I installed my new-to-me 300R (actually a 250R as they are identical) pipe/silencer this afternoon. Super easy install. Sounds good. Feels good low to mid, but definitely needs a bit more gas on the top as it was surging. Also, a very nice subtle decel burble - not quite a pop. Even started way easier.

I know I need to go from 122K to a 125K main but I'm dreading digging into the bottom of the carb. Wondering if I could play with the clip position from the top and approximate the same jetting as a 125K.

My question, after all this time, is what is the ration of clip position to MJ size? For instance, would the 122 at clip position 5 equate to a 125 at clip position 2 by some freaky unlikely chance?

Or, is it easier than I think to unhook the throttle cable, unclamp and rotate the carb to get in the bottom end? I may need to get to the bottom anyway to play with the mixture screw. I'm guessing it needs to be richened by a 1/4 turn or so with the decel burble. If I do rotate, do I rotate the bottom to the right or left side of the bike?

As always, thanks in advance.

 

the more open the muffler is the more you'll hear the burble, it's there with a corked up pipe but it gets muffled good enough you don't hear it. With a free flowing pipe if you enrichen the mixture enough to kill all the burble you'll be too rich on the idle circuit. Some burble is acceptable. Loud bangs and pops not.

The 300 muffler itself probably doesn't need much change in fueling, especially if the stock 300 end plate is intact. If the pipe is done along with a airbox mod than you'll want some more fuel.

clip change on the needle will make the needle 'hand off" to the main sooner at some slide position, only at that point might it be a substitute for a (too lean) main jet). Beyond that the main is too lean.

what needle are you working with?

 

Thanks RB.

The 300 exhaust is gloriously without the buttplug. I added a CNC power tip from ebay for effect.

Prior to adding the new pipe/silencer I was running 122 Keihin with a UNI filter and all the cheap/free mods and it was running well. The new muffler changed the flow enough that I can now do a second gear wheelie with power only so I know it needs more fuel in the mid to upper rpm range. Low-mid rpm power is clearly better as is (and so is the starting) so I will leave the pilot alone.

I was hoping for a common sense rule along the lines of mixture screw vs pilot size. That is, if you need to turn the mixture screw out beyond 3 turns or in beyond 2 turns - you probably need a different size pilot jet.

Maybe clip position and main jet don't have the same fine-tuneability because they affect different portions of the rpm spectrum.

 

fuel screw is just the fine tune for the PJ, a 38 pj at 3 is like a 40 at 2.5 (maybe not exact but one pilot size isn't much of a screw turn).

people often change the pilot size when they should be changing the needle root diameter, it just easier or cheaper to change the pilot or crank the mix screw out. downside is you end up with it too rich at idle (ie dynojets instructions)

I run a 300 pipe too, switch back and forth between the ebay alum tip and stock peashooter depending on where I ride. Not a big fan of loud but it does run better,

 

If it is a jetting issue the needle and the main jet affect different things and each need set up properly

 

Here's a decent, general description of carb operation, and figure 7 shows a general overlap of the idle circuit, throttle valve cutaway, needle/needle jet, and main jet. Our throttle butterfly doesn't really change the basics to any large degree.

Motorcycle Carburetor Theory 101

 

Thanks TNC. That's a great tutorial. Let's see if I can use it successfully tomorrow.

 

idk why people treat jetting like its a huge deal i woud rathe tear into a carb than a throttle body i have a 140 main 40 pilot 2nd clip but its pumper carb and a moded motor, the way i check jetting is hookup a a:f guage that you can ride with and take off after and plugh the bung on the pipe up easier to do if you can tig weld, that will show you where you are running through the whole range under load and give you the best way to tune the bike a setup for that should set you back 50-120 but will save you on the headace of guessing all the time

 

It's not a huge deal. I'm just being lazy. I played this AM and it's definitely a bigger MJ that I need. So I'll rotate the carb and replace the 122K with a 125K.

Don't have an A/F guage, and don't have welding equipment, and I'm not likely to buy those things when I can get close enough by seat of the pants and my other bike is FI. I don't mind wrenching but my weekend time with family is more important to me.

When you say you have a 140 MJ, do you mean a Keihin or Dynojet or Mikuni MJ? They're all a bit different. Wish I had access to the comparison chart of the different makes but I can't find it.

 

Here's a conversion chart that's been floating around here on this site. Don't know how correct it is.

Keihin Conversion Chart

Here is a conversion chart


Width------Kehein # -- DynoJets # -- Mikuni #
0,0350---- 92,5--------- 92----------- 86,3
0,0360---- 95----------- 94----------- 88,1
0,0370---- 97,5--------- 96----------- 90,0
0,0380---- 100---------- 98----------- 91,9
0,0390---- 102,5------- 100---------- 93,8
0,0400---- 105--------- 102---------- 95,6
0,0410---- 107,5------- 104---------- 97,5
0,0420---- 110--------- 106---------- 99,4
0,0430---- 112,5------- 108--------- 101,3
0,0440---- 115--------- 110--------- 103,1
0,0450---- 117,5------- 112--------- 105,0
0,0460---- 120--------- 114--------- 106,9
0,0470---- 122,5------- 116--------- 108,8
0,0480---- 125--------- 118--------- 110,6
0,0490---- 127,5------- 120--------- 112,5
0,0500---- 130--------- 122--------- 114,4
0,0510---- 132,5------- 124--------- 116,3
0,0520---- 135--------- 126--------- 118,1
0,0530---- 137,5------- 128--------- 120,0
0,0540---- 140--------- 130--------- 121,9
0,0550---- 142,5------- 132--------- 123,8
0,0560---- 145--------- 134--------- 125,6
0,0570---- 147,5------- 136--------- 127,5
0,0580---- 150--------- 138--------- 129,4
0,0590---- 152,5------- 140--------- 131,3
0,0600---- 155--------- 142--------- 133,1
0,0610---- 157,5------- 144--------- 135,0
0,0620---- 160--------- 146--------- 136,9
0,0630---- 162,5------- 148--------- 138,8
0,0640---- 165--------- 150--------- 140,6
0,0650---- 167,5------- 152--------- 142,5
0,0660---- 170--------- 154--------- 144,4
0,0670---- 172,5------- 156--------- 146,3
0,0680---- 175--------- 158--------- 148,1
0,0690---- 177,5------- 160--------- 150,0
0,0700---- 180--------- 162--------- 151,9
0,0710---- 182,5------- 164--------- 153,8
0,0720---- 185--------- 166--------- 155,6
0,0730---- 187,5------- 168--------- 157,5
0,0740---- 190--------- 170--------- 159,4
0,0750---- 192,5------- 172--------- 161,3
0,0760---- 195--------- 174--------- 163,1
0,0770---- 197,5------- 176--------- 165,0
0,0780---- 200--------- 178--------- 166,9
0,0790---- 202,5------- 180--------- 168,8
0,0800---- 205--------- 182--------- 170,6
0,0810---- 207,5------- 184--------- 172,5
0,0820---- 210--------- 186--------- 174,4
0,0830---- 212,5------- 188--------- 176,3
0,0840---- 215--------- 190--------- 178,1
0,0850---- 217,5------- 192--------- 180,0
0,0860---- 220--------- 194--------- 181,9
0,0870---- 222,5------- 196--------- 183,7
0,0880---- 225--------- 198--------- 185,6
0,0890---- 227,5------- 200--------- 187,5