I am at the end of my needle!

[yzbluebeast]

Hey Bruce, have you tried lowering your fuel level in the float bowl? It will lean the mixture across the spectrum. If I understand, you have the main pretty dialed and are having a problem with the slide cutaway, pilot circuit, needle jet and jet needle. It will almost be like starting over but you could put larger jets back in it and have more room for adjustments.

Just a thought.

 

[bclapham]

nephron, the 125 ktm pulls that carb well, so i recon my 144 would pull it but i dont know if it would be a step in the wrong direction.

Yz: yep, we though about that- the suzuki manual has quite an ambiguous picture/description of setting the float level. however, when i checked it, it appears it is a touch lower than stock already- i didnt change it since the last thing i want to be doing is trying to reverse a float change at the track. good idea though!:)

 

[NO HAND]

Originally posted by nephron
...39.5 Keihin on an RM125? I don't know enough about it, but it seems a little largish. That's as big as the one on my KX500, and the same carb that's on the ATK700 Intimidator 2 stroke. :eek: Probably would work well all the same, with proper jetting.

It's funny the subject comes up here, I actually tried this over a year ago on a 00' cr125. I bought the carb from a 98'kx500 and realized I was in more troubles than I ordered. It was easy finding the low speed and main, but finding a good needle for the setup was quite a pain. In the end the increase in overrev was more noticeable than the loss in throttle response down low. I think it's worth it if you are looking for a more "pro oriented" powerband.

 

[bclapham]

No Hand; i am glad you chimed in since i was reading some of your old posts about that carb swap, i rememeber at one point you were strangly getting more low end????? i think if i were to do it, the best way forward would be the 36mm pwk since i could do with a tad more bottom, but i might try another pipe to get around that.

back to todays testing. i went to glen helen today, despite a drought, they had watered the track to the point where it resemblled one of those winter battles from WWII Europe, a quagmire with knee deep ruts all the way around! I went to 20% MTBE with the C12, it leaned the bike out just a little bit more to the point that it is nearly where i want it, still just a tad rich in the middle and top, but i am confident after looking at a couple of plugs that i can go down another size on the main.

i think the next time i ride, i will try a needle from a yz125 and see if that works out. i really dont want to get into this carb swap thing since i could spend that cash on a new pipe or radvalve......lets see what will happen.

 

[NO HAND]

Originally posted by bclapham
...since i was reading some of your old posts about that carb swap, i rememeber at one point you were strangly getting more low end...

Yeah I remember. I found out later it was probably the v-force that was responsible for the low end part. I could only use that 39mm carb with a 1999 intake manifold, so I bought it and butchered it to go with the v-vorce, that I had just bought also. I could only change the carb and reed cage as a set because of that. Now I sold the bike with the stock setup so I still have these parts lying somewhere in my garage. It reminds me the pain it was to jet it with a needle that wasn't good at all. I think it must be the hardest part in a carb switch, finding the right needle.

 

[shifter125]

Just noting the carb bore issue and thought i'd add that I ran a 39mm Keihin PWK on my RM125 with a straight manifold of my own design and i had some mid range issues. i ended up making 'stuffer plates' to fit in between the reed cage and the block. it picked up power across the board.

MC

 

[jmics19067]

Bruce,

Have you found anything more out yet on your situation?

 

[nephron]

Bruce, if I were you, I'd call Bill's pipes and find out what they do to their motors. Apparently, Bill's does most of the 125 (motor) work on DeCoster's 125's, while as you know, ECC uses Bill's motors exclusively; and they work well. Give them a call, telling them what mods you've done. I'm sure they could work with Gorr's 144 motor. They've been around the block or two with Suzuki motors, and in the end, it's experience that's going to get you where you want to be.

I have a feeling that since KTM's are the only ones using 39PWK's, it's got something to do inherently with their straight intake tract, and would not be suitable for your application. I could be wrong. I just think it's like putting a 1050 Dom on a 400 horse 350. It'll work, but at the expense of many issues.

 

[bclapham]

OK here's the update!

Rich lent me a copy of his Mikuni manual and said to let everyone know what i learned, so here it goes.

1. when i swapped to the wider OD needle, i wasnt really changing much- the needle OD only effects 1/8-1/4 throttle so there is a bit of overlap with the slide and pilot circuits and thats about it.

2. so, i needed a leaner needle, ie a needle where the taper starts further down- unfortunately all the mikuni needles are ~2.5-2.6mm wide, wheas the ones in this carb are 2.75mm wide- a step in the wrong direction. when suzuki states about leaner needles in the manual, the needles in this series dont change much at all.

i was thinking what could i do, just to drop the needle 1 more clip position- i thought about drilling a hole inside the slide with a flat mill bit, just a bit deeper so that the needle sat a bit further down, i talked myself out of it, but then the next day i got 2 emails from marcus and james dean suggesting that mod, so i went for it. (had to file off 1mm from the end of the needle too).

i took it to the track yesterday and it seems to have done the trick, i actually raised the needle about 0.5mm with a washer and i am happy with the result. one note- this is a dangerous mod, i took the time to make sure the needle sits properly and has a little bit of "float" and i also had to use a tight fitting nylon washer ontop of the needle to take up the room.

i still need to pay a bit more attention to the main now, ive been eering on the side of caution with the main after the problems i was having with detonation with the old head/port timing specs- when i lost momentum in the higher gears going up hills full of deep soil it needed a bit of clutch to get back on the pipe.

Nephron- i though about calling bills, but i dont have the heart to since i am running an FMF pipe!:p its motoworld down near me in el cajon that are running the bills rm125- ironic since they dont sell suzuki's! ECC are running the Varner/FMF engines i think- my FMF pipe came of one of the ECC bikes, but i think this "rev" pipe had only one ride on it for a reason!

you are correct about the 39.5mm carb being a step in the wrong direction- everything i am hearing is that the 36mm carb is better, if i got a 36mm pwk it would be an easy starting point since i could use the older rm jetting starting point- i dont think needle selction is trivial for these swaps.

thanks again everyone :thumb:

 

[jmics19067]

cool glad to hear it worked out for you :thumb: