Bonneville America Forums Forums Technical Forums Performance Mods Shimming vs jetting

I am currently running open Harley pipes and 130 mainjets to tide me over. Runs fine too! But I have a jetting kit I still haven't used by "6 sigma" the kit wants me to shim the needle and use a 115 120 or 125 mainjet depending on what my bike needs (supplied all 3)

Could someone explain the difference between these 2 approaches and what is the benefit of the race kit over just jetting?

My airbox is stock btw the kit still suggests doing it this way. It has setups for airbox, pods, and airbox removed snorkel
Thanks in advance

Does it load up/pop when you go to dead throttle slowing with the clutch out or downshifting?

If so I would leave the 130s and put a larger (45) pilot in and turn out the AF about 1 full turn.

There is a jetting chart in the tech vault that may help you.

web page go to that site tons of info on jetting all about your bike!! "look at the different links" about carbs and jetting..

he is a member and mod on this form..

Ed

It runs fine as is!
I'm purely curious why a professional racing kit has adjusted the needle when it's obviously not necessary. Does raising the needle aswell have a effect on performance

Needles are taped and go through the main jet so if you shim the needle it is setting higer allowing the thinner portion of the needle to be in the orafice of the jet. Causing it to run richer through out the throttle range until the needle is removed completely from the jet opening then you are at what ever the jet is.
Having a larger jet will result in the same thing as it will allow more fuel through the space between the needle and the jet the difference comes in when you are at full throttle and the tip if the needle no longer effects the amount of fuel that can flow. In this case you will be running richer at full throttle than with a smaller jet and shimmed needles.

You should adjust the pilot screw the right way not any predetermined amount of turns.
A larger main doesn't do the same as shimming the needle. a larger main will allow more fuel through it. Shimming the needle increases the amount of fuel at a given slide lift point as a thinner part of the needle is in play at that point.

In many cases a lean bike will run great, fantastic even right up until you burn a valve.

So which is better? On one hand I have a kit with instructions telling me to shim the needle and then step by steps on carb tuning and the other I've got a forum full of folks who all swear I just dump in a 130 main adjust the mix and that's it.

Really I just don't want to fit this kit if it's not neccasary and I don't want to bugger up my valves at all. Im thinking really id better bite the bullet and fit the kit and doing a side by side to be sure.

Thanks for your input guys n gals I appreciate it :-)

fwiw Proper jetting procedure is to start at the top and work your way down. Dial in the main first. Then the midrange. Then the pilot.

Have you looked at your plugs? That's one of the first steps when you start dialing in your air/fuel mix and an easy indicator of lean/rich conditions. Generally speaking, shims help tune out dead spots in your throttle response while main jets or needle taper affect the overall performance. If the bike is running fine and the plugs don't show a lean running condition I'd happily leave everything alone.

You can't think of it as one being better than the other you do the adjustment you need. If you are jetted pretty well but have a mid range flat spot you probably need a shim under the needle or a different needle.

I wouldn't have said I had any issues but fitted the kit anyway and. Ow tuned it's a fabulous improvement. More power across range top end remains the same as expected seeing as the jets I used were same size as I had just labelled differently.

Well with the effort shimming and recalibrating everything again.

i am basically running same pipes harley shorties,snorkels out k&n filter im about 1500 ft above sea level,well I tried 45s/135s 42s130s shims in shims out 1 and two at a time and several different variables and many trips to this sight to beg for help..lol long story short I stuck with 132/42 no shims and it runs great,when its hot if I twist the throttle she will backfire so i just dont do it she starts great anyway.Everytime i changed the jets out which is timeconsuming I took her for a ride at normal temp cranked her on pulled the clutch and killed her.Pulled the plugs and checked I went from white to black and now im running brownish tan.I always pulled both because i had to tweek both sides.Now im waiting on a carb balancer to get her as close to right on as my newbie mind can handle.My next step is a freak kit so i will do it all over again.I would like to dyno it but im 9 hrs away from the nearest one and its in the biggest city in canada and I like country running and to haul it I drive an 81 ford 4x4 so its out of the question Id be like crocodile dundee down there, so I rely on the old hands and they have never steered me wrong. I apoligize for babbling on but i live in the boondocks of northern ONT canada and I dont get to talk to many people about my beloved triumph speedmaster.very few and far between up here!
07 speedmaster
harley aftermarket shorties
K&N single
132/42 thumb screws(a must I must add d screws suck)
custom leather saddle,temp/oil guages another must I dont trust idiot lights with my baby
barks like a dawg/purrs like a kitten
Mac

Hello Northernmac,I ride a 07 TBA and just drilled the airbox.I'm running short TORs,all snorkels removed, K&N filter.I had 130 mains & 40 pilots & stock needles/no shims.It ran great before drilling the box, but was a little lean on start-up and part throttle, now after upping the pilots to 45s, my air mixture screws have no effect when turned all the way in!Think I went to far with the 45s,going to try 42s and see if it helps.But I do believe drilling the airbox made a differance!Bike even sounds better!

Sorry about not replying earlier ive had some strange electrical issues to deal with.

My bike (original poster btw) has now got harley open shorties and snorkel out. And I've learned ALOT since my original post.

It's absolutely spot on for performance thanks to some great advice to help fine tune the setup. I'll save you some of the messing about and tell ya what I'm running as a starting point.

132 main jets with 2 metal shims on each needle. I didn't think it needed the shims but boy was I wrong. Made a huge difference.

Stock Pilots are out exactly 3 and 1/8 turns.

My springs have about 3mm trimmed from them also which made the bike much snappier in response which I quite like but it won't suit everyone so be carefull

Very very occasionally if I crack it open i also find it will pop and then Proceed to accelerate like a frickin banshee! Not entirely sure why but I'm about 90% sure it's a leak in the system that under hard vaccum aka fast throttle opening is allowing air in but is otherwise sealed. It's either that or my petcock or filter isn't actually allowing a fast enough flow of fuel. I've had all the valves checked both myself and by a trusted mechanic friend.

Thanks for your input fizzyhair,I'v got shims & 42 pilots on the way from fasteddy.Going to leave the 130s in for now and see how she runs, easy enough to to replace the mains later if I need to!Thanks again!