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73-87 Chevy _ GMC Trucks => Performance => Topic started by: 1979C20 on December 12, 2010, 03:31:14 PM

Title: Carb question
Post by: 1979C20 on December 12, 2010, 03:31:14 PM
Would a Holley 750cfm double pumper part#r84013 be too much for a basically stock 350 with a 440 292 comp cam? Stock heads, stock crank, stock pistons, stock intake, stock distributor, headers, about 2000mi on engine. Daily driven, like its a race car. Haha. I only get about 8 or 9mpg with my stock qjet that needs replaced/rebuilt. So I dont expect much mileage.
Title: Re: Carb question
Post by: Captkaos on December 12, 2010, 11:04:37 PM
Yes.
Title: Re: Carb question
Post by: 1979C20 on December 13, 2010, 01:00:10 AM
Really? I searched online and was told the stock rochester q-jet was a 750-800cfm....
Title: Re: Carb question
Post by: Irish_Alley on December 13, 2010, 04:14:14 AM
The quad can be tuned on to run that much. A Holley you want no more than 650 with a stock engine. You will find if you want better gas mpg than your gearing should be lower than it is and drive it like an old man
Title: Re: Carb question
Post by: Grim 82 on December 13, 2010, 09:23:11 AM
To save money and get better mileage rebuild the q-jet. If you just want a shiny new carb a 600 cfm Edelbrock or Holley would be plenty for a stock 350. You would need the adapter plate to put it on your stock manifold if you buy a square bore carb.
Title: Re: Carb question
Post by: Captkaos on December 13, 2010, 11:31:05 AM
Q-jet is MAX Flow of 750-800cfm.  It runs on 2 small primaries for the most part and the secondaries work on Vacuum demand, generically speaking the motor will only pull what it needs.

A double pumper has a mechanical secondary and when it is engaged it will dump the fuel in regardless if it needs it or not.

Title: Re: Carb question
Post by: 1979C20 on December 13, 2010, 02:16:23 PM
How do you bolt the adapter plate on? My dad had on in the shed out back, mr. Gasket square to spread. It has 4 2sided studs, 4 nuts, and 4 washers.
Title: Re: Carb question
Post by: Irish_Alley on December 13, 2010, 03:13:35 PM
Bolt it to the intake then bolt the Carb on
Title: Re: Carb question
Post by: 1979C20 on December 13, 2010, 04:05:26 PM
But how? I dont understand how it would bolt on.
Title: Re: Carb question
Post by: Grim 82 on December 13, 2010, 04:12:52 PM
There should be recessed holes to bolt it to the intake, then 4 studs that thread into the adapter, then put the carb on the studs and put nuts on them.
Title: Re: Carb question
Post by: 1979C20 on December 13, 2010, 04:19:20 PM
Anybody have pictures of how to install one? Because there are several holes and what now. Like I said, I have 4 2 sided studs, one side is course thread that I believe threads into the intake manifold, and the other side is fine thread which matches the 4 nuts.
Title: Re: Carb question
Post by: Grim 82 on December 13, 2010, 04:28:37 PM
And you need 4 bolts to bolt the adapter to the intake. The fine thread end of the studs thread into the adapter. Make sure you use 2 gaskets.
Title: Re: Carb question
Post by: Grim 82 on December 13, 2010, 04:35:19 PM
http://www.4wheelparts.com/aux_incl/pdf.ashx?pdf=2696_2697_SqBoreCarbtoSpre.pdf&line=EDE
Title: Re: Carb question
Post by: 1979C20 on December 13, 2010, 05:22:35 PM
There are no threaded holes on the adapter plate. how does it bolt to the intake and carb? nuts on either side of the plate?
Title: Re: Carb question
Post by: Grim 82 on December 13, 2010, 06:03:03 PM
Lets see a pic of the adapter.
Title: Re: Carb question
Post by: Captkaos on December 13, 2010, 06:05:16 PM
Did you check out the link Grim 82 posted?  shouldered allen bolts on the adapter to the intake, studs from the adapter to the carb.
Title: Re: Carb question
Post by: 1979C20 on December 13, 2010, 11:37:15 PM
I'm on my phone, so I cannot upload a pic of mine, but I found a retail pic of it. [url]http://www.jegs.com/images/photos/700/720/720-1932.jpg[url/] on this side of the plate, the hex holes are on the outsides, but on the reversed side of the plat the hex holes are on the insides. I only have 4 equal length 2 sided studs, 4 nuts, and 4 washers
Title: Re: Carb question
Post by: 1979C20 on December 13, 2010, 11:49:09 PM
(http://www.jegs.com/images/photos/700/720/720-1932.jpg)
Title: Re: Carb question
Post by: Irish_Alley on December 14, 2010, 04:31:46 AM
(http://www.jegs.com/images/photos/700/720/720-1932.jpg)
Title: Re: Carb question
Post by: Irish_Alley on December 14, 2010, 04:39:58 AM
ok you put the silver bolts threw the bottom facing up, then you set the gaskets on now the trick part is to keep all the bolts in place while its sitting over the intake donít drop any bolts down then you take the black bolts "Allen/hex" key if I can remember right and tighten the adapter plate to the intake, then you set the carb onto the adapter plate and use the nuts to hold it down. As far as the studs I donít think you use them with your application
Title: Re: Carb question
Post by: Irish_Alley on December 14, 2010, 04:44:19 AM
Your pic was close to the code just move the backspace over in front of the img /img
Title: Re: Carb question
Post by: 1979C20 on December 14, 2010, 04:25:23 PM
Thanks Irish, for the advice on the img posting and the help with the plate. Thanks everyone else too. Sadly, the guy on craigslist flaked out on me like a loser and didnt call or answer his phone. So I'm stuck with my qjet. My dad said he would rebuild it for me. So, new question! How do you rebuild a qjet? Like, what do you need. Obviously a rebuild kit. 45 bucks at orielly's. What else? Can or two of carb cleaner? Vat of carb cleaner? Any instructions on how do disassemble and reassemble a Rochester q-jet carb from a 79 c20 with a 350?
Title: Re: Carb question
Post by: Irish_Alley on December 14, 2010, 07:47:03 PM
A good tip buy a book on the quads wish I could help but they are at the parts store. Its not that hard and one of those shows on power block rebuilt one I'm sure it was Ian
Title: Re: Carb question
Post by: 1979C20 on December 14, 2010, 08:54:44 PM
Okay! New new question. My dad has a holley carb out back that is in really good condition that isn't being used because it is dumping fuel into the venturis. He says it isn't the needle and seat and that the bowl is not overflowing. He says it is dripping out of the power valves. I do believe it was rebuilt not too long ago. So, what would this be? What would cause a carb to leak out of the power val
ves?
Title: Re: Carb question
Post by: TexasRed on December 14, 2010, 09:02:58 PM
a blown power valve would dump fuel
Title: Re: Carb question
Post by: Irish_Alley on December 15, 2010, 12:19:49 AM
does it dump after the engine is shut off?
Title: Re: Carb question
Post by: 1979C20 on December 15, 2010, 01:03:22 AM
It dumps ALL of the time. At idle right after start up. It just drips out of the booster valves in the primaries. Would it really be the power valve in a rebuilt carb?
Title: Re: Carb question
Post by: HAULIN IT on December 15, 2010, 03:00:09 AM
A bit off of the real topic, but I'm going to mention a few things based on reading your original post. For starters, it is a real shame that guys abandon the Q-jet carb on so many projects...the ones they are ideal for seem to be the ones they get tossed off of most. That being said, a properly tuned Q-jet will work very well for what your doing. Also you don't end up with "rigged": fuel hose, carb linkage, air cleaner, choke system, ect. ect. like so many people do when ditching the stock carb.
 Now to the other things. I'm not sure what cam you have based on your "440 292" numbers. The .440 would be lift, which they show a .440 lift cam in there "High Energy" line with an advertised duration of 260. The 292 you mentioned is the advertised duration...Comp has one of those, but with a .501 lift. If you really have the first cam, that should work well with your mostly stock engine, however if you really have the 292...it should be removed, it will be killing the little bit of performace & efficiency your engine could have.
 If you do have the "High Energy" cam, a nicely tuned Q-jet should make for a fairly good runner with reasonable manners & mileage. My Two Cents. Lorne
 
Title: Re: Carb question
Post by: 1979C20 on December 15, 2010, 02:37:29 PM
I just went and read the specs card from comp cams, you are correct. It is 260 duration. I can grab the part number in a bit. The reason I'm 'abandoning' the qjet is because it a pain to rebuild. I'm looking for something in good condition I can just throw on and tune to my truck.
Title: Re: Carb question
Post by: ToddN on December 17, 2010, 08:16:24 PM
I second the thumbs up for the Q-Jet.  If you are running the vehicle at the strip and you need to take the carb off every other run to do adjustments then get a Holley or an Edel.  If you want to hop in your truck in the morning and stomp on it to get to work on time then stick with the Qjet.  The Rochester Q jet is PLENTY of carb for a stock 350.  In fact...I just pulled off an Edelbrock 1407 600cfm and put an electric choke coil on an old Q jet and it runs twice as good.  This Q jet was also sitting on a rusted out delivery van and with two pumps on the pedal, it fired right up and I haven't looked back since.
Title: Re: Carb question
Post by: ToddN on December 17, 2010, 08:19:54 PM
Whats there to rebuild on a Q jet?  9 times out of ten the choke coil is shot or the choke pull off is shot.  Replace those two things, throw some carb cleaner around and some compressed air and I bet she screams.