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Discussion Starter #1
I read your archived threads and man is that some good info ! you are indeed the best speedmaster guinia pig ever ! :-D You've tried it all it seems. But i have to ask.....you seem to have said that with stock needles that 130's worked great, but that with the much richer thruxton needles that it was better with 125's. Do you still believe that, and what would you do with the mains in my setup.....

130's
thruxtons, no shims
stock pilots
3-1/2 turns
UNI very lightly oiled
no snorkel
bottom of filter/airbox drilled to same size as top opening

Would you go to 125's? I had 125's in it with heavily shimmed TBS needles but went back to 130's and it felt stronger. But since then i went to thruxtons wioth no shims and it seems a bit rich but just short of running faulty. (bogging,stumbling etc) So i have no experience with 125's while the thruxtons were in. Would you think the 125's would definatly be better or just THINK they probably would, and in what ways?
 

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daz - I have an '03 T100 with Thruxton needles, Unifilter, no snorkle, AI reomved, 42 idle jets, 1 turn out on idle mixture adjustment, and Norman Hyde Togas. I am running the stock (110) main jets. I think I might still be a bit on the rich side, although the midrange is much improved from the stock needles and 120 jets I was running. If you were jettted right with the stock needles and 130 main jets, I would think that 125s with the Thruxton needles would be way too rich. The Thruxton needles are a lot thinner and more tapered than the stock ones. Hope this helps.
 

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Discussion Starter #3
Thanks Bill, but my 05' speedy is actually quite different than the bonnie. It's jetted pretty close with 130's and thruxtons but just a tad rich in the middle i think. (not 100% sure tho) It runs 120 mains and needles that aren't that far off from thruxtons as it's stock setup, so with all my mods it's definatly not way off. But as i said i think it's a tad rich and wondered if the 125's might be better with the thruxtons as WA53JHO seemed to think at one point in a very old thread. i'm not having a problem with how it runs, as it runs quite nice. I just don't want to be missing a drop of power, and not having run the 125's with the thruxtons has me wondering if i should put them back in after reading those archives.
 

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Daz

Thanks for reading the archives.

After a lot of playing around I found big mains on my 790 Speedmaster gave good strong mid range up to 135 mains with STD 03 SM needles various shims/

With Thruxtons and larger than 125 mains I found the strong mid range was still there but too rich at low rpm and heavy feeling WOT from @ 3000 rpm with shims fitted.

130 mains and above with with Thruxtons on a long run with the engine thoroughly hot, mid range response suffers with the engine more dead about 4000-5000 the larger the main jet.

All my settings have been finalised with the bike setup as :-

790 Engine
Short Slash-Cut TORs
No AI
Gutted Airbox and hole through UNI
Std 16 tooth gearing
3mm hole in throttle slide
std 42 idle jets
2 to 2 1/4 turns on idle screw

I find that in general my bike responds the same with Thruxtons + 0 shims as STD + 2 shims
Std + 0 shims and 135 mains great mid range roll on acceleration strong from 2000 in 5th gets sluggish about 4000 loses 10 mph top speed
Std + 2 shims and 130 as 135s but better top speed
Thruxtons + 2 shims and 135 needs gear changes to get engine revving high in 5th but when it's above 5000 pulls strong still loses 10 mph
Thruxtons + 2 shims and 125 mains engine feels quite lively and cleaner running pulls nearly as strong as 130s in mid range but nothing pulls top speed the same as 120 mains.
Thruxton no shims and 120 will pull to just under indicated 120 mph with this main jet but mid performance is about as bad as standard from manufacturer.
I find the best overall setup on my bike is 125 mains Thruxton needles no shims (I find these needles tend to make my bike splutter just off idle and have to lean the idles in slightly to 1 7/8.)
Because of this slight low end richness I would also go with STD needles 130 mains and 2 shims and forget about the top speed because it gives very slighly better tractability at slow speed.

Any of these settings must be about rich enough for my particular bike as it will choke up as soon as I put the STD paper filter in with its closed end.

There's something else to be done in order to make the bike respond better to full throttle from very slow revs as there is a lag which I have never been able to get rid of and is probably due to the CV carbs. Slightly less of a handful gets rid of this and it's definitely a lot better than the breathless feeling the engine had when new and untouched.

Speed increase is not the target for me as the bike won't go faster with these sort of mods but throttle response and the ability to overtake as quickly as possible with the least hassle and fewest gear changes certainly is.

I always know when my bike is setup OK as it feels like it wants another top gear and starts to spin the rear wheel in 2nd at 40 mph with a handful of throttle. The engine always feels a bit dead just below 4000 rpm in top and nothing I have done gets rid of it other than changing to 4th. I'm a bit heavy at I guess at 245lb and 6'2" so I probably need a bigger bike.

Hope this helps.

:hammer:
 

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Daz

God I'm tired.

Read your post again.

My bike's a 790, different to yours.

What I would look for is

If you keep trying for a 6th gear.
The acceleration makes you grin
The rear wheel tries to spin in 2nd and 3rd
And it picks up clean from idle you've got it right whatever settings you use.

I keep going back to Thruxtons + 0 shims and 125s as the best compromise for my 790.

I do wonder if you are rich on the idle screws as with Thruxtons I have found a tendency for low speed richness and the idle screw will affect almost 3/4 of your throttle range to some degree. If it starts good with idle set at even 2 turns out leave it there and see what the effect is.
 

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Discussion Starter #6
Thanks. I may have to read you first post a few times ! theres just so much. But good info never the less. Of course your results may vary just because it's a 790. I tied 2 turns but it seemed as tho more turns was better. maybe i'll try that again tho. I'm also going to try going back to me previous setup (TBS needles with two .5mm shims and another thats about .7 mm...a washer i got from a hardware store, so equiv. to about 3-1/2 shims) and see how it feels now that i'm familiar with the thruxtons. (TBS are longer and need shims to make em the same length as the stock and thrux needles) I always find it's good to go back and check because it's easier to tell once you're familiar with both. The thrux with no shims is similar to the TBS shimmed but seems to have better pull off the line. But the TBS may have been better in midrabge roll-ons. But going back to them will tell for sure. The mains are another story. The difference between 125 and 130 seems to be more of a smoothness and exaust sound change more than performance, but the 130's *may* be a hair better in performance. the hard part i guess is the interaction between the needles and mains. There are so many combinations as your findings show. So for all i know i WILL see a considerable difference in mains in the right combination with respect to needles. Thanks again.....very informative.
 
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