Jetting question and brass screw problem

[Dirtjump9]

Hi everyone... It's been a while...
I decided it's just about time to take the plunge and *gasp*..... jet the carb on my '05 YZ 125. I'm pretty sure it's running too rich because the plug is always wet and fouled. When I go to put rubber down on my driveway, the bike will bog out when I drop the clutch and grab a handful. I'm pretty sure going up a clip on the needle to lean it out would help a lot but I can't seem to undo the two brass screws on the top of the carb. I've never opened the carb before so there might be some loctite on them. I've tried to unscrew them but it seems like it will strip out and leave me in a jam.
Anyways, I was wondering what you think I sound do jetting wise for my bike. I know there is no definitive answer for the perfect jets but a good guideline on what to change would help. The bottom end and the lower part of the mid is pretty crisp and perky but when I go to really kick up some roost or do a fast 2nd gear start, the bike will bog and I find my nose 4 inches from the bars.
Also, what am I going to do for those screws? I normally use a lighter to soften the loctite before I go to unscrew them but I could never do that on a carb... Remember that they are brass and brass snaps and strips easily

If anyone can help me here, I would really appreciate it! Thanks much!
-Mike

[crazyrydermx]

To get the screws off I would just try using a clamp if it will fit or some sort of monkey wrench or pliers or something that can clamp on. I do things the ghetto way though...so don't listen to me unless you have back up screws or just wanna risk it.
If you drain all the gas out of the float bowl and quickly wipe the carb, then using a flame near it should be no problem.
Maybe something non-flammable to spray and wipe or just water to clean it just in case.
I would start with the needle once you do get inside, then go from there. I think that will probably solve your problem.
Take it a step at a time though, and see what works best. I learned that the hard way, as I usually do everything else:

[Aus_Rider_22]

I had same prob on my YZ.

Those screws and the 3 on the bottom of the carb are soft and get rounded pretty quickly. So I replaced them with allen-head bolts that don't round out.

[KX02]

I agree with aus. One way or another you have to find a way to get those brass screws out with out stripping them. Once you have done that you might also find some stainless steel phillip head screws, I used those on my last bikes carb. As far as the jetting goes, you need to jet the bike from the bottom up. Meaning start with the pilot, then the needle position and then the main jet. There was an article posted on here I believe it was called Spanks jetting guide or something like that. Try doing a search for that here or google it maybe. Good luck!

[crazyrydermx]

Ask Faded about jetting if you really want help...he's a GENIUS!!!

[AKColby]

Originally Posted by Aus_Rider_22

I had same prob on my YZ.

Those screws and the 3 on the bottom of the carb are soft and get rounded pretty quickly. So I replaced them with allen-head bolts that don't round out.

Yes, replace with allen heads, much easier

[wamxp1mp]

There is no loctite on them the trick to those bolts it to use the right size phillips for one and you push down on the screw as your slowly turn it. It takes a good bit of steady pressure definetly watch as your turn it stop if the screw driver twists! They almost like snap so they tend to just give all at once when the come loose, this is why most people strip them out. I stress taking your time an caution when loosening them. Replacing with allen heads wouldn't be a bad idea either. I don't know what your '05 YZ comes with as stock jetting but on my '06 I ended up going down one on the pilot to a 37.5 from a 40 one up on the needle clip to pos #2 and it ran great I think any leaner would be too lean at least on my '06 it seems that way. oh yea and becareful pulling off and putting the E clip back on the needle! They are really easy to bend/break if your not careful when you see how thin and flimsy it is you'll understand why i've broken 2 in the past week jetting my '06 YZ 144.

[Dirtjump9]

Thanks everyone, I really appreciate all the tips
When I have time I'll just pull the carb off and try again. I assume they are standard threads so when I get 'em out i'll swing by the hardware store and see what they can do for me. I'm not in any real rush because it's still 40 degrees here and it rains every couple days so I don't have any oppertunities to go riding.
Once again, thanks for the help!

[Dirtjump9]

Well, I was feeling confident in my abilities after I tore down the carb on my 185 last night so I decided to tackle the 125. It took me an hour to locate the necessary tools then another 40 minutes to get the carb off the bike. Finally, I got it off and tried getting the screws off of the top cap on the carb... I used some small vice grips and I squeezed the living crap out of them and turned them until they budged. With all that done, I got to the needle and went up one clip position to lean it out. The stock position was one up from the bottom clip so now it's in the middle position. I was going to try for 2 clips up but I decided not to push my luck. I then threw some white grease on the slide and threw it back together.
It's 12:45 PM here so I'll wait until the afternoon before I go and try it out. Hopefully it will have gotten rid of the bog and livened up the powerband a bit. I don't want to mess with the other jets right now until I have the chance to properly experiment with different setups in better weather. For now though, this should help

[crazyrydermx]

Good!
Tell us how it goes when you do ride it...

[Dirtjump9]

Yeah, I'm going to take a quick spin on it in a few minutes when the parents leave...
Next time I get to the dealer, I'm going to pick up some new pilots and main jets, 2 sizes leaner and 2 sizes richer than stock and I'll experiment from there.

[Dirtjump9]

Well... I just got back from a little test run in the yard. The bike started in 3 kicks so I was pretty impressed.... Normally it takes me 10+ kicks. When I took it off the choke and revved it, it seemed a little healthier and freer-revving. I popped it into first and it seemed to come on a little smoother. I decided to lay a few streaks of rubberon the driveway to see if the bog was still there when going from idle to full throttle in a literal second. Yep still there, but not as bad as before. With a few more spins around the yard, I noticed that when you try to grab a handful to throw some roost, it bogs.

It seems the bog only occurs when you accelerate quickly from a slow speed and really twist the throttle. When riding, it seems to occur mainly between 1/2 and 3/4 throttle. The first 1/4 of the throttle's rotation is a little rough but not too bad. Full throttle operation seems okay but I didn't really get to rev it that high because of lack of space in my yard and lousy neighbors who call the cops. I'm guessing that if I go up one more clip on the needle, it will help the bog. Yamaha was nice enough to give me another needle (I don't know what the difference is between this one and stock) and two main jets.

I really don't feel like changing jets now, only to find out later that with fresh gas and warmer temps that it is way off again. I think my best bet is to go up one more clip on the needle and call it good for now... Atleast now I know how to do it all

Anyone have any advise for me?

[crazyrydermx]

Did you do anything to the pilot circuit? That sounds like your next move if you haven't messed with that yet. I wouldn't mess with the needle too much, because then you are doing it the wrong way...

[ossagp1]

First off, the screws are NOT BRASS. Simply plated. Small vise grips work in the case of really stubborn ones. Removing the carb and putting it on the bench in a wooden jig (NOT A VISE) seems to work for my stubborn ones. Even ones that have been in for years. Lots of threads on jetting,,,read some before you start so you have a plan.
The manual is a good place to start on the air screw. Then go from there.

[Dirtjump9]

Well, I tried 4 out of the 5 clip positions and I decided that one clip up from stock worked the best. As of now, I haven't messed with anything else yet. I have two main jets here that came with the bike which are marked 430 and 420. I don't know what size they are in relation to the stock main jet (leaner or richer). When the weather warms up more and I have fresh gas and a chance to go riding, I'm going to experiment with the other jets. When I do, should I start with the main jet, the pilot jet or the pilot air screw?
Thanks for the help so far!

[ossagp1]

If you are not going to ride it in this kind of weather,,then don't jet it for this kind of weather. Weather and altitude changes are two of the reasons you change jets in the first place. I would busy myself doing other maintenance or improvements if you have time to kill. Wait for the weather you are going to be riding in. But in the meantime, cleaning the carburetor and finding out what is really in it won't hurt either. That way you have some time to come up with the "two larger and two smaller pilots and mains" that you were talking about.

[Dirtjump9]

My plan was to wait for the nice weather so I could jet it properly but it was kind of a spur of the moment thing last night to crack open the carb and see what made it tick. I've been telling myself for a while to get in there and lean it out and get it running good so while I was in there, I decided to just change the clip position and see what effect it had in relation to the stock jetting.
I've really only rode the bike 4 times since I have had it so it's just past break-in. There isn't really any issues I need to address aside from the jetting and the suspension set-up. Both of these issues can't be addressed until the next time I get to go riding. I changed the tranny oil after the last ride and the bike is pretty darn clean so there isn't much to be done in that department.
I guess during the week I will go run down to the hardware store and get some better quality screws to replace the soft stock ones on the carb. I'll get some spare brass so next time I ride I'll get it dialed in.

[crazyrydermx]

Originally Posted by ossagp1

First off, the screws are NOT BRASS. Simply plated. Small vise grips work in the case of really stubborn ones. Removing the carb and putting it on the bench in a wooden jig (NOT A VISE) seems to work for my stubborn ones. Even ones that have been in for years. Lots of threads on jetting,,,read some before you start so you have a plan.
The manual is a good place to start on the air screw. Then go from there.

He already got the screws off
I don't think you need to mess with the main jet. You may, but you say it is having problems everywhere. This leads me to believe that you have to tune the pilot circuit correctly because it is the one circuit which effects everything in jetting, throughout throttle pullback whether it's idle or WOT.
Pilot will usually yield the most positive results when fine-tuning anyway, and it's a good thing to rejet for each season.
Once again, moving any more clip positions and you will be doing it the wrong way most likely. Usually, moving more than one clip position is just a temporary fix and the only real time you should drastically change the clip position like that is if you have an extreme change in climate and/or altitude, which it still usually isn't needed.

[Dirtjump9]

Yeah, I've been thinking about it and it seems like you are correct about the pilot circuit. I now have the clip in the middle position (one clip leaner than stock) and that seems like what it runs best at. I'm going to leave the main jet alone for now. Maybe tomorrow I will fetch some fresh gas and I'll mix up a little bit and see if I can adjust the pilot air screw for better response.
With the clip in the middle position, it runs much healthier but it still has the bog when you grab a handful. Hopefully the air screw will clear that up. I'm taking a guess that it is too rich right now (based on plug readings and the results I got when I leaned the needle out). Instead of waiting until warmer weather, I am going to go ahead right now and atleast get the jetting in the ballpark of where it needs to be because I may go riding next weekend if the weather is decent.
Also, I just won an FMF Shorty off eBay! W00T!