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View Full Version : Exhaust/carb tuning without a dyno



rjwatters38
07-10-2014, 10:41 AM
Ok, so here is my situation.

Bike is running, if not perfect, pretty well. plugs are coming dry and tan, no burning, no wetness and the bike starts up and idles and runs great with half choke and a single turn key.

Stock across the board except for a .010 over, the DynaS ignition I have on there, a Super E, the sportyparts 2 into 1 and a Supertrapp S/C muffler with 12 discs.

now I have good acceleration, not fantastic, but good. good power through the lower, but when I hit maybe (no tach so completely just feeling shit out) the end of the midrange it bogs, sometimes will even kind of slow down a little before pushing through to the higher end of the powerband, but weakly and kind of choppy.


In my mind, I'm thinking the Super E needs to be rejetted. But could the exhaust be causing this? Coming from open ended short drag pipes to a closed up, muffled, 2 into 1 system and doing nothing to the Jets or Timing I knew was going to need an adjustment, but I'm not sure where I should start at.



By the way, If you're around Orange County/LA area and wanna help me tackle this, libation of choice (or whatever) on me I'm getting tired of trying to figure it out on my own, and I couldn't find any similar set ups to get a good base setup on. I'm going to email Supertrapp and see if they have any experience with a setup like this, but I doubt it. No Ironhead love these days.

SamHain
07-10-2014, 12:35 PM
sounds like your main could be too big(which closing up your exhaust would affect), tough call over the interweb. Do lots of googling and after feeling dumber and experimentation, hopefully you'll figure it.

rjwatters38
07-10-2014, 1:33 PM
sounds like your main could be too big(which closing up your exhaust would affect), tough call over the interweb. Do lots of googling and after feeling dumber and experimentation, hopefully you'll figure it.

Thanks! it's really what I'm thinking as well, and was looking for someone to come to the same conclusion without me saying it. Gonna have to rebuild the carb anyway, a little soggy, so I'll do that and see what size is in there as is and post.

seaking
07-10-2014, 1:50 PM
ran across this in the morning, my CV is running like shit. Basically you run a new set of plugs and cut the threads off, that gives you a baseline to jet.

http://xlforum.net/vbportal/forums/showthread.php?t=642408

farmall
07-12-2014, 4:46 PM
Downloaded and followed the S&S tuning guide from their website and checked out the S&S videos on Youtube yet?

Sky
07-12-2014, 8:47 PM
Keep the 2-1, loose the super-trap. Defiantly a bottle neck at higher rpm. At least ditch that last solid plate.
Plug reading is an art form. Never have seen the cutting in practice. Plug chop yes, plug cutting , no.
Sluggish usually means too rich. Accelerator pump squirt is a big factor during, you guessed it, acceleration.
Timing is another factor. Don't forget you can tune the advance by swapping springs or shaving the weights.

rjwatters38
07-12-2014, 10:17 PM
got an email back from supertrapp, they're suggesting I add discs, or swap to one of the open end caps.

My question is, could I just cut a hole and flip the current end cap, saving myself $40? or is there more invovled than just opening up the end x"

rjwatters38
07-12-2014, 10:21 PM
Downloaded and followed the S&S tuning guide from their website and checked out the S&S videos on Youtube yet?

yea I've done the S&S tuning, but I don't have extra jets laying around, so I thought that I would investigate other options before buying new jets, see if the new hardware was causing the lag. I'm working on getting some more discs, and/or an open end cap or opening my cap up, and seeing how that rides before going to rejet the carb that was running well prior to the newly restrictive exhaust

I love doing things that no one else does just to try and figure out something new.

I used to drag and drift a volkswagon with a porsche engine. suspension set up taken from a toyota ae86 and tried to put a turbo on it before I blew the motor up.

Why would anyone do that to a 71 super beetle?

fucking because.

farmall
07-12-2014, 10:36 PM
In that case just uncork your exhaust to test then gradually add restriction.

Nottso
07-13-2014, 9:21 AM
12 disks and a closed cap is pretty small. More disks will definitely lean it out some. If you add disks, add them 2 at a time. If you overshoot, it will be better up top but get soft down low. When you're in the right range, just a few disks can make a difference that you can feel in the seat of your pants. On my particular engine, 23 disks makes max ponies up top but it loses some tq down low. 19 disks is good for max tq down low but decreases the top end hp a little. so I run 21 with a closed cap for a happy medium. Or 15 with the open cap (more on that below).

Below is the open cap that I use. ($24 at Summit Racing) The conical shape forces a lot of the gasses through the disks at cruise, keeping it civilized and the neighbors happy. At WOT most of the gasses exit the center hole and it barks pretty hard. The general rule of thumb is that this cap is good for 6 disks. For instance, as I mentioned above I run 15 disks with the open cap on my warmed up 95" Twin Cam or 21 disks with the closed cap. Dyno numbers are nearly identical either way with the open cap making just a tiny bit more up top. I switch back and forth depending on my mood or what I'm up to.

I hope this helps at least a little. Best of luck going forward.

http://www.summitracing.com/parts/sup-405-3046/overview/

49787

rjwatters38
07-13-2014, 1:16 PM
12 disks and a closed cap is pretty small. More disks will definitely lean it out some. If you add disks, add them 2 at a time. If you overshoot, it will be better up top but get soft down low. When you're in the right range, just a few disks can make a difference that you can feel in the seat of your pants. On my particular engine, 23 disks makes max ponies up top but it loses some tq down low. 19 disks is good for max tq down low but decreases the top end hp a little. so I run 21 with a closed cap for a happy medium. Or 15 with the open cap (more on that below).

Below is the open cap that I use. ($24 at Summit Racing) The conical shape forces a lot of the gasses through the disks at cruise, keeping it civilized and the neighbors happy. At WOT most of the gasses exit the center hole and it barks pretty hard. The general rule of thumb is that this cap is good for 6 disks. For instance, as I mentioned above I run 15 disks with the open cap on my warmed up 95" Twin Cam or 21 disks with the closed cap. Dyno numbers are nearly identical either way with the open cap making just a tiny bit more up top. I switch back and forth depending on my mood or what I'm up to.

I hope this helps at least a little. Best of luck going forward.

http://www.summitracing.com/parts/sup-405-3046/overview/

49787

Exact info I was looking for! thanks man. I think I'm gonna grab that Open cap from summit (where I got the supertrapp) they get shit to my house faster than Drag Specialties can get it to the dealership, and in this case even with shipping it's a good 10 bucks less than going through Drag OR directly through Supertrapp. go figure!

The biggest thing for me was the tuning, but the sound really bugged me too. Bike lost a lot of bark when I changed from open drag pipes to this set up, and I've noticed a huge difference in Cage Awareness of me on the roads. I have to really make myself obvious for them to know I'm about to whiteline past them or something, where as before they were parting the red sea like I was fucking Moses or something. I miss that.

Nottso
07-13-2014, 1:36 PM
I'm glad I could help. One thing I forgot to mention, that you will definitely want to do, is use anti-seize on the entire length of each screw. Yours being relatively new, you shouldn't have any trouble but when they get older the screws will sometimes break if they weren't anti-seized full length. It's not a real big deal as they don't break in the threaded hole, they break in the middle because they get seized to the disks. That's why you want to anti-seize them for their entire length. Every one that I've ever broken spun right out after sliding the disks off of the broken stub.