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Discussion Starter #1
My results from Saturday. This is a stock engine Thrux, with airbox delete and dominator sports with no crosspipe on the headers:

1st set of 3 runs:
Mains: 145
Pilot: 42
Shim: 1

2d set of 3 runs:
Mains: 150
Pilot: 42
Shim: 0 (see the severe rich condition at low rpms and how this improved by about 1/3d when I removed the shim?)

3d set of 3 runs
Mains: 145
Pilot: 42
Shim: 0

Ten and I are thinking that I need to find a longer needle. I noticed that Dynojet has an adjustable needle which would seem to be ideal.

Input from the nut gallery?

Thanks...Jack
 

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I have a dip at the same position you do - though not as severe.

I am surprised at your numbers to be honest - I would expect higher power with the airbox removal.

If I understand what I have read correctly (no gaurantees there) then I would think that needle needs to be lifted some more - another shim maybe? The 150 main looks right doesn't it? from an a/f point of view.
 

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Discussion Starter #3
I lowered the needle by removing the shim for the second run, which leaned it out at low range and improved the throttle response noticeably.

Got to confess it seemed counter-intuitive but there you go.

Also surprised by the low bhp numbers, which maxed at 54.

Jack
 

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alot of that rich dip at low rpm comes from drilling the slide holes out the slide opens to fast at low rpm.Once it gets past that point it looks good all 3 runs are rich enough on the main maybe to rich even only max hp numbers can tell you that did you run it with a 140 main? if so what was the max hp?
What i would play with to fix that dip is get some extra slide springs and strech them alittle to give it more spring pressure so slides open a little slower thats about all you can do with the slides drilled. You would of been better off putting dyno-jet lighter springs in. if the slides where opening to slow (not all of them are) what the shims do is richen it up in relation to where the side is .if you make it leaner with shims it will be lean from idle to around 3/4 throttle not just in that one point where your trouble is.Hope that makes since to you.
 

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You can probably revert back to the original hole size if you fill in the hole in your carb slider with JB weld, and then drill it back to the original size.

Alternatively, keep an eye on ebay, I have seen quite a few pairs of Bonneville stock carbs go up for sale fairly inexpensively.
 

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Discussion Starter #7
Bigger pix. And I didn't drill out the slide hole; not sure where mikeinva picked that up.

Last 3 dynos:


2d set of dynos:


1st set of dynos:
 

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Discussion Starter #9
Hey Sito how much does the dynos cost?
His price varies with how much he does with the tuning but he has more knowledge and gear for efi than carbs. I paid $100 for the 3 hours we spent on the 9 runs and changing jets twice and shims once.

I'm not that fast on taking those bowls off... :D
 

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so what did you end up going with?

the 150mains 42 pilots with no shim..? @ 51hp

or the 145mains 42 pilots with 1 shim @ 154hp even though it was too rich down low?

im about to try 150's in my bike. i dont have a pair of 145's just incase. im thinking that my setup will be ideal

i have the same zaust and no box
 

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Maybe you should consider going back to the stock 40 Pilot jet to avoid the over-rich low end?

Just a thought.........

V.
 

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well if you look at the run it dont have that lean dip till he wacks it open I dont know pilots might help some but you can turn the screws in and make up for the big pilots ,Idont think its pilots but worth a try.Ibet if he dynos it with 140 mains the hp will go up alittle that dip is in the slide opening though.More spring pressure might cure that.
 

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Hey sito is your clutch set up right? Would clutch slip explain the low power numbers? Just a thought. $100 is a pretty good price for the runs you did. I paid $60 for a baseline run, and follow up runs are $40 each.
 

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Discussion Starter #16
The last 3 runs is with the 145 mains and no shim (42 pilots).

I went up from 140 mains b/c they were causing a massive flat spot at about 65mph, warm engine. With the 145s it went away.

Hadn't thought about changing the pilots. According to this chart from Jenks, the pilot jets should not come into play. Not sure what to do; I'm at low rpm but WOT; it's the "spool up" or throttle response that's suffering.



I remember hearing about a shop in New Braunfels or San Marcos that offers a full service dyno and tune. If I get obsessive over it, which is only partly likely, I may drop the $400 to get it sorted.

Clutch is a good thought? I do get a little shudder when starting off in a gear too high but do not experience the de-clutch when hitting it in a gear too high so I would probably rule that out. It's just damn rich and you can hear it bogging as it spools. Got better when we took the shim out.

Thanks for all the responses so far...Jack
 

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Discussion Starter #17
looks like 150 mains with no shim is the best run a/f wise. How does it feel with that combo?
I couldn't tell the difference but Ten recommended that we go back to the 145s, stating that my bike liked to be lean. It did make marginally better hp and torque with the 145s but not a statistically meaningful improvement.

In general, though, I thought that you wanted to set your bike up so that it was as safely lean as possible to make as much hp as possible.
 

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Discussion Starter #18
I have heard something about the needles wearing out on thruxes after as little as 5k miles.

Thoughts??
 

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did you do a dyno run with the 140s ? you need to get the mains that make the most hp (pull the best at high rpms )before you try to get the bottom right.You can be to rich and it will feel good on the bottom but not be as fast. You allso need to run it at steady throttle opening say 2500 rpms 1/8 to 14 throttle on the dyno to see what the mix dose if its ok like that its all in how fast the slides are opening.If its not then play with shims and pilots.The butt dyno can fool the hell out of you.All you can feel is ft/lbs the only way you can see hp is on a dyno or on the stop watch.Where hp comes into play lets say your bike makes max hp at 7000 rpm when you speed shift it at 7000rpm if it drops to say 6000 rpm with one main jet setup and 6500 rpm with another the one that drops to 6500 rpm is making way more hp.
Nows lets look at ft/lbs say you slam the throttle open at 3000 rpm with 2 main jet set ups on one of them it picks the front wheel up and the other does not the one that picks the wheel up makes more ft/lbs although it runs out of power at top rpm more then the other.
looking at your dyno charts the fuel mix at max hp didnt change much going to the bigger jets so you need to try going down on jet till you see it go leaner say 13.5 to 14to1 and watch the hp number see if it goes up or down when it goes down you need to go back up 1 size you will be real close then.Hope that makes since to you.
 

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Hadn't thought about changing the pilots.
According to this chart from Jenks, the pilot jets should not come into play. Not sure what to do;
The reason I mentioned Pilots was that I recently fitted 42's to my bike.
With the aid of the A/F gauge I have, I can see the effect real-time while I ride.

The only area where they make any substantial difference is at lower speeds as you start accelerating thro the lower gears
i.e. during around town riding, as revs start to increase, but at lower throttle position.
They made the difference between being at about 13.5:1 (with the 40's) to being much richer at 12:1 (with the 42's) under these conditions.
They obviously also effect the idling mixture, but that can be adjusted out with the screws.
They have NO effect, as you would imagine, at higher speeds, revs and throttle positions.

I'd be a little wary of quoting that graph as the absolute answer to our carb set-ups.
Its an excellent guide, dont get me wrong, but in the experiences Ive had it doesnt show with whole accuracy the range of
effect of main jet, pilot jet or idle screw has.

V.
 
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