Manual choke and cold weather - PeachParts Mercedes-Benz Forum

AlexCole · #1 01-15-2009, 08:57 AM

Please Moderator, I know this is not about a diesel MB, but I DO own one, and yall are knowledgeable and willing to help, so I was hoping to get some answers without you junking this thread...............................

I have a 1977 Jeep CJ5, I6, 258, with HEI distributor and MC2100 2bbl carb (obviously a gasser).

I'm a south Louisiana boy transplanted to NW Ohio, and this cold weather is completely alien to me (NEGATIVE 4 degrees this morning). Driving to work this morning, I was playing around with my choke and found that even while driving, the jeep ran better with the choke pulled. Now, I have always thought that the choke was just for warming the car up prior to driving off, but when it's really cold out, is it okay/normal to drive around with the choke pulled? I know it sounds like a dumb question, but where I come from, 50 degrees is cold, and I have never encountered this problem. I would ask one of my friends around here, but I'm the only person sane enough to drive a 30 year old vehicle (in fact I have 2) and no one else even remembers what a manual choke looks like. Thanks in advance, Alex.

fruitcakesa · #2 01-15-2009, 09:22 AM

I think the main issue will be excess fuel use and possibly plug fouling.
When did you last tune this baby?
Carb adjusted, fresh plugs, plugged fuel filter?

t walgamuth · #3 01-15-2009, 09:33 AM

Traditionally (and I don't know if this is true with your vehicle or not) most american cars have a setup on manual chokes where the first part of the travel simply increases idle speed and actually does not enrich the mixture. In any case even if you are enrichening it I would think it is ok as long as the engine is running smoothly.

If the car is completely warm though and requires choke to run smoothly it may have a vacuum leak.

pizzachef · #4 01-15-2009, 09:36 AM

Quote:

Originally Posted by t walgamuth

...If the car is completely warm though and requires choke to run smoothly it may have a vacuum leak.

...or is not warming up completely, is the thermostat stuck open?
Also, does it run okay with no choke in the warm weather?

LUVMBDiesels · #5 01-15-2009, 09:40 AM

I have a '74 CJ5 232 with the single BBL carb.

When starting you can have the choke closed off.

You can run with the choke partially closed until the engine warms up. This should also set the fast idle.

Here is what I would check if it runs better with the choke closed once it is warm.

Look for vacuum leaks Spray some carb cleaner around the intake manifold. If the engine rpm changes when you spray a certain spot, air is leaking in from there.

Make sure that the carb is not adjusted too lean. If it is leaned out too much when you block the carb throat with the choke, you are really putting the ratio back to where it should be

Check the slow idle speed. It could be set too low.

Check to make sure all the plugs are firing. On my CJ only two plugs were firing when I got her.

!! A set of plugs, points and wires fixed that!

Check the heat riser pipe. There should be a metal tube running from a fitting on top of the exhaust manifold to the air cleaner. This lets warmed air enter the carb and helps warm up the engine faster.

Do you gauges work? If they do it is a minor miracle

Check the thermostat and cooling system. Does the Jeep get up to operating temp?

KarTek · #6 01-15-2009, 09:47 AM

Another tell tale of a lean condition is backfiring or "puffing" when slowing down or down shifting. On my first car, I used to think it was cool to pull a vacuum line and drive around with it running lean - stumbling idle and big poppy sounds from the exhaust every time I slowed down.

AlexCole · #7 01-15-2009, 10:55 AM

Carb was recently adjusted; fuel filter, plugs and wires are new with distributor (< 6 mos), engine runs fine without choke once it warms up in warm and (reasonably) cold weather. But now that it is ultra-cold, even when the engine is warm, it will stumble and make those big poppy sounds from the exhaust when accelerating or changing gears too soon (so that I have to either downshift or press in the clutch and give it some gas, then ease back on the clutch to re-engage)-- just the opposite of what Kartek described above. When the carb was recently adjusted, I asked specifically for the mechanic to check for vacuum leaks and he gave it a clean bill of health.
It looks as if the only thing that pulling the choke actually does is close the flapper, which decreases the air flow linearly (the more you pull, the more it closes).
Pulling the choke makes all of the problems go away. Is it really that simple, and am I hurting anything? Alex

curtludwig · #8 01-15-2009, 03:34 PM

Was the carb adjusted in warmer weather?
I don't know anything about car/truck carbs but on a snowmobile you rejet (richen I think) for very cold temps. On a snowmobile that means consistantly below -20F, that said the normal outside temp for a snowmobile is consistantly colder than for a car/truck/jeep so maybe a slight richening of your carb is in order...

KarTek · #9 01-15-2009, 03:55 PM

So, when you're going downhill in say 2nd gear, with the clutch out, foot off the brakes or accelerator and the Jeep is coasting against the compression of the engine, you saying the exhaust doesn't pop and burble with the choke in? A hesitation/buck when pressing the accelerator after a shift is another sign of a lean condition.

It's definately a lean condition of pulling the choke clears it up. As long as the engine is at full operating temp ~185 or so, it should run fine with no choke no matter how cold it is, even 0 deg.

I think it's just a matter of finding either an intake leak, vacuum hose broken/split or the carb is out of adjustment.

Pulling the choke is a temporary fix and it probably kills your gas mileage and lowers performance. Running too rich can also wash down the cylinder walls and remove vital lubrication.

LUVMBDiesels · #10 01-15-2009, 04:32 PM

I would turn the needle valve 1/4 turn counter clockwise and see if it helps.
Also again check the heat riser as these carbs sit away from the engine and can start to ice up.

Simpler=Better · #11 01-15-2009, 05:34 PM

I think you're running too cold, if it's -4* outside you may want to block part of your grill off.