RC Power Valve not opening fully?

JW381
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JW381
Edited Date/Time 4/5/2013 3:52pm
Is that what's going on here? This is 2nd gear, but it did this in every gear. Hit the revs quick, then held that hovering rev in the air over most jumps. Not a ton of powerband pull. That's what it seems like to me, I haven't had the chance to check my cables today, but what do you guys think?



Don't comment on how slow I am, please lol. Trying to get my bike dialed and avoid arm pump two laps in.
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JCollins762
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JCollins762 3/25/2013 5:43pm
3/25/2013 5:43pm
I didn't hear anything, except for a slow dropping RPM.. sounds like a lean issue to me.
captmoto
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captmoto 3/25/2013 5:54pm
3/25/2013 5:54pm
Nice track, where is it?
jhansen510
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jhansen510 3/25/2013 6:25pm
3/25/2013 6:25pm
you need to get in touch with Thomas Jefferson on here. He can help you out!
JW381
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JW381 3/25/2013 7:41pm
3/25/2013 7:41pm
I guess its hard to explain, its hitting the Revs but not really pulling, just always feels like I need to shift up. Then the slow drop in RPMs like you heard over this jump.

This is the famous Albany MX haha it was a great day, super rutty!

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mynewcr250 3/25/2013 9:02pm
3/25/2013 9:02pm
hit up thumpertalk. theres a few guys there that can get you setup.

i have no experience with the case reeds hondas and their PV setup, but the only real issues ive seen people bring up so far are the servo motor taking a dump, and the cables needing adjustment fairly regularly.
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JCollins762 3/25/2013 9:14pm
3/25/2013 9:14pm
If its revving all the way out, maybe it isn't the powervalves. Typically when powervalves don't open (or at least all the way), the bike will rev and sound almost like a chainsaw in a way. If it's revving out and not going anywhere, sounds more like a clutch to me, then the lean issue is the most common thing that would cause slow decel.

But I mean, you can check the powervalves, although I don't really think they'll cause the issue you're explaining.
JW381
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JW381 3/25/2013 9:33pm
3/25/2013 9:33pm
Hmm, okay thanks gents, that's why I came here with the question. I didn't think there was an issue with the clutch, but I'll check it out. Along with the jetting and the PVs.
JW381
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JW381 3/25/2013 9:34pm
3/25/2013 9:34pm
I have finally signed up at TT as well.
Travis_Hudson 3/25/2013 11:33pm
3/25/2013 11:33pm
Ditch the carb....check you pwr valve cables, if they get loose it will do some weird shit.
JW381
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JW381 3/26/2013 2:04am
3/26/2013 2:04am
For sure, that's first on my to do list next time I'm over at my mum and pa's where i gotta store it. I'm thinkin It's one of those too or a combo. It just didn't pull as hard as the first time i rode it and always wanted to be shifted. I've changed so much shit since then its hard to know. Could be the new reeds? Or I did something wrong on my new top end? Or just adjusted my PV cables allll wrong.
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JW381 3/26/2013 3:38am
3/26/2013 3:38am
JCollins762 wrote:
If its revving all the way out, maybe it isn't the powervalves. Typically when powervalves don't open (or at least all the way), the bike will...
If its revving all the way out, maybe it isn't the powervalves. Typically when powervalves don't open (or at least all the way), the bike will rev and sound almost like a chainsaw in a way. If it's revving out and not going anywhere, sounds more like a clutch to me, then the lean issue is the most common thing that would cause slow decel.

But I mean, you can check the powervalves, although I don't really think they'll cause the issue you're explaining.
Could it be a combination of the RC valve and a lean air screw? I did turn the air screw out after my initial warm up laps, so that could be causing the slow decel. Because jetting works based on throttle opening, not revs, so that would explain the lean sputtering slow decel when i have the throttle closed.

Yet I still feel like the PV isn't opening because the bike is getting to what sounds like revved out before I'm practically done twisting the grip, then not as strong of a pull or over rev like the first time I rode it, just wanta to grab another gear before doing the same kind of thing.

I guess I had so much Damn fun riding again, second ride ever on my new bike, first ride after my first rebuild job of any sort, new pickup even, because this is causing me to lose sleep right now. Not in a "bad, stressing" way, just an anxious and curious way.
Thomas Jefferson 3/26/2013 6:57am
3/26/2013 6:57am Edited Date/Time 3/26/2013 7:04am
remember the day i told you that your jetting was way off? you're running something like a 420 main in your mikuni, it's probably drowning.

air screw is 0-1/8th throttle. won't affect WOT.

check your PV cables, it takes all of 5 seconds to pop your RC valve cover off and check the tension. I doubt that's it.

One more thing to check on when the bike isnt running right up top is the reed petals. check the ends of them. if they are frayed or damaged at all, that's also a culprit. My oem reeds were missing material all together on one corner.
Thomas Jefferson 3/26/2013 7:07am
3/26/2013 7:07am
just remember when you troubleshoot, to start with the simplest, least expensive solution and work your way up to the most difficult, expensive solution. Also, know that if your bike isn't 100% functional, swapping out jets is pointless.
JW381
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JW381 3/26/2013 9:25am
3/26/2013 9:25am
Thomas Jefferson wrote:
remember the day i told you that your jetting was way off? you're running something like a 420 main in your mikuni, it's probably drowning. air...
remember the day i told you that your jetting was way off? you're running something like a 420 main in your mikuni, it's probably drowning.

air screw is 0-1/8th throttle. won't affect WOT.

check your PV cables, it takes all of 5 seconds to pop your RC valve cover off and check the tension. I doubt that's it.

One more thing to check on when the bike isnt running right up top is the reed petals. check the ends of them. if they are frayed or damaged at all, that's also a culprit. My oem reeds were missing material all together on one corner.
Well I ran 410, only because it was pretty cool out, and was just staying on the safe side for the first tank. When i said air screw, I solely meant the slow decel. The reeds are brand new boyesen reeds, don't think I installed them wrong, but I'll check.

Thanks for the input
Thomas Jefferson 3/26/2013 9:38am
3/26/2013 9:38am
bear in mind that rich can be just as dangerous as lean, as the extra fuel will wash the rings out.

post a picture of the plug.
JW381
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JW381 3/26/2013 9:43am
3/26/2013 9:43am
Okay, I'll do that after work. i checked it at the track and it was rich, but it wasn't soaked by any means. And you can hear in the YouTube clip how it seems to be lean on decel and idle, which is why i thought maybe i dialed the air screw out too much.

But the reeds, top end, and whole clutch are new, so i don't have reason to suspect its any of that, beyond me doing something wrong, which is obviously possible. But it seems like it runs well, minus the shortened power band and unwillingness for Revs to shut off when the throttle shuts off.

I'm just new to most of this, man.
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JW381 3/26/2013 9:45am
3/26/2013 9:45am
Plus I got the boyesen exhaust flange to correct the factory one, so i should be pretty good with an air tight system, but maybe I have some hidden air leak somewhere..
JW381
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JW381 3/26/2013 10:27am
3/26/2013 10:27am
If I have some hidden air leak, would my plug color reflect it at all? Seems to me that it would show a lean F/A mixture, despite running richer jets, but maybe I'm wrong there..

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JCollins762
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JCollins762 3/26/2013 10:37am
3/26/2013 10:37am
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage.

Although checking the Powervalve is the first thing I would do, as TJ said.. it's not hard to do, takes a couple of minutes at the most. Also go ahead and clean them if you have the time.
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JW381 3/26/2013 10:47am
3/26/2013 10:47am
JCollins762 wrote:
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage. Although checking...
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage.

Although checking the Powervalve is the first thing I would do, as TJ said.. it's not hard to do, takes a couple of minutes at the most. Also go ahead and clean them if you have the time.
Yeah definitely makes sense, its just brand new, and doesn't creep or anything. I'll keep my eye on the clutch tho.
Thomas Jefferson 3/26/2013 10:53am
3/26/2013 10:53am
JCollins762 wrote:
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage. Although checking...
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage.

Although checking the Powervalve is the first thing I would do, as TJ said.. it's not hard to do, takes a couple of minutes at the most. Also go ahead and clean them if you have the time.
You're not cleaning the powervalve without pulling the jug.

I think you are just starting off down the path of finding out what a hunk of shit the Mikuni TMX is. The slide in that carb is one big airleak in and of itself.

Basically, Honda wanted to hit 50hp to put it on paper and sell bikes. Mikuni helped them hit that peak number, but at the expense of power/ridability/jet-ability under the curve.

Junk that carb.
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JW381 3/26/2013 10:58am
3/26/2013 10:58am
JCollins762 wrote:
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage. Although checking...
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage.

Although checking the Powervalve is the first thing I would do, as TJ said.. it's not hard to do, takes a couple of minutes at the most. Also go ahead and clean them if you have the time.
Thomas Jefferson wrote:
You're not cleaning the powervalve without pulling the jug. I think you are just starting off down the path of finding out what a hunk of...
You're not cleaning the powervalve without pulling the jug.

I think you are just starting off down the path of finding out what a hunk of shit the Mikuni TMX is. The slide in that carb is one big airleak in and of itself.

Basically, Honda wanted to hit 50hp to put it on paper and sell bikes. Mikuni helped them hit that peak number, but at the expense of power/ridability/jet-ability under the curve.

Junk that carb.
Okay, I can do that. I really appreciate the feedback, ya'll.

And i can probably pull the jug to check how things look, would be worth the effort.
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JCollins762 3/26/2013 10:58am
3/26/2013 10:58am
JCollins762 wrote:
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage. Although checking...
Yeah, my initial thought when you said "Revving out, but I feel like I need to change gears the whole time" was clutch slippage.

Although checking the Powervalve is the first thing I would do, as TJ said.. it's not hard to do, takes a couple of minutes at the most. Also go ahead and clean them if you have the time.
Thomas Jefferson wrote:
You're not cleaning the powervalve without pulling the jug. I think you are just starting off down the path of finding out what a hunk of...
You're not cleaning the powervalve without pulling the jug.

I think you are just starting off down the path of finding out what a hunk of shit the Mikuni TMX is. The slide in that carb is one big airleak in and of itself.

Basically, Honda wanted to hit 50hp to put it on paper and sell bikes. Mikuni helped them hit that peak number, but at the expense of power/ridability/jet-ability under the curve.

Junk that carb.
You cant use a scotch brite with expansion pipe off? I've never tried to clean them on a New Gen honda.
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JW381 3/26/2013 1:08pm
3/26/2013 1:08pm Edited Date/Time 3/26/2013 1:09pm
Alright I did it, forked over the cash for an air striker from JD jetting. I know that you can get carbs off older YZs, I just figured I'd fork over the cash for something that is new and in working condition. I'll keep the Mikuni around until I try it out, but I'm sure it'll be on eBay shortly after.

I'll be off work in about 4 hours, then I'll go check the PVs and snap a pic of the plug and check the reeds, all that good stuff.

Hopefully this works, I'm ready to get this baby cookin past some 450s.
JW381
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JW381 3/26/2013 2:14pm
3/26/2013 2:14pm Edited Date/Time 3/26/2013 2:15pm
In your opinion(s) is straight 100LL AVGAS better than a 50/50 blend of premium and 110 Sunoco leaded race fuel? My internals are stock. Because the 50/50 mix would be cheaper, and it seemed to run super strong the first time I put it thru. Just wondering.
Thomas Jefferson 3/26/2013 4:33pm
3/26/2013 4:33pm
Stick the Mikuni on eBay and sell it to a Malaysian kid in Singapore trying to make his scooter f aster. I'm not making that up, there i a big scooter scene over there and they love those TMX Mikunis.
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JW381 3/26/2013 4:42pm
3/26/2013 4:42pm
Thomas Jefferson wrote:
Stick the Mikuni on eBay and sell it to a Malaysian kid in Singapore trying to make his scooter f aster. I'm not making that up...
Stick the Mikuni on eBay and sell it to a Malaysian kid in Singapore trying to make his scooter f aster. I'm not making that up, there i a big scooter scene over there and they love those TMX Mikunis.
Sounds good, I'll include that in my list of keywords on my eBay ad.

So plug color - if it's darker black, does that make an air leak less likely? I'd like to do a pressure test anyway while I have the Mikuni off, but it would be nice to know that it's less likely that I have some major air leak problem. Again, it seems that if plug color is based on your F/A, and your F/O, mixtures, then an air leak would give me a lean colored plug, despite rich jet settings. But correct me if I'm wrong.
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JW381 3/26/2013 6:14pm
3/26/2013 6:14pm
Just started it up and took a look at the RC valve assembly, it definitely wasn't opening up all the way at all, I had it adjusted all wrong. Gonna go work on that now before I take the Mikuni off (for good).

Started with the choke on, it would barely run, so I'm assuming it was too rich on bottom, but I've also read that if you turn the choke on, and the bike doesn't run differently, then it's likely an air leak. So this should also ease my mind concerning an air leak, correct?
mynewcr250 3/26/2013 7:19pm
3/26/2013 7:19pm Edited Date/Time 3/26/2013 7:21pm
JW381 wrote:
Just started it up and took a look at the RC valve assembly, it definitely wasn't opening up all the way at all, I had it...
Just started it up and took a look at the RC valve assembly, it definitely wasn't opening up all the way at all, I had it adjusted all wrong. Gonna go work on that now before I take the Mikuni off (for good).

Started with the choke on, it would barely run, so I'm assuming it was too rich on bottom, but I've also read that if you turn the choke on, and the bike doesn't run differently, then it's likely an air leak. So this should also ease my mind concerning an air leak, correct?
relax man. fix the power valve issue first.

a hanging idle or really slow to decel is a lean condition on the pilot circuit.

either the airscrew needs to be turned in, you need a richer PJ, or you have an air leak (make a leak down tester. i made one years back for $26 plus a bike pump). use the airscrew to determine if you need a richer pilot.
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JW381 3/26/2013 8:00pm
3/26/2013 8:00pm
Here's the plug. I knew it was on the richer side, so I'm not really surprised here.



Here's the reed assembly, just making sure I did this right. I had it installed with the open side on the left, which matched the case intake shape.


Here's my PV set up, I think I got it tighter, and it seemed to open more when I turned the throttle, but I'm not sure if it's right. The cables are definitely tighter now.

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