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Discussion Starter #21 (Edited)
Hi VMF

Last week, I noticed that my primary float was that metal one and my secondary was (out the box) a notched Nitrophyl float with jet extensions. I that that was a bit strange so I ordered a Nitrophyl primary as well as 6.5 PV. I have a bit of OCD regarding symmetry (don't go grocery shopping with me) and the float thing was nagging me. Just got done swapping both of those out. I also have a jet kit but I think something is not right as the new jets didn't thread in easily. It was like the thread was wrong or something. So I didn't change jets. The kit I bought is 1/4" - 32 which is the standard replacement part. I just buttoned it back up with the old jets on there but then I thought I should try a different jet (as I only tried one) before returning. Maybe tomorrow. *shrug*


Anyhow - I noticed something I thought was pretty cool on the Quick Fuel Carb......the PV restriction channels. Looks like there is removable insert in each of the channels that you can swap out if you want to change the size of the power channel. (see pics). They have a flat head slot on them that looks like they can be backed out and replaced. I always thought you needed to drill those out if you wanted to enlarge them. I guess not for quick fuel. Just wanted to share as I thought that was cool. Am I crazy or do those look like they can be changed out?

I had a thought as well regarding timing and wondering what impact this may or may not have on the overall AFR and engine vacuum (if any). I decided to re-check my timing after my last tune and my initial timing is at 12. I have a Comp Cam grind 270H. I've been doing some reading and it seems people have some good experiences advancing it to 14. What are your thoughts on that and what can I expect out of advancing the timing? I'll probably hit up Google/SIRI after I post this but figured I'd ask as I was posting.

Thanks for reading
-J
 

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Discussion Starter #22
Actually - looking at those pics again - almost looks like jets in in the PV circuit.

I’m calling Holley tommorow to ask them. This seems odd to me
 

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One of the big problems that usually crops up for mild Windsors with big carbs is poor mix quality at low RPMs. While you can tune these so that they do well at mid to high RPMs at WOT, even if you get it jetted rich enough to deliver enough fuel at low throttle, the droplet size can be very large. When that happens, the car can be in a weird state where it's getting 'too much fuel', spitting a lot of wasted gasoline out the exhaust and fouling plugs, but it's not in a very burnable form, which means your engine is acting 'lean' in regard to power production and stoichiometry.

Most of the time, you'd only see a 750 used with a small block Ford on the drag strip, because drag racers typically only care about what happens at WOT, and if it runs like garbage on the street (part throttle), they can fall back to "Well, it's a race car! of course it has bad manners!" I am not mentioning this to give you a hard time, or naysay your efforts - just pointing out the obvious! =)

If I am not mistaken, you can actually use annular boosters for your QF 750, and those would probably make a huge difference for you vs. the typical ones Holley style carbs come with. They deliver a much finer mist of fuel and get better signal under any conditions. They would certainly work better for a street driven car in every way, but you would also be back to square one with the tuning.
 

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Bump your timing up to 14. if that works good try 16.
That Power Valve channel restrictor which is essentially a jet for the power valve circuit.
Use it for WOT tuning. I doubt that is what you are fighting.
For idle, the idle jet in the metering block along with the idle air restrictor control idle mixture.
Remember everything is additive.
for cruise up until the power valve opens, its the main jet.
If you have a power valve, the the power valve channel restrictors control the mixture along with the high speed air bleed.
Look at this forum :
https://www.tapatalk.com/groups/racingfuelsystems/viewforum.php?f=25
BTW don't get caught up in exact AFR numbers. Strive for what runs and feels good.
 

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WOT - vacuum drops to less than 4 and further riches to high 11's - mid 12's.

So wondering if this is expected behavior in terms of vacuum. I'm not sure.

Thanks
J
you should see less than 1 at WOT with that setup if you throttle is opening. Something is wrong. Likely your gauge or something.

primary jet should be quite a bit smaller than your secondaries. you are probably make the cylinders closer to the primaries way richer than the other....
 

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Discussion Starter #26
Yeah - I should update this thread but I've gotten distracted with timing things. I swear I have the attention span of a gnat. Now that I think I've got that part nailed down (timing and advance) - i'm back to primary and secondary tuning.

But I'm revisiting idle again after the distributor recurve. Went with the small silver advance stop and a blue/silver (light) spring combo. Total advance should open up fully at 2800RPM and give 25 mechanical. Car seems to like 12 initial the best.

I seem to keep hitting a snag with the 4 corner idle as I only have an AFR on one bank. *shrug*. I'm contemplating closing up the secondary corners and just working with the primaries.

Prior to this I've bumped the primaries down to 71 and have the secondaries at 81.

Oh yeah - suprise - got too much electrical "things" running on my car now. The alternator is throwing up. I see an upgrade there as well but I'm going on vacation next week. My Mustang is the kid that keeps on asking for more more more........but I still love it.

-J
 

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Discussion Starter #27
you should see less than 1 at WOT with that setup if you throttle is opening. Something is wrong. Likely your gauge or something.

primary jet should be quite a bit smaller than your secondaries. you are probably make the cylinders closer to the primaries way richer than the other....
I should have clarified - the engine vacuum drops to nothing at WOT (as expected). I threw 4 in there as that was when the old PV kicked in.
 

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Just an update. The 4 way idle adjust was critical. I considered turning the rears all the way in and shutting them off too but adjusted the rear throttle blades in closer by the hidden allen head screw. All four of my idle screws are now 1/2 turn out and my afr is around 13.7. I have my curb idle at 750 rpm. As a note the engine would idle down to a smooth 500 rpm as where I made my adjustments. Drivability is nice now but quick accel had a lean issue. As Macstang had mentioned about a pink accel pump cam, mine had one. I installed a red one and it has cleared up my issue. Driving normally (whats that?)accel and cruising I'm between 12-14 afr. On to secondaries next week.
 
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