[dotrpaul]

2004 FXDX
STOCK MIKUNI 45
95 JUGS
SE HTCC PORTED HEADS AND MATCHING PISTONS
SE 257 CAM
SE AIR CLEANER KIT
THUNDERHEADER 2-1 EXHAUST
3:37 GEARING

Guys, we pulled the plugs after we machined more metal from the rocker boxes, and she is running lean. My buddy recommended getting the next higher jet size from what I have now, which is stock 45. Any suggestions? Am I going the right direction? BTW, clatter seems to be gone, tho I have not kicked her in the flanks yet because of the lean issue.

any suggestions much appreciated

 

[shinbone1028]

I think they have a 175 main, stock in the 45.Mine did anyway. After dyno,mine ended up 190. Great carb!

 

[hotshotfxdl]

You can go online to http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf
and see it all. My HRS45 came with a 175 in it and I am running a 170.
There are also some tune and test suggestions in the tuning guide that are very good. I have tried several combo's and always come back to the 170 with the HRS45 on the dyno. They really come pretty close out of the box.
I have a few friends running the same carb with the 170 also. Dyno will tell for sure. A 190 on a TC sounds pretty rich but I only know enough to be dangerous:blink:
I also got to say I have tested on the dyno with a 170 main and a 175 main, and looking at the plugs couldnt tell the difference.

 

[dotrpaul]

jet

Hotshot - what do you think a stock 45 has? 175? If I move to a 170 would that be leaner? It sounds like it if a 190 is rich.

I have been wanting to Dyno it but don't want to burn a hole in the piston because it is too lean!

thansk

 

[LittleBear]

The main has very little to do with burning a hole in a piston, unless you are running WOT.
The idle air screw, pilot jet, needle, and clip position would be the things that need looking at first. As hotshotfxdl suggested, you need to read the tuning manual for the carb. Mikunis are great carbs, but have more circuits than other carbs.
If you can not street tune it per the manual, take it to a dyno ASAP and get it done right.
If you are worried about lean, up your pilot jet one size, adjust the idle air screw and drop the needle clip one notch, but here again, it all depends on how it runs, not how the plugs look. Then take it to a dyno.

 

[hotshotfxdl]

Hotshot - what do you think a stock 45 has? 175? If I move to a 170 would that be leaner? It sounds like it if a 190 is rich.

I have been wanting to Dyno it but don't want to burn a hole in the piston because it is too lean!

thansk

My Mikuni manaul list's a 175 as stock

Yes a 170 is leaner. I would really recommend that you read the Mikuni tuning manual. It looks like your combo is close to mine. I would read up, and get to the dyno. You could put a 180 in there but that seems pretty rich to me. First pass on the dyno and you will have an idea of your AFR, I think that will tell you way more then looking at any plugs. Besides it is my understanding that the Twin Cams like it lean to make hp and tq. Some may find the optimum on the dyno and then go up a main jet size to be safe. I am not a guru but think you are pretty safe with the 175.
I think it takes a trained eye to look at a plug especially with today's gas.
Leaded gas was easier to read (guess you know how old I am)
If you are going to try to read a plug you want to be sure that you have been running the bike at a higher rpm for a good stretch, then pull in the clutch shut it off and coast to a spot where you can pull the plug and look at it. Of coarse all things should be at full operating temperature too.
Good Luck

 

[ohiomotoxer]

My Mikuni manaul list's a 175 as stock

Yes a 170 is leaner. I would really recommend that you read the Mikuni tuning manual. It looks like your combo is close to mine. I would read up, and get to the dyno. You could put a 180 in there but that seems pretty rich to me. First pass on the dyno and you will have an idea of your AFR, I think that will tell you way more then looking at any plugs. Besides it is my understanding that the Twin Cams like it lean to make hp and tq. Some may find the optimum on the dyno and then go up a main jet size to be safe. I am not a guru but think you are pretty safe with the 175.
I think it takes a trained eye to look at a plug especially with today's gas.
Leaded gas was easier to read (guess you know how old I am)
If you are going to try to read a plug you want to be sure that you have been running the bike at a higher rpm for a good stretch, then pull in the clutch shut it off and coast to a spot where you can pull the plug and look at it. Of coarse all things should be at full operating temperature too.
Good Luck

REMEMBER that dyno pulls are done at a full throttle position (which is the main jet)
First off you need to adjust the air screw in or out till you get the highest smoothest idle.
This will cure off idle and any popping on decell or through the carb.
Make sure the accelerator pump is timed properly, (see the MIkuni tuning manual.
Needle clip position should be close with what Mikuni specs.
Main jet, if the machine does not revv out or plain signs off at the 3/4 to wide open throttle position it is lean, you can down and dirty verify this by riding in the 3/4 to wide throttle position and slowly pulling the choke, if it runs better it is lean, if it runs worse it is rich if no difference it is close.

Check out this good plug reading info, this IS the correct way a plug should look with todays fuels.
http://www.dragstuff.com/techarticles/how-to-read-plugs.html