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Also, upon further reflection I think I can clarify something...
I do agree that PV and main jets don't effect idle...but pure static idle at 800 rpm with no throttle plate movement is not what I am referring to. I am saying that: 1. warm vacuum is 11" 2. cold vacuum is 7.5" 3. that when the engine is cool and trying to warm up, I can't keep it running without feathering the throttle. I can't just start it and let it warm up at steady idle and vacuum with no help from me - I don't have a choke...throttle needs to be feathered. 4. That feathering brings the vacuum down to about 5" let's say. As I feather it, a 6.5 pv opens the throttle plate and allows pv enrichment to happen and drowning my motor, bring the a/f to the 9s...it barely runs at that rich level. 5. pv of 4.5 is just low enough for not trigger "warming up" vacuum dips. See what I mean? |
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https://www.facebook.com/Braswell-Ca...-320755068324/ As Brent mentioned, if you want Quick Fuel, the Q-Series is very good. I used to have one, and it's super adjustable. |
but does adding a choke then take away all of that adjustability?
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The choke itself doesn't cause a loss of adjustability but it's a function of the level of carburetor. Most "race" carbs which are infinitely tunable will not have a choke horn.
Fwiw, the qft blocks are made by jones machine here in Louisville. |
blykins,
Yes; that's what I meant; I'd rather have a "race" carb with the tunability than have a carb with a choke that didn't have the tunability. |
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Ive used the electric throttle solenoid in the past or you can use a manual choke throttle cam if the mounting boss is still in the carb body. |
Jac Mac
That's a good thought and could potentially implement it but...I don't think the PV size is really my problem; I think 4.5 pv with 11" of vacuum should be fine. We kind of got off into a side discussion about PV and MJ impact on idle. My bigger issue is still my bigger issue, i.e. too lean in the 2ndaries, especially at WOT. |
The Holley HP/XP carbs are great on paper, but I have seen and read so much about the problems they have.
I bought a QFT 750 for a mates 355, the ebay seller asked for our specs, and amazingly works perfect out of the box. I pulled it down for inspection first, and to keep records, set throttles, set float levels, warm engine, set mixture etc. You can get Quick Fuel metering blocks in black, ;). |
Why don' you take it to a dyno and let it be adjusted and tuned there?
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I took it to the dyno and they didn't do a very good job...they changed the PV and the MJs and declared it "done"!
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Progress!
Moved the 1 and 3 emulsion bleeds from 29 to 21 Also moved rear pv from 3.5 to 4.5 (not much impact but didn't hurt) And main jets from 93 to 98 (no impact imo, see note below) Secondaries and wot now in the low 13s. Gonna move hsab from 26 to 23. If that doesn't do it I might block off one of the two unblocked emulsion bleeds but that might be pushing it. Blp sells a 14 and an 18 so might try those. I think that the main jets can handle a jet bigger than 88. Maybe the metering block ext channel resitriction maxes out at about 88. |
I meant: "can't handle"
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Do you have jet extensions in the secondary main jets?
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No jet extensions...hadn't thought about getting them but will look into them.
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Btw, the 23 hsab didn't help much so still at low 13s to low 14s over varying ranges of hard to wot throttle.
Still trying to improve it but it's livable now. Used to fight me between 3-4k rpm...that has smoothed out considerably. If I didn't have a n a/f gauge wouldn't really feel it. However, I know that there is some performance gains still yet to be achieved. |
Figured I would try increasing the front main jet from 81 to 84...it helped a lot, especially into secondaries (but not as much in WOT - but better)...since the rear main jet is maxxed out and not helping much above 88, moving the front jet to 86 or 88 will help even more but...
cruise is becoming too rich...will see if I can lean out cruise by increasing idle air bleeds or decreasing idle feed restrictors... |
Increased front main jet to 87 from 84 to richen hard throttle and wot and increase idle air bleed to 73 from 67.
Now hard throttle is 12.5-12.75 and wot is 13-13.5 and cruise got a bit rich in the 12-12.5 Gonna increase pvcr to 80 from 76 to help wot and decrease ifr from 36 to 32 to lean cruise. Feel like I'm close the right combo. |
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If you are really keen, I would setup a gopro to watch the fuel level in the float bowl windows. |
final chapter in my tuning saga:
carb is pretty close now. prolly as good as ill get it save some fine tuning over time. i went to 78 on pvcr, 34 ifr, 86 front jet, 90 rear all in all i think the 850 carb is probably too big - 750 would have been better especially since this is not a high rev engine - 5500 rpm is max more or less. thought the 850 ok since the original quadrajet was 850 on the stock 250 hp 400 but i think that comparison to the holley 4150 is a bit apples to oranges, esp since the qjet is a spreadbore. alls well that ends well though. learned a bunch about tuning - thanks again for your help. |
You would find a lot more throttle response and maybe even some more performance from a 650-750 sized carb.
You're running almost the same size jets that we run on our 1050 sized carbs on MUCH bigger engines. When you have to do that, it should be a clue that the engine just doesn't have enough signal to use that carburetor correctly. |
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