Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level) - Page 6 - Hot Rod Forum : Hotrodders Bulletin Board
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  #76 (permalink)  
Old 03-25-2011, 04:22 PM
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Here are the pictures of the parts as installed on the truck and after rebuild.


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  #77 (permalink)  
Old 03-26-2011, 04:09 PM
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- Mystery Dashpot -


Quote:
Originally Posted by cobalt327
The part you were wondering about the name is a "dashpot". It acts as a slight delay, preventing the throttle from 'slamming' shut. It's unnecessary for the most part.
EDIT- I see yours has a vacuum barb on it. This may still be just a dashpot, or an idle speed modulator of some type- I do not recall ever seeing a vacuum barb on a dash pot- so I'm at a bit of a loss as to what it is, exactly.
I feel the "mystery dashpot" is indeed the Throttle Lever Actuator. The system as described here seems to match. The only issue is, the nut in the front is twisted in a "locked" position so that it doesn't move (see picture below). Perhaps the intention of the previous rebuilder or owner was to permanently set a maximum throttle? Please refer to the set of pictures in the previous post for more angles.






Quote:
Originally Posted by cobalt327
What action occurs when vacuum is applied to it- does it retract, or ?
After unlocking the nut, I did test it by sucking on it and it moves perfectly with out requiring much pressure.



Please do chime in if you have anything to add or correct. Thanks
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  #78 (permalink)  
Old 03-26-2011, 06:03 PM
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I've never seen, adjusted or otherwise dealt w/such a device, but then I've not hotrodded or even worked on 20-series truck emission devices.

GM came up w/a LOT of Rube Goldberg-ish devices to deal w/emissions, and this is yet another one that needs to be relegated to the trash bin- as long as your jurisdiction's emission testing doesn't require you to keep it.

I would consider it TOTALLY superfluous and I wouldn't hesitate for an instant to remove it and it's related encumbrances- or at the very least to render it inoperable (like what seems to have been done previously) and retain it for visual inspection compliance only.
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  #79 (permalink)  
Old 03-26-2011, 07:26 PM
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Quote:
Originally Posted by cobalt327
GM came up w/a LOT of Rube Goldberg-ish devices to deal w/emissions, and this is yet another one that needs to be relegated to the trash bin- as long as your jurisdiction's emission testing doesn't require you to keep it.

I would consider it TOTALLY superfluous and I wouldn't hesitate for an instant to remove it and it's related encumbrances- or at the very least to render it inoperable (like what seems to have been done previously) and retain it for visual inspection compliance only.
I have a strong feeling it is because of emissions that it was kept (it is California, after all). But then the only issue is, this truck is missing an EGR valve and the intake doesn't have the provisions to install one. Boy I would love to talk to the guy who worked on this.

By the way, just for added info, the device on the manifold that provides vacuum to the actuator is also connected to the carb via hose up front. below are pictures with the cap off, as well as the inlet/out let where the other hose slips on. (Sorry, should've done this a while back).

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Old 03-26-2011, 07:46 PM
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Quote:
Originally Posted by lt1silverhawk
I have a strong feeling it is because of emissions that it was kept (it is California, after all). But then the only issue is, this truck is missing an EGR valve and the intake doesn't have the provisions to install one.
Not having an EGR valve is common w/the larger truck series. So even though the aftermarket intake was bought w/o one, it probably didn't have one originally. Considering how everything else seems to have been retained that had to do w/emissions, it would have been easy to replace the intake w/an EGR-equipped version if the engine had an EGR to begin with.

You should be able to determine whether an EGR was necessary when the truck was made by checking w/the emission refs or possibly online. You will probably have to go by the gross vehicle weight.
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  #81 (permalink)  
Old 03-26-2011, 08:04 PM
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Quote:
Originally Posted by cobalt327
Not having an EGR valve is common w/the larger truck series. So even though the aftermarket intake was bought w/o one, it probably didn't have one originally. Considering how everything else seems to have been retained that had to do w/emissions, it would have been easy to replace the intake w/an EGR-equipped version if the engine had an EGR to begin with.

You should be able to determine whether an EGR was necessary when the truck was made by checking w/the emission refs or possibly online. You will probably have to go by the gross vehicle weight.
Well, the local smog police (aka smog shops) didn't even want to smog test my truck because the EGR valve was missing. The mechanic looked it up in his book and it said that it was supposed to have come with one (assuming it is a California truck, which I believe it is). The motor itself isn't the one the came originally came with either (provided the Goodwrench 350 valve covers werent just tossed on). But of course, you do have a point when you say that the rest of the emissions equipment was retained.

I'll see if I can dig up some info online.

Thanks!
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  #82 (permalink)  
Old 03-27-2011, 12:59 AM
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- Idle Screws -

I went ahead and reinstalled the two idle mixture screws and the idle adjusting screw. I put them back in the same length they were before assembly by mtaching them up with the pictures. Not the most accurate way, but it is a start.






--------------------




- Completed Carburetor -






This concludes the rebuild. Endless thanks to everyone who helped get this far.




Tomorrow, I should have the carburetor installed back on the truck and begin tuning it. Due to the fact the truck this carburetor is being used in was having fuel delivery and ignition problems, I am debating whether I should continue covering the tuning portion on that thread (1977 Chevrolet K10 - Starting Problems, Weak Idle and Power Loss). My reasoning is that, because the truck was having issues that eventually led to the carburetor needing the rebuild, it may not be appropriate for this thread, since the issues will be specific for my truck. However, if anyone feels otherwise, please do mention it.

Any tips and tricks on what to look out for and expect when tuning are greatly appreciated.
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  #83 (permalink)  
Old 03-27-2011, 09:24 AM
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Tons of good info here
http://www.digitalcorvettes.com/foru...ad.php?t=88376
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  #84 (permalink)  
Old 03-27-2011, 09:33 AM
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Hey impalaman63,

Quote:
Originally Posted by impalaman63
Thanks! Been reading up on so much on many sites, that I totally forgot about the paper by Lars. Thanks again
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  #85 (permalink)  
Old 03-27-2011, 12:48 PM
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That red carb must really set off the smog police. They notice anything that does not look stock. It might be a good idea to have a extra carb when you get it smogged. No smog here, anything goes.
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  #86 (permalink)  
Old 03-27-2011, 05:19 PM
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Quote:
Originally Posted by V8&4spd
That red carb must really set off the smog police. They notice anything that does not look stock. It might be a good idea to have a extra carb when you get it smogged. No smog here, anything goes.
Oh it is getting ridiculous with smog here. I remember "Hot Rod" did an article a few months back back about the California Air Regulatory Board (C.A.R.B.). The writers held a meeting with them about smogging their Crusher Camaro with a newer engine back in the 90's. Long story short, although the Camaro put out excellent emissions results with the newer motor (comparable to the modern cars of the time), the boys at CARB said that the smog shops would lose money if the visual inspection portion was eliminated.

As for me, the biggest concern is not having an EGR and, as cobalt327 pointed out, I need to look up whether it came with one or not.
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  #87 (permalink)  
Old 03-27-2011, 09:17 PM
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- Reinstallation -


For reinstallation, I pretty much went in reverse of of what I did during the removal process. The pictures came in very handy. I did secure everything down, but did not fully tighten in case it had to removed. I also did not install the throttle lever actuator at this time, so as to have more space to access the idle adjusting screw.






--------------------




- Initial Startup -

The battery seemed to be holding some juice after being parked for over two months so I thought I'd go ahead and fire it up. You can see the video of here. The truck didn't start and the battery began to die. I hooked the battery up to the charger and also noticed that I had not installed the choke as well as the small hose that runs from the choke pull-off to the carburetor. Please see images above for reference. The video shows that the linkages seem to be working and the fuel can be seen being delivered in the glass-cased filter.

After setting up the choke, linkage, the small rubber hose and also charging up the battery I gave it another go. You can see the video here. This time, the truck still struggled to start and would die right after catching on. I gave it gas a few times. Unfortunately, I did not realize that the rod connecting the choke to the linkage and come out of place. in the end, I saw a flame shoot out of the carb and immediately stopped everything.

As of now, the battery is charging, and some Stabil has been added to the gas tank. I still need to put the choke rod back in place. A Youtube video by HolleyPerformance gave some info as to what causes backfires and how to eliminate them.

Aside from the choke not working and possible ignition issues, anything else I should be on the lookout for?
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  #88 (permalink)  
Old 03-27-2011, 09:28 PM
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A quick way to check for bad gas is to buy a few feet of rubber fuel line and hook one end to the fuel pump and put the other end in a gas can of fresh gas. Also check your spark plugs to see if they are fouled.
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Old 03-27-2011, 10:02 PM
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Do you have a thick base gasket? If not, use a thick base gasket and make sure the carb it tightened down good. Plug all the vacuum ports on the carb until after you get it running, that way you will know if there are any problems before you put them back on.
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  #90 (permalink)  
Old 03-27-2011, 10:09 PM
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Quote:
Originally Posted by V8&4spd
A quick way to check for bad gas is to buy a few feet of rubber fuel line and hook one end to the fuel pump and put the other end in a gas can of fresh gas. Also check your spark plugs to see if they are fouled.
Bad gas is what eventually led to the rebuild. Somebody dumped water and debris into one of the gas tanks. And its always possible that the gas I put in afterwards has also gone bad from sitting around for a couple of months. The spark plugs I do plan to check asap. I think there is a gapping issue.





Quote:
Originally Posted by V8&4spd
Do you have a thick base gasket? If not, use a thick base gasket and make sure the carb it tightened down good. Plug all the vacuum ports on the carb until after you get it running, that way you will know if there are any problems before you put them back on.
That's what I forgot! The base gasket! And yes, it does appear to be very think when compared to the other gaskets used. (Is it obvious that I am getting carried away by the excitement of finishing this, to the point that I'm forgetting things? Lesson learned).

Thanks for pointing that out V8.

Last edited by lt1silverhawk; 03-27-2011 at 10:15 PM.
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