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Hard time with new quick fuel carb

42K views 34 replies 9 participants last post by  eric32 
#1 · (Edited)
I'm having a really tough time with this carb. Over the weekend i finally got the idle right, or so i thought, turns out the secondaries where all the way shut, there's an adjustment screw to open them alittle to allow more airflow at idle. This is what Quick fuel recommended i do because i couldn't get idle speed up with the primary idle speed screw, and the carb was not responding to idle mixture adjustments. After opening the secondaries plates a hair i was able to set my idle mixture (tac + vac gauge) and correctly trim idle speed with primary idle screw.

I had the engine idling at 1000-1100 right where it was with the Qjet, that's where my cam manufacture recommends i keep it idling at. Parked it over the weekend and fired it up Sunday to go for a cruise, ****ing thing will not hold an idle, and now when it stalls at a stop light with the engine up to temp (160-190f) it's having hard starts.

Also i went from a 72 to a 74 primary jet size, and it still surges at part-mid throttle cruising, it's fine when accelerating. At WOT it's fine as well, my plug reading is giving me a slightly lean reading. The surge is light, i figured going up 2 sizes would cure it but it still surges the same. It surves between 1900-2700 RPM cruising, fine on acceleration.


The engine is absolutely in time( had to go back and check for peace of mind), solid compression on check, it's a fresh engine with somewhere around 100 hours. With the Qjet carb i never had any of these problems. I pulled replaced the Qjet because at the time i THOUGHT it was leaking fuel, turns out it was a heatsoak issue and the fuel was boiling out of the vent. That's since then been resolved with a 1.5" plastic carb spacer.

The only off thing about this carb was when i unboxed it i noticed the accelerator pump was way loose, it had not been preset from factory, Quick fuel said that was strange as all carbs should be preset. Is it possible this carb has some internal issue? :confused:


At the end of the rope with it, if i can't nail this problem i'm buying a spacer for my Qjet and re-installing.

Carb is a Quick fuel hotrod series 780CFM vacc sec.
 
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#28 ·
That is what is nice with the quick fuel carbs you can adjust every circuit on the carb and always go back to out of box settings with no drilling of anything. I had to really lean my quick fuel 680vs out as well as it was just a pretty rich fuel curve on the idle part of things.
 
#29 ·
Alright sorry for the late response, before i got on here to read what you had posted eric i called quick fuel and they said that because the carb showed up missing a few things out of the box that it may be best to call summit and exchange it, so i did. This was yesterday at around 3:30 PM, the new one showed up at about 3 PM today LOL! I'm heading to work early tomorrow so i'll have time in the morning to remove the 1st quick fuel, place the factory jets/air bleeds back in and inspect to see what wen't wrong, i'll take some pics if i'm able to find anything. I'll snap a few shots of the gaskets and metering block, yall might see something i don't.

The new carb showed up with allot more in the box than the original, and i can tell the accelerator pump is set from quick fuel. When the 1st one showed up the accelerator pump was wound all the way in (spring fully compressed and really sloppy). There's allot of hardware and gaskets that came with the new one, that were not in the box with the 1st. I'm confident that tomorrow i'll be having some fun >:) and hopefully back to normal dialing in.
 
#30 ·
That is the problem with things today is quality control. Not saying quick fuel carbs are junk or any brand as its across the board in general for all things made but the really most important thing is companies standing behind there customers and quick fuel has been one of the best companies I have delt with and even when I had a carb that I could no longer return they checked it out for me and all I had to do was pay to ship it to them. From my experience they have excellent customer service and I always recommend there carbs.

I know that any future carburetors I buy will be quick fuel as they are the best bang for the buck for adjusting features compared to a same price holley brand. Good luck on your replacement and hope it works out for you.
 
#31 ·
Ok so before i boxed up and sent back the old Quick fuel i pulled the metering block off to inspect, and install factory jets. Yall called it, emulsion circuit was full of trash. I might not be calling the ports by the right name so..



ports 8 and 9 were packed almost full of something i couldn't identify, it looked like fishing line? beyond me. My setup has a new tank/pickup, filter, lines and pump, and i changed the filter again with this carb install for good measure. There's no way that trash came from my setup..

Anyways, i installed the 078 air bleeds and 074 main jets, installed the carb and BAM! The difference is night and day lol, runs just as good as the Old Qjet, and holds a STRONG idle in gear, im really happy. Thank you guys for helping me figure this out, i greatly appreciate it.

Now i can continue on tuning, after a few test runs i noticed when i go to WOT from part throttle it's not as responsive as the qjet was, it doesn't bog or hesitate, it just doesn't feel like i'm getting the full punch. Good example is, with the Qjet i could hold 1st till 5000 RPM and then grab second, and on a hot day i would loose traction and have to bleed throttle to regain, now it grabs 2nd, the tires chirp alittle bit but that's all. Where should i start?
 
#32 ·
A little hard to tell which is which in the picture but #'s 8 and 9 are the idle well feed channel to the idle mixture needle and the idle feed restrictor itself(the small brass insert)....so it is easy to see why you had a problem, glad you found out what was wrong. Blockage there will affect both idle and transition circuit.

As far as tuning now, I'd be looking at lighter secondary pod springs or the screw adjustment if your QF carb has that adjustment on the pod. You may not have the secondary's open soon enough or even fully open if spring is too stiff or screw restriction setting is too tight.

What is the rear jetting?? I'd expect to see something like #80 to maybe #86
 
#35 ·
Glad you found out what it was. That kind of thing happens on the occasion and it would be nice if all the companies had better quality control but some things do slip buy as that is just part of manufacturing and they make things so quick nowadays in order to keep up with demand and with less work force and more machine work then by human hands. I knew you would be able to get the quick fuel carb to work good. They along with summit and jegs always have excellent service. Glad your happy and up and running.
 
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