Tuning With Air Bleeds
05-12-2009, 06:55 AM
#12
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Join Date: Apr 2007
Location: Texas Hill Country
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Yes, I got the 0-82751. I am not sure what the secondary linkage is, but it is stock and is not 1:1...I am guessing 60%.
That was my thinking too, that the stock air bleed setup was wack. All the documenation from Holley indicated that was in fact the stock street config...strange. I have been considering purchasing a set of precision drill bits. If I get them, I will use them as a hole sizer to determine what size IFR is in the primary and secondary metering blocks. I can only assume they are the same as a stock 750DP.
Based on what I have read and what you are saying, 67mustang302, I am going to set the secondary LSAB to 71 to match the primary. I will then watch the LM-2 at 1500 or so rpm to see what the AFR is. If I am in the high 13s, I will then set the idle mixture screws and idle speed. That should get the low side lined out
.
Once I get the low speed stuff dialed in, I will feel comfortable striking out and tuning the HSAB, jetting, and accelerator pump. That should be fairly easy based on my prior experience with carb tuning.
I feel confident now in what each of the holes do, but I am sure the carb will throw me an elbow at somepoint.
On a side note...what aftermarket metering blocks do you guys know of and like? I started looking for a metering block with adjustable IFR (not sure I really need adjustable emulsion jets). The difference in price between a Holley HP and Holley HP Ultra is considerable when the cost of an aftermarket billet metering block is only $100 or so. Seems like the regular HP and an aftermarket metering block is the econonmical way to go.
Oh, and FYIa they make an HP main body now for about $125. I thought about converting my old 750DP over to an HP as a backup. Basically you take your old throttle plate, metering blocks, and bowls and slap them on the new main body with LSAB and HSAB. I think that is cool.
That was my thinking too, that the stock air bleed setup was wack. All the documenation from Holley indicated that was in fact the stock street config...strange. I have been considering purchasing a set of precision drill bits. If I get them, I will use them as a hole sizer to determine what size IFR is in the primary and secondary metering blocks. I can only assume they are the same as a stock 750DP.
Based on what I have read and what you are saying, 67mustang302, I am going to set the secondary LSAB to 71 to match the primary. I will then watch the LM-2 at 1500 or so rpm to see what the AFR is. If I am in the high 13s, I will then set the idle mixture screws and idle speed. That should get the low side lined out
.Once I get the low speed stuff dialed in, I will feel comfortable striking out and tuning the HSAB, jetting, and accelerator pump. That should be fairly easy based on my prior experience with carb tuning.
I feel confident now in what each of the holes do, but I am sure the carb will throw me an elbow at somepoint.
On a side note...what aftermarket metering blocks do you guys know of and like? I started looking for a metering block with adjustable IFR (not sure I really need adjustable emulsion jets). The difference in price between a Holley HP and Holley HP Ultra is considerable when the cost of an aftermarket billet metering block is only $100 or so. Seems like the regular HP and an aftermarket metering block is the econonmical way to go.
Oh, and FYIa they make an HP main body now for about $125. I thought about converting my old 750DP over to an HP as a backup. Basically you take your old throttle plate, metering blocks, and bowls and slap them on the new main body with LSAB and HSAB. I think that is cool.
05-12-2009, 07:11 AM
#13
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Join Date: Dec 2006
Location: Citrus County, FL
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all i can add to this is that when we were trying to get my car to idle in gear we stuck paperclips in the idle air bleeds to partially block the holes and i had the car running @ like 400 rpm in gear which i never thought was even possible. after seeing that i know my next carb will be a proform with fully adjustable everything lol
05-12-2009, 10:33 AM
#14
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05-12-2009, 12:30 PM
#15
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Join Date: Apr 2007
Location: California
Posts: 10,468
As far as metering blocks there are several options. Proform and Quickfuel both make billet metering blocks with varying ranges of adjustability(Proform actually manufactures the main bodies for Quick Fuel). I'm not 100% sure on Profroms choices, but the Quick Fuels you can get for around $40-45 starting out and up, and you have a choice range from the basic preset 3 circuit calibration(what my QFT 650 came with) which is tapped for screw in restrictors if you want to tweak the emulsion, but it comes pre-drilled(their standard calibration). All the way up to like 4 or 5 circuit adjustable emulsion. All of their metering blocks come standard with screw in IFR and PVCR so you can chance the idle and power valve circuits. Proforms are probably similar.
http://quickfueltechnology.com/home_2.htm That's Quick Fuels site.
I'd try tuning your's first, if you don't need to adjust the IFR or PVCR then there's really no need to get metering blocks.
http://quickfueltechnology.com/home_2.htm That's Quick Fuels site.
I'd try tuning your's first, if you don't need to adjust the IFR or PVCR then there's really no need to get metering blocks.
05-13-2009, 12:53 PM
#17
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Join Date: Apr 2007
Location: California
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Sometimes carbs can be a total pain to tune. In my case my 650 happened to be off quite a bit from what I needed out of the box. Now that's it's running just about where it should it makes great power, with awesome throttle response and gets good mileage.
05-13-2009, 03:13 PM
#18
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Join Date: Aug 2007
Location: Socal
Posts: 1,235
Quickfuel makes profrom. If you ever ask them a question at proform they can't answer, they will just tell you to call quick fuel.Haven't needed to ever change any of the e-holes in the metering block myself.
If you ever ask them a question at proform they can't answer, they will just tell you to call quick fuel.Haven't needed to ever change any of the e-holes in the metering block myself.
05-13-2009, 04:09 PM
#19
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So, Proform billet metering blocks are really made by Quick Fuel? I guess I should go straight to the source (Quick Fuel) if i go that way.
How rare is it that performance motors need the IFRs or PVCRs tweaked if the carburetor is close the right size? I found that the stock tune air bleeds, jetting, and accelerator cams are pretty far off what works best on my motor. I just wonder if the IFRs are far off too??? I know the PVCRs my old 750DP were pretty small compared to other street carbs. I never did see much difference in AFR when the PV came on (maybe a .75 richer). I am not sure about this carb.
How rare is it that performance motors need the IFRs or PVCRs tweaked if the carburetor is close the right size? I found that the stock tune air bleeds, jetting, and accelerator cams are pretty far off what works best on my motor. I just wonder if the IFRs are far off too??? I know the PVCRs my old 750DP were pretty small compared to other street carbs. I never did see much difference in AFR when the PV came on (maybe a .75 richer). I am not sure about this carb.
05-13-2009, 05:41 PM
#20
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Location: California
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On my QFT to give you an idea, it came with 68/74 jets, .031 IFR's with 70/36 air bleeds and .037 I think PVCR.
The PVCR was just right, but I've changed the jetting to 63/69 and it's probably still a tad rich, and the bleeds have been changed to 70/42 and I had to go to a .028 IFR. The .031 squirters stayed the same, but changed some cams. Basically out of the box on my setup it was pig rich and trying to flood at 2,000-2,500rpm at WOT because of excessive booster signal(hence the larger HSAB's required).
I'm pretty sure the emulsion is good, it seems to run great everywhere, but I wouldn't be able to tell for certain with an O2 setup. I'm sure their factory emulsion calibration is REALLY close for 99% of street engines. Some engines just want something different from the carburetor. There's a reason factory carbs were application specific.
They have excellent customer service and they know their poop when you ask them questions.
The PVCR was just right, but I've changed the jetting to 63/69 and it's probably still a tad rich, and the bleeds have been changed to 70/42 and I had to go to a .028 IFR. The .031 squirters stayed the same, but changed some cams. Basically out of the box on my setup it was pig rich and trying to flood at 2,000-2,500rpm at WOT because of excessive booster signal(hence the larger HSAB's required).
I'm pretty sure the emulsion is good, it seems to run great everywhere, but I wouldn't be able to tell for certain with an O2 setup. I'm sure their factory emulsion calibration is REALLY close for 99% of street engines. Some engines just want something different from the carburetor. There's a reason factory carbs were application specific.
They have excellent customer service and they know their poop when you ask them questions.