I have3406c mechanical engine boost won't come up till 1500 rpm

Id be getting the governor weights, pins, and the thrust bearing that the 4 Weights all share.

 

It sounds like the air to fuel ratio is adjusted a bit too lean. It is easy to adjust.
This is not a PEEC engine, but mechanical, correct?
Oops, re-read title, mechanical.

 

Kinda a far out there, but with super cold temps cold you get an ice chunk restriction in your afrc tube if intake temps stayed low? Just a thought and easy check.

 

I played with the adjustment on one of my B models to see how the a/f ratio adjustment affects smoke. If you go to "lean" (trying to get less smoke) you will not be able to gain speed even bobtailing. There is a point where you wait and wait and wait to finally get enough boost to allow more fuel, and then it will take off, which sounds like the symptom that OP has.

I didn't play with the adjustment the other way, because I can get mine to smoke just fine as it is. Adding more fuel without boost doesn't seem to me as if it would give much benefit.

I know, if one is delicate with the right foot there is no need to control it with the a/f ratio, but there are times when I temporarily loose that discipline!

 

Totally agree with you Oxbow! Didn't know if this just started with OP in cold weather.

 

It sure seems odd unless he had recent work done and the adjustment was out. Your explanation is plausible I suppose in extremely cold temperatures.
Isn't there a diaphragm in the a/f? I wonder if it could have a pin whole in it. If the diaphragm was shot it never would open the fuel up would it?

 

Pin hole would do it for sure too! I would agree it somewhere in the air to fuel control. Hope we get an update from OP.

 

I don't see how he would get full boost with a pin hole in the diaphragm.

 

With that boost number, I was assuming that this engine was not at stock settings on pump rack screws and afrc adjustment. If this was case, it would never need as high boost number for higher rack travel. Less pressure on diaphragm (pinhole, not tear) would tack longer for more fuel increase and would result in longer for boost to build was my thinking. Guess should never assume it has been tampered with.