Carb rejetting

[Lumi Ints]

Hi,
I have a stock 2007 Mastiff. Now I decided to change exhaust, to get more sound. One of my friend built me the custom one, it looks like the stock but is 2 into 1, without the baffles. Size is the same as stock so I can use the original covers. Sound is super, start to rejet the carb on dyno.
Original setting was interm 0,295 and main 0,74. First I put 0,32 and 0,78 - horrible backfire and the dyno results were worse than in original setting.
Then I put 0,31 and 0,76, this was better, but still worse than original. Finally put back the original jets, Engine works better and best results.
I have KN airfilter and S&S teardrop aircleaner. Any ideas? As much I have read threads about this theme, there is no logic here.

Regards, Indrek
from Estonia

 

[Sven]

Temp in the building = Throws off tuning.
Air pressure of the time tuning = Throws off a carb type.
Compression throws off the tune = And the numbers are?
From 295 to 32 is fat rich down below = Unspent builds in the pipe.
From 74 to 78, more unspent is filling up the pipe = Backfire is to refire the unspent once the flame-front of the flame licks under the open ex valve and she boom she booms.

Lean&Mean is a fighting machine.

Ever let a lawnmower run out of gas and you hear it revs higher, then shuts down after that? That last lean mix of the fuel/air is making more HP is the higher rev being most efficient... But would probably burn up with less fuel cooling down the head, so it is WOTit is. Your friend's pipe needs no tuning sounds like... most efficient backpressure holding the fuel from exiting on the, 'for every action-equal-reaction.'

And that more or less sounds the most logical to my way of thinking.

 

[Mikeinjersey]

Hi,
I have a stock 2007 Mastiff. Now I decided to change exhaust, to get more sound. One of my friend built me the custom one, it looks like the stock but is 2 into 1, without the baffles. Size is the same as stock so I can use the original covers. Sound is super, start to rejet the carb on dyno.
Original setting was interm 0,295 and main 0,74. First I put 0,32 and 0,78 - horrible backfire and the dyno results were worse than in original setting.
Then I put 0,31 and 0,76, this was better, but still worse than original. Finally put back the original jets, Engine works better and best results.
I have KN airfilter and S&S teardrop aircleaner. Any ideas? As much I have read threads about this theme, there is no logic here.

Regards, Indrek
from Estonia

Make sure you don't have an intake leak or an exhaust leak . Jetting will never be correct if a leak is part of the mix. Consider a Big City Thunder baffle. I had great success and sound with that baffle .

 

[Mr. Wright]

Weld a washer in the exhaust so it has some back pressure. Had the same problem with my Paul Yaffy's.

 

[Lumi Ints]

Weld a washer in the exhaust so it has some back pressure. Had the same problem with my Paul Yaffy's.
View attachment 83129
View attachment 83130
View attachment 83131

Thanks

 

[john sachs]

You can weld a washer on a bolt (looks like a lollipop), and this way you can bolt it in, and even make it perfectly tunable.
John