Good evening, all. I hesitated to retread a well-documented subject, but spent the last couple mornings troubleshooting when the truck is fully "cold" and welcome suggestions.
Over the past weeks, temps have fallen here in Nor Cal. Not "real" cold, but the nights have dipped into the high 20's F over the past week in my area.
In the pre-dawn hours as I start up to head to work I've noticed some changes over the last couple of weeks:
Normally, my cold starts are pretty smooth, but in the summer months, I dial back my cold idle. I figured with the cold, I should bump it back up to the emissions sticker recommendations. Before I did, I fulfilled the entire (I think) choke check:
*Pull off Check- Checked and adjusted pull-off clearance to a sharp 3/32"
*Re-indexed fast idle (it wasn't far off, but now it's now spot-on the "V" on the cam after the adjustment above)
*Set fast idle speed (a high of 2k according to my emissions sticker)
*Choke cap index- I returned it to the spot it was prior to my 90 degree turn for fast idle index- between hash mark 1&2 on the rich side
*I tested voltage to the choke cap (reads 7v)
*I verified the choke stove tube to the manifold is sound
*I've verified my air intake vacuum motor is working properly (closed and pulling from the 2" air duct to the manifold, although don't believe that would affect the first cold start of the day)
*checked to make sure linkages aren't binding.
Generally, I just need to move the key to "on", pump the pedal once, and turn the key to start the engine and it idles just fine through the warming cycle. It catches on the first turn over.
Over the last few days though, it's catching, trying to run up the RPM's, but then dying within the first 2 seconds. It takes about 4 tries until it finally idles as it should. I can feather the gas and bypass the single- pump choke set, and it'll run fine, too. No other issues with acceleration hot or cold at any speed.
Rolling the choke cap richer doesn't make a difference. I've watched the choke close, pull-off work correctly, and open through the warming cycle with my son starting, so I I'm puzzled.
Could I be dealing with a float issue? Maybe winter gas formulations are messing with 80's settings? Anything I'm missing?
Mark - I'm not sure I understand what you mean by "I can feather the gas and bypass the single- pump choke set, and it'll run fine, too." But, if you mean that you can pump it a bit while it is wanting to die and it'll run then I understand.
And if that's the case I think you have the pull-off opening the choke too much. I say that because that's about all that can overcome dialing in more choke, which you said makes no difference. The pull-off can overpower the choke's bi-metallic spring, regardless of how far you turn the choke housing.
So I'd back off on the pull-off a bit, maybe to 1/16". And actually, there's nothing magic or precise about those measurements. They are really to get you into the ball park, but each vehicle is slightly different, so you have to fine tune from the factory settings if you want things to work spot-on.
Thanks Gary. Yes, that's what I meant. I can lightly pump it and keep it going. However, prior to the last couple of weeks, I could start with the single pump that closes the choke and sets the fast idle cam.
I'll adjust the pull off and reset the index again tomorrow before the tribe is out of bed or when everyone is swadging, and report back.
Raw fuel on the floor of the intake won't hurt, but I'm pretty sure that the pull-off is opening the choke too much as that fits the symptoms. And I'll bet that just before the engine dies it tries to run again since as it stalls the vacuum drops and that closes the choke a bit.
I really like the vacuum pull-off on a carb as it provides a feedback loop - lots of vacuum says the engine is running well and that opens the choke more. But if you have it set too aggressively it'll kill the engine rather than make it run better, and there's nothing you can do with the choke adjustment to fix that. In fact, in my experience it is better to have too little pull-off than too much.
One item related to the choke pull-off diaphragm, some later (80s model) Autolite 2150s had a staged pull-off, where the pull-off has a spring loaded link that can be pulled out further by a higher load. On these, there is no adjustment spec for the initial opening, the spec is for the full portion.
See if your pull-off has this design, rather than a simple slotted piece the link slides in it will have a barrel with the slotted section coming out of it and you should be able to pull the slotted portion further out. If it does, recheck the setting with the spring loaded portion held in as far as it can go. If this is the style pull-off that should solve the problem.
I used to keep a hand vacuum pump on the bench where I did my rebuilds as so many of the later carbs were finicky on vacuum pull off settings (I really loved the dual pull-off ones, NOT!).
"Getting old is inevitable, growing up is optional"
Darth Vader 1986 F-350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator
Wife's 2011 Flex Limited
Daily Driver 1994 Taurus LX
Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413
Thanks Jim- that's funny. We *do* get scolded when we use mowers and blowers on Spare the Air days.
I don't see smoke on shifts, at quick WOT sprints or even loaded with 1/2 yard of gravel last week when I was using the engine to brake on the hills towards home.
But now that you mention it, I'll be paying closer attention. I don't use much oil between changes at a 3k OCI. What little that goes seems to be about equal to what I catch out of my timing cover. That's an upcoming project when I don't need to be anywhere for a day or two and I'll be checking in for advice prior.