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  #1  
Old 2nd May 2011
kowboi kowboi is offline
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Default Which cylinder runs leaner?

Front or rear?
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  #2  
Old 2nd May 2011
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My front runs leaner than the rear.
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  #3  
Old 2nd May 2011
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the front.
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Old 2nd May 2011
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Just for carb'd bikes, right?

I guess the fuel in the pilot and needle circuits has more time to lose velocity and maybe even see a level drop in the greater time it takes the front cylinder to pull from the carb.
I don't know if the slide moves much in synch with the pulses at normal operating rpm range and not sure how that would affect mixture strength, but I'm sure somebody on this forum does!
Good thing that the front cylinder gets more cooling air tho.
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Old 2nd May 2011
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Quote:
Originally Posted by Dave1200s View Post
Just for carb'd bikes, right?

I guess the fuel in the pilot and needle circuits has more time to lose velocity and maybe even see a level drop in the greater time it takes the front cylinder to pull from the carb.
I don't know if the slide moves much in synch with the pulses at normal operating rpm range and not sure how that would affect mixture strength, but I'm sure somebody on this forum does!
Good thing that the front cylinder gets more cooling air tho.
I have only seen it on carb'd bikes. Big twins and sportys both. one of the reasons the front runs hotter. Jim McClure ran a sniffer on a few of his gas bikes and noted that the rear had to run a bit fat to get the front into the 'safe zone'. He was also one of the first to play with angling the carb to favor the front to help combat a lean condition. The old Triumphs even favored one cylinder when they ran a Tiger head (single carb) and Amal/Triumph/Red Circle/Baxter had a special high performance manifolds that kicked the carb to the right.
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I hadn't heard Jim McClure's name in a while.
Some of the T/F Harleys actually have an air bleeder valve on the rear leg of the manifold to try and get the two cylinders at the same temp during staging! Since they're running multi-channel data-aq and that includes head temp's.
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Quote:
Originally Posted by Dave1200s View Post
I hadn't heard Jim McClure's name in a while.
Some of the T/F Harleys actually have an air bleeder valve on the rear leg of the manifold to try and get the two cylinders at the same temp during staging! Since they're running multi-channel data-aq and that includes head temp's.
I grew up around his shop and worked there when I was teenager. I had an old Virago he hot rodded that I raced at the dirt drags. I was 12 and it was so fast, they moved me into the 1200cc hot street class. He helped me build my first hot rod Triumph that ran on alcohol...it was a street bike! Had to use an HD trans because none of the brit trannys could take the abuse. 750cc pre unit with the heads flipped and the 2 932s could suck up small animals and children. Had to run a mag wheel out back because it would destroy spoke wheels. Used a rotary pump to pressure feed the top end with its own return line. its was way too much bike for the street (and me) and he talked me into selling it to a guy from the west coast when we were in Maryland at the track in 94. Jim was a cool dude....
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Old 3rd May 2011
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With the EFI bikes about 56% of the fuel comes out of the front injector.

AW
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Old 3rd May 2011
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Wow, whittlebeast...there is a 6% difference!...you would think that Moco would have done something to address that issue. One cylinder running stronger than the other could not saying that it would but could put undue torque on the crankshaft. When I first got my bike I put X14iED's on it but then later after talking to Steve at Nightrider about the front cylinder running leaner I switched to AF-XiED's because they are individually adjustable and I was able to fatten up the front. Now that I have a Power Commander the situation is resolved.
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Old 3rd May 2011
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I figured that since the cylinders have their own injectors, it would be what ever the o2 sensor says it wants. i put mini squirts on my 81 XJ650 and the sniffer and 02 sensors both confirm that the 2 center cylinders need a little more fuel to help with heat. So they are tuned with a touch more fuel. 14.6, 13.9, 14.0, 14.6.....best performance and cleanest burn on the dyno and with the maps. i don't know if HD uses stand alones, but the 2 injectors should be independent of each other and flow should be separate. All this is based upon you meaning that the front gets 56% and the rear gets 44%....doesn't make sense if that is indeed what you mean. 56% of the fuel that pump is pumping for correct A/F mixture or 56% of the fuel that the injector can flow??
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