Im hoping someone can help with this one. Ive got two trucks, one with 351w & 4160 holley, the other 300 & 1bbl carter.neither has emmisions. The reason I bring both of them into it is because the problem is the same on both rigs even though they are so obviously different set ups. When I first start em in the morning (only first start) they both start up just fine, then about half way to warm up they both idle down by themselves almost to stallout, and then without touching anything the idle comes back up on its own.Ive tried to adjust on both of them; choke setting both sides of specs, idle mixture both ways. other than this prob both of them are in top running order. Ive done two very different things to keep them running during warm up. On the 1bbl I bent the choke linkage to whereI can insert an 1/8 bit between air horn and choke plate in closed position. Its a little harder to start because it is never fully closed, but it keeps me on the high cam longer and keeps me runing. On the holly I uncapped a temp controlled vacume valve on the engine creating a vacume leak only when the engine is cold. So I thought I was running too rich but my plugs are perfect. So it seems that Im running to rich only on warm up, but if I lean out the choke on either rig they get worse. I am so confused could you please point it out to me.

 

This is a common problem on these old trucks. It is called carb icing. The damp cold air in the mornings causes icing in the air bleeds which cuts off the airflow to the idle circuit causing an over rich condition. It took me quite awhile to figure this out. To verify. Start up the V8 truck, let it run until it starts acting up. Let it do this for a minute, then, stick your finger on the screws on the side of the metering block where you adjust your air/fuel mixture. I'll bet that they are ICE COLD, maybe even frosty if it is damp enough.
REMEDY- Hook up or repair the hot air intake to the air cleaner that runs from the exhaust manifold to the factory air cleaner. It is the only way to eliminate this problem.I hate it because I run a Chrome, 4" open element air cleaner in the summer, but I have to put the old stocker on in the cool months.
I even made a piece that clamps to my headers that my hose goes to since I don't run stock manifolds any more.
Jimmy

 

Damp weather? We sure get plenty of that. 192" a year. The bronco used to ice so bad that frost would cover the entire base of the carb making the plates stick open. Untill I found a valve in the intake that used to be hooked up to emmisions that was closed and was cutting off the warm air from the manifolds (heat riser). I opened it and hooked up heat to the air cleaner and it got better but not completley fixed. I bought the stuff to hook up the 77, manifold shroud, aircleaner. But I had to take the damper and use it for the bronco. I will try to locate another and get the 77 heat going again. Is there another way to get more heat to these carbs? Thank you.

 

you can take alum, flexable dryer duct and bend it to fit the large air intake on the aircleaner, and then anchor the other end to the manifold.... i've used that in real hot weather for a cold air intake, and might try it this winter to stop icing...

 

 

thanx all for the suggestions. Ive got the 77 going strong but still having a problem with the 351. Ive got the flex hose from the shroud to the air cleaner. she starts up fine but a couple minutes into it she gets real low and stalls out. I let her sit for a minute or two (warming up the carb?) start her up again and everything is o.k. One thought I had; They sent me the wrong spacer with the carb,so what I am using is the egr spacer w/out the egr. I removed the egr from the plate and blocked the ports. It doesnt leak but do you suppose this could cause any problems?

 

No,it shouldn't. Make sure that the air cleaner is sealed good. Also, check for proper function of the flap and valve. It may be opening too soon.

 

O.k. I am convinced it's iceing. But I cannot get it to stop. Something ive noticed is that it only does it when its cold and raining. It rains nearly every day here, but weve had a dry spell the last few weeks with the same cold temps. After making some adjustments I thought I had her licked, but it started raining again and it was back. That is when I became aware that the moisture (100%) was a strong factor. I tried putting some gaskets between the carb and air cleaner, no help. heat riser working and warm air duct working as well. tried gas heat, no luck either. So here is my question. Could it be in the intake passages? All emissions have been removed but the AIR pipes running in the back connecting the manifolds are still in place (capped off). The EGR is removed but the spacer still being used with a bolt thru the diaphram plate. The hot air should go from the manifold on the heat riser side and flow under the carb to the other side? Could the Air pipes w/o the fresh air being pumped into them be effecting the hot air flow?

 

tamarackstyle, If your EGR valve has been removed, then that is most likely a big part of your problem. The valve is there to circulate hot exhaust gasses under the carb to aid in warm-up.

I just finished an 82' F-150 w/300 I-6 that was having the exact problem you are. The carb would ice during low temp, near 100% humidity situations. Changed the EGR valve and presto! No more problems.

The hot air riser tube running to your air cleaner snorkel will help during warm-up but if it's working properly, once the flapper valve warms up it should shut off hot air flow and pull in cool air.