Quadrajet question

[wilyesteve]

I have been trying to tune my rebuilt 5.7... still only maxing out at 4100rpm according to the tach, and cold starting is not easy. Bought a rebuilt carb while I was at it too.

Idle is around 900rpm. Carb seems to like its idle mixture screws about 5 turns out.

If I try to lower the idle with the idle speed adjustment screw, I will get a whistling sound when I get the screw to a certain spot.... is this normal? Doesn't seem like it. The fact that the whistling is dependent on the throttle blades makes me think the air is NOT leaking around the intake or carb base, but rather within the carb. Carb cleaner spray around manifold or carb base does not indicate any leakage.

Any ideas?

 

[John_S]

I have been trying to tune my rebuilt 5.7... still only maxing out at 4100rpm according to the tach, and cold starting is not easy. Bought a rebuilt carb while I was at it too.

Idle is around 900rpm. Carb seems to like its idle mixture screws about 5 turns out.

If I try to lower the idle with the idle speed adjustment screw, I will get a whistling sound when I get the screw to a certain spot.... is this normal? Doesn't seem like it. The fact that the whistling is dependent on the throttle blades makes me think the air is NOT leaking around the intake or carb base, but rather within the carb. Carb cleaner spray around manifold or carb base does not indicate any leakage.

Any ideas?

Did you have a similiar problem with the original carb?

Is the replacement an exact replacement or a generic 305/350 calibration?

Any discussion with the rebuilder about the issues you are having?

Is the choke closing (stove or elec?), when you pump the throttle before cold start?

What is your engine vacuum at idle? If vacuum is low, q-jet will have metering problems.

 

[Stamey]

Re: Quadrajet question

I don't know about the whistle, but I just learned quite a bit about Q-Jets when I went through the rebuild of 3 of them for 2 boats. Turns out the throttle shafts are famous for wearing and causing a vacuum leak. Sounds like you already checked for that. The other thing I learned was that Q-jets can have internal vacuum leaks. Whouda thunk?
Can't really be of more help though. Sorry.

Chris

 

[LX Kid]

Re: Quadrajet question

I had problems with my q-Jet so I rebuilt it twice and still had nightmare problems. Bought a factory rebuilt and it was a nightmare also. "Then" I bought an Edlebrock 1409 and a spacer plate and all my problems went away! Idles beautiful at 500 rpm or even lower if I wanted!

 

[strok351w]

Re: Quadrajet question

AMEN to that brother, I did the same thing and all of my ilde and performance problems went away, It's a nice little carb.1985 5.7liter, four winn liberator 211.

 

[wilyesteve]

Re: Quadrajet question

Did you have a similiar problem with the original carb?

Is the replacement an exact replacement or a generic 305/350 calibration?

Any discussion with the rebuilder about the issues you are having?

Is the choke closing (stove or elec?), when you pump the throttle before cold start?

What is your engine vacuum at idle? If vacuum is low, q-jet will have metering problems.

Original carb just did not like to idle so I replaced it... i'm going to rebuild it, but for $230 from National Carburetor, I figured I might as well start fresh. Maybe I was wrong?

It was listed as a rebuilt Quadrajet for a 5.7 with Mercruiser linkage.

Choke closes.

Need to check vacuum... need a gauge. How much should it be pulling at idle?

I'm just wondering if that whistle actually means that the shafts are leaking or if there is some internal vacuum leak somewhere.

For the record, I had a Motorcraft 4350 on a Ford 460 engine in a Lincoln, and switching that to a Holley 750 Vacuum Secondary was the best thing I ever did for that car.... so I hate these Quadrajet type carbs. Is there any problem with doing a spreadbore to squarebore adapter in a boat?

 

[jmorgan87]

Re: Quadrajet question

Electric or Manifold choke?

I can't help but think you shouldn't need to rebuild a carb you just got from national, they rebuild and test prior to shipment. I orderd a mercruiser linkage with electric choke for my boat. It went from not able to idle no matter what you did, and unable to run without manually choking the carb using your hand(ouch) on the old original carb, to cranking and idling perfectly right out of the box with the carb from national carburetor.

It's a chance you got a bad one from national carb, but considering they bench test prior to shipping..i'd seriously check everything else out first and, if possible, try your new carb on a known good engine or a known good carb on your engine if you have any SBC's laying around.

I highly recommend national carburetor after trying them, and tried them thanks to suggestions from here.

 

[John_S]

Re: Quadrajet question

Original carb just did not like to idle so I replaced it...

So it didn't have the same issue with the mixture screw adjustment? or not able to get the rpms down?



i'm going to rebuild it, but for $230 from National Carburetor, I figured I might as well start fresh. Maybe I was wrong?

It was listed as a rebuilt Quadrajet for a 5.7 with Mercruiser linkage.

I have no exp with NC, but a bad exp with another builder. Have you opened discussion with them?



Choke closes.

Good.



Need to check vacuum... need a gauge. How much should it be pulling at idle?

My 350 mercruiser experience says around 17-18, and see info links below. It can provide allot of info on the condition of your motor.



I'm just wondering if that whistle actually means that the shafts are leaking or if there is some internal vacuum leak somewhere.

Don't try to go by the sound. Your idle speed is too high, and have spark arrester and cowling removed. Let the vacuum gauge tell you, and/or leak checks.



For the record, I had a Motorcraft 4350 on a Ford 460 engine in a Lincoln, and switching that to a Holley 750 Vacuum Secondary was the best thing I ever did for that car.... so I hate these Quadrajet type carbs. Is there any problem with doing a spreadbore to squarebore adapter in a boat?

While I would say its not ideal, Mercruiser did it, and have seen a number of positive iBoat members that have gone that way with Edel 1409.

http://www.secondchancegarage.com/public/186.cfm

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm

 

[wilyesteve]

Re: Quadrajet question

It's manifold choke, and it seems to pull off as it should....

John, thank you for those links. Very informative!

 

[chrismurr1]

Re: Quadrajet question

i just went through a long bout with my twin 305s. bough 2 rebuilt merc q-jets from national as well. they just threw them together, jets and primary rods were different, secondary hangers were different... it was a painful process.... my local experts here recommended i stick with them as once you get them tuned, they stay tuned. i rebuilt them and purchased a set of rods/jets and hangers. now they are perfect.

the Q-jets are very sensitive to vacuum leaks so make sure your base gaskets are new and in excellent condition. if you pull the carb off the engine several times you will compress them to the point that they wont seal. if your running a wedge plate under the carb to level it (as i am) make sure that gasket (to the manifold) is in prime condition too.

I had the whistle on mine, turned out to be a leaking gasket. Here are the specs i have on mine now.

Primary jets - .081
Primary rods - .051M (yes, these have a larger power tip)

Secondary rods - DP
Secondary hangers - K

Brass floats (the ones they give you tend to stick if you let the engine sit over a week)

5 turns out on the air/fuel mix screws and 2 turns in on the idle speed and wala.... 800 rpm (650-700 in gear).

hope this helps... let me know if you want to discuss it more, i have done a TON of research on these for tuning and rebuilding. I am an edlebrock junky too and was just about to buy 2 new ones when i replaced the base gaskets on both sides and poof..... i will tell ya in a month or so if they are as good as the local mechanics say they should be. they are very complicated carbs... which is why most people hate them (IMO)

 

[wilyesteve]

Re: Quadrajet question

Thanks for the detailed reply, Chris.

I actually am using a pretty stout carb to manifold gasket (Mr. Gasket) because the paper one that came with the carb totally leaked. The guy at Advance said it was the kind that should be able to be reused for a few installations.... Though now i'm looking at ebay and I see a bunch of 1/4" gaskets, which I think are thicker than what I'm using... Maybe I'll try to switch the gasket out and see.

 

[Beachcraft 1]

Re: Quadrajet question

I bought a national carb Q-jet, same setup and I am having the same problem. See my thread "Bizarre Idle Situation." I have tried everything under the sun, but the problem is I have $500 wrapped up Q-jets and I hate to give up and simply buy a Edelbrock, Holley, etc. I have pulled intake manifold, bought brand new Q-jets, that thing is sealed tight and still have the sucking sound and no idle.

 

[Alpheus]

Re: Quadrajet question

I made this video to help others to rebuild their Q-Jet carb. Its higway robbery what some of the rebuilders are charging for a basic rebuild of a Q-Jet. Its just a cleaning with a new float,needle,seat and some gaskets.

Check out the videos in this link. It should explain things...

http://forums.iboats.com/showthread.php?t=362542&highlight=QUADRAJET+VIDEO

Also read post #7 in this link. It will explain how to tune your idle mixture screws...

http://forums.iboats.com/showthread.php?t=388794

 

[chrismurr1]

Re: Quadrajet question

I assume the gasket you got from National was a 1/4" purple? that is what i got and those are made to compress and seal minor imperfections... its what i am running under the carb itself. i have 1/8" paper under my wedge plates. I agree, they are good for a few installations but in my experience, after 6 compressions max, they stop sealing. You can get that same 1/4" gasket at west marine or a good pro shop for under 10 bucks or you can buy a rebuild kit from Advance for 22 bucks (I have a spare rebuild kit for each carb in the event i needed a part).

I assume that since you just purchased these you have not opened up the carb at all? I know it voids the warranty from National but if you do open it up, dont reuse any gaskets more than twice, and if you tear it at all.... replace it.

Also, it helped me a ton to understand what was going on by using a vac gauge, go get one from Advance, put it all together leaving the vac tube hanging from it. you can pull the vac pulloff hose from the front of the carb off and the tube will just fit into the carb fitting. good idle vac at this port is between 15 and 16, anything below that and you will have a rough unstable idle and in my case, indicated a vac leak.

 

[wilyesteve]

Re: Quadrajet question

Alpheus, thank you for your work in making those videos. Luckily, I didn't send the core back in, so I will give it a go. I have rebuilt a Rochester 2GC before, so hopefully I can do a 4bbl.

Chris, the gasket from National was purple, but I don't think it was as thick as 1/4". In any event, the engine raced to 2000 RPMs with that gasket with the idle screw all the way out, indicating a severe vacuum leak. The gasket under the old carb was a much thicker rubber gasket, but I was afraid to reuse it.

I'm going to try to rebuild the old carb. If that solves my problems, then I will return the National Carburetor under the warranty (haven't touched it internally to keep this option) and hope that I get a good replacement to use as a spare. They claim it was bench tested, but who knows.

 

[fastimz]

Re: Quadrajet question

Im going to chime in on the National Carbs. I bought a quadrajet for my 454 that was bench tested and blah blah blah. When I put on my bench (454) it ran like a turd. It stumbled and sputtered and backfired. I adjusted on it and adjusted on it with no improvement. I called them and they said they would send me a second carb. I bolted it on and the engine wouldn't even stay running. I had an old Holley on the shelf, bought a rebuid kit and it ran like a top. Im sure some of the carbs that come from them are good but i had two that where terrible. Im with you, I hate a quadrajunk, but I am a Ford guy! haha. Hope you get things fixed up.

 

[wilyesteve]

Re: Quadrajet question

Just wanted to update you guys on where I'm at as I finally got out to the lake this weekend.

Rented a Vacuum gauge. Tweaked the idle screws and advanced the distributor slightly so that it was pulling 16 inches at idle, though the needle was fluttering erratically down to 14. It was never really was that steady on the gauge. Sprayed the heck out of the base with carb cleaner with no effect. Still get a slight whistle from the carb from time to time. Idle is better and low speed manners are pretty good. I want to get a second opinion on my tach's accuracy, as the needle doesn't always seem to match what my ear is hearing.

The only real problem is a hesitation on acceleration at mid-throttle. I'm guessing that this carb is just junk. 2-4 foot seas today and I would like the immediate throttle response when fighting back against the waves.

 

[John_S]

Re: Quadrajet question

Rented a Vacuum gauge. Tweaked the idle screws and advanced the distributor slightly so that it was pulling 16 inches at idle, though the needle was fluttering erratically down to 14. It was never really was that steady on the gauge. Sprayed the heck out of the base with carb cleaner with no effect. Still get a slight whistle from the carb from time to time. The only real problem is a hesitation on acceleration at mid-throttle. I'm guessing that this carb is just junk.

If there was a pattern to the drop, that could indicate something with the valves.

 

[wilyesteve]

Re: Quadrajet question

If there was a pattern to the drop, that could indicate something with the valves.

Lifters don't sound noisy, and this is a new rebuilt engine so I'm hoping it was put together correctly.

http://www.secondchancegarage.com/public/186.cfm

It looked more like Scenario 3, but with another inch of movement, as opposed to a steady ticking like Scenario 5, and was a much faster flutter than Scenario 7.