I've only ever owned 2 vehicles, a '70 D100 and a '73 W100. Both with Carter carbs. And in both cases, when the weather is rainy and between 32 and about 45 degrees, the engine is prone to run extremely rough for short (and sometimes longer) periods, to the point where the exhaust absolutely reeks of fuel and the rpm's will drop to a stall if you don't put your foot on the accelerator a bit. It has all the symptoms of a stuck carb. float, except not necessarily the black smoke.
Choke can be wide open, no difference. I tend to rebuild my carbs. periodically and keep the float levels properly adjusted, everything clean and up to specs., and they run great except in those particular weather conditions.
Have you all experienced this? What exactly is happening? If I understood the physics of it I might stand a chance of solving it (or at least I could have the satisfaction of knowing there's nothing I can do about it!).
I wonder if it's a condensation issue, but can't tell. If it's below freezing, never a problem. If it's dry, never a problem. If it's warmer than about 45 degrees, never a problem. Just cold, humid air seems to wreak havoc.
Any ideas?
84 Ram
10-08-2007, 07:09 PM
You might want to see if you are getting moisture in your distributor cap. I think that moisture won't affect the carb as much as it would the ignition.
Megunticook
10-08-2007, 07:58 PM
Good point. I should check that next time it happens. You mean the spark would be weak? How would moisture cause that? (not saying you're wrong, just want to know what's at work here).
84 Ram
10-08-2007, 08:07 PM
Water is a conducter if there is water or moisture in the distributor cap it will let the spark travel across the moisture not letting the full spark make it to the plug.
bherder
10-08-2007, 11:47 PM
Yeah, you might wanna try some WD-40 (That really is what it was made for ;) ) inside the cap/rotor next time it's a 'trouble' time for ya.. Can't hurt! :D
Megunticook
10-09-2007, 08:49 AM
Hmmm, I was wondering what to do with what's left in that can of WD-40 I never use anymore.
So you guys know what I"m talking about? You experience the same symptoms?
Speed Dragon
10-09-2007, 09:10 AM
Look at the base of the carb next time it does it, I bet it's frosted up ;)
Megunticook
10-09-2007, 11:42 AM
Doubt it--only happens when the temp. is above freezing. But good thinking, I've read that ice can form in the carb. throat and cause issues. Doesn't seem to have happened to me yet, though.
Speed Dragon
10-09-2007, 05:29 PM
It can happen at temps over freezing. If the heat riser tube from the exhaust manifold is gone, it can happen. I've seen it on mine, only cold rainy days. I assume it's from the cool moist air rushing around the throttle blades. Maybe not really frosted, just looks like it. But basically it's condensing water and at idle it will run rough and stall out. Will run fine going down the road though, as long as the throttle's open a bit, or rpms are over 1200-1500.
acton mike
10-09-2007, 09:19 PM
carbueretor icing, although almost unheard of these days can occur in weather above freezing
you need to examine the devices that keep the carb warm
it can also happen on long highway runs
people who fly piston engine aircraft can control the carb heat so they can prevent carb icing - for them the results of it can be most upsetting
Megunticook
10-09-2007, 09:22 PM
Interesting...I had a feeling it was related to the carb. and condensation. A mechanic who worked on it years ago did something to the heat riser, I think he may have removed it.
Yet another reason why I decided to take over all my truck maintenance last year.
I'll read up on the heat riser in the FSM and see what I might be able to do to restore it.
bherder
10-10-2007, 08:46 AM
Just to throw another wrench in the gears (Yeah, like we all need that one.. :D ).... Or just something to keep in mind...
A few years back when I was having engine problems, the local 'Crusty Old Mechanic' told me that older SB Mopars had a problem with that center exhaust port (The one in the center on the intake side of the head ... Right where your EGR valve - If you have one - is) plugging up with carbon after about 50,000 miles or so. He said that when plugged, it wouldn't allow the base of the carb to heat up (Or at least not as much) and your carb can ice up.
Now whether this is true or not, I don't know. He's been wrong about things before, but he is usually right about stuff.
I pulled my intake and sure enough, those ports were plugged solid. Although, I don't think the intake had ever been off before. It turned out, that wasn't what my problem was, but I think maybe I at least headed off some future prob. I dunno ... Just thought I'd throw that out there .. ;)
GHS
10-10-2007, 08:48 AM
Your heat crossover chamber in the intake manifold is probably plugged with carbon, which slows carb warm-up.
I also agree with the distributor cap moisture problem. Most aftermarket caps are poorly manufactured and no longer contain a vent like the OEM caps did.
bherder...you must type faster than I do...you beat me by 2 minutes!
bherder
10-10-2007, 09:09 AM
bherder...you must type faster than I do...you beat me by 2 minutes!
(I think I just got up a little earlier than you did ;) .... gotta get out there and collect the cow eggs and milk the chickens, y'know... :D )
DiverDwnPowrRam
10-10-2007, 11:34 AM
If you want to detect a bad cap (carbon or moisture) start your ride at night and watch the light show around the dizzy.
I would lean ..on icing...to a heat source around the carb...heater hose to close. Not sure if the cross-over being clogged would do it as I have ran aftermarket non egr/non crossover heads and intakes and did not have this problem. I have found it is either a bad carb gasket allowing heat transfer or a heat source too close. With your rig running after 15 minutes feel the carb..if it is hot then it is not correct.
bherder
10-10-2007, 06:12 PM
If you want to detect a bad cap (carbon or moisture) start your ride at night and watch the light show around the dizzy.
Hey, does it sync up well with 'Dark Side of the Moon'?? :D
