Geeez, just gasket it and run it.
It is a carb keep it simple.
Geeez, just gasket it and run it.
It is a carb keep it simple.
In reply to 03Panther :
Well, it is a manual trans with 4.10's so that's the reason for the mechanical secondaries.
bobzilla said:In reply to 03Panther :
Well, it is a manual trans with 4.10's so that's the reason for the mechanical secondaries.
That and a low weigh in, is a great recipie for fun!
Ranger50 said:Geeez, just gasket it and run it.
It is a carb keep it simple.
True. Unless the jets are completely wrong for his engine. Of course, it sounds like about a 90% chance that its the wrong jetting for his engine, so, I would say some time getting the jetting correct is well worth it. Of course we know that has to be done on the engine, otherwise any guess will be about as good as another.
So, just get some gaskets, run it to without kicking in the secondaries to see what primary jets it needs, and then get the secondaries right, and then run it. till the weather changes enough to need to re jet it. But otherwise, you are correct. Carbs are simple. Simple does not necessarily mean easy.
In reply to 03Panther :
Last scaled at 3780 with the old cast iron engine, cast manifoldsm cast iron intake etc. I lost almost 100lbs total on the engine, so I kond of expect it to be around 3650-3700 lbs total now.
In reply to frenchyd :
Well, since this is a discussion on fixed bore SBC holley application your jag crap has no relevance nor bearing on this discussion. Now, if you'd like to discuss the merits of Jag carbs you are welcome to start your own thread.
03Panther said:Ranger50 said:Geeez, just gasket it and run it.
It is a carb keep it simple.
True. Unless the jets are completely wrong for his engine. Of course, it sounds like about a 90% chance that its the wrong jetting for his engine, so, I would say some time getting the jetting correct is well worth it. Of course we know that has to be done on the engine, otherwise any guess will be about as good as another.
So, just get some gaskets, run it to without kicking in the secondaries to see what primary jets it needs, and then get the secondaries right, and then run it. till the weather changes enough to need to re jet it. But otherwise, you are correct. Carbs are simple. Simple does not necessarily mean easy.
Jetting is remarkably tolerant of a lot of things - air in is still air in, and it is air in that determines fuel out. It's only when you go off to extremes that things really go sideways. I don't mean engine size, I mean things that affect airflow quality. Things that increase airspeed through the carb for the same CFM (usually caused by more staccato airflow) will want smaller jets, things that increase reversion/standoff will also want smaller jets, because some of the air is going through the carb three times before it gets to the cylinder. A mild V8 on a dual plane is going to be remarkably similar to other mild V8s on dual planes.
That said, you can't really look at the main jets without also looking at the air bleeds. I never paid attention to how QFT carbs are jetted, because they always worked "right" right out of the box. Given that they feel like they have superior atomization compared to most 4150 pattern carbs, I wouldn't doubt it if they had something funky going on in the air bleeds/main well/booster shape situation.
In reply to Pete. (l33t FS) :
I've never had any experience with any Holley's (including other brands of same) except the cheap and well used variety. Have always got 'em close with out really having to mess with the air bleeds... just jets, power valve size and pump adjustment. But close enough was good enough for non racing.
Have found 99% of the holley's I've touched that some one else bought and bolted on, or jetted themselves, were pig rich, and they cant figure out why it doesn't run right. Like I say, either cheapest new they could get, of some used and abused from a friend "that knew what they were doing". And we're still only talking a dozen or so, not like you guys that have done a lot.
The little I do know, and the little info we have, I predict he will report smaller jets, if he follows through with this carb, and reports back. Hopefully we'll get to find out.
Pete. (l33t FS) said:
I never paid attention to how QFT carbs are jetted, because they always worked "right" right out of the box. Given that they feel like they have superior atomization compared to most 4150 pattern carbs, I wouldn't doubt it if they had something funky going on in the air bleeds/main well/booster shape situation.
even though I've never touched one, from everything I've heard, I would suspect you are entirely correct. 
WELL, the rebuild kit thingy showed up yesterday so IF i get time this weekend I'll put it back together and run it. But I also have to change the throttle and choke cable on the mower and mow he yard and work all day saturday.
Look up the list # for your carb to see if it has been modified or rejetted.
In reply to 03Panther :
A lot of why I am strongly in favor of just leaving it as-is until you know if there is a reason to change, is that I used to do carb tuning, usually Holley, because 95% of them out there are Holleys.
What would happen is, I'd get drivability nailed. Crisp idle, tip-in, cruise, everything. Some of the adjustables are not always obvious, like tweaking tip-in response with secondary idle position, not the accelerator pump... Anyway, what would often happen is that a car I'd tuned would come back in a couple months. Stumbling, fouled plugs, who knows. I'll open the hood and the vacuum advance is disconnected, pull a fuel bowl off and everything is all different compared to my notes. The story would invariably go something like "me and a buddy were having beers in the garage and he said you never hook up vacuum advance/run a power valve/use smaller than .035 squirters on a 383 so he took that off"
Well, was it running poorly before?
"No, it was running GREAT, but he said you don't do that"
So the guy you drink beer with is more trustworthy than the guy you paid $800 to set up your carb (at which point it was running GREAT)...
So I'm kind of salty about Internet advice that starts with "that sounds wrong" and not "how is it running?"
*resisting the urge to talk about our lord and vapor The Qjet
*resisting the urge to talk about our lord and vapor The Qjet
*resisting the urge to talk about our lord and vapor The Qjet
Holleys are actually great carbs, and a QFT is even better. I never got into the finer points of guessing on jet sizes so I suggest you throw it on and try. Read your plugs and use your nose and you'll figure it out.
Rule of thumb when replacing a power valve... it all depends on your cam and tune. As a starting point, tune the snot out of it. Get your timing and idle mix just right to make sure you know your tune is really good. Measure idle vacuum. Let's say it's 15"Hg. Start with a power valve that is half of that value, or 7.5. If you notice (I doubt you will, given your combo) that you are running leaner than you should be on cruise tip-in and/or steady cruise (might notice a ping) then you can up that to 8.5" or 9" to get it to come open a bit sooner.
Too many home enthusiasts will slap a heads and a cam on an engine, tune it poorly, their idle vacuum plummets, and they have trouble running super rich because they have dropped the vacuum so much that the power valve opens too early.
Rule of thumb is start with half and increase from there. My guess is that you're probably fine as long as it is anywhere between 6.5 and 9". It will be stamped on the gold-ish galvanized or brass part with something like an 8 and a 5 indicating 8.5"
I know that 18 months ago we got it running decent pulling 19" vacuum. These PV I will need to scrub them to be able to read anything on there. E10 is soooo bad after sitting.
In reply to Curtis73 (Forum Supporter) :
Power valve shouldn't affect idle.
Idle WILL go uncontrollably rich with low idle vacuum, because the throttle plates are open so far that the transition slots are uncovered. Get out the drill bits 
In reply to Pete. (l33t FS) :
Not usually, but I have seen it happen. Someone takes a stock 350 with 17"Hg, throws on some AFR heads and a lumpy cam without enough compression and resets timing to stock and suddenly the 9" power valve is opening at idle. Hence why I wanted to make sure he had it tuned correctly before choosing a power valve.
... but if he's at 19" of vacuum.... Power valves are the last thing I'd worry about
In reply to Pete. (l33t FS) :
Just in case anyone is following along, I agree with every word of your rant, and have been kinda saying the same thing.
My advice is get a few sizes of jets, put it on the car, and use the jets it needs. I even offered to send some jets. I hope no one misunderstood, and thought I was telling him to just guess at what it needs.
I didn't go crazy on the cam. I think it's in the truck thread buried somewhere in there.
In reply to Curtis73 (Forum Supporter) :
But the power valve should only affect fuel flow through the booster. At least, the idle circuit should not be affected by what is essentially a main jet change.
The only time I've heard of it happening is on a setup that needed 52 main jets. In that case the main jet may have been smaller than the idle jet, so opening the power valve effectively allowed more fuel through the idle jet.
In reply to Pete. (l33t FS) :
Since the idle circuit pulls off the primary, and since the primaries are still flowing small amounts at idle, the power valve being open at idle will certainly affect tune. As you clamp down the idle to try and chase a rich idle you screw up tip-in and will forever chase a bog because you've effectively defeated the power valve system by holding it open all the time.
But, like we have determined.... if he has 19"Hg, he could probably run any one of 10 power valves from 4" to 9" and not have an issue.
Everything I've experienced is that a bad power valve can affect idle, not terminally but affect it.
So why not contact QFT / Holley tech hotline. Give them your engine and cam specs and see what they suggest for a baseline mechanical setup of the carb?
866-464-6553
In reply to QuasiMofo (John Brown) :
Don't you bring logic in here.
In reply to QuasiMofo (John Brown) :
That would be great..... but I can't find any record of the cam I bought. Anywhere. I know the heads, I know the bore is stock and the pistons are flat tops. But I can't find any record of purchasing the cam.
FOUND IT... https://www.summitracing.com/parts/cca-08-423-8
FROM HERE: https://grassrootsmotorsports.com/forum/grm/cam-choice/141059/page4/
Man I love recording everything here.
If you're getting 19"Hg vacuum with that cam, I will never doubt your tuning abilities again. I would hope for 17" and be happy with 16"
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