I dont have a choke on my 650 DP, so when I crank it, I have to pat the gas and then I have to feather it for a while til it wants to idle without intervention. Even after that, if Im driving down the road and push in the clutch and put it in neutral, sometimes it will just die out. It doesnt seem to want to run normal at all until the temp gauge gets to around 150-160.

The idle, when it finally will run on its own but is still cold, is around 600 RPMs or so, barely runs. When it warms up it idles around 850 or so. I've got a pretty mild cam that should have no problem idling in the 700 RPM range, but I have it turned up precisely so that it can run sooner when its cold.

After it his 160 and the T-stat opens up, it runs GREAT. Great power, great throttle response, great manners all around, will even cruise at 1200 RPMs on the interstate in 6th gear. No complaints with general drivability when warm, but the bad manners when cold really get on my nerves. Is it normal to have to spend 3-7 minutes in spring/summer/fall weather feathering the throttle until it warms up? I know some amount of care is necessary due to the lack of a choke, but after reading a few things on the net about it, it seems like most people dont ever have a need for the choke unless they live WAY up north, and Im Georgia and I assure you it gets HOT down here.

And it's not really that big of a deal I guess to warm it up for nearly 10 minutes on some cooler days (cool, 50 degrees F, not 10 degrees F) since it rns fine warm, but I have to deal with it every single time I drive the car, just gets kind of old.

Given how good it runs, I suppose it's possible it might be a little lean, but it cant be too far off... is it worth trying to tweak it to improve its cold manners? Any suggestions?

Im at somewhat of a crossroads with where I want to take the car. Maybe go more extreme with it, giant cam, Holley HP mainbody, that sort of thing... or go TPI + standard port heads (probably 083's) and daily drive it again. Maybe there's a way to get the best of both worlds with the carb and get it to behave better cold...

or I can just buy a choke for it, but I dont want to run cables, and I dont have enough clearance to run a choke flap under my air cleaner. I've been wanting to mill off the choke horn for a while anyway.





(The cowl hood is gone, have the factory hood these days)

 

I daily drove mine with a 750 Mighty Demon for two years (except winter...no hope in the snow). A choke helps, but you don't need it. What you do need is:

1) The proper timing curve, especially initial timing with the vacuum advance hooked up.
2) Propoer idle setting with the main AND secondary idle screws. If you are adjusting just the main, you may get the blades too far open and cause all sorts of problems.
3) Float level set correctly and correct pressure too the carb.

That is it. Men drove carbureted cars for 80 years before electronic fuel injection. We can still do it today.

 

my 750dp will idle after about 30 seconds

 

Have you played with the idle mixture screws? You want to set them for best idle WARM, but you don't want them on the lean side when you do so. Set them where the engine idles the fastest, not as lean as you can go before the engine slows down. Might be only a 1/4 turn different than where you have them now, but it makes a difference on a cold engine.

You really should mill that choke horn off if you're going to run an air cleaner that short. You've got no "free height" above the choke horn for the air to make the turn and go down the primaries in an orderly fashion. Not to mention the little "mail slot"-sized opening you have for air to squeeze in there between the choke horn and air cleaner lid. This is important with carbs.

 

Infernal, I've got the same cam and similar carb to you, also without a choke plate as it happens. I just accept the hard cold idling is part of the situation. It gets 3 pumps, crank and start, then straight to about 1800 rpm for about 60-90 secs, with a bit of rpm feathering. Like a mini cam break-in. It then idles fine after this, with all the manners it should have.

If I don't do this and try to go straight away, it will die when stopping or surge when accelerating for the first few miles. I forgive it for this, figure it likes waking up about as much as I do

 

This is the procedure you need, holding the gas @ 1500-1800 rpm for 60-90 seconds gives the heads time to heatup and burnoff the gas better....

 

Those men were smart enough to have chokes, though.

It just seems like 5 minutes of feathering before I can leave is a bit excessive. I guess not. It starts easily, I just have to baby sit it.

Maybe I should do an electric choke on it. Ive heard stories about how annoying the electric chokes are.

 

I have a modified 750 DP with now choke on my 86. I start it and hold the throttle at 1500-1800 for a minute or so and I'm fine. Sounds like you have some tuning issues. After its wwarm, if should not be dieing on you when driving.

Add a choke if you want, it will help and they are pretty simple

 

a choke will help but getting it running proper without one is a better idea. there are probably a few thing you could do to fix this issue that would help your cars performance overall

 

Im not gonna say the tune is perfect, but it's really running so well that I really dont want to change much. What can I do that wont affect cruise, WOT, and pump shot? I've tried tweaking with the idle mixture a little bit but it just makes the car run like crap. I only have idle mixture screws on the primaries. Could it be the secondary throttle blade position/transition slot deal?

I wonder if it's just that all the regular driving circuits are set up fine and all the idle-type circuits are way off, or if maybe the thing is just tuned to the limit of being lean and so its grumpy when cold.

I started off with 67/73 jets, and 70/76's make it run much better. Maybe I should go to some 72/78s? I read somewhere that if you have to deviate too far from stock jetting you're doing it wrong.

 

Not a carb genius.. Isn't this just fixed with the choke? My old 396 with a 750 D.P. had an electronic choke.

 

Of course, but I guess the question Im asking is whether or not this is symptomatic of a tuning issue.

 

You need to richen your idle feed. Adjust your timing for best vacuum you can get at idle. You have to adjust your power valve for how much vacuum you produce on idle.

I have a mighty demon 750 with a very heavy lope cam. Even in the mid 50 degree weather one or two blips on the throttle and it stays idling fine.

 

I already have the timing set for the proper total advance, not for perfect idle advance which is, in my mind, kind of pointless. But I will go messing around with the mixture screws again. Seems like every time I do that the results are terrible, though.

 

Idle and most low speed driving will run of the idle and transition cicuits. WOT will mainly be affected by the PVCR circuits, but the jets also play a part. In-between those two areas, the jets have the bigger influence. It is absolutely possible (and likely) that your jets and PVCR/PV are fine. They will not affect idle. Also, don't chose the PV based on idle vacuum...chose it based on light cruise vacuum. With a bigger cam and no choke, idle is the tricky circuit. Get your base timing up, don't use too light of springs in the mechanical advance (it can cause surging issues when coming down off of a high idle when going from park to drive) and make sure the transition slots are set correctly (primary and secondary side).

 

Well its not pointless . That's probably some of your issue. You dont set your timing for total and leave it. You set your initial timing, once that is set you sets a selection of springs/weights and bushings to get your total advance where you want it.

Remember the more initial advance you pull the more you can close your butterflies and the more vacuum you can pull at idle.

The less initial advance the more you have to open the butterflies to keep a nice idle, which means less manifold vacuum.

 

Actually you set the total and then worry about the idle.

 

Don't know why you're so averse to putting a choke on it, when the choke is there to alleviate the exact symptoms you're having. Remember that get you the fast-idle function too, which should help. Restore it, or live with it. I'm going to fix mine one day, but for the sake of an extra minute or two out of my day warming up, it's not a priority.

The weather gets hot here too in summer, and the warmup period is way less necessary then. But in winter, even though the temps are still pretty moderate compared to some places, it is definitely required.

 

Guess I have been doing it wrong all this time.

I always changed the weights bushings and springs to get me right in the ball park of what I needed before I touched anything. Then when I set initial, the total is usually right where I want it to be + or - a couple of degrees.

 

Weights and springs don't control the total. They control the rate aat which the total comes in. Set your idle (with vacuum unhooked) to somewhere around 16-20. Your total you may need to mess with (bushings or welding up slots) to limit it to around 34 total. Springs and weights configured so that total advance is in by 3000RPM. These are geberal numbers, but a good start. Hook up the vacuum to full manifold vacuum so your total at idle is somewhere around 40 degrees. I have a much bigger cam, so my iidle is around 52 and it runs real good.

If you have a smogger HEI and set your total to 34, your idle will be too low for any kind of performance camshaft. That is why idle should control, not total.

 

He doesn't really have clearance to run a choke. I daily drove my old 84 with no choke and a cam, yeah it had to be babied a bit at first, but then it drove really well. Including winters below 30*.

 

so did you play with this any more kyle?

 

Not much room above the carb! That can't be good performance wise!

What intake are you running?

 

Hm, I don't have this issue, most mornings if its 30+ I don't have to touch a choke on mine, just give the peddle a tap or two before I crank it over and it will always start right up and idle without me touching the peddle. Sometimes if I touch the peddle it will try and die after start up lol. Another suggestion. Are you running an adjustable fuel regulator? If so make sure that is set correctly, too little or too much fuel pressure can cause the same issues when cold.

 

Electric chokes rock use 1 simple wire and very very easy to adjust.
Make your world much simpler.

If you dont like said above get your timing curve just right then go to work on the carb. If its too lean when cold go down a few sizes on your idle air bleed that will solve the problem. when you look down your primary, just inside the choke tower youll see 4 small "jets". They are the two outers. If they have plugs youll have to drill for the appropriate size call Holley first.
It it were me put a choke on it and call it a day.

 

I havent been able to mess with it much. But I was thinking running vacuum advance would probably help a lot. Any thoughts on this? Up until now Ive left the vac advance alone. The car runs great when warm so its just one of those things I never wanted to mess with. Did a little research into it and apparently there's no reason not to run vacuum advance. But I figure cold starts will be a lot easier if the idle vacuum can advance the timing a good bit. Thats just what im thinking in my head...

 

Electric choke is the way to go. Will make your life easier! Also if your are using a distributor with vacuum advance, hooking it up to a ported vacuum source on the carb will help.