Bonneville America Forums Forums Technical Forums Performance Mods Carb questions

I'm looking to get the extera preformance possible from the relatively easy and inexpensive mods I read about here and I just don't get a few things. Needles- I understand the concept but don't understand the differences in the brands and benefits associated with each. Same goes for the shims on the needles. I also noticed when I was playing around on the new jetting calc that this adjustment would also effect you jet size. Does this also improve your mileage?

To answerer your last question, these carb mods don't necessarily improve milage... but improve the longevity of your motor by trying to keep the A/F ratio ~13:1

The needles have different tapers and lengths effecting the flow of fuel. It is mostly from about mid range on. The shim moves the needle up so it allows the taper to effect the mix sooner, this is often the way to fix a mid range flat spot.

I've been contemplating over the different needles vs pilot jets sizes myself lately, and it's hard to wrap my head around it.

So, let me see if I have gotten this right. If have 42 pilots, and have a flat spot in the mid-range, I can use a different needle to fix it, like a TBS or thruxton, or I might shim my stock needles. I could ALSO keep the stock needles and go up on the pilot jet and the result would pretty much be the same? Same result different flavor?

Or could changing the pilot end up making you to rich when idling, but be perfect in the mid-range, so to fix just the mid-range you swap the needles, and low end with the pilot, and the top end with the mains aren't that much affected? (I now they are affected but perhaps not my THAT much…)

Sorry for the thread-jacking but I but thinking about this much lately.

Understanding carbs is about like understanding women.
SOME SAY they understand them, and can achieve the perfect set-up, but I think it's just that THEIR carbs LET them THINK their on top of it!

The pilot adjustment won't fix the mid range flat spot but the needle will. The needle adjustment may effect the pilot size though or at least the pilot screw adjustment. I saved this when it was posted here before to help people understand when explaining this. The pic should help you understand at what point each carb part is in play and how they interact.

Sounds like I need a pro

No you don't need a pro at all. Just some time studying to understand your machine a little better and some time playing with it. Remember to change one variable at a time so you know what made the desired change. You'll get good advice from this forum.

I know that more amateurs F-up their carbs by trying to tune them, spend COUNTLESS hours trying to correct what they did, and end up going to the pro's for corrections, BUT THATS HOW THE PRO'S GOT STARTED!

Remember how difficult your first auto transmission rebuild was?

Check out this sight.
It shows step by step and where to start.

http://www.factorypro.com/tech/carbtun.html



.

http://dinqua.com/Triumph/carbs0.html
try this one as well.It makes it LOOK easy enough anyway.At least the mechanical part of it anyway.Still seems like voodoo to me to figure out what you need.

Now I've never rebuilt a trans, but I'm gonna have to say carb work on our bikes is easier than that. I'm not talking about changing cfm's for the guy with boring out his carbs. Just switching jets and needles and maybe a shim. I agree there doesn't seem to be any exact science. But with dinqua's site and hopefully some good advice from those that know more than me he could tweak a few more lb-ft and hp out of that twin.

Yep, that REALLY helped.
Lets see,
1. Select the best main jet. Ok?

2. Select the best needle height/clip position.Ok?

3. Adjust the best float height. Ok?

4. Then dial in pilot circuit. Okkkk?

THATS IT!

Well dang!, What was I thinking? BRILLIANT!

Now IF your wondering just WHAT the BEST is, they have that covered too;
"If your not sure which main jet is correct, use the one that is FOR SURE NOT INCORRECT"

WELL DANG! What was I worried about!?

(BE SURE TO GET THAT TECH. PHONE NUMBER. YOU'LL NEED IT.)

Jetting is trial and error, that's what makes the jetting calculator such a great thing. Thanx Pat. The calculator gives you a good place to start that is close if not on the money. Then the best way to finish up is to put your bike on the dyno to dial it in.

B0S24-"The tuning really needs to be done out on the road, or at least on a dyno & fine-tuned on the road. The A/F meter is great."

erle,,,,,after 1200+ posts, you finally come around,,,,hooray! People have told me that its hard coming out. congrats!

Cause i do have an "Innovate" AFR meter with individual sensors on each header, monitoring each lung, being able to record idle, cruise, WOT,,,,everything.
Other websites suggest the same steps. Mains 1st, needles 2nd, pilots 3rd. Float levels aren't mentioned except on http://www.factorypro.com/tech/carbtun.html


This post http://www.bonnevilleamerica.com/forums/...ge=0#Post456262
shows realtime graphs of my setup that i'm running now.
Cruise speeds run slightly lean, nail the throttle brings it down to the performance AFR ratio's.

Pats jet calculator is a geat starting point. Main jets are spot on if not 0.5 rich.

When you dyno your bike have the person record your idle, 30 mph cruise, 60 mph cruise and WOT, Air Fuel Ratio's.
10 seconds each besides WOT
Idle and cruise AFR's will help ya on needles(shims) and pilots (and the "closet" float level)



I have one more adjustment to make and thats to balance the carbs. I invested in vacuum sensors that plug into the "Innovate" system. Once completed the whole setup (headers, sensors, the works)will be available for other members to perfect their bikes with

Did you catch the part of Chris's post about "relatively easy & inexpensive mods"?

What was the total bill for the AFR meter, sensors on each header, vacumn sensors, and the time & cost & labor involved?

Post that info., along with YOUR experience level, to Chris and lets see IF HE thinks thats what he considers "easy & inexpensive".

How about it Chris?

.

Jeez cwildman, just ride on up here for NorEast Rally in September, about 200 miles from Chocolatetown, and we'll dial her in for ya for a few cold beers fetched from the coolers.
Ok? Easy enough?

So I started with the suggested settings from the jetting calc. and played around for a bit on the road with different settings. Stopped the popping on decell and definately got a little more WOT responce. The mods ARE relatively easy and inexpensive. It's wrapping my mind around the tech thats the hard part. As far as the hours involved, I wouldn't ask if I didn't want to learn, and I am definately learning. Thanks to most for the help.
Cheers

Where can I find details about the rally??

Nevermind. Found it.