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A couple of weeks ago a big puddle under my truck and some investigation alerted me to the need to change the intake manifold gasket on my F100. Seems the rear seal on the china wall had failed.
Specifics:
1977 F100, 302, Motorcraft 2150, automatic, stock engine, intake manifold, and most everything else as far as I can tell (with the exception of a non-working dealer installed AC system), and 153K (or 253K?) miles.
After pulling the manifold (and the valve covers, as I couldn’t be sure where the leak was coming from) and cleaning everything up, it looked so nice I figured I’d rebuild the Motorcraft 2150 carburetor as well.
Before After
I thought this comes just a shade shy of my ‘never tinker with more than one thing at a time’ rule.
However, in the process of reassembling the carb, I noticed the accelerator rod was on the 4th, (top) hole. Everything I read indicated the rod is supposed to be in the 3rd (counting up from the bottom) hole for a 302.
Originally in the top (#4) hole
I also noticed the choke rod linkage was in the ‘STD’ slot.
'STD' and 'ALT' choke settings
Thinking that I’m at 7,200 feet at the top of my driveway, and I work about 18 miles away at about 6,100 feet, and the sticker on the valve cover seemed to use 4,000 feet as the cutoff for being at altitude, I decided to completely ignore my ‘one thing at a time’ rule, and put the choke rod in the ‘ALT’ slot, assuming it was ‘ALTITUDE’.
I put the carb back together with the accelerator rod in hole #3, and the choke rod in the ‘ALT’ spot.
The truck now seems to run a little on the rough side, and there’s a bit of hesitation when accelerating (both from a stop and after coasting). I should point out the idle seems just fine, and the cold start is great – ‘pop’ the pedal to close the choke and it starts very quickly.
I know I can easily put the two things I changed back to the original configuration: hole #4, and the ‘STD’ slot, and see if this clears up the problem(s).
My question is this, is hole #3 and ‘ALT’ correct for my altitude, and should I try to diagnose the rough running because something else needs adjusting/replacing, or just put it all back the way it was and if that clears up the rough running and hesitation count myself lucky?
Also of note, I’m using the truck to commute to work and putter around town. No extended trips, and no racing up and down the roads – I’m not sure I’ve ever been faster than about 65mph in the thing, yet. I have still not bought a tach, so I adjusted the carburetor mix screws using a vacuum gauge on the manifold t. I was able to pull about 14-15 lbs with a steady needle and behavior consistent with the revving the engine and the vacuum reading guide(s) I have for reference. This may be a bit low, but it’s what I’d been able to get before the intake manifold gasket gave out. Timing is at 10* BTC, as before.
Any advice or suggestions is, as always, appreciated!
That's called an overtravel lever, the one connected by the pump rod, the correct position is based on the temperature. It changes the amount of "pump shot" or extra squirt of fuel the carburetor accelerator pump provides every time the accelerator is pressed, to prevent a bog or hesitation.. In warmer weather less pump shot is needed, so it's a seasonal or climate adjustment. Info I have is for the 2100 but is no doubt similar. Hole 3 (second from top) is used when temps are 40° to 80° F, the top hole or #4 is used below 40°, hole 2 is used above 80°.
At the front of the carb, the other end of the pump rod, is another link, with two holes, the inboard position will tend towards providing more fuel overall than less. If you have the shop manual or a Autolite/Motorcraft carb manual it's chock full of stuff like this, these carbs are simple but there are a fair number of settings to be made. It probably depends on application, gearing, etc. Choke setting I'm not sure. There's usually a procedure using a 1/8" drill bit to set the choke plate clearance when closed iirc. This is an important one too. The way a carb choke works, for startup it doesn't so much cut off the air but it really increases the amount of fuel that is pulled from the well, it needs a certain opening clearance to work right. If you dig around the intertubes I bet you can find an old school copy for your carb in .PDF.
Thanks for the information!
I'm getting that I'm just going to have to set the overtravel level, or leave it as is, and see how it runs. In Colorado, where I'm at, it can be in the 20's when I leave for work in the morning, but in the 50's-60's by the time I head home. I really can't see swapping between holes #3 and #4 on an almost daily basis, based on the temperature changes, especially during the fall and spring seasons....
Maybe I'll just change it twice a year?
I'll have to see if I can dig up a manual for my carb. I do have the FSMs, so maybe digging through them some more might help.
And yes, I do enjoy tinkering, but not on the side of the road when it's bone-chilling cold out, dark, and with a stiff wind blowing. That's more 'cursing and shivering' as opposed to fun.
A little rich would be preferable to a bog or hesitation, but it's worth experimenting, too rich can do the same thing. A lot of things have changed over the years, including the fuel, and maybe your engine has a different cam, possibly a little different ignition timing, a dual exhaust that breathes a little better etc. So see what works for you.
Altitude, you mentioned that, also plays a role in power valve #, a lot of people overlook this. Everyone has usually heard about jetting changes, but a lower opening PV number is used at higher elevations.
However, in the process of reassembling the carb, I noticed the accelerator rod was on the 4th, (top) hole. Everything I read indicated the rod is supposed to be in the 3rd (counting up from the bottom) hole for a 302.
What did the REBUILD KIT INSTRUCTION SHEET say about the setting(s)? That is what you go by. You only deviate if you have performance problem(s).
That's called an overtravel lever, the one connected by the pump rod, the correct position is based on the temperature. It changes the amount of "pump shot" or extra squirt of fuel the carburetor accelerator pump provides every time the accelerator is pressed, to prevent a bog or hesitation.. In warmer weather less pump shot is needed, so it's a seasonal or climate adjustment. Info I have is for the 2100 but is no doubt similar. Hole 3 (second from top) is used when temps are 40° to 80° F, the top hole or #4 is used below 40°, hole 2 is used above 80°.
At the front of the carb, the other end of the pump rod, is another link, with two holes, the inboard position will tend towards providing more fuel overall than less. If you have the shop manual or a Autolite/Motorcraft carb manual it's chock full of stuff like this, these carbs are simple but there are a fair number of settings to be made. It probably depends on application, gearing, etc.
That is some very interesting information. I always wondered what those different settings would do. Thanks!
I tried to find everything I could for references, but I never did come across a Motorcraft carb shop manual. The rebuild kit from Sorensen (96-551), came with the Fuel System Service Instruction Worksheet GF3701-9. There is nothing in the instruction sheet defining the ‘STD’ and ‘ALT’ hole markings on the choke rod lever. I couldn’t find anything definitive, but most of the rebuild guidance I could find online indicated ‘ALT’ is for altitude.
The specifications data on the worksheet shows using hole ‘B’ for a 1977 302. However, the note in Fig. B, Pump Rod Adjustment, does state, “Note: Winter Use: Increase length of stroke (Holes C, D); Summer Use: Decrease length of stroke (Holes A, B)”. No definition of ‘winter’ or ‘summer’, but I’ll use Tedster9’s temperate ranges as a guide.
Anyway, I wound up running some trial and error tests on my commutes to and from work.
First I moved from the ‘ALT’ hole to the ‘STD’ hole, and it seemed to run/idle a bit better, but the hesitation was still there.
Next I moved the pump rod from hole 3 to hole 4. Another improvement, but still not satisfactory.
Then I moved a back to the ‘STD’ hole, leaving the pump rod in hole 4. Better yet, but still with the hesitation.
I finally readjusted the wet float level and the hesitation went away!
The only problem I continued to have was a surge at low speeds, but I think that’s timing related and I asked for advice about that in another post (have to update that next, as I managed to fix that and now it's running idling, accelerating, a cruising just fine at all speeds).
Thanks again for all the advice and knowledge, guys!
Hopefully this might help someone else who may run into the same problems.
11-15-2018, 04:34 PM
