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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Hotrodding Basics> Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level)
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Thread: Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level) Reply to Thread
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Topic Review (Newest First)
06-24-2012 11:52 PM
lt1silverhawk I wanted to give some updates on the carburetor since the rebuild.




First off, all of the information on this thread was compiled and properly organized into this wiki: "How to rebuild a Rochester Quadrajet 4MV carburetor". A few members have added additional info to what is found in this thread, so please do check it out.




During the rebuild, I did dab 5-minute epoxy over the plug wells as a precautionary measure. The carb was recently disassembled for a clean up, and the epoxy had corroded and had become flaky. It was cleaned off. The wells don't seem to be leaking.






It was noticed during this past dis-assembly that the main well bleed tubes in the air horn were clogged. They were cleaned out using Hobart 770085 Welding Oxy-Acetylene Tip Cleaner. The procedure involves dissembling the top end of the carb, finding the largest tip cleaner that fits inside the bleed tube, and slowly filing away. Keep moving a size up until its all cleaned out.







Another thing that was missed during the first rebuild was the eccentric plastic cam in the air horn that is responsible for the secondary metering rods. It was found during a recent reassembly in the float bowl body, where the key that operates the choke plate is found. The part was ordered from Cliff Ruggles' site. The kit also included new screws for the air flaps.


The procedure replacing the cam involves removing the air flaps and shaft assembly, and is outlined in the images below.


05-02-2011 01:54 PM
cobalt327 The choke pull off needs replacing regardless of the idle situation. It controls the opening rate of the secondary air valve. It applies force when it has vacuum applied (like at idle ) to the air valve linkage that holds the air valve and everything else attached to it (this depends on the exact carb in question as to what else, if anything, is included) in the proper position.
05-02-2011 01:09 PM
kikkegek
Quote:
Originally Posted by lt1silverhawk
That looks like a nice setup.

About the choke pull-off, according to "How to Rebuild and Modify Rochester Quadrajet Carburetors", Ruggles says to "vacuum-test the factory choke pull-off and replace as needed." (page 87). If sucking on it isn't working, it might be time to replace it. (Damaged diaphragm?)
okay, thanks for that. But in my setup, I dont need the choke. My engine will start however cold it is, because I run LPG for main fuell and only have regular fuel for backup.

So I will only repair the pull off if it is causing the high idle. And as far as I know, it has no relationship to that. Or does it?

@Willy, thanks for the nice and clear picture. Looks nice and clean!
05-02-2011 12:57 PM
lt1silverhawk That looks like a nice setup.

About the choke pull-off, according to "How to Rebuild and Modify Rochester Quadrajet Carburetors", Ruggles says to "vacuum-test the factory choke pull-off and replace as needed." (page 87). If sucking on it isn't working, it might be time to replace it. (Damaged diaphragm?)
05-02-2011 12:11 PM
kikkegek yes I mean the choke pull off. I unhooked it, tested it, sucked on a hose and it didnt do nothing. what does this thing do and how can it keep my linkage from going to normal (low) idle?

and as for the linkage setup .I have it setup just like that now with a double spring. Check this picture out:



so I am really in the dark why I ca fix the high idle problem.
05-02-2011 12:00 PM
lt1silverhawk Hey kikkegek,
Quote:
Originally Posted by kikkegek
alrighty,

checked the choke unloader. unplugged it...first put a hose on it and sucked on it, but the unloader doesnt move...

I then plugged the connection to the carb and drove it a bit. But no change.
Are you referring to the choke pull off? See the picture attached for the part I am referring to.


Quote:
Originally Posted by kikkegek
Still got the annoying high idle when I dont kick the throttle...

I made two short films (As requested) hope you guys can see what I mean...

first one without engine running (sorry movie is upsidedown)
http://www.youtube.com/watch?v=lAIkJiofIAA

second one with engine running (sorry again upsidedown)
http://www.youtube.com/watch?v=3ZKK1kIdVZ4

As you can see it is only a very little bit that the throttle stays open.

and it's almost like the little play there is in the linkage seems to be gone when the engine is running. I can not feel any play when the engine is running.
I really couldn't hear the engine over the wind noise, but Im sure the experts on this forum will come through. Btw, did you consider trying the single or double-spring set up that cobalt327 and Willys36 posted pictures of (posts 127 and 138)?
05-02-2011 03:09 AM
kikkegek alrighty,

checked the choke unloader. unplugged it...first put a hose on it and sucked on it, but the unloader doesnt move...

I then plugged the connection to the carb and drove it a bit. But no change.

Still got the annoying high idle when I dont kick the throttle...

I made two short films (As requested) hope you guys can see what I mean...

first one without engine running (sorry movie is upsidedown)
http://www.youtube.com/watch?v=lAIkJiofIAA

second one with engine running (sorry again upsidedown)
http://www.youtube.com/watch?v=3ZKK1kIdVZ4

As you can see it is only a very little bit that the throttle stays open.

and it's almost like the little play there is in the linkage seems to be gone when the engine is running. I can not feel any play when the engine is running.
05-01-2011 11:21 PM
willys36@aol.com Here is a photo of the 'better' spring bracket I made for my grandson's Elky. Cut it out of a piece of scrap 1/4" thick aluminum I had lying around. Took all of 30 minutes to make including the polishing. Mounts on front head bolt.


04-22-2011 03:29 PM
lt1silverhawk
Quote:
Originally Posted by kikkegek
I mounted it to on of the big screws of the A/C bracket.

I didnt help me sofar though. I still have high idle. I did notice that with the engine warm and not running the linkage runs smooth and free. When I turn on the engine and it is warm...the last bit of the linkage...1-2mm is not smooth...

I checked if the fast idle cam is keeping the idle high, but it isnt...what else can it be?
While I don't know the answer to your question, I'm bumping this post up so hopefully someone responds soon. If it is possible, can you make and post a video showing what happens? Maybe two videos, one with engine on and the other with engine off?
04-21-2011 02:59 PM
kikkegek
Quote:
Originally Posted by lt1silverhawk
Hey kikkegek,

That looks pretty good. Where did you mount the bracket to?
I mounted it to on of the big screws of the A/C bracket.

I didnt help me sofar though. I still have high idle. I did notice that with the engine warm and not running the linkage runs smooth and free. When I turn on the engine and it is warm...the last bit of the linkage...1-2mm is not smooth...

I checked if the fast idle cam is keeping the idle high, but it isnt...what else can it be?
04-21-2011 01:39 PM
lt1silverhawk Hey kikkegek,

That looks pretty good. Where did you mount the bracket to?
04-21-2011 01:36 PM
kikkegek OK,

heres some pics of my forward "better" spring setup. Its hard to take pics, but here they are.

I noticed that in my setup my spring was about half an inch shorter stretched in "idle" position then in the carbs original setup.

So today I drilled two more holes too stretch it a little more. I'll take a drive tonight and report back on it.




04-21-2011 08:59 AM
dsraven
heavy throttle

check the throttle shaft bushings for wear. that is common problem. the throttle shafts bind because the butterfly valves never end up in the same place twice. thery also leak vacuum so it is hard to adjust the idle mixture. also check all the rest of the linkages and pull offs on the carb. some are affected by the choke so if the choke is still on a little that part of the linkage isn't operative. like the 4bbl lockout won't owrk if the choke is active. grab some carb cleaner/lubricant spray at the parts store and do a little clean up of all the rods etc. if you have a little extra cashola, get a new aftermarket carb and some new distributor weights and springs (recurve the distributor) at the same time. that will perk it up. have to spend a couple hundred though.
good luck,
dsraven
04-21-2011 04:02 AM
kikkegek
Quote:
Originally Posted by kikkegek
I made a custom bracket myself tonight and mounted it to the brakcet of my A/C pump. The springs are still not puling hard enough for my setup. I will have to fine tune it. I'll takes some pics tomorrow.
To add to the information. It seems that only when the engine is warmed up, I have the high idle problem, because the throttle linkage last bit has extra resistance. So the last 1-2 mm before it hits the idle screw feels heavy. So heavy when warm, that the springs dont pull it back to full idle, making it idle at about 1000-1100 rpm.
04-20-2011 02:56 PM
kikkegek I made a custom bracket myself tonight and mounted it to the brakcet of my A/C pump. The springs are still not puling hard enough for my setup. I will have to fine tune it. I'll takes some pics tomorrow.
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