Choke

[LFD1935]

35 B series fire engine. We continue to make progress with the old girl. One thing we can not figure out is the choke. The truck is happiest running at a quarter choke. Idles nice, runs fine. If I push the choke in, it stalls out. We have replaced the choke cable, Carb was rebuilt to factory spec (Zenith side mount down draft), fuel lines cleared, new fuel filter, fuel pump torn down and cleaned, fresh fuel, we also checked that the choke mechanism is functioning correctly. 

So the question is, do we continue to try and solve the issue or just accept that this is where she is happy and move on? It was suggested that we cheat the choke cable and set the quarter open as closed. Thoughts?

[j hancock]

I am not familiar with the carb on your particular truck but most carbs have an idle mixture screw.  Since it seems happier with a little choke sort of indicates it is running lean.  You can try "unscrewing" the idle mixture screw by 1/4 of a turn and see how it runs.

One thing that would be good is to get a notebook and record EVERY adjustment made.  If the carb shop didn't supply info about the number of "turns" on the adjustment screws, GENTLY screw the adjustment in and count the turns so you can reset it if necessary.  Let's say it is 2 turns to seat the idle screw.  Try 2 1/4 back out.

[HarryS]

Sounds like you may have a vacuum leak. Just saw J Hancock's post. Try that first if no change check vacuum system. Good Luck.

[fxfymn]

My vote is a vacuum leak also. Try spraying the intake side with ether. You will hear a substantial difference in the way it runs if the ether gets sucked into the leaking area. If it has a brake booster you need to check that and the lines running to it, especially the filter if so equipped, and depending on the pump you may have vacuum lines running there as well. A quick check would be to block the vacuum lines running to those areas to see if it makes a difference.