Problems w/ Electronic choke on a 4 BBL Rochester

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  #1  
Old 05-17-08, 07:16 PM
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Problems w/ Electronic choke on a 4 BBL Rochester

Any help would be grateful!

I'm having problems with the electronic choke on a Rochester 4 BBL. At leaset, It's not operating correctly. From what I believe, on start up with a cold motor the primary flap should be mostly closed?..slightly open? After the motor get nice and hot the primary flap should be wide open?

There never seems to be a time when the flap is wide open after the motor is hot. I't always slightly open. I say it's electronic because there are two hot wires that go to the choke along with grounds. I've taken the cover of the choke off and played w/ the lever to make sure it moved freely and reset the coil to the lever. I've been playing with adjusting the tension on the coil by either turning it back and forth but haven't had any real change in the flap opening. This carb is on a Mercruiser 190 boat motor.
 
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Old 05-18-08, 04:38 AM
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Does it have a "choke Pull off " vacuum valve?. I used to have a Merc 4 cyl with Carb, but I'm not sure since it was little over 10 years, I traded up for bigger boat with EFI, but anyway.

If you have choke pull off valve, the primary choke would be "loosely" closed on a cold engine, when engine started, the choke pull off valve will pulls the primary choke open via engine's vacuum about 1/8 ", at that time, your electric choke will slowly heats up and approx 10mins, your primary choke plate would stay wide open, if not, check power and ground at the electric choke and replace it if necessary.

If you don't have a choke pull off valve, the primary choke would stay open at about 1/8" when engine is cold (overnight) and the electric choke would works the same way when engine is running.

You can also check the electric choke without running the engine, assuming you have good power and ground at the choke housing, remove the flame arrestor and notice the position of the choke plate, if it open, close it by pushing on your throttle close to wide open, that will reset the primary choke plate to "close" position, (if not, readjust it). Then just turn the key on without started the engine and sit there and watch the choke plate, push the throttle once or twice once in awhile and see if the choke plate open more to it wide open, if the choke plate doesn't goes to wide open,( it should goes to wide open approx 5-10 min) adjust it or replace it if neccesary. Hope it help.
 
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Old 05-18-08, 08:32 PM
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Yes, it has a vacuum break diaphram assembly. I played with it again today. Not sure if the motor was running for more than 10 mins but I have some more observations. The primary did open a slight amount but never was completely open. When I gave it gas it would open fully. I mean, when nailing it it opened fully. I'd have to see what it does as I slowly increase the throttle. I checked the power going to the choke. There is about 12 V going to the thermostatic coil.

Another question about the secondary plate operation. How should this behave? When I nail the throttle, it opens only slightly. Maybe I have some problem with the vacuum unit? Maybe I need to make some adjustments to the choke rod and vacuum break?
 
  #4  
Old 05-18-08, 10:04 PM
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sounds like it needs a new choke thermostat its not uncommon for them to fail if you want to double check it remove the stat and cool it off in some water and reinstall and adjust it to just where the choke plate has just enough tension to close and if it still dont open fully within five to ten minutes of operation I would just install a new one.
the secondary normally will open slowly and it probably didnt have a chance to fully open by just snapping the throttle although the choke pulloff linkage is sometimes hooked to prevent secondary plate opening, it will allow it to open as manifold vacum drops under wide open throttle conditions it may just take a few seconds for it to do so.
 
  #5  
Old 05-19-08, 04:20 AM
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I'd replace the electric choke with new one, it should completely open within 10mins of running.

There's also another vacuum pull off for secondary choke, make sure linkage are free of obstruction, you can also make some adjustment on it depending on how soon/late you want it open when snap the throttle.

It seem like the secondary choke works ok, you may not be able to see it wide open without the load, the more load you put on it, the faster the vacuum drops = the wider the secondary plate open.
 
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