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Old 04-01-2007, 04:09 PM   #1
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Default rb c6 BB tuning problems

hi i am having a problem tunning my c6 bb engine. i reset to factory but it was running to hot nearly 300f so i have richened up i'm now at 4 1/4 turns on the hsn. when i bring it in its idleing high for 5 secs then settles down.i have leaned the lsn now that is at 4 turns but no difference. the engine is now running great about 250f but still have this problem with the idle.and i cant understand why it needs to run richer than factory. i have checked for air leaks but other than a little bit around the carb throttle slider thingy it is air tight. i am useing byrons 25% no6 rb plug 2047 pipe. any help would be great
thanks chris
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Old 04-01-2007, 07:29 PM   #2
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you mean a 2045 pipe? i bought mine as a combo 2045 pipe with 192 manifold and added a .1mm shim to run 30% mine runs awesome. c6's like to be a little rich on the low. I would ask RB themselves on their website forum link is at www.rbproducts.com VERY helpful forum.
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Old 04-01-2007, 10:06 PM   #3
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Sounds to me like its a little lean on the bottom. Richen the low speed needle 1/8 turn at a time until it gets pretty sloppy on the bottom meaning kinda boggy lots of fuel spitting out. Then start adjusting the high speed needle leaner until it just starts to clean itself out durring a run on the top end. At that point you can adjust the bottom end needle just slightly turn 1 hour. Always remember just because you have your high speed needle set really rich doesnt mean it wont get hot if you have a lean bottom end and you are spending very little timne on the top end needle. Hope this helps.
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Old 04-02-2007, 12:30 PM   #4
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thanks for your help.
nitrosteve at what point in acceleration does the hsn take over from the lsn. i always thought that the lsn was basically just for idle. but if it controls the mid range aswell this could be my ovrheating problem

cheers chris
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Old 04-03-2007, 09:59 AM   #5
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I dont know at what exact point it comes off the low speed needle but it is after idle. Example would be I had a similar situation on a tight track where it would get really hot and lean bog, but when I would accellerate down the strait it had plenty of smoke. I found that the low speed needle was way lean. A good rule of thumb is always tune from a rich setting. After you find a rich setting on the low and high speed needle then start at the high speed needle adjusting 1-2 hours once it cleans itself out at the top end then adjust you low speed needle for punch. Once you have done all this the pinch test is a good test to see if your too lean. Just pinch the fuel line and the engine should wait 4-5 sec then raise the idle and die if it goes up right away your lean if it takes longer than 5 sec to increase then idles up and dies your rich but if it drives good alittle rich I would leave it there. Dont forget to do all this after the engine has heated up.
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Old 04-03-2007, 12:10 PM   #6
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Chris the "low end pinch test" like Steve suggested is the best way to nail that low needle setting. This is a very good methode, I use it all the time.
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Old 04-03-2007, 12:13 PM   #7
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i tried that but question is you pinch before or after the fuel filter?
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Old 04-03-2007, 04:51 PM   #8
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After the fuel filter.
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Old 04-03-2007, 04:59 PM   #9
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when i do it runs for about 5 seconds but the rpm goes up immediately
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Old 04-03-2007, 08:14 PM   #10
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Here this should help!!!!
1. Start your engine and warm it up for about 30 seconds by revving the engine from idle to mid-throttle while holding the wheels off the ground.

2. Allow the engine to idle for 10 seconds. If the low speed needle tuning is so far off that it won't idle, simply bump the idle position higher until the engine will reliably run at a higher idle.

3. With the engine at idle, pinch and hold the fuel line near the carburetor, cutting off the fuel flow and carefully listen to the engine rpm.

If the low speed needle is set correctly, the engine should increase rpm only slightly and then die.

If the engine increases several hundred rpm before dying, then the low speed needle is too rich and needs to be turned in.

If the rpm doesn't increase at all and the engine simply dies, the low speed needle is set too lean and should be richened or turned out.

After doing this a few times you'll get the hang of it, and tuning the low speed needle will become easy. The only way to get that last 5% performance on the low speed tune is through careful track testing. By evaluating the engine as it accelerates from a dead stop or out of slow corners during actual race conditions is the only way to get those last few percent of power from your engine. Variables like the clutch setting, gearing, traction, atmospheric conditions and even the car's weight will have an effect on this last 5% of tuning performance, and the optimum setting can only be reached by careful on-track tuning.

Last edited by nitrosteve; 04-03-2007 at 08:32 PM.
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