Bonneville America Forums Forums Technical Forums Performance Mods Carb advice requested -- Jets and Needles

Thanks to this site and to those that have created good "how to" sites, I am starting to better understand how our bikes are put together and how different mods affect different performance attributes...However, I still have a few questions.

First, here is the set up on my '03 America.
- Air Injection is gone
- Freak Installed
- Running completely open (no baffle/packing) Off-Road Shorties
- 155 Mains installed
- Carb screw at 3 turns

I talked with the mechanic that originally set up the bike and he isn't sure (I am checking today) if he installed shims for the needles. Not sure of the size of the pilots.

Before the Freak install with 120 Mains, screws at 4.5 turns and everything else above the same, I had very good performance and almost no decelleration sounds (popping or gurgling). After I installed the Freak kit yesterday with 155 Mains, and screws at 3 turns I now am getting moderate gurgling on decel.

I went by the shop yesterday and talked with the mechanic about his suggestions. He said that I should check to see if there are shims installed (he couldn't remember if he had shimmed or not). He recommended that I remove any shims that may be present and give it a try.

My confidence in him is very high and have no complaints at all about advice he has given in the past. However, he is a Triumph Dealer Mechanic and my guess is that this isn't something that he is asked to do day in and day out. If nothing else, I am trying to build my knowledge.

So first, any opinions on tweaks to this set up to get the most out of her and to "clean up" the gurgling? I have been reading more about shims and needles and it appears that a few of you are going with Thruxton needles.

What I can't seem to find (or comprehend from reading lots of posts) is cause and effect related to needles, shims, and pilot screws. For example, if shimming adds more fuel (more rich) what is the impact on things like gurgling, power, etc. Also, am I correct that turning out the screws adds more fuel (more rich)?

If the above is correct, and I assume that popping/gurgling is a sign of being lean, then removing the shim (if there is one) per my mechanics recommendation seems to be going the wrong way.

I greatly appreciate any pointers or thoughts that can be offered.

Thanks,
Steven

Take a look at the "test ride in january" thread. I am having the same issues basically except that I run TBS needles, no shims. I am thinking you are correct in assuming removing the shims would be going the wrong way. Ron suggested goung up to 45 mains (or is that pilots? I always forget).

Tsk, tsk Benny. 45 mains?

I'd try upping the pilots to 45 first.

Semantics...

yeah, sounds like wierd advice to me. removing shims would make it leaner, and what i've always found is that when i'm getting popping, enrichening the mix always removes that problem. And if it doesn't i go even richer till it does. And i also tend to find that at the point it's rich enough to eliminate popping it's also at or close to it's ideal mix because if i go any further it usually doesn't help add any more power or even farts out. And with the freak your needles should be shimmed w/o a shadow of a doubt. In fact i wouldn't hesitate to pass on shimming and go right to thruxton needles which are quite rich w/o any shims. Then you could shim them if necassary, but i don't think you'll have to.

after changing my needles to Truxton needles i gained much better performance than stock ,throttle response was much better and the speedo needle climbed over those numbers much faster than before.

My setup is
125 mains (but needs more like 130s or 135s)
45 pilots
thruxton needles(with 1 shim)
modified stock airbox
modified stock pipes
air injection removed
just installed 18 tooth sprocket (makes a big differance on the open road)

I guess I'm close to Phil's set up. Specialty Spares long slash cuts, 130 mains with 45 pilots, 1 shim (all came with the SS exhaust kit). No AI, stock airbox but with UNI filter. Just changed Saturday to 18T sprocket and rode 2-up yesterday. I am amazed how much the one tooth change made. 1st is still fine, but now I have an overdrive and no looking for "6th".

I went back to 17 teeth since I missed the oomph at takeoff with the 18, especially when riding two up. Maybe now with the Freak installed I can go back. 400-500 rpm less is quite a relief at highway speeds.

I immediately noticed some loss of quickness in fast take offs but hated looking for a 6th gear. No doubt either is a compromise. But with better exhausts larger mains/jets and less restritive filter, the bike handles the higher ratio fine. I don't think it would be smart to go up from 17T with a stock bike. I need to ride more to get the feel but I think the 18 will be the best comprise for me. The added plus is better gas mileage - especially for highway riding.

Popping on decel (throttle closed) is from too lean mixture screws or pilot jets. 3 1/2 turns is max, then go to next larger pilot jet and start over. Needle choice/shimming is for midrange tuning. Not an expert, everything I know I've learned on these forums, but when I turned my D-screws out 3 1/2 turns, popping on decel almost dissappeared entirely. Waiting for 45 pilots now. Someone smarter than me said to change only one thing at a time, or else you don't know which mod did what.

As an update...
I took the top ends of the carbs off this evening and indeed, they had been shimmed. Since they were shimmed and my mechanic had suggested that I remove the shims if present, I decided to give it a try.

I let the bike warm up and then took it out for a VERY brief test. My initial reaction was that it felt stronger than Saturday and my gurgling had been reduced. It's a bit chilly out tonight so I kept the ride very short. I did get one good Pop, but I really need to take it out for a better overall test.

My next step is to take some time for a real test and try to compare it against what I heard and felt over the weekend. If I am still getting strong gurgling or popping, I'll first try 1/4 turns (out) on the carb screws and see what changes.

Knowing now how easy it is to get to the needles, I am going to see about getting a pair of Thruxton needles so that I can compare and contrast them against my stock needles.

By the way, who sells the Thruxton needles? I assume that I can get them through my dealer...

Thanks for all of the help and advice,
Steven

You can get needles from your dealer. I would start with the TBS needles however. The Thruxtons will probably be too rich.

Thanks bonnyusa...I suspect that needles aren't too expensive so I am going to see if the dealer can get me a pair for a TBS and a pair for a Thruxton.

I'll take the advice and start with the TBS needles once I get them.

Again,
Thanks,
Steven

They should be about $12 a pair. Best cheap investment ever.

Ok, I'll toss in my 2¢.
Read this CV tuning guide it is very well written and can explain how to totally dial in your carbs.
Just remember, use throttle position, NOT RPM or speed to adjust with.

And who's got that great little chart "Where the parts do their parts"? That is a nice graphical map and you can use that once you figure out the dynamics of these carbs.

Is this the chart you mean? Funny, I lifted it out of one of your posts. This was the first time I had seen it described graphically...a very nice visual on what does what and when.
Steven

Thats the one Steven, a great reference tool. (Can't call it a guide as some may be offended)
Notice the three curves related to the needle - position (shims are our positioning tool), Taper (check the stock/TBS/Thruxton side by side and you will see huge differences in the three. The diameter is also different at differnt places. So, shims and needles will give you a lot of wiggle room for almost the entire throttle range - at least the parts we use 99% of the time. Now can you see how needles have a dramatic effect? Simple things are sometimes the simplist answer.

I see the instigator has awoken again...

Where ya been Pat? Didja' finally go on a honeymoon? Or did your new bride take off the leash for a bit??

Where's that pic you took of all the needles we had last year? That sucker was a great one. Get that posted again!!

Never mind. You're probably face down in a pool of Schlitz by now so I found it.

Check this out guys and feel free to discuss: