How long to warm up a 1725?

[mferris]

(today is my day for questions).

My 1725 with 32/36 with Pertronix conversion is having a hard time warming up and then seems to run lean - maybe. I'm not sure if this is typical.

It will start on the first turn of the crank, but I have to keep my foot on the throttle for a few minutes (2-3) before it will be able to idle on its own. Typical symptom is that if I take my foot off the throttle, idle is at 200-rpm to dead within a few seconds.

On startup, depending on how much I keep my foot on the throttle, there is black smoke for a few seconds and typically I get 1-2 "hiccups" back through the carb while trying to get it to idle.

When warm, it idles fine around 800 and it runs best with about 1/4 choke - but on warmer days I don't seem to need choke at all.

I have followed the 32/36 adjustment and jetting instructions I've found online, but have not noticed much difference.

My wife and kids who refuse to ride in the car - but have followed me on occasion say that the car stinks, and I can rarely see some white smoke when I floor it - but only if the sunlight is right.

The dichotomy is that it seems lean when running?, but rich when starting?

My plugs are pretty sooty black, but I have not put new one in yet to see if my adjustments have changed anything.

 

[Acollin]

Very similar

My 1966 series V does something very similar. I have a stock setup -- no Petronixs.

I just believe that I have not got my carbs right. I do not have the smell you do when underway. My exhaust appears pretty clean.

My process: Full choke to start from cold. It starts quickly but takes forever to reach a driving temperature-- could be more than 5 minutes or longer. I have experimented with driving with the choke out just a bit and while the driving is great, I get the carboning up of the plugs. Once fully warmed it starts great and quick but seems a bit lean and as I play with the choke the car goes much better. I asked the forum months ago about the cars being cold blooded, but never really got an answer that satisfies me or fixed my problem.

I look forward to what ever replies you get. Thanks for asking the question.
Andrew

 

[Tom H]

Mike, there should be a "cam plate" operated by the choke that holds the throttle more open than the normal idle stop, when the choke is applied. This is called the Fast Idle cam or plate. Without that any carb operated engine will not idle fast enough to stay running until it is warmed up. Check to see if opening the choke holds the throttle open more than at the normal idle stop.

My 32/36 carb does not have that cam, because it was converted from electric choke to manual and I did not bother to acquire the extra pieces, so I always have that problem for first few minutes after start up.

And black smoke at start up is about normal for an old carb operated engine. Keep in mind that these old carbs, compared to modern fuel injected, computer controlled, fuel systems, are really an amazing "approximation" as to how much fuel and air is needed at all the various operating condition.

But you should not need any choke once warmed up. That seems to be a jetting issue. Do you know what jets you have?

Tom

 

[RootesRacer]

Rich/lean "feel" is a fine art.

If you have sooty plugs, it means that it runs more rich than lean for how you have been driving it.

Its entirely possible for one regime of the engine operation to be at one running extreme (like a rich idle), then have another regime (like cruising) to be quite lean.

To know the difference you really need an air fuel meter.

Some people seem to like colortune, but in my opinion, its only useful to determine the idle condition.

A good AFR meter will tell you whats going on under all conditions and let you plan accordingly.

 

[Finaddict]

After several trials & errors, I had my Weber DGV dialed in by a mechanic with an exhaust gas analyzer stuck up the tail pipe. 'Worked well at all speeds.

 

[Nickodell]

I'd also check for air leaks at the inlet manifold/head or carb/manifold joints.