Cold Weather Choke

[ACK]

I have a 250 with a Rochester B and manual choke. It was running great all summer, but now that it's below 30 degrees in the morning, she needs the choke to warm up. When she's warmed up, I leave the choke pulled out about 1/2" or the idle drops really low and she'll buck a bit when moving from a dead stop. The further I drive the better she responds, so I'll decrease the choke as the engine improves, but the choke is never fully off by the time I get to work, which is an 18 mile drive. When I arrive at work, the choke is out about 1/4".

I've raised the idle a tad and adjusted the fuel mixture for max vacuum. Is this just part of my trucks personality or is there something else I should be looking at and adjusting?

[K98AL]

Are you running factory exhaust? If so, check the heat riser under your carb - if you're running headers, you need to install some water heat.

[Sharps40]

Check to see if your manifold heat riser valve is stuck in a position I call Open....(no/little exhaust gas being directed upwards to the intake manifold base.) Easiest way is to simply drop the exhaust pipe and look up inside at the flap....flap horizontal, no heat rising it all go's out the pipe....flap vertical, heat rises to warm the carb and intake manifold.....

On a cold engine ya need heat goin up, once its fully warm, can be 30 minutes or so to stabilize the carbie, the flap should go horizontal via the springs and direct all the heat down and out.

Carbs will be cold natured, specially up there and with high ethanol gasoline. Might be as much as 40 miles on the freeway till yer carb comes up to full temp.

If its really bad, ye'll see ice on yer carb base even when the manifolds are too hot to touch.

[ACK]

Originally Posted by K98AL

Are you running factory exhaust? If so, check the heat riser under your carb - if you're running headers, you need to install some water heat.

The pin that sticks out of the manifold that holds the heat riser spring rusted/broke off 2 weeks ago and I'm not sure how or if it can be fixed. I need to find out what's the max work temp for JB Weld

[AnlaufJohn]

Don't waste your time trying to repair it. They aren't cheap, but can be found for about $50.00 or so. Those valves live in a terrible environment and if they aren't lubed every couple weeks, they're prone to rust in one position or the other.

[Sharps40]

Actually on the v8s you can replace em. On the I6s you can replace em but its much more involved since the I6 valve lives in the manifold instead of a bolt on doughnut like the v8s.

First though....find out what the problem is....might not be this valve at all....

[TJ's Chevy]

If your exhaust manifold valve is stuck open you will be fine. I would leave mine open on my 292 and it would be 30-35 degrees out and the motor would run fine. I had a similar issue...when mine was cold or hot everytime you stepped on the pedal it would hesitate majorly. That was caused mostly by a bad accelerator pump and a wobbly throttle shaft. So it ended up having a vacuum leak from the carb itself. Rochester 1 barrel carbs are prone for that. I would bye a new carb or switch to a slightly bigger one...like a holley 2 barrel and try that. Or fiddle with your air mixture screw and Idle adjustment again...I think it is just a worn carb. My 2 cents. T.J.

[ACK]

The butterfly and weight move fine, it's the pin circled in red that's MIA. I don't know if the pin can be replaced ... I imagine it's added after the casting, but can I get what's left out? I'm hesitant to hit it with a drill, but then again, no guts no glory.

[Sharps40]

Originally Posted by ACK

The butterfly and weight move fine, it's the pin circled in red that's MIA. I don't know if the pin can be replaced ... I imagine it's added after the casting, but can I get what's left out? I'm hesitant to hit it with a drill, but then again, no guts no glory.

If you are set on fixin it....remove the manifold....drill and tap an install a nice stainless or brass bolt to replace the pin.

If not, put a hose clamp around the weight in a position to hold the valve so all the exhaust is dumped down.

First I'd make sure its in the right position for a warm motor then go for a long ride with the radiator grill covered in cardboard to see if its actually a carb/manifold warmth issue. If it gets warm enough to come off choke in say 50 or so steady miles....yer heat is the problem.....if not then the problem could be elsewhere like in the always old cranky unreliable leaky Rochester Mod B carb......but that's not sure, just a grumpy ol mans prejudice against that particular carb.

[TJ's Chevy]

Rochester model B carbs were pretty junky anyhow. I would chance getting a new one....probably would fix alot of the issue.

[63burban]

195 thermostat will help also

[ACK]

Originally Posted by 63burban

195 thermostat will help also

My 6 has a V8 radiator, so that might help a lot. The temp gauge is pretty low now that the weather has dipped.

[Sharps40]

When I lived up yer way and drove 37 dodge flathead - winter was ol school. Blockradiator or grill at least 75 p2rcent to keep engine temp up and had best drivability that way. In spring pull the blocks to cool the motor.

[luvbowties]

Be careful if u drive at all with cardboard blocking airflow--see sharps40 reply #13--about leaving a sizeable portion of the flow UNOBSTRUCTED. This can be dangerous, so watch temp gauge CONSTANTLY!
sam

[Sharps40]

JC witney used to sell nifty Zip up vests ya outfitted yer grill with. Course they always tore out at the zipper!

[Sharps40]

Course back in them days we had Alcohol thermostats and 160 was a hot one!!

[ACK]

An update ... Partially blocking the radiator helped a tad, changing to a 195* thermostat helped a lot. Thanks for the advice.

Two questions:
- I live in PA, should I leave the 195* thermostat in for the summer or go back to 180*?
- Any thoughts about installing a clutch fan on a 4.1L?