carburetor adjustments
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Joined: Dec 2009
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From: Macomb Michigan
carburetor adjustments
Hi everybody,
I finally got my 75 running after it has been sitting in the garage for about 6 years. Cleaned the tank, got a new fuel pump. Did the breaks, cooling system and pretty much everything else. We also took the carb out and rebuilt it. Now it needs adjustment.
Now when I start it up, the engine doesn't stay running. The rpm goes up to about 800 but I need to stay on the accelerator to keep it there. Otherwise it stalls. I had a buddy over and we got it to the point where it idles at about 1600 rpm and when put in gear it drops to about 600. Then it stayed there. As soon as we brought the idle rpm down to about 800 -900 it stalled when put in gear.
We adjusted the idle screws based on the manual we had and played with some other things but could never get it to the point where it had a lower idle speed and didn't stall when in gear.
Any ideas ? I don't know anybody that can adjust a carb anymore.
The carb is a Rochester M4MC quadrajet.
Thanks
I finally got my 75 running after it has been sitting in the garage for about 6 years. Cleaned the tank, got a new fuel pump. Did the breaks, cooling system and pretty much everything else. We also took the carb out and rebuilt it. Now it needs adjustment.
Now when I start it up, the engine doesn't stay running. The rpm goes up to about 800 but I need to stay on the accelerator to keep it there. Otherwise it stalls. I had a buddy over and we got it to the point where it idles at about 1600 rpm and when put in gear it drops to about 600. Then it stayed there. As soon as we brought the idle rpm down to about 800 -900 it stalled when put in gear.
We adjusted the idle screws based on the manual we had and played with some other things but could never get it to the point where it had a lower idle speed and didn't stall when in gear.
Any ideas ? I don't know anybody that can adjust a carb anymore.
The carb is a Rochester M4MC quadrajet.
Thanks
Le Mans Master
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From: Oxford MA-----You just lost the game!!!!
Thread Starter
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Joined: Dec 2009
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From: Macomb Michigan
did you rebuild it too?
The link is a word doc.
try this:
http://api.viglink.com/api/click?for...13125749600083
The link is a word doc.
try this:
http://api.viglink.com/api/click?for...13125749600083
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
Hi everybody,
I finally got my 75 running after it has been sitting in the garage for about 6 years.
Now when I start it up, the engine doesn't stay running. The rpm goes up to about 800 but I need to stay on the accelerator to keep it there. Otherwise it stalls. Thanks
I finally got my 75 running after it has been sitting in the garage for about 6 years.
Now when I start it up, the engine doesn't stay running. The rpm goes up to about 800 but I need to stay on the accelerator to keep it there. Otherwise it stalls. Thanks
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Joined: Dec 2009
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From: Macomb Michigan
Race Director
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sounds like an internal problem, the power piston may be hanging, float level not adjusted correctly, etc. Other possiblity to check first would be a vacuum leak at carb mounting surface or airhorn or any line connected to carb.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Are you referencing the Chevrolet Chassis Service Manual in the "Fuel System" section? It has all the details and sequences of making adjustments to the factory installed carb. You need to adjust choke and carb per those instructions. This assumes that you got a quality rebuild kit and installed it properly. Also, you should have purchased a new float, as the rebuild kits do not include them. A plastic float that has been sitting 'dry' for 6 years needs to be thrown away. Buy a brass float at NAPA and stick it in a mug of water when you open it up. If you see any bubbles, take it back; otherwise, it should be fine for many years.
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From: Chapel Hill NC
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I recently bought a truck with and Edlebrock carb that had been sitting for six years. Rebuilt the carb but it would not idle. Took the thing apart three more times, thoroughly cleaning it each time, before it would idle correctly. Six years of sitting will really gum up the internals and if the internals are not completely clean, adjusting will not get it to run. I've read somewhere that some guys boil a gummed up disassembled carb in water, but I have never tried this.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
It's best to put all the metal parts (no plastic or rubber) into a can of carb cleaner/dip and let it sit a day or so. Another alternative is to spray out all dirt/deposits with spray carb cleaner. Use it to clean out all the little passages, if you don't have compressed air available.
But it won't idle if it doesn't get any fuel. That's usually because of the needle/seat and/or float. Both should be replaced when doing any carb rebuild.
But it won't idle if it doesn't get any fuel. That's usually because of the needle/seat and/or float. Both should be replaced when doing any carb rebuild.
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From: Macomb Michigan
thanks guys,
when we took the carb apart we soaked it in carb cleaner overnight.
7T1vette, you got me thinking about the float. I bought a rebuild kit but it didn't have the new float in it. I go a brass float but not sure if I replaces it or not. Do you think that could be the reason for the erratic rpm behavior ?
when we took the carb apart we soaked it in carb cleaner overnight.
7T1vette, you got me thinking about the float. I bought a rebuild kit but it didn't have the new float in it. I go a brass float but not sure if I replaces it or not. Do you think that could be the reason for the erratic rpm behavior ?
Team Owner
Joined: Jan 2006
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From: Crossville TN
If you already had a brass float and it worked OK when you 'mothballed' it, your problem is not likely due to the float. I more suspect the reassembly process and/or the gaskets in the kit were not right for the carb. You really have to check all the holes and see that they mate up with the adjacent part.
There are lots of possibilities to end up with an idle problem when you rebuild. If it is a Q-Jet, I highly recommend that you buy a copy of Cliff Ruggles "How to Rebuild and Modify a Quadrajet Carburetor". It's less than $20 and has everything you need to know in it.
With your present situation, you have a couple of viable alternatives: take carb off and check it out again; find a knowledgable "helper" that can advise you and help test for the idle problems. It can be due to carb; but it can also be due to a vacuum leak, timing problems, ignition issues, etc., etc. Without being there, it's difficult to advise.
There are lots of possibilities to end up with an idle problem when you rebuild. If it is a Q-Jet, I highly recommend that you buy a copy of Cliff Ruggles "How to Rebuild and Modify a Quadrajet Carburetor". It's less than $20 and has everything you need to know in it.
With your present situation, you have a couple of viable alternatives: take carb off and check it out again; find a knowledgable "helper" that can advise you and help test for the idle problems. It can be due to carb; but it can also be due to a vacuum leak, timing problems, ignition issues, etc., etc. Without being there, it's difficult to advise.
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Joined: Dec 2009
Posts: 94
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From: Macomb Michigan
thanks everybody! I got her running.
I leaned a lot taking the carb apart about 5 times.....
btw one thing I couldn't find out is, what opens the secondary (big) air flaps? just airflow?
Thanks again.
I leaned a lot taking the carb apart about 5 times.....
btw one thing I couldn't find out is, what opens the secondary (big) air flaps? just airflow?
Thanks again.
1969, 1997, 58, adjustment, adjustments, c3, cab, carb, carburetor, corvette, idle, lower, rodchester, vette
