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Discussion Starter #1
I sent this email to Thunderbike and this what they had to say. Read on.

From me:

Hello,

I have a set of your TB slip on mufflers on my 2006, 865 Scrambler. I have a simple jetting question that you can hopefully answer.

I have been running the stock carbs and no airbox with K&N pods for 2 years now.

My current jetting is: 40 pilots, 2 (.5) shims, 2 1/2 turns out and 152 main jets. This set-up seems to be ok, but maybe slightly lean. It was leaner when I was running 150 main jets. Everyone tells me the mains should be around 135s. I’ve tried this and it was terrible. I ran 130’s when I had the airbox on the bike.

I recently went up to a 155 main just to see what it was like and it felt even better, more power. Do you know if jetting this bike with 150 mains and above sounds about right with the slip on mufflers? It feels right. My plugs are clean, too clean really. I have no leaks anywhere. Do you have any exact info on jetting for the set-up I described? And lastly, does the full TBP exhaust system require a leaner set-up?

Thank you in advance.

Todd

From Thunderbike:

Hi Todd, Thank you for your interest and enthusiasm for our products we do appreciate that. As far as an exact setting for your bike is concerned we do not have any info for that I'm afraid. The set up you report with the airbox removed sounds just about bang on to me as you will find, as we have done in the past, that the airbox elimiation kit suppliers usually supply 150 main jets with them. I did feel initially that they were waaay too large but testing proved otherwise.

I should mention that the motor performs most effectively and happily in what we might consider the 'weaker' end of the mixture scale. A good piece of combustion engineering is evident in its behaviour and mpg etc.

To answer your final question I do not recall any significant changes being required for the full system either (from what you currently run)

I hope this helps put your mind at ease.


Best Regards
Graeme Lawson
Thunderbike Powersports Ltd,
PO Box 674, 29 Bolt Rd
Tahunanui
Nelson
New Zealand.
 

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Hi Malibu,
I just bolted on the BC Customs Performance Kit this weekend on my 06 scrambler. The kit came with 135,140 mains & 42 pilots. I read what seems like every thread in here on jetting with airbox removed. I placed close attention to yours because I live near Santa Cruz. I know sea level is sea level anyway you know what I mean. I was reluctant to even start with a 140 main but, I figured I'd start there.The bike runs great. On the highway at 70mph I rolled the throttle on, no coughs it pulled strong & smooth. I did not think it would be this good first time out. I noticed you said you ran 130's even with your airbox. Just a shot in the dark but I wonder where your float level is. I don't know it's just that 150 or 155 mains seem rich compared to what other people are running.
 

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Discussion Starter #5 (Edited)
I like my bike to pull in 4th at lower speeds. I found that with a smaller main jet this just didn't happen. However, I don't use 42 pilots. I find (after going from 40's to 42's probably a dozen times) that the Scrambler works better with 40 pilots and stock needles. I don't know why, but it does. It runs smoother and breaks away faster from stops. I should also add that since I received their email, I went back down to 150 Main jets. I rode for about 200 miles with 155's and about 500 with 152's. I'm convinced again that this (150 main jets, 40 pilots, stock needles, 2 shims and 2.5 turns out.) is the winning set-up.
 
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