snorchel removed, main jet ? - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 21 (permalink) Old 11-23-2012, 05:20 PM Thread Starter
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snorchel removed, main jet ?

Hi,

did already some work on my jetting, can somebody please tell me the baseline in jetting (main jet) just for removed snorchel and aftermarket exhaust with baffles. Airbox baffle is still inside, will not take it out for the moment.
thx
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post #2 of 21 (permalink) Old 11-23-2012, 05:47 PM
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122-125 mains would be a good starting point.

Mike (UK)

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post #3 of 21 (permalink) Old 11-23-2012, 05:53 PM Thread Starter
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ok, thank you very much
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post #4 of 21 (permalink) Old 12-01-2012, 04:31 AM Thread Starter
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my jetting is completed now and i will tell you the results.

2002 Bonneville 790, 42 pilots, 2 full turns idle mixture, 125 main jets, stock Bonnie needles 2 shims = 1mm, drilled slides-hole 3mm, stock carb springs, restrictor still in the box. Italian Shark exhaust with baffles, AI removed.

Before rejetting I had some cold run issues, hard starting coughing an farts and a very long choke time concerning cold starts. (lean)
As I know a long time ago, the best way ist doing one thing after the other.
So first I was looking for air leaks in the intake section. This was ok.
Then next step was turning the mixture screw 3 full turns out with the stock 40 pilot jets. This was already 70% of the solution. At least I had the same results with the 42 pilot jets and 2 full turns, but around 3000 r/pms the bike is running better wir 42 pilots. (those are my old Harley pilot jets, everybody is changing there to 45, but main jets from Harleys Keihin will not fit) Coughing while fast opening throttle was almost gone. After shiming the needles with two shims, ist was completely gone. (perhaps I could remove one, will see) After opening the vacuum section I saw the results of backfiring an coughing, the black dust beside the needle hole ist the result of misfiring due to to lean conditions.
Then I had different test rides with cutted carb springs (1,5 turns cutted) as recommended in the german thruxton-forum, drilled slides and undrilled slides.
With drilled slides, removed snorchel and stock springs I can feel a totaly different bike - I´m very happy with the results.
Drilled slides and cutted springs together will only work with restrictor removed, (airbox vacuum conditions are different) Drilled slides + cutted springs are moving in my configuration to fast, and mid range is to rich. So I went back with stock springs and now I´m on the point.
The recommendation from Pie Man for main jets was 100% correct.
My first pilot jeting 40 and three turns out worked already very good !! Stock conditions, no other things to do
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Last edited by DéDé; 12-01-2012 at 05:02 AM.
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post #5 of 21 (permalink) Old 12-01-2012, 05:07 AM Thread Starter
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carb

forgot to tell you that I polished both slides for improved slide-moving and throttle response, pilot jets fom Harleys Keihin CV
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post #6 of 21 (permalink) Old 12-01-2012, 02:02 PM
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Did you remove the restrictor plate?
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post #7 of 21 (permalink) Old 12-01-2012, 03:42 PM Thread Starter
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no, restrictor is still in place
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post #8 of 21 (permalink) Old 12-30-2012, 08:36 PM
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What/where did you drill the slide ? Why ?
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post #9 of 21 (permalink) Old 12-30-2012, 08:54 PM
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Definitely remove the plate. It's night & day in terms of airflow.
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post #10 of 21 (permalink) Old 12-31-2012, 02:31 AM Thread Starter
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Quote:
Originally Posted by STANIMAL View Post
What/where did you drill the slide ? Why ?
This is very simple to answer:
after changing jets`and tuning mixture screw my idling was fine, but when I tried to open throttle a little bit I still had some caughing and backfiring, not much, not often, but sometimes. When the bike was warm, I didn´t had that at all. The problem was generaly solved.
As you can see the slides in the pictures, they suffered a lot from lean mixture. So I drilled the side holes (holes beside center holes) up to 3mm.
This allows the slide to move a little bit faster upwards, an allows higher lift of slide with throttle is already a little bit open.
From my other an earlier bikes I know very well how this carb works.
But drilling the slides is not good if you do not raise the stock needle at the same time. Drilling slides only do cause a leaner condition at lower rpms till the taper of the needle begins to work.
So I had to shim the stock needle up to 1mm, 2 shims, perhaps a thruxton needle doesn´t need that or only one shim.
At least you can say, the drilling and shimming makes a better Throttle response an eleminates my caughing completely, also in the time when I´m running with choke.
But let me tell you again one thing:
70% of solving those problem is not drilling the slides or raising needles: It is the correct tuning of the idle mixture screw. Bought my bike a few months ago with 30k miles on it, completely stock, carbs never touched. And my bike ran first time correctly with those screws 3 turns out (40 pilot jet) or 2 turns (42 pilot jet). I cannot imagine if there is any Bonnie in this forum with (40 pilot jet) 2,5 turns out + open pipes and uni filter running correctly in lower rpm´s at sea level.
But as you can see, I still had sometimes with that enriched slow circuit some caughing while warming up. Ok, I could have been riding like this, test ride was done and everything was ok at the moment the engine was warm. With drilling and shimming I eliminated this caughing completely. But be careful, caughing can also be caused by air leaks in the intake section, check this first before starting any other changes. Running without or with snorchel hadn´t had any influence of the slow jet circuit at all, bike was also with snorchel too lean
I would strongly recommend to do settings of idle mixture screws and choice of jets at first before any other changes, and do always one thing after the other and make test rides. After changing exhaust and pulling snorchle follow the major recommendations of main jet sizes here in the forum.
If you´ve finished all changes go to the dyno and see results while controlling AFR.

Last edited by DéDé; 12-31-2012 at 02:39 AM.
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