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1969 Camaro RS Z/28
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Discussion Starter #1
Can't seem to get this 4777-1 carb to idle down, with the curb idle backed all the way off. Seems it has a vacuum leak, but might be more of a Holley rookie brain leak?
What the hell is this fitting with a small screen about 8 o'clock on the outside of the electric choke? It fdraws a bit of vacuum (see the screen), but only helps a little when plugged.
Also, I don't have the typical vacuum advance fitting port up high on the metering block like supposed to. Instead I have it running to the front plate, where Holley literature states should be capped off.

Any help would be appreciated.

Thanks in advance,
Mark
 

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Ben - Delaware - 67 Camaro
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the full manifold vacuum may be causing your high idle. this is where you want your advance source but you also need to install a limiter plate in the distributor to use this source. without one, you're likely seeing full advance at idle and thus causing your high idle condition. have you driven the car? is there any sign of detonation or pinging?
 

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Ben - Delaware - 67 Camaro
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511 Posts
if you pull the vacuum advance hose and plug the port on the carb does your idle come down? that would be my first check to see where your problem is. if that turns out to be the issue there are simple stop plate limiters you can install on the vacuum advance rod inside the distributor to limit the vacuum advance to around 10*. set your base timing between 12*-18* and total mechanical advance another 18* and you should be in the money
 

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First, the "air leak" at the brass fitting on the choke housing is normal, as the electric choke fits to the original exhaust heated choke housing. The air leak is actually an inlet to allow a metered amount of cooler air into the choke to keep the electric heat stove from overheating to failure. Don't block it off.

The full manifold vacuum sourcing for the vacuum advance is what you want, BUT, if the advance isn't set up correctly to meter the number of degrees it delivers, the engine will over time, and idle rpm's can rise above a proper setting. A pimple procedure, and either a home made degree stop, or a crane stand alone adjustable stop can be added to stock and adjustable vacuum advances, to get them dialed in properly.

If you want a vacuum advance stop info package, they are absolutely free, and show how to do it right, send an email asking for them to: [email protected] The stop methods work on both point and HEI distributors, and are not expensive to do.

Then, you can set the degrees to supplement initial timing, to attain IDLE settings of 20 to 24 degrees, which the engine will like. This would be an initial setting, with full manifold vacuum advance degrees combined to give a total IDLE timing.
 

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Al - Waterloo, Iowa
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I had a similar problem with a Holley not idling down. Turned out the secondary
butterflies were too far open. On mine there is a small screw accessible from the
bottom to adjust the secondary butterfly. It's located on the base just behind
the choke. I was able to use a mirror and small screwdriver point from a 1/4"
drive set to adjust it. Technically you're suppose to remove the carb and measure
the butterfly position from the carb base. Go to the Holley web site for instructions.
 

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On the secs stop adjustment, on most Holley carbs, that IS NOT a supplemental idle screw, it is there only to keep the secs plates from binding in the bores when closed. The procedure is, with carb off the engine, back screw the screw past the place the secs butterflys bind in their bores when closed. than, back up to no clearance between screw and shaft end stop, plus 1/8th turn. This should met the secs plates close, and not bind.

Don't confuse the anti bind screw for ones that are on special "4 corner idle" specialty Holleys.
 

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1969 Camaro RS Z/28
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Discussion Starter #9
All good answers. Thanks guys. I will check timing again, order the distributor plate that is settable for vacuum restriction, and if those dont work, off with the carb. Actually think I will pull ithe carb and double check the butterflies anyway.
I'll report back on the root cause, and corrective action. Again many thanks for all if those replies.
 

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Why is full vacuum what you want? I had read that using vacuum that is gradual allows for the distributor to advance as the air coming in increases.

I think this was refered to as ported vacuum? My Holley has a distributor vacuum advance port on the front side, which I believe "sees" vacuum from the front throttle bore.
 

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Al - Waterloo, Iowa
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Attached is a screen shot of the Holley instructions I was referring to in my initial post.
Holley does call the adjusting screw I was trying to describe a secondary idle speed screw
and it should be adjusted along with the primary idle adjusting screw. Please note these
are instructions for a 4175 carb and may not be applicable to the 4150. I'm not trying to
dispute what Dave stated. More of just backing up my statement. I still recommend
checking out the Holley tech website.

 

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read the attachment in my last post

X2. This is a good article. Make the changes suggested there and your car will run much better, mine did. As pointed out, make sure to add a positive stop to your vac advance.
 
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