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Proper choke operation
https://www.slantsix.org/forum/viewtopic.php?t=44938		 Page 1 of 1
Author:  gtaw [ Thu May 12, 2011 10:20 am ]
Post subject:  Proper choke operation
Hi guys and gals. I've been fiddling around with my BRAND NEW 1966 Dodge Dart's 170ci engine and I have a few questions.

First of all the car runs and drives fairly well. Good power from 1 to 75mph.

My only concern is during take off from a dead stop it hesitates a little if I try to take off too quickly and will sometimes die (When I get on the highway I double foot it just to be on the safe side, but I don't like doing that). It will fire right up if it does die, but it's still not something I like.

It idles real nice while in park or neutral but when in gear it seems (to me anyways) to idle a little rough. This morning I was tinkering under the hood and noticed that when I hit the throttle the choke closed and stayed closed (it hadn't even been started so it was cold). I looked at the mechanism I noticed the screw wasn't riding on the steps themselves, but past the steps on the cam. It also seems like the screw is too far to the right of the cam.

Image

It doesn't really seem to run any faster when the choke is on so I'm not sure about the fast idle. Sometimes it will leave a spot of black soot after firing it up, or may smoke a little black. After the engine warms up and I kick it down the choke never stays in a full, upright position, but more like the photo below. Maybe open a little bit more, but not much. I got pulled away before I could check the vacuum pod.

Image[/img]

If I prop the choke to full open after it's been warmed up and pop the throttle I noticed it will idle a little quick for a moment and then go back down to normal idle. I think it idles a little rougher and hesitant when the choke is propped open.

I've never owned an engine like this so I don't really have any idea what proper choke operation should be. Could this be causing the slight hesitation on take off?

I have to finish the PO's tune-up and double check their work, but I think it's that darn choke.

Any suggestions, advise, insight, jokes or spare change would be greatly appreciated.

Jim
Author:  SlantSixDan [ Thu May 12, 2011 10:42 am ]
Post subject: 
The choke issue isn't causing your hesitation; that's a failing accelerator pump. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Mass-market carb kits are getting poorer of quality and less and less complete; get a good one from www.daytonaparts.com . That is assuming your carb is in basically sound condition; it appears to be a later-model unit that has at some point in its life been "remanufactured".

When the fast-idle screw doesn't sit squarely on the steps of the cam, it is usually because the throttle lever is bent. Use long-handled pliers to bend it into the correct position so the screw sits squarely on the steps of the cam.

Proper choke operation is for the choke plate to snap shut completely when the throttle is opened with the engine cold and off, but not so tightly it can't easily be pushed open with a single finger. When the engine starts, the choke plate should open about 1/4 to 1/3 of the way -- pulled open by the vacuum-operated choke pull-off acting on the choke lever, and pushed open by the air flowing past the offset-pivoted choke plate.

Tune-up parts and technique suggestions in this thread.
Author:  Doc [ Thu May 12, 2011 10:49 am ]
Post subject: 
The problem could also be caused by a blown vacuum advance chamber on the distributor or mis-adjusted / non-working initial or mechanical distributor advance.
If the engine does not get a shot of fuel and more spark advance, when you "hit the gas"... you can get the stalling you discribe.
DD
Author:  gtaw [ Thu May 12, 2011 5:44 pm ]
Post subject: 
I suspected the accelerator pump, but when I checked it I got a nice, steady squirt of fuel. Ah well. I guess it's time for a rebuild. Got the numbers off my carburetor and I'm going to get one of those kits from Daytona Parts. Pretty much limited to E10 around here.

Thanks for the advice folks :)
Author:  Jester [ Thu May 12, 2011 11:39 pm ]
Post subject: 
Every 1920 Holley I tried on both my '72 Darts had a bit of a hesitation off idle, when trying to take off quickly. I tried replacing the accelerator pump, moving the accelerator pump lever to different holes, and even changed the Jet. No dice.

Actually, the last 1920 I had was original to my Dart and was rebuilt completely by me. It didn't hesitate when the choke was on, nor after the car was warm... But there was a hesitation between the time the choke pulled off and before the car was completely warmed up. It's dangerous to me when turning left at a busy intersection.

Did the super 6 conversion (holley 2280, 318 spec) and never had a stumble or hesitation since. Only poor cold starts, and hot starts after sitting for 10 minutes or so. I chalk it up to a misadjusted electric choke for cold starts, and a sealed bowl vent allowing the fuel bowl to evaporate during hot starts. Yes, I did the fuel line mod.

My opinion: Finding a decent 1920 is a crapshoot. Supersix the bitch.
Author:  Doc [ Fri May 13, 2011 8:55 am ]
Post subject: 
When I have a vehicle with a hesitation or "flat spot", durung acceleration, I check for the pump shot, (strong and occurs right off-idle) then check the vacuum advance and timing. (advance comes-in strong, off idle)
If those systems look OK it's time to pull-out the vacuum gage to see if the "economizer valve" (power valve) setting needs adjusting. (shim the spring so the carb goes into enrichment, sooner.)
DD
Author:  deepfringe [ Fri May 20, 2011 12:41 am ]
Post subject: 
I may not help, but i had literally the same issue, and i discovered that the rod coming from the choke thermostat on the exhaust manifold was in the wrong hole on the carburetor so that the clip that holds it in would stop it from opening all the way.
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