Engine "loads up" when it rains or is damp outside. Why?

[88GW]

When it is damp or rainy out my 88 360 with a Holley 4Barrell loads up. It will idle high then start to bog down until the motor is hot and then it runs fine.

The history of this Kinda long: When original never had this probelm, stock carb, cam etc. Slightly modified installed .488 lift cam, installed Edelbrock 600 carb. All stock ignition except for TFI upgrade. Motor starts to act up and do this. Next stage of modifications to hopefully help this out was a new Holley Truck Avenger 670 carb, MSD ignition box as well as the previously installed TFI upgrade, not using exixting Motorcraft ignition box, strictly runnig off of the MSD. New Msd wires, plugs several caps and rotors new distributor etc. It still loads up when warming up and idle drops and almost stalls out, until I hit the highway and really get it warm it runs fine. Other things I have done. I have coated all the boots and connections of cap rotor and plugs with tune up grease, I have changed caps and rotors several times and even used wire dryer. I have disconnected the choke plate so that when I engage the choke (I converted to manual choke) it acts like a high idle control and does not make the mixture any richer.

Is there something i missed or a connector that I can't see that is getting wet and causing this? Or is the cam too big to run in cold/wet weather? Or is the carb too big for the motor (they say stock to 350 horse)? Or could the cam not be degreed right and cause it to run like this? Thanks

[88GW]

BTT

[Bombadier]

carb icing??? :confused:

My cherokee doesn't like it when it's damp out, either....

[netbear]

The problem could be caused by any number of
problems but check these out:

1. Hook the heat tube back up that runs from
the exhaust manifold to the air inlet
of your air cleaner assy and ensure the
vacuum tube is still hooked up correctly.
This prevents the problem you are having
in most cases.

2. The carb may not be getting enough heat
from the heat crossover. This could be
caused by blockage due to crud buildup
in the exhaust crossover passage or by
a carb adaptor which blocks heat from
the exhaust crossover from reaching the
carb until you have run it long enough
to transfer heat through the adaptor.
Carb "icing" occurs above 32 degrees
when there is moisture in the air.

3. Your 360 was low compression to begin with,
adding the larger cam decreased compression
and in doing so the heat or temperature of
combustion. You may want to try a set of
spark plugs one heat range "hotter". This
will likely help some but if pinging results,
return to the cooler plugs.

3. I would focus on item 1. It is a common
problem. Item 2 next and lastly item 3.

Good luck!

[joe]

I'd bet on netbears option #1. If you didn't re-install it after the rebuild, do it.
I'm not sure when you say you disconnected the choke plate and now run a manual choke but it just controls idle speed? You need to hook the cable up so it opens/closes the choke plate so it "does" restrict the airlow into the carb and not where ever you have it hooked to raise/lower idle speed. Properly hooked up manual chokes can be a bit finicky to set especially if you have an el cheapo $5 conversion kit. The cable and housing is usually of such poor quality smooth operation and precise setting is tough.
I would get the heat stove hooked back up to the air cleaner and then work on your choke set up.

[Lindel]

You probably need to lean out the mix, just a fraction on the idle mix screws. They're located on the sides of the metering block. Use a vacuum gauge, and adjust for the highest vacuum.

What intake are you using, and are you using the valley pan gasket? If you're using aftermarket gaskets on the intake, they'll block off the heat passage, and the intake won't warm up, nearly as quickly. Hooking up the heat stove will help quite a bit.

[turtlejoe]

I'm going a long way back to my '63 International days, but can't a leaking/cracked coil cause this too? I seem to remember the primary symptom being poor or no running when wet outside.

Please forgive me if this is way off, just thought I'd add another possibility. If you have the OEM can style coil check it out for grins.

[OJTDJPR]

Dont forget a cracked Dizzy cap will do that same thing. It will draw moisture inside when it is damp out, and make it run like crud. Pull it off and look for a hair line crack in it. If you dont see one, next time it rains and does that, pull it off and spray it on the inside with hair spray or WD 40. Hair spray will seal it for a bit, and WD40 will dry it out. Doesnt hurt to check, I have had a few do that and all it needed was a new cap.

[ March 21, 2003, 08:43 PM: Message edited by: OJTDJPR ]