Brandon Ott

My 300 i6 runs terrible (low rpms and sputters, eventually dying) during cold/humid weather. We recently moved from Texas to Colorado. It had the same issue in Texas as it does now. I adjusted the carb and tinkered with the timing but with no result. I have noticed the carb tends to ice badly and I have to stay on the throttle about half way to keep it running. I did notice a tube that goes to the exhaust manifold up to the top of the carb, which I assume is some sort of heater. Could this be my issue? It also seems to run rich, as I noticed a strong gas smell when I parked it after a short drive today. Any tips for fuel ratio adjustment as well? I'm afraid to go too lean and damage anything. Any advice?

raski

Icing of carb is prevented by introducing some heated air with the intake air.Some older carbs use a small metal tube to heat the carb or a butterfly valve at the exhaust manifold which seizes..I believe on yours, there should be a door within the air snorkel which is attached to a vacuum motor on the intake snorkel. Many times the heat shield which is bolted to the exhaust manifold rusts away or the heated air tube attached to it falls off and there is no heated air coming in. Not sure which system you have but this information is something to look at.

Brandon Ott

I believe it has both. Im not sure if the exhaust heat riser works or not but I know the flap in the intake is broken. It isnt siezed it just stays open all the time. I cant find any diagrams to see if the vac lines are in the right spot or not. Could it be the little valve at the top of the air cleaner that the lines go to? If so is there a name for the part? As for the heat riser, is it replaceable or is the solution a nee manifold?

raski

I would fix that broken flap, you are getting a hot and cold mix of air and that might not be warm enough to keep the moisture down. You can check the vacuum motor by removing the vacuum on a cold engine and see if vacuum is present and the door closes when vacuum is removed. This applies once you get that stuck/broken door replaced.

maco

If I'm remembering correctly....there is 1 for sure & sometimes 2 steel 1/4'' vaccum lines...
They are attached vertically top & bottom to the exhaust manifold @ (maybe 2-3'' from the tailpipe connection) the one on top faces up & down it goes to the input of the automatic choke.
It also was warped in a brown/grayish heat insulating material..... It via slight vaccum sucks warm air from exhaust manifold into the choke housing of carb & should eventually kick off the high richer idle.......
we used to drill & blowout the holes top & bottom to accept new lines.....bottom hole is horizontal & is the input air side of this system....We sometimes didn't put in a new line into the bottom hole......I think this line picked up air from the air cleaner vs the real cold air from outside.....
As others explained it also had a pickup warm air system going to the air cleaner........basically there was a heat shield around the exhaust manifold under the carb.....And via a + 2'' silver flex tube went to the snorkel end of the air cleaner.....The snorkel end of air cleaner had a vaccum control to open & shut to restrict or allow warmer air to enter system....
At best anything over 5-6 years old had one or all of the systems fail due to rust etc & required attention....
others mentioned vaccum motors....I believe any vaccum was picked up directly from the engine itself (no separate motor)

Been over 3 months since I last had a 300 6.....so don't remember everything exactly but this is the drift of the system....."GoodLuck"