sticking choke

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  #1  
Old 09-12-03, 06:09 AM
dsbike
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sticking choke

I have an 85 Chevy PU with 305 4bbl Rochester carb. I replaced the carb with a rebuild about 3000 miles / 1year ago . The choke sometimes sticks and floods the engine . I can't find anything causing it to mechanically stick. I have to manually open air cleaner and move the linkage to open the choke. As I mentioned before it only happens about 1 out of every 5 times I start the truck when it is cold.
 
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  #2  
Old 09-12-03, 07:42 AM
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UNFORTUNATELY, THAT TRUCK WILL NEVER BE THE SAME WITH A REPLACEMENT REBUILD ON IT.....
ANYWAY, WHEN DOES IT FLOOD OUT? IF IT STARTS TO FLOOD WITHIN SAY, 10 SECONDS OF STARTING COLD, IT MAY BE A CHOKE PULL OFF CONCERN. SOME CALIBRATIONS HAD ONE, SOME HAD TWO PULL OFFS.THEY NEED TO BE GETTING VACUUM. THE PRIMARY PULLOFF, WHICH HAS THE SHORTEST ROD BETWEEN IT AND THE CHOKE BLADE LINKAGE, IS A STRAIGHT SHOT TO INTAKE MANIFOLD VACUUM.THE SECONDARY PULLOFF, MIGHT HAVE THE VACUUM RUNNING THROUGH A TEMPERATURE SENSOR FIRST. THIS ONE IS NOT AS IMPORTANT ANYWAY.MAKE SURE YOUR VACUUM HOSE TO THE PRIMARY PULLOFF IS A GOOD HOSE, WITH SUCTION IN IT AT IDLE....
 
  #3  
Old 09-12-03, 09:01 AM
dsbike
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sticking choke

checked vaccumn,checks good,hose clear & no cracks. only one vac. point. It appears to me that the linkage behind the electric choke cyl that holds the throttle lever up for higher idle may not always release and holds the butterfly at about a 30' angle from being closed. Is there a way to adjust this?
I realize that a rebuilt carb isn't always the best replacement , but with 200k+ the old carb was not working well. Alot of hesitation , come to think of it that choke didn't work quite right either. not that it stuck closed but instead open. Any other suggestions? thanks for a starting pt anyways.
 
  #4  
Old 09-12-03, 12:49 PM
Joe_F
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Arrow

The age/mileage of the carb had little to do with it, I know where BG is going.

The original carb had a casting #. That casting # is specific to your emission combination,engine, year, and vehicle.

Rebuild companies use "anything that fits". They may use a 1982 core on a 1985 application. Will it "work"? Sure, but it will never be right. This is because Rochester changed jets, control parts and passage ways year to year.

Best bet is to find the original core # from the dealer's parts computer/literature and find a complete junked carb in the yard. Then have THAT one rebuilt and adjusted.

Sounds like the carburetor is STILL out of adjustment.
 
  #5  
Old 09-12-03, 01:10 PM
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STILL NOT SURE ABOUT THE SYMPTOM. IS IT THAT THE CHOKE IS NOT OPEN FULLY WHEN THE ENGINE IS WARM? AND THAT THE IDLE IS STILL FAST? OR IS THIS A PROBLEM THAT IS HAPPENING AS THE ENGINE IS WARMING UP? OR IS IT SHORTLY AFTER A COLD START, AS IN 10-15 SECONDS?
IF IT IS WHEN THE ENGINE IS HOT, AND IS STILL ON FAST IDLE, THERE MAY BE AN ISSUE ABOUT THE POWER SUPPLY TO THE CHOKE THERMOSTAT...THOSE I THINK GOT THEIR POWER FROM THE OIL PRESSURE SWITCH.
I NEED TO KNOW AT WHICH ENGINE TEMPERATURE WE ARE TALKING ABOUT...
 
  #6  
Old 09-12-03, 01:16 PM
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STILL NOT SURE ABOUT THE SYMPTOM. IS IT THAT THE CHOKE IS NOT OPEN FULLY WHEN THE ENGINE IS WARM? AND THAT THE IDLE IS STILL FAST? OR IS THIS A PROBLEM THAT IS HAPPENING AS THE ENGINE IS WARMING UP? OR IS IT SHORTLY AFTER A COLD START, AS IN 10-15 SECONDS?
IF IT IS WHEN THE ENGINE IS HOT, AND IS STILL ON FAST IDLE, THERE MAY BE AN ISSUE ABOUT THE POWER SUPPLY TO THE CHOKE THERMOSTAT...THOSE I THINK GOT THEIR POWER FROM THE OIL PRESSURE SWITCH.
I NEED TO KNOW AT WHICH ENGINE TEMPERATURE WE ARE TALKING ABOUT...
IF U DRIVE FOR TEN MINUTES, AND THE CHOKE IS STILL PARTIALLY CLOSED, AND IT IS STILL ON HIGH IDLE, DISCONNECT THE WIRE AT THE CHOKE, TAKE A FUSED JUMPER WIRE AND JUMPER FROM THE BATTERY POSITIVE TO THE TERMINAL AT THE CHOKE THERMOSTAT. SEE IF AFTER A FEW MINUTES THE CHOKE OPENS..
 
  #7  
Old 09-14-03, 10:27 AM
dsbike
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sticking choke

It is when the engine is running for 10 min. already warmed up . As I stated before it is intermittent when it sticks in the fast idle. You mention the oil sending unit, This engine has 2 both mounted on the rear of the block, I have replaced the one that operates the Instrument Gauge due to leakage.
I should have had the original carb rebuilt in the 1st place I guess. Never gave it a thought , now I have to deal with what I have. I'm confident that I can get this carb working with youall's help. I have also purchased The Rochester Carb book by Doug Roe. I've been told it is the best written info you can find. Again thanks & I will try the hot wire to the choke.
 
  #8  
Old 09-14-03, 11:36 AM
Joe_F
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Doug Roe's book is very good, but the GM shop manual for the truck is a bit better. Roe writes from experience---he was a Rochester Products Engineer at GM. The Q-jet is his career

Again, as noted, it will be nearly impossible to adjust a core originally designed for a 1982 truck in a 1985 model. Find the correct core for this and rebuild it to spec.

You'll never get it 100% correct (or even near to that) with a different core on there---too many internal differences.
 
  #9  
Old 09-15-03, 07:17 AM
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I think it is the 3 prong sender you wanted to go after.....
 
  #10  
Old 09-17-03, 07:37 AM
dsbike
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sticking choke

I checked for voltage to the choke ,I have 14v. Of coarse this time the choke opened up fully automatically after about 3 min. I did find that the air cleaner gasket was pretty much worn out and squeezing out of shape inward. With the air cleaner on it appears that the gasket may be pushing up against the butterfly rod. Sounds almost to simple of a fix. I replaced the gasket and haven't had any more problems, however it has always been intermittent. If and when it happpens again I will check for voltage and run the jumper wire to see if this oil sending unit or choke has an intermittent short. I will keep you posted.
 
  #11  
Old 09-17-03, 07:39 AM
Joe_F
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Ok....
 
  #12  
Old 10-31-05, 05:45 PM
tommy
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Sticky choke

Did you ever resolve that choke problem? I realize that this is a few years old but I now have the exact problem, same truck, year, story, and diagnosis. Have not checked the air filter gasket. Will do that tomorrow. Any help appreciated.
 

Last edited by tommy; 10-31-05 at 06:05 PM.
  #13  
Old 10-31-05, 06:50 PM
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First thing I do with a sticky choke is take off the cover (often a black plastic round one), and spray WD-40 in it
 
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