Disabling divorced choke
 

For the most part, as a Sunday driver on warm days I'm not seeing enough of a need for a choke to warrant dealing with some of the quirks of a divorced choke. The engine starts and idles fine with a couple of pedal pumps at anything 60 degrees or warmer.

Anyway, I want to leave all the choke components in place and perhaps wire it in the full open position so I don't have to remove things like the secondary air valve lock, and it still appears as stock as possible. I'd like to leave it completely intact so at some future date it would be very simple to "re-activate" it.

Any suggestions on the best way to accomplish this while leaving all the parts intact and as original looking as possible?

Yes, you can do what did to accomplish that years ago and it’s a 20 minute mod that can’t really be seen with a air cleaner on.

I simply drilled and taped a 8/32” hole ( it was either 8/32” or 6/32” I forget) into the air horn where the rod passes thru up to the screw on lever of the end of the choke flap.

This machine screw simply jam’s that rod against the main body of the carb.

Use a big enough diameter machine screw to jam that rod and note that before you even drill the hole that the rod does swing thru a bit of a arc when the choke flap is open or closed.
Be sure to drill that so that it jams the rod in it’s open position that you want!

Use some blue Loctite and your set.

This is best done with the carb off the motor but if you have another person hold the shop vac hose right there when your drilling and taping it can be done on the car, which is what I did.

Now that I ponder this again there may be another way to do this which involves no drilling or taping.

The key would be having a longer machine screw to replace the one the holds that rod lever to the end of the choke flap rod.
You would need atleast two washers , one with a big enough center hole to clear the boss on the body of the air horn where that lever screws on, and then another washer who’s center hole keeps that new longer screw from just going thru into the bigger washer.

When the screw is tightened up the washer stack just jams up the motion of that lever,

You could remove the choke stove, (1 screw, 1 hairpin clip). Then wind the bi-metallic spring 1 additional full turn to keep the choke fully open and re-install. Nobody would know the difference but you.

Wire the forward facing, weighted end, of the fast idle cam in the full down position.

done deal
Clay

Just use a wire tie and secure the fast idle cam in the down position. Takes about 15 seconds and even less time to snip it off if you want the choke working again......

I would leave it and adjust for warmer climate shortening the rod for L (lean) location.
Remember an engine not reached its normal operating temperature is cold and a cold engine needs a somewhat richer A/F mixture to run right.
Also, to prevent the movement of the bimetallic spring by locking it can destroy the spring.

I wasn't having much luck bending the choke coil rod enough to effect the changes I wanted ... tends to bind up in the holes. I don't think it's intended to have the range of adjustment I was trying to get out of it.

Excellent suggestions folks, thank you.

Fix the choke so that it works PROPERLY and the choke will be so seamless you won't know the difference between it and fuel injection, except for having to press the gas pedal to set the choke when starting.

Disabling the choke is not the right way to accomplish your goals.

You can EASILY make a new rod from a piece of aluminum TIG wire. Much easier to bend than steel and dirt cheap.

I would make a slightly shorter rod with a bend in it for custom tuning the choke release time.

Not having a working choke isn't a good thing when outside temps cool off some, unless you are using a carburetor that is "pig" rich right to start with. With a well tuned carburetor even in hot weather it works much better with a choke than without one......

Cliff, the carb was set up with a kit you provided so hopefully it isn't pig rich :) I also based part of my decision on some information in your book which said about 1/3 of the carbs you build have no chokes and work just fine.

I've got tons of TIG wire that's for sure.

At present when I press the pedal and set the choke it snaps completely shut (with proper small gap to horn) and stays there WAY longer than necessary. Tested the coil with a heat gun while it was installed and it does eventually release the choke and open all the way.

I'm using the choke coil from Ames PN N139C.

What I was looking for was to make it release quicker (at lower temps). I was leaning towards disabling because when I closed the loop on the rod far enough to accomplish this it would screw up the geometry enough that the rod would bind.

On the test stand before I installed the engine, and it had no choke coil installed I'd just flip the choke flap close, start it, flop it open all the way and within 15 seconds or so it would idle without me tapping throttle ... this was in 70 degree temps.

I'll give it a shot bending up a rod or two, see if I can get it to behave differently.

I guess I could have the idle mixture too rich .... both screws are out about 3/4 turn from closed.

WHAT CARB IS THIS? "Parts from Cliff" make me think it's likely a Q-Jet, but that's not a given. How many choke pulloffs does it have? Do they work?

Depending on ambient temperature, that's NOT proper. The choke blade should be fully shut.

Do you have a heat-riser valve? Does it work? Is the exhaust crossover passage in each head, and the intake manifold plugged with carbon, or deliberately plugged? The exhaust crossover, that heats the choke coil, should be SCREAMING HOT when the engine has run awhile. Even "high temperature" engine paint tends to burn off of an exhaust crossover.

What driveability problem are you having? Runs bad just after starting? Or runs too rich after the engine has run awhile?


Adjust for highest vacuum in-gear, fully warm. Then turn each screw "lean" just enough to lower the vacuum about 1/4" each--1/2" combined.

Basically got the answers I was looking for.
Appreciate all the input.

A working choke is a good thing to have with a wet-flow system. It becomes mandatory if/when you want to start and drive the car in really cold weather. It can be optional for vehicles that are used mostly in warm weather, have blocked heat crossovers, etc. I ran without one for many years but finally got tired of the "drama" involved trying to start the engine in cold weather. With a working choke and fast idle one pump of the throttle and the engine roars to life instantly in any weather. When the choke coil s set correctly it will start to unload the choke as the engine warms up. No negatives anyplace if things are correctly adjusted. This means that you fast idle speed screw is right, the choke pull-off unloads the choke to precisely the correct angle so it's not going lean and stalling or rich and "blubbering", and the choke coil itself has the choke flap fully open about the same time there is enough heat in the intake so the engine will idle on the curb idle speed screw.

It sounds easy but may take some "tweaking" to get it all dialed in perfectly for your combination. Once you do the engine will start instantly weather, stay running, drop RPM's as you depress the throttle and the fast idle cam drops to lower positions and within a few minutes it will be idling fine on it's own.

With no choke you will find a LOT more fuel is needed to get it to fire, and you'll have to act like the fast idle cam until some heat gets into the intake so it idles on it's own. How long that takes is directly dependent on engine and outside air temps. Some folks can deal with all that better than others as i see a LOT of these engines using carburetors that don't even have a choke on them anyplace..........

Played with it more last night, engine not running, hooked up a vacuum pump to the unloader, heat gun on the choke stove ... seems close to acceptable in the 55 degree shop. Hard to tell until I get it on the road.

This NOS carb seems pretty well adjusted from the get go, choke flap closes to the specified 3/32" gap to the horn when set, opens up about 1/3 the way when the unloader kicks in. The two fast idle steps work.

Heat gun gets the choke flap to open all the way without a dramatic amount of heat. Good since I have the driver side cross over blocked. Again I won't know for sure until the car is running in the driveway how well it's going to work.

I'm transitioning from outboard motor fuel tank sitting under the engine, to the fuel tank right now so can't run the engine at the moment.

I'm one of those guys that never minded a minute of warm up and peddle messaging before driving away. The only time it's ever needed a choke was when I moved from TN to NY. At that point I installed a Holley with a manual choke ... that was 40 years ago.

At the moment I'm confident it's not too far off base.

(Not long ago I actually bought the parts to build a micro-processor based, servo controlled choke (because I'm a tinkerer) With maybe a week of screwing around I think I could build a programmable servo that would attach to the choke coil rod and respond to a temp sensor anywhere on the engine you wanted to put it. :) )

I've never even heard of a micro-processor based servo controlled choke set-up, sounds complicated.

I can tell you one thing for certain here. I ran w/o a choke for a few years when I was racing the car couple of times a week. Also no primary metering rods, RPM intake, loud mufflers with turn-downs, etc.

At one point I decided to put the car back on the street and absolutely HATED not having a choke in cool/cold weather. As I get older I have LESS tolerance for things that don't work as they should. When I was younger I never gave a second though to having to pump the accl 10-15 times only to have the engine ROAR to life, run 3-5 seconds then die out. After 3-5 cycles of that nonsense it would stay running but I'd have to sit in the seat and "feather" the throttle 2-3 minutes till it got enough heat in the intake to stay running on it's own.

Anyhow, put the electric choke back on the carb, metering rods as well, factory intake, stock Shaker parts (had "cobbled" up things to use the taller RPM intake), quiet mufflers and full length 2.5" mandrel bent tail pipes.

I figured the car would slow down quite a bit but it was a LOT nicer to drive on the street and INSTANT starts in any weather. When I finally wondered over to out local 1/8 mile track for a Friday night Test & Tune I was expecting to slow down 2-3 tenths and 1-2 MPH.

To my surprise the car left HARDER and quicker 60' times. This equated into running about the same ET as it did with the "race" set-up but did fall off about 1-2 MPH. I still to this day can't believer I dealt with all that "race" oriented stuff to not run any quicker at all in ET, and it's a LOT nicer to have all the factory parts in place when someone walks by the car in the pits and takes a gander under the hood then glances at the ET on the windshield........those looks are PRICELESS!.........

If this car was going to be a daily driver, or if I ever expect the wife to drive it I'd never even consider not having a choke. I'm hopeful it will work out right, if not I might try and electric choke .... if you can put one on a 704 carb.

Hey ... I bet you looked way cooler though nursing that chokeless engine to life, very "racy" :)

You haven't heard of a micro-processor based servo controlled choke because no one has built one yet :)

A Nano-processor, about the size of a little box of matches, a servo about the size of your thumb. Processor goes under the dash, servo mounted to the carb, temp sensor the size of an M&M. Sensor sends analog to the processor, processor converts and sends a position signal to the servo, servo pulls or pushes on the rod. USB port on the processor to program to any temp/position curve you want.

Probably very similar to half a dozen different systems on a modern vehicle.

Just a thought exercise ... I bought the necessary parts for under $50. The hardest part would be designing and building the mount to attach the servo to the carb.

I hesitate to even mention it on this forum because it would cause too many heads to explode :)

I simply avoid that sort of thing because electronics HATE me. Sticking with simple/reliable things over the years has served me well. I can't even get my cell phone to work correctly half the time, it does what it wants when it wants and has been nothing but a complete POS since I got it. Didn't have it a week and splashed a couple drops of water in the right places and the speaker hasn't been worth a chit since.........and NO, I'm not going to replace it as I'd just get one that hates me more than this one does!..........

That doesn't sound right to me.

I'd have figured choke blade closed ALL the way, opening ~1/4" via the choke pulloff.

Linkage to the fast idle cam will have the highest step of the cam active with choke closed, pulloff partially-opens the choke and allows fast idle cam to rotate to second-highest step.

Yeah, that's going to make things more difficult. Probably not impossible, though.

I convert ALL of my older vehicles to manual choke.

Don't even think about considering the possibility of pondering contemplating installing an electric choke if you have blocked heat cross-overs, and a dogmatic transmission. OR borrow Cliff's cell phone to call the tow truck! ;)

Jon