I want to replace my quadrajet..

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Kyle700

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« on: October 11, 2012, 12:03:59 PM »
I have a chevy 350 with a jacuzzi jet pump. The carb came off a car (I am told) and I would like to replace it with something a little more user friendly since it doesnt have any manual adustments, just metering rods. If I go Holley, should I put a 650 ot 750 (spread bore)  or what else out there is user friendly?

Thanks


IRRebel

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« Reply #1 on: October 11, 2012, 12:45:20 PM »
I have a chevy 350 with a jacuzzi jet pump. The carb came off a car (I am told) and I would like to replace it with something a little more user friendly since it doesnt have any manual adustments, just metering rods. If I go Holley, should I put a 650 ot 750 (spread bore)  or what else out there is user friendly?

Thanks

Depends on what you're familiar with. If Holley is your game, then an adaptor plate and square bore is where I'd go if you don't want to change the manifold and just feel like spending money. The Q-Jet was a car/marine carb, but only available now as marine, so it's quite probable yours IS a marine carb. As far as user-friendly? The Q-Jet is about as user friendly and maintenance free as they get! Tuning a Holley, I swear, sometimes I think should require a 2 year college degree. They ain't that complicated, but man they CAN give you fits! I always call Crewcheif (who can tune a Holley over the phone while on the can "pinching a loaf".........he's done it.......)

Personally, and just going from Hot Rod performance from back in the "olden days" as you kids call it now and not really messing with them much on boats, you're going to be very hard pressed to beat that Q-Jet (Or a ThermoQuad) in performance by just switching to another carb such as a spreadbore Holley. The money saved by just learning the carb, rebuilding it and tuning it will pay for more than a few weekends of fuel. Those carbs can run, and run HARD, and reliable as all get out!

Now, changing the intake manifold, that opens up a whole new world to you. As well as your wallet.

Get with GTJets here on the boards. He probably has more experience with the Q-Jet than he does with the Holley, to be honest, and can help you if you're having issues with yours.

Ray
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways totally worn out shouting 'Holy Shit what a ride!"---Crewcheif22 AKA Keith

Kyle700

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« Reply #2 on: October 11, 2012, 02:28:31 PM »
It was actuallt GT Jets that posted this to me.....".Someone just threw an automotive motor in your boat......."

lbhsbz

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« Reply #3 on: October 11, 2012, 08:28:40 PM »
If its a non feedback q-jet, I'd keep it.  They go for 100K miles in a car without looking at 'em....and perform damn well if they haven't been screwed up by someone.  If you've got a stock 350, there isn't a carb out there that will run any better without plenty more changes being made

GT Jets

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« Reply #4 on: October 11, 2012, 11:20:37 PM »
If its a non feedback q-jet, I'd keep it.  They go for 100K miles in a car without looking at 'em....and perform damn well if they haven't been screwed up by someone.  If you've got a stock 350, there isn't a carb out there that will run any better without plenty more changes being made

I love me a good Quadrajet on a small block...

It was actuallt GT Jets that posted this to me.....".Someone just threw an automotive motor in your boat......."

I did..... And the problems that I remember that you face are that you have an OEM iron EGR intake manifold, improper linkage attachments and an automotive HEI.

If you want to do something on the cheap, I still stand by rebuilding the Q-Jet.

These carburetors are an engineering marvel...

As far as user friendly tune-ability... They have replaceable jets, metering rods, an adjustable secondary butterfly among some other tweaks that the average Joe can do....

If you want the best performance you can get... Get an Edelbrock RPM Air Gap and a square bore 650-700 CFM Holley or Holley clone (Quickfuel has some nice stuff), but be prepared to drop some coin.

I have built some mean small blocks and the secret is in the camshaft and the compression ratio, you more than likely have neither.

What are you trying to adjust? Literally everything on that carburetor is adjustable.

Float level, idle mixture, secondary pull in point, secondary fuel metering, primary fuel metering, accelerator pump stroke...Everything..

Lemme know what it is or is not doing and we'll see if we can figure it out... 8)

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

Kyle700

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« Reply #5 on: October 12, 2012, 05:58:54 PM »

Thanks
« Last Edit: October 12, 2012, 06:22:58 PM by Kyle700 »

Kyle700

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« Reply #6 on: October 12, 2012, 06:18:01 PM »
I have a backfire issue the exact same as "Santee_Native."  I've been told the motor is leaning out at WO, but my plugs arent white. GTJets...you mentioned something about my intake manifold, should I replace it?  What should I replace it with if I keep the quadrajet?

The carb has hoses on it that are plugged with bolts or screws. Maybe I will shop around for a marine version and chase from there. I nothing else...a piece of mind that the carb is OK
.
As far as I know, the motor is as old as the boat..1976. I was think about replacing the valve springs which "cured" Santee_Natives problem.
« Last Edit: October 12, 2012, 06:27:43 PM by Kyle700 »

GT Jets

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« Reply #7 on: October 12, 2012, 11:01:33 PM »
I have a backfire issue the exact same as "Santee_Native."  I've been told the motor is leaning out at WO, but my plugs arent white. GTJets...you mentioned something about my intake manifold, should I replace it?  What should I replace it with if I keep the quadrajet?

The carb has hoses on it that are plugged with bolts or screws. Maybe I will shop around for a marine version and chase from there. I nothing else...a piece of mind that the carb is OK
.
As far as I know, the motor is as old as the boat..1976. I was think about replacing the valve springs which "cured" Santee_Natives problem.

Many things can cause a backfire.

Here is the simple list, this is off the top of my head so please forgive any misinformation.

Ignition "cross talk" this is when the spark in the distributor cap "jumps" from pole to pole...

Valves hanging open, not all together impossible given you don't know the history of the motor.

Lean condition, you may typically experience a hesitation or "stumble" along with a backfire... Could be carburetor...maybe not.

An electrical gremlin, these are total ass kickers, lets just say you have either a voltage drop or an intermittent loose connection from the ignition circuit, it will cut in and out causing some weird crap to happen.

Fuel pressure loss at high loads, this can be caused by a weak fuel pump, plugged up fuel pickup, degrading hoses, plugged filter etc...

An ignition coil breaking down at load (should have been above, but I'm feeling lazy and I aint getting paid anyway)..

Low system voltage....


So....In short, now it's on you.

You need to obtain a vacuum gage, a fuel pressure gage, a good volt meter and some jumper wires...

You want to see a consistent 13.5+ volts anytime the engine is running.

You want to see very stable vacuum levels, a bouncing vacuum needle potentially means valve issues..

Your carburetor requires 5-6 PSI fuel pressure, more it will flood, less it can run lean, typically speaking an automotive fuel pump is barely up to the task. A low float level can do it too...

As for the intake manifold, there are a lot of opportunities for vacuum leaks. Not a fan of EGR manifolds with block off plates.

As for a replacement, if you really want to stick with the spread bore (nothing wrong with them) I would say go with an Edelbrock RPM Air gap and an adapter to go from square to spread bore, the spacer/adapter can help with plenum velocities and also afford you the ability to go with a square bore carburetor later.... Win win.

Good luck, now go get some data...When I get a couple minutes tomorrow I will head over to the shop and get you some settings for that Q-jet.





  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

IRRebel

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« Reply #8 on: October 14, 2012, 06:44:07 PM »
I had a similar thing with my old boats BBC, not to that extreme as to backfire though. The boat would balls out to 5100 rpm forever if you flat footed it and held it. If you lifted at all, then flat foot it again, it fell flat on is face and spit and sputtered trying to get above 3500. Did the same thing if you just rolled gently into it. Weirdest thing I ever had to mess with. Spark plugs were perfect.

Immediately thought, Carb, or vacuum leak (Did find a couple small ones on the carb base gaskets and the same thing you described with "bolts and screws" plugging vaccum ports. This was a Holley 750, BTW. Replaced the base gaskets, put real caps on the unused vacum ports, 3 different carbs (2-750's and 1 850, all known good).

Still did it.

Also had the HEI on it. Replaced the cap, rotor, coil, plug wires and also noticed a lot of oil under the rotor, in the reluctor area, so cleaned that up and replaced the module in there also.

Still did it.

When I pulled the dizzy back apart, still in the engine, to check and see if I messed something up installing, was oil everywhere in there again (I had always noticed some oil gathering around the base of the dizzy and running down the back of the engine, but figured it was a bad O-Ring on the body of the dizzy to the block and I'd get to that someday. Didn't leak enough to really worry about)

A-HA!! Pulled the dizzy and the bushings inside were so shot that I think if I yanked hard enough, I coulda pulled the shaft clear out the top with the gear still attached!

I replaced it with a Unilite and Hyfire 6AL box,

Problem gone!!   :thumbup:  HEI's are just not my gig, so fixing that thing up AGAIN (was $115 into it already) wasn't even on the menu.

Just one thought. Another simple one COULD, just maybe be, some on the site have seen this one also, that the rockers are wayyy overtightened and cranked down from someone trying to get rid of a lifter "tick" that was really a collapsing/failed lifter issue and not a simple adjustment issue. This would give every indication of a bad valve spring or two.

Ray   
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways totally worn out shouting 'Holy Shit what a ride!"---Crewcheif22 AKA Keith

Kyle700

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« Reply #9 on: October 15, 2012, 07:18:50 AM »
Thanks guys, I looks like I have my work cut out for me..  Ray, we did tighten the rockers to try to get rid of a noise top left (helped a little), didn't overtighten though, had some loose ones. I think I will still do the springs and go down the list.

GT Jets

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« Reply #10 on: October 15, 2012, 07:47:04 AM »
Thanks guys, I looks like I have my work cut out for me..  Ray, we did tighten the rockers to try to get rid of a noise top left (helped a little), didn't overtighten though, had some loose ones. I think I will still do the springs and go down the list.


We call this "the smoking gun"...How were they adjusted?
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

IRRebel

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« Reply #11 on: October 15, 2012, 09:23:21 AM »

We call this "the smoking gun"...How were they adjusted?

I think Glenn has just pointed out, you found enough evidence to warrant a wiretap and surveilance on the lifters and or valve springs in question.

Ray

PS: If you were in there adjusting rocker nuts and didn't notice any broken springs, etc, not much else evidence really needed IMO. You are going to see between 50 to 500 failed hydraulic lifters before you see a failed valve spring.

Don't go changing or replacing parts until you KNOW what failed and WHY!

Just my .02, But I think you're dealing with a few crapped out lifters, given what we NOW know.

How's the oil pressure been through all this?
« Last Edit: October 15, 2012, 10:18:50 AM by IRRebel »
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways totally worn out shouting 'Holy Shit what a ride!"---Crewcheif22 AKA Keith

Kyle700

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« Reply #12 on: October 15, 2012, 08:56:25 PM »
The rocker nuts were adjusted by exact directions from a Chevrolet repair book specifically for the 350. If the engine is original, those springs gotta be tired after 36 years. No?

GT Jets

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« Reply #13 on: October 15, 2012, 09:21:58 PM »
The rocker nuts were adjusted by exact directions from a Chevrolet repair book specifically for the 350. If the engine is original, those springs gotta be tired after 36 years. No?


Engine running, or off and cold? GM has changed these instructions numerous times...

As for the springs getting tired.......I once saw a 350 Chevy go 395,000 miles and it never had the valve covers off. So judjment call, depends on how long the motor has been on a boat. Boats be harder on stuff than a car.

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

Kyle700

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« Reply #14 on: October 16, 2012, 04:02:27 PM »
The engine was off and cold.

GT Jets

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« Reply #15 on: October 16, 2012, 06:50:32 PM »
The engine was off and cold.

You have a collapsed hydraulic lifter.... ;) JMHO

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

 


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