I will first apologize if you are sitting there thinking...."oh no.....more???", but, I could use some help. I've reset the idle mixture screw back to 1 1/2 and then tweaked it via vacuum reading and idle speed while in idle drive. It is pretty steady at 15" and just slightly more lean, the engine wants to stumble. I believe I it's heading the right direction. I notice that as soon as I blip the throttle a little, it's responsive and you can see the power piston come up which puts the tip in the jet. But it seems to still be a little too rich because when I disconnect the accelerator pump and blip the throttle, it seems slightly more responsive. A very light push on the the throttle pump, and pushing it down just a minor amount of about 1/4 inch, the engine wants to die which tells me that the idle is still too rich. I am thinking that a smaller diameter jet will correct this and possibly improve the cruise response. Thoughts?
I guess I missed a prevoius thread with what kind of carb? Most carbs used on hamb; changing the "jet" is the main jet, which does not affect idle mix
It's a varajet 2se. I guess I am a little confused. Maybe what I mean is the off-idle mixture is rich? Based on the diagram of the 2se, there are two points of feed for the fuel through the bowl too the idle ports in the bore. One point is an adjust part throttle screw that is used on the fixed metering rod hanger carbs. The adjustable metering rod hanger type carbs do not have this adjustable part throttle screw, in which case, fuel to the idle ports is fed via the main metering jet. On the carbs with the adjustable part throttle screw, fuel is fed through the main jet, and through the bottom of the float bowl and past the adjustable part throttle. see the picture added:
Unless it has been heavily modified a stock Rochester Varajet 2se is going to be always lean. Put you hand or a shop rag over the primary and see if the vacuum or rpm increases. The 15"hg is low on a stock motor. What happens if you advance the ignition timing? Run at 2000-2500 and advance timing to highest vacuum and retard .5 to 1 inch of mercury. Now what happened to the stumble?
But it seems to still be a little too rich because when I disconnect the accelerator pump and blip the throttle, it seems slightly more responsive. A very light push on the the throttle pump, and pushing it down just a minor amount of about 1/4 inch, the engine wants to die which tells me that the idle is still too rich. Thoughts?[/QUOTE] By pushing on the accelerator pump the carb should be running rich . That is made so when you hit the throttle , it gives extra fuel to the carb to make up for the sudden need for it . It really sounds like the carb is running fine by what you are saying . I missed the first post but can you tell us exactly what is wrong that you are having problems with ? Retro Jim
To interstatemaster: The 15" I mentioned was with the idle screws adjusted for max vacuum with the engine in Drive. In park at idle, it's running about 17". (note: I am at an altitude of about 2800 feet above sea level.) My ignition is set per the label, 12 degrees. I've also seen same make/model trucks with labels stating 8 degrees. I'm not sure why my truck is 12 degrees unless it's an altitude thing. I will do as you suggest and see what happens. Out of curiosity, should I set the timing to get the most vacuum, then back off an 1" or so then peak the idle mixture? Can you give me more information as to how you know that varajets run lean? I am just asking because I've not really found anyone who knows these and actually seem to know what they are talking about. To Retro Jim: I am confused though by the amount of gas being provided by the idle circuit. I've read, (from a Lars Grimsrud paper), that if you disconnect the accelerator pump from the throttle assembly, and blip the throttle so that the plate opens and the pump does not move, you would see a seemingly better response if the idle mixture is rich. I suppose that blipping the pump without moving the throttle plate would create a significantly rich situation.
OK, so I've done the "timing by vacuum" thing and am pretty much back to where I began for all the trouble began. Initial timing is now at 14 instead of 12 and is sounding better than it did. I think at this point, I need to start focusing on rebuilding the 3.4l block i've got instead of trying to continue to make this old engine run better. I should not complain really as I am averaging about 21 mpg with the a/c running constantly.
The Jalopy Journal
