QuickFuel 680 leak? hesitation?
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QuickFuel 680 leak? hesitation?

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    New here Beer:30's Avatar
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    Default QuickFuel 680 leak? hesitation?

    Ok, '69 Camaro fresh 355, Comp Xtreme 274H flat-tappet straight-up, 1.5 alum rollers. 9.8:1, iron heads, 2.02" x 1.60", port-matched to Performer RPM intake. Pertronix billet flame-thrower distributor / wires / coil. AC-R44 plugs, .050 gaps, 12* initial, 35* total, vac advance (after setting timing) is hooked to timed port on primary metering block. Doug's 1-3/4" long-tube headers, AC mechanical fuel pump. On top is a brand-new QFT HotRod Series 680 vacuum secondary, out of the box stock. Vac power brakes hooked to rear (large) port, no PCV yet - just breathers on the covers. Both small vac ports down under the front fuel bowl are plugged. No vac ports on the intake.

    By fresh, I mean break-in time (40 minutes) plus about 150 easy street miles. So, fresh. I've just got the electric choke / fast idle speed dialed in. Hot idle is 750-770 on my timing light, got it to about 10.5"-11.5" vacuum and all four corners just off of the rich side. If I open them each even a HAIR more, idle goes DOWN (rich). Point is, they are closer to the rich side than the lean side. Starts fine, idles great, haven't checked WOT quite yet. But, there's no indication it would be a problem. When it's running, the fuel is half-way across the fuel-bowl sight windows. So, floats are set.

    Here's the deal you carb guru's: 1) Tip-in (idle transition) has a slight hesitation, like the accel pump is weak. There is squirt from the squirters IMMEDIATELY upon moving the throttle. I even lengthened the accel pump bolt (with spring) a few turns, but nothing changed. The hesitation is just a split-second and then it's clean and crisp. Cruise acceleration is immediate with no hesitation unless throttle is closed, then cracked open again for accel.

    2) Overnight, the fuel bowls are EMPTY. No external leaks showing along the intake. WHERE CAN THE FUEL GO? Power valve(s) leaking and emptying the bowls into the motor??? What else is below fuel inlets (not draining back to the pump) that is open to the fuel in the fuel bowls?
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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  3. #2
    gn7
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    Quote Originally Posted by Beer:30 View Post

    2) Overnight, the fuel bowls are EMPTY. No external leaks showing along the intake. WHERE CAN THE FUEL GO? Power valve(s) leaking and emptying the bowls into the motor??? What else is below fuel inlets (not draining back to the pump) that is open to the fuel in the fuel bowls?
    Beer, the power valve can leak fuel into the motor if the diaphram is ruptured, or the gasket isn't sealing correctly. It would have to be a small leak or it would have a considerable effect on how the thing idles.

    OR, and this may sound crazy but crazier things have happened.
    Because the idle and trans slot discharge are lower than the fuel level, the fuel has to go up to the top if the metering block, mixes with air from the air bleed, and then down to the bottom of the metering block across to the main body and into the base plate to the discharge. The air bleeds ALSO act as vacuum breakers to keep the fuel from being siphoned up and over the top of the metering block. If the air bleeds are blocked, not drilled, what ever, it will allow the fuel to be siphoned out of the bowls. The only two ways I know of that the fuel can get out of the bowls with the engine off is the idle circuit by siphone, or the PV. The PV can only empty the bowl about half way, the idle circuit can drain the bowls complely.

    Try putting you finger over the idle air bleed and see if it effects the idle. They are the air bleeds to towards the outside of the carb. The ones closer to the bowl vent are the main bleeds.


    And there is always EFI



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    Last edited by gn7; 01-09-2013 at 08:53 PM.

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    New here Beer:30's Avatar
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    Quote Originally Posted by gn7 View Post
    Beer, the power valve can leak fuel into the motor if the diaphram is ruptured, or the gasket isn't sealing correctly. It would have to be a small leak or it would have a considerable effect on how the thing idles.

    OR, and this may sound crazy but crazier things have happened.
    Because the idle and trans slot discharge are lower than the fuel level, the fuel has to go up to the top if the metering block, mixes with air from the air bleed, and then down to the bottom of the metering block across to the main body and into the base plate to the discharge. The air bleeds ALSO act as vacuum breakers to keep the fuel from being siphoned up and over the top of the metering block. If the air bleeds are blocked, not drilled, what ever, it will allow the fuel to be siphoned out of the bowls. The only two ways I know of that the fuel can get out of the bowls with the engine off is the idle circuit by siphone, or the PV. The PV can only empty the bowl about half way, the idle circuit can drain the bowls complely.


    And there is always EFI
    The only other thing I noticed that is different from all of the other carb'd vehicles is - it's not pumping up fuel on it's own after overnight. Meaning, the bowls are DRY, so normally spinning the motor over a handful of times will get enough fuel for accel pump to give a few squirts and let the choke take over. I have to give it a shot of start fluid to get enough fuel pump action. 3/4 tank fuel, has had no starvation problems. I don't see how the empty bowls and stingy fuel pump can correlate - as the drain back would have to siphon the bowl fuel back through the needle/seat. I don't see how that could happen.

    Checked the oil, does not appear diluted. Still at the full mark and doesn't smell like gas.

    The car is going to be EFI anyway....this is just to give me time to decide WHICH setup to go with. I want to keep the cowl-induction air cleaner setup, so it'll be a multi-port dual-plane with TB. All of these problems will go away with the EFI, but it is just weird to have a high-dollar brand-new carb give simple little issues like this. Have had several new carbs in the past and all have been just fine.

    Gonna drive it to work tomorrow and play with the timing a bit during the day. I am thinking maybe try 8* initial and see if that changes the hesitation. After that, I'll pull the carb off this weekend with the bowls at running-level and see if it's dripping anywhere down through the venturies.
    Last edited by Beer:30; 01-09-2013 at 09:05 PM.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    gn7
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    Don't see how is possible to siphon back through the fuel inlet. Even if it had fuel chute bowls, there is an air gap at the top of the bowl.
    Can't explain why the fuel pump isn't delievering fuel to it except to say it may not be moving as much fuel as you think it does per stroke. I know my Clay Smith in the boat takes more than a little cranking to get enough fuel in the bowls for the accel pumps.
    Odd that BOTH bowls are draining. I could almost see one on a brand new carb. But both?



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    Quote Originally Posted by gn7 View Post
    Don't see how is possible to siphon back through the fuel inlet. Even if it had fuel chute bowls, there is an air gap at the top of the bowl.
    Can't explain why the fuel pump isn't delievering fuel to it except to say it may not be moving as much fuel as you think it does per stroke. I know my Clay Smith in the boat takes more than a little cranking to get enough fuel in the bowls for the accel pumps.
    Odd that BOTH bowls are draining. I could almost see one on a brand new carb. But both?
    Yeah, pretty much impossible for siphoning. Just ruling out what it CAN'T be.

    I would guess the possibility of acclerator pumps, since they are at the bottom of the bowls - - but there's only one here.

    I ran the car and drove it last night after changing an accumulator spring to soften up 2nd gear. Parked it and idled for quite a while as I adjust the electric fans, which were coming on too soon. Shut if off for the night, took the truck to work this morning so didn't touch it. Got home and went to start after mounting the coolant recovery jug. Spin, spin, spin, not lighting. Pumped it twice again, no light. Took flashlight to the sight glasses and could see the bottom of the bowl on the opposite side.

    I would expect to see fuel all over the intake manifold (external).
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    gn7
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    It isn't 125 in your garage is it. My GN can empty all 4 bowls in about 12-18s in a closed havasu garage during the summer

    Its a strange one Beer. If you should call QF on this, let us know what they say or what you find. I'm stumped.
    The both bowls thing is what has me scratching my head.

    No chance the manifold temperture is so hot its boiling the fuel up and out the boosters is there?
    Have you tried starting this thing after driving it around, maybe a little idle time, and then let it set for a 1/2 hour or so.



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    One of my friends had a similar problem with a brand new Edelbrock carb on a hot rod. Maybe I can catch him and find out,, seems like it was siphoning back out.
    Last edited by obnoxious001; 01-09-2013 at 10:06 PM.

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    Senior Member Hass828's Avatar
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    Metering plate gaskets. And possibly warped metering plates, but not likely on that carb. Probably just a set of PV & metering plate gaskets would fix the leak. I had a simular thing happen with a brand new holley, the thing would leak down over night but other than that it ran great EXCEPT on really cold mornings, it would go fat as if it was getting additional fuel from some place. And the fuel levels were perfect. I was checking stuff and put a 5/16 wrench on the bowl screws & snugged them up one cold morning while it was idling rich and it immediately cleaned up. The metering plate gasket were leaking. I replaced them and the leak problem & cold morning problem was gone.
    As for the hesitation.
    You might also have to change the amount of mech advance in that dizzy. 23* is quite a bit. It would probably lose the hesitation with a little more initial in it. Just for a quick test see what happens if you remove the vac advance line from the timed port and move it down to one with manifold vac.
    Rich idle, slow timing, and a slow idle with a little camshaft all make it tuff .
    Last edited by Hass828; 01-10-2013 at 05:53 AM.
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    Quote Originally Posted by gn7 View Post
    It isn't 125 in your garage is it. My GN can empty all 4 bowls in about 12-18s in a closed havasu garage during the summer

    Its a strange one Beer. If you should call QF on this, let us know what they say or what you find. I'm stumped.
    The both bowls thing is what has me scratching my head.

    No chance the manifold temperture is so hot its boiling the fuel up and out the boosters is there?
    Have you tried starting this thing after driving it around, maybe a little idle time, and then let it set for a 1/2 hour or so.
    Car is outside this week on the lift, since I am dialing in the details. It's 37* this morning and gets to about 50 during the day. If it were July and 110 around here, I would just sluff it off to evap. My other cars with Holley Ultra Street Avenger, Edelbrocks, or Quadrajets can still do accel pump squirts for starting a week after running. This one, no.

    I think the only way to see what is happening is take the carb off after running, place it on a stand, and see what comes out of where.

    Thanks guys.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Quote Originally Posted by Beer:30 View Post
    I think the only way to see what is happening is take the carb off after running, place it on a stand, and see what comes out of where.

    Thanks guys.
    Thats one way. Will be interesting if it stays full.



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    Or Seth, either one Budweiser's Avatar
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    Just a view from the outside... If there were a "common denominator" between the two issues, it would be the accelerator pump. Just sayin'.

    If it were me, I'd take the bowls and metering blocks off, take the power valves out, remove the acceletor pump diaphragm, and blow air through all the passages... not omitting the air bleeds on the main body.

    And... Just a mention... Probably not any part of the issue, but isn't the fuel level supposed to be at the bottom of the sight glass? Never had one with sight glasses, just plugs... and always set the floats to ever so slightly, just barely, dribble out of the hole.

    Hope the fix is easy and cheap Beer!
    Good luck!
    -Seth-

    PS, try tuning the idle mixture just a smidge off of lean instead.
    Last edited by Budweiser; 01-10-2013 at 02:38 PM.

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    Thats how I set my level.......Just till the fuel seeps over the bottom of the site hole.....They say do this while running the car.......be careful.....Souds like stuff I'm going through......Slight bog.....just off idle......You prolly seen my post..."lil 350 project"......Gonna blame it on the weather for now....only mid 30's......Will tackle it in the Spring.....I rebuilt Distributor.....so I'll start there..also added adj vacuum can.....You may need more Initial adv....less vac adv, with more mechanical at 1500 + all in at 3500.....a lot of varibles...as you know.....Good luck.

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    Quote Originally Posted by Budweiser View Post
    And... Just a mention... Probably not any part of the issue, but isn't the fuel level supposed to be at the bottom of the sight glass? Never had one with sight glasses, just plugs... and always set the floats to ever so slightly, just barely, dribble out of the hole.

    Hope the fix is easy and cheap Beer!
    Good luck!
    -Seth-

    PS, try tuning the idle mixture just a smidge off of lean instead.
    The opening in the screw cap float bowls is higher than the sight glass bowls The sight glass bowls are a no brainer. They actually have indicators to let you know the correct level.
    Notice that the bottom of the plug port is about even with the top of the fuel inlet notch out. So is the center of the sight glass.





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    Last edited by gn7; 01-10-2013 at 03:55 PM.

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    Or Seth, either one Budweiser's Avatar
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    Quote Originally Posted by gn7 View Post
    The opening in the screw cap float bowls is higher than the sight glass bowls The sight glass bowls are a no brainer. They actually have indicators to let you know the correct level.
    Notice that the bottom of the plug port is about even with the top of the fuel inlet notch out. So is the center of the sight glass.
    Well... Shit. Good stuff to know for sure. Thanks!

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