator, OEM rubber insulators are no longer available from Honda...
The 250s were notorious for having squish clearance of 1.9-2.0mm, which was too large leading to detonation and difficulty jetting. I don't know the 125's reputation, but ideally a 125 should be 0.9-1.1mm, if it's more than 1.3mm jetting will be problematic.
Some people will swear the Mikuni carb can be jetted, other people will recommend going to a Keihin 38mm PWK Air Striker, the Keihin is less sensitive to temperature and pressure changes.
Is that bolt the RC valve exhaust deposit drain?
Or did Honda use the same cases as the earlier model, which had the governor, and it's the retaining screw for the pinion gear...
I’ll go with exhaust deposit drain. Looking at the schematic, it has a crush washer. Thank you.
Regarding the air flow guide in the Reed block, I had to remove the rubber stuffers while installing a V-Force reeds on my 250. Stock, there was no flow guide so, that was my reasoning for the thinking to remove the guide on the 125.
The cases haven’t been split. It was a very low hour bike when I got it and, there was no play in the crank/rod when the top end was replaced.
I have a Keihin Air Striker on my 01 CR 250. The Mikuni was a pain in the ass so, I gave up after fighting it every 15* change in weather.
I’m sure with this bike, it’s something small and, dumb on my part. I’ll check the float height and, float valve gasket tomorrow.
Thanks once again.
Honestly that part in the reeds,I think it MIGHT go without it, 2 strokes are only limited in rpm by how well they can breath, (and it’s easy to put back if it doesn’t work out) I’d try it myself to be honest, may be a bad idea. But I don’t see how it could hurt anything, could add a little top end at the best, or could just not start.
Nope, Honda has used that reed stuffer for ages. Remove it and it will lag hard then blast off, i.e. narrow powerband. The CR125 didn't benefit from installing RAD Valve, as it already had throttle response improved with the stuffer.
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Worth a try? I’d definitely bore it out if it was my bike, anyways I only had a few Hondas and they were mostly quads, one 2003 cr144 and 1986 cr80, the 03 144 didn’t have this block when I got it, and I never installed it, pulled like a team of mules on 110 at 30:1.
Due to the stock cylinder wall thickness, the 04 can only be punched out to a 134 I believe.
10cc’s isn’t worth it in my opinion. At least on this bike. With minimum wall thickness of the cylinder, the exhaust bridge is known to crack on this year. I think Gorr was the only one who offered a 144 but, the cylinder had to be sleeved.
I just want to get it running correctly. That’s been the biggest issue. With spotty jetting specs, choked air flow, and, power valves that rely on cables, it’s a very flawed system stock. The only thing I like about the bike is the chassis. Not much more. But, since the bike is here, I might as well make the best of it and try figuring it out.
Still wish I bought a 96. But, with limited parts availability, I thought the 04 was the best choice.
Man, I was wrong 😂
Get a keihin air striker 38, or swap one from your 250 you mentioned, and see if it would run better. If it does, replace mikuni, if not, jet mikuni to manual specs and go from there? If it starts without choke it’s too rich on pilot, if it doesn’t transition into the power clean it’s too big of a main jet. Needle i always leave at manual specs, and check what slide you have, bike sounds rich as a pig.
4.5 slide.
2nd clip position from top on the needle.
My 03, while not "fast", ran very strong and crisp. Not sure how close the jetting will be but my setup was the following: 134cc cylinder, 05-07 airboot, Vforce3 (port matched intake area to try to maximize flow), HGS pipe & silencer.
Jetting I usually used in SoCal was 430 main, 37.5 pilot, 6DGY28-68 needle on 3rd clip, 4.0 slide, air screw 1.5 out
Lets keep in mind that the reed stuffer isn't likely smaller than the carb bore. So it's maintaining air velocity and it's clean flow. Not plowing into a larger void with hard angles. Just sayin'
Make it run and sell it. Consider a better bike if your boy comes back around again. Why wait, he'll be chasing tail and later you'll get $800 for the bike.
My practice bike came with a single carbon reed no epoxy reed. A guess would say there boyeseen. 1 corner has a chip but they seal yet. I pu carbon tech Mt reeds from boyeseen 54.95. I didn’t install them yet. Pull pv cover run bike to see if pv is opening & closing& not fluttering. Use hrc method for adjusting cables. I use a long 13 mm socket with a couple wraps of electrical tape to hold it in the exhaust port. Get a new coil , grind mounting points to fresh metal. The 04,s like a new coil. Get a ikat if you can find 1, if Really works great on the 04. Runs like a really good ignition. It helps with jetting also if it’s off a little from a 15 degrees +. Practice bike stock pipe, best with a pc shorty, fmf is good too. A reg pc is a little slower to hit, fmf long is too restrictive. Stock silencer is restrictive, a 06 is not. I run 110 leaded 3 gal with 2 gal super unleaded. I think my pilot is 37,5 , needles I hv 1/2 step leaner ones. I always run it in the middle clip, main 390,400 I think. I hv mine running a little on the rich side but it runs clean. I added a 05 air boot, it made low to mid response better took a little hit away but breaths better threw top to bottom. Power flow cage added more throttle response & better breathing, a little more pull. It runs super clean. Next time it’s apart check how smooth the pv operates. I took a dremel to my mod bike 1st hole in cylinder that the pv shaft goes threw. And just smoothed it out a very tiny bit. It’s butter smooth now. My practice 04 just got the shaft rollers polished. It’s a quick bike now but momentum has to b kept up. Landing from a floater hill jump into a corner to pull a steep hill & drop into a valley. I pulled little boys on there new yz & Ktm,s.
A racer elite piston came with my practice bike. Practice bike is replated ports r chamfered. Pv was packed with hard gunk. It ran crappy when I got it. I rode my 5 hr 04 with a rad valve & fmf pipe with reg fmf silencer. I didn’t adjust the pv. It ran like a good 134. I,m shocked on his well my practice bike runs . Quick strong hit then the back wheel is chattering off the ground like a gp bike . Strong mid pull I just shift 2-3 times real quick on the upper mid. A lot of ovr rev it’s flat way up at 12k + but it works on a fast sweeper. Deck , port , diff carb taper & the bike is totally different. From the hit to the ovr rev the working part of the engine the mid range. Is much stronger & longer & sounds Super sick. You can up shift 2-3 gears real fast & it pulls real hyper. Soo fun to ride .
Oh that hole is nothing. I think it was Honda trying to loose weight. Remember the 02-05 Honda talking about shaving 300 grams of wt off a part. Tara Gieger was a rookie in 04 at LL I think. She beat the hvy hitters on 250f,s . Last cr125 to win a LL title.
I ordered new brass (waiting on it). Along with new reeds.
I found a screw that matches the exhaust deposit port. After digging through a bunch of Honda hardware I’ve saved. Turns out a carb float bowl screw fits lol. Even found a copper washer for it.
Well, I finally got just about everything sorted on this bike.
After chasing brass since this thing was first acquired, I learned a couple things while going through it.
I was amazed to finally figure out how closely an improperly adjusted power valve mimics bad jetting. Here’s a link that breaks down how to properly adjust it.
https://youtu.be/_3Vt4rh2fGU?si=8FKMbGKNIGZnYXML
Since adjusting the power valve, there isn’t a huge bog snapping the throttle I was previously dealing with. I did add Boyesen reeds and, here’s the jetting I’m currently using.
Pilot- 35
Main- 400
Needle clip- 3rd
A/S- 1.5 out
Hopefully, some of this helps others because I have a feeling a lot of hate (though it’s slow AF) and, jetting issues came down to an improperly adjusted power valve.
Just wrapped it up. All that’s left to get is a new chain and, sprocket set.
I ran it up my street a twice before throwing the chain in the trash. It actually pulls cleanly through the entire RPM range (surprisingly).
Thank you for all the responses. They were quite helpful.
Onto the next project. 👍🏼
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