Tuning quick fuel ss 650 DP

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brsmustng99

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Hey members, looking for a little help with carb tuning. My carb currently idles at 12.6, cruises at around 14.8 AFR at light throttle. WOT is a solid 12.8 AFR. My problem is at half throttle I go lean 17-18 AFR, then if I mash the pedal down a little further back into 13-14 range. How do I get rid of this lean part/half throttle condition?? Carb is currently setup as follows.
65 main jet
76 secondary jet
8.5 PV
.063 PVCR
.040 HSAB
.074 IAB
31 front shooter pink cam
35 rear shooter orange cam
19 degrees intial timing
34 total
 
You can open the PVCR a bit. Like .072ish.

Also, you may need a 10.5 power valve to get it open a touch quicker. Check your manifold vacuum at a cruise and set your PV a bit lower than that.
 
brsmustng99 said:
Check vacuum at idle 10" and cruise is 15"
Click to expand...


You might try a 12.5 power valve if you can find one. I have about the same vacuum as you do and I'm running a 10.5 power valve like you and am having the same issue.

As soon as I get it back together I'm going to try a 12.5 power valve.

IMO, if you are running close to being on the main jet at a cruise you want as little time between cruise vacuum and power valve opening as you can get. That's my guess right now, but I haven t been able to test my theory yet because the brown truck hasn't brought my scatter shield back yet.
 
brsmustng99 said:
Hey members, looking for a little help with carb tuning. My carb currently idles at 12.6, cruises at around 14.8 AFR at light throttle. WOT is a solid 12.8 AFR. My problem is at half throttle I go lean 17-18 AFR, then if I mash the pedal down a little further back into 13-14 range. How do I get rid of this lean part/half throttle condition?? Carb is currently setup as follows.
65 main jet
76 secondary jet
8.5 PV
.063 PVCR
.040 HSAB
.074 IAB
31 front shooter pink cam
35 rear shooter orange cam
19 degrees intial timing
34 total
Click to expand...
No way I would be running a .040 MAB put the .031 back in.
31/31 nozzles, move the orange cam to front and pink to rear.
Move the IFR to the bottom of the metering block and drop the IAB to .070
67 or 68 primary jet up front.
Running a carb to lean is causing your stumble.
 
brsmustng99 said:
What about a bigger pump shot or different pump cam?? Would the 10.5 or 12.5 pv effect my idle AFR??
Click to expand...


No, PV won't affect idle AFR. Mark Whitner did a you tube video to show how it works. If you google Mark Whitner power valve idle test or similar you can find the video.

Also, I agree with mderoy. I'd trim down the MAB back down. Why did you open the MAB up that much? I also forgot to ask if you are using T slot resticters. You may be better off restricting the T slot and using the the smaller MAB.
 
yellow rose said:
No, PV won't affect idle AFR. Mark Whitner did a you tube video to show how it works. If you google Mark Whitner power valve idle test or similar you can find the video.

Also, I agree with mderoy. I'd trim down the MAB back down. Why did you open the MAB up that much? I also forgot to ask if you are using T slot resticters. You may be better off restricting the T slot and using the the smaller MAB.
Click to expand...

I opened up the MAB to try and tune my WOT AFR. It was a little rich 12.2, I was shooting for 12.8-13
 
I did have my carb originally jetted at 68 main 76 secondary. I was trying to have my cake & eat it too. Fuel economy and max wot power. I have been playing with decreasing my main jets for economy and PVCR to dial in WOT
 
brsmustng99 said:
I opened up the MAB to try and tune my WOT AFR. It was a little rich 12.2, I was shooting for 12.8-13
Click to expand...
Drop the jet size to change AFR. Jet for MPH at the track until car slows down then drop 2 jet sizes, if street car anything mid 12s WOT is good.
 
brsmustng99 said:
I did have my carb originally jetted at 68 main 76 secondary. I was trying to have my cake & eat it too. Fuel economy and max wot power. I have been playing with decreasing my main jets for economy and PVCR to dial in WOT
Click to expand...
Better to jet the carb for best overall performance. When you need economy drive it like grandma.
 
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