Strange Warm-Up Issue

[JBeau]

I have a 1978 Spider with a Weber 32 Adfa carb. When starting from cold, the car idles high, with the choke working as expected. When the I get to what I'll call 'mid temperature', basically anything between 120 and 170-ish degrees according to the temp gauge, the car idles really low. There is not a performance loss when I hit the throttle, but the tach is basically on zero at idle and it almost sounds as though the car is not running. There has not really been any indication of a stall, but it is disconcerting. Once the car is at temp, everything is just fine.

I have set up the carb as indicated in Brad Artigue's book and various threads here (as well as the Weber guidance), even using an external optical tach to set the idle speed because I was concerned that there was an error in the tach reading. I wonder if this is an indication that there is something wrong with the choke or if there is an adjustment there that needs to be made. I have never adjusted the choke at all.

As always, thanks in advance for any guidance or advice you can provide.

[18Fiatsandcounting]

It sounds like your carb is coming off of the "high idle" cam a bit early, before the engine is fully warmed up. The point at which the choke comes off the high idle is set by the rotation of the spring inside the choke housing, and the high idle speed is set by that long screw that rides on the high point of the cam.

The adjustment for the point at which the high idle "stops" is by rotation of the round choke housing. It's held by three screws, so you loosen those and rotate as needed. I forget which direction to rotate, so you might have to play with this.

I assume the idle is fine when the engine is fully warm? Under these conditions, the hot idle speed is set by the screw that moves the throttle shaft ever so slightly. In conjunction with the idle mixture screw. The choke doesn't play a role once the engine is fully warm.

-Bryan

[JBeau]

Bryan,

Thanks for your response. You are correct, the engine runs fine when completely warm. I'll take a crack at adjusting the choke position next and see if that resolves the issue. The funny thing is that the car runs just fine when idling that low, just well out of the typical 850-900 RPM that is spec.

Thanks again for your advice. You are certainly a valued resource here.

[18Fiatsandcounting]

Thanks again for your advice. You are certainly a valued resource here.

Thank you. I don't get compliments very often, so it's appreciated!

Let me know if you need any other suggestions. By the way, the Fiat tach can be quite inaccurate at low rpms, so sometimes when it's bouncing around zero, it's actually idling at 500 rpm or so. I occasionally have to check with a separate shop tach if that's the case.

The good news is that if your engine idles fine at 500 rpm, it's in a good state of tune.

-Bryan

[Nut124]

Cars with carbs cannot and will not run like modern FI cars. They need TLC.

[Italfiat79]

Hi guys,

I presently have an issue with my ADFA Weber during warming up and I was wondering if anyone here had similar encounters.

I’ll explain the number of steps I did before.
I rebuilt the carb with replacing new gaskets and diaphragms. I set the timing right and during fist startup runs perfect and choke working fine with warming up. Adjusted the mixture to about 2 1/2 turns out with RPM at around 850, 900. I took it for a spin drives really well and good response. Here where the problem starts. If I leave the car sitting for about 15min shut off and then try to start it, it runs rough and need to give it gas to keep running. I checked the choke and it’s fully open. I have 3PSI fuel pressure by using electric fuel pump. So there must be something I’m missing. Let me know if someone has some suggestions for me, really appreciate it. Thanks in advance! Mike

[Italfiat79]

Hi guys,

I presently have an issue with my ADFA Weber during warming up and I was wondering if anyone here had similar encounters.

I’ll explain the number of steps I did before.
I rebuilt the carb with replacing new gaskets and diaphragms. I set the timing right and during fist startup runs perfect and choke working fine with warming up. Adjusted the mixture to about 2 1/2 turns out with RPM at around 850, 900. I took it for a spin drives really well and good response. Here where the problem starts. If I leave the car sitting for about 15min shut off and then try to start it, it runs rough and need to give it gas to keep running. I checked the choke and it’s fully open. I have 3PSI fuel pressure by using electric fuel pump. So there must be something I’m missing. Let me know if someone has some suggestions for me, really appreciate it. Thanks in advance! Mike

[18Fiatsandcounting]

Some of the cars / carbs do this, and while I haven't totally figured out the reason, hard starting when hot can be caused by the engine being flooded. A couple quick things to try:

1. Loosen the gas cap slightly and see if the problem is still there. You don't need to take the cap off, just loosen a turn or two.

2. Before doing a hot start, press and hold the gas pedal all the way to the floor while cranking (don't pump it). When it fires, let off the gas. If the engine was flooded, this helps clear it out.

-Bryan

[Italfiat79]

Hi Bryan,

Thanks for responding, really appreciate it!

I remember the gas cap trick with the old carb and there was quite a bit of pressure but I haven’t try it with the rebuilt carb yet. Thanks for the reminder!

That is very possible that it’s a little flooded before starting it again. I wonder that is an issue using the electric fuel pump. Yes, good idea not to pump the pedal. I will look into it this weekend and make sure I got the fuel mixture right. I did adjust the cam and works perfect along with choke opening and closing. I will give you an update how things went. Thanks again for your help!

Mike

[Italfiat79]

So I did a little tweaking with the carb this weekend during cold starting and warm starting. I took the car for a good run and filled it up with always 91 octane. Finally by adjusting the fuel mixture and idle screw, it must of took me about 20 times though! Seems it’s working very well at the moment.

One issue that I have, is the original air filter housing is hitting the hood. At the moment, I removed the hood insulator and hood closes well. Actually noticed this issue right after I replaced the motor mounts. What I did find odd that there is a double phenolic spacer which there should be only one at 4.5mm plus the two paper gaskets. I would imagine that using one spacer should do the trick along with the new oval chrome housing which is another 3/4¨ shorter than the original and then I could reinstall the hood insulator.

Mike

Mike