What do you mean "older" engine? It's only 18 years old! Does this mean I have my foot in the grave before 30?
Uhhh... hate to break it to you! Actually, I've got you beat by a couple decades, sounds like.
49 Dodge - I'll bet that's a tough old workhorse!
Clean and white plugs actually would be consistent with an engine that's stumbling because of too lean mixture under acceleration.
Turns out there are not one but two accelerator pumps on your carb - the primary, on the side of the carb with a lever that pushes on a diaphragm (4 mounting bolts) and the "auxiliary acceleration pump" opposite the primary that has 3 mount bolts. The primary provides extra fuel when accelerating, the auxiliary is vacuum actuated and provides extra fuel when the motor is cold.
There's also a "power piston" inside that you can test to be sure it moves freely by pushing on it with your finger (once you have the carb part way disassembled.) That and the auxiliary acceleration pump's diaphragm sounds like the two most likely suspects for your symptoms. You can check the AAP's diaphragm with the carb in place, according to the author of the first site linked below.
It sounds like many 22R owners have successfully rebuilt their carbs, so it may be worth attempting. The only kits worth bothering with, apparently, are NAPA's. Even the dealer apparently recommends them. They have carb-specific kits (you'll need to give them the number off the tag (probably aluminum tag) that's attached to your carb. Other rebuild kits are generic and will lack some of the parts you need. Several of the carb's diaphragms apparently are included with the kit. Of course, any time you remove a carb, you'll need a fresh mounting gasket.
Also, very important to use proper torque in all areas of a carburetor - it's easy to overtorque the carb screws since the threads are fine and the aluminum soft. I'm not sure of the torque specs on your carb but most carbs specs are measured in inch/pounds instead of ft/lbs. Typical carb screw specs are (all in inch/lbs) 30-40, 40-50, 45-55 (divide by 12 to get ft/lbs). The carb mount nuts take more torque than the assembly screws, of course. Having said all that, the first thing I do to an old carburetor is run around and tighten all the screws I can reach as they tend to get leaky with age. So how's that for a bunch of contradictory hogwash!
I recommend cleaning the outside of the carb with carb cleaner before removing it - the less grime there is to contaminate the carb the better.
After disassembly, I like to use the gallon cans of parts cleaner - there's a wire basket in there so you can lift the parts out after their bath. Watch where you spill it - stuff will soften any sealant & won't do your paint any favors, either.
Here are some links:
An excellent owner Aisan carb faq site, but for an '86:
Thread on accel feature of Aisan carbs:
To adjust the float height, there are tabs that you bend. Autozone has a good write-up
on it in one of their Vehicle Repair Guides, but now they require registration to get to it. Here's an old copy from the internet archive, unfortunately without the pics:
Float and Fuel Level
See Figures 8, 9 and 10
Float level adjustments are unnecessary if the fuel level falls within the lines on the sight glass when the engine is running. The sight glass is located on the side of the carburetor and is literally a window to the float bowl. Removing the air cleaner is usually required for access, although it can be done with an extension or dental mirror.
With the carburetor off the engine, there are two float level adjustments which may be made. One is done with the air horn inverted, so that the float is in a fully raised position; the other is with the air horn in an upright position, so that the float falls to the bottom of its travel.
The float level is measured either with a special carburetor float level gauge, which comes with a rebuilding kit, or with a standard wire gauge.
Fig. 8: The sight glass is located on the side of the carburetor
Turn the air horn upside down and let the float hang down by its own weight.
Using a special float gauge SST 09240-00014 or equivalent, check the clearance between the tip of the float and the flat surface of the air horn. The clearance should be 0.386 in. (9.8mm).
This measurement should be made without the gasket on the air horn.
If the float clearance is not within specifications, adjust it by bending the upper (A) float tab.
Fig. 9: Bend portion (A) of the float to achieve a 0.386 in. (9.8mm) gap
Lift up the float and check the clearance between the air horn and the float bottom. A Vernier caliper works well for this measurement. The clearance should be 48mm (1.89 inches)
If the clearance is not within specifications, adjust it by bending the lower float tab (B).
Fig. 10: Bend portion (B) of the float to set 1.89 in. (48mm) of clearance between the air horn and the float bottom
There is an interesting alternative to rebuilding your Aisan: a Weber conversion. Of those who have taken this route, some are satisfied and some dissatisfied. Apparently they are tough to tune. Cost is about $300, but once you get it properly tuned, you have a brand-new carburetor that will likely help your truck to run right.
There are two Weber carbs that can work well with a stock 22R. Both are progressive 2-barrel carbs. Progressive meaning the primary barrel opens first, and the secondary opens when you stand on the throttle a bit, giving extra cfm. The first carb is the 32/36DGEV (32 mm primary bore/36mm secondary) and the other is the 34DGEC which has 34mm primary and 34mm secondary.
The 32/36 gives better mileage, but if you have a heavy foot, not so much. Power is probably similar or a bit better than the Aisan, but the two carbs have nearly identical cfm. The 34/34 is a bit newer design, and gives more pedal response than the 32/36. Supposedly because the primary is larger, the secondary doesn't tend to open as frequently as with the 32/36. It's supposed to have better driveability. The cfm of both Webers and the Aisan appear nearly identical.
There is a 38/38 Weber available but it would be pointless to put that on a stock motor.
Pros of the Webers include:
- New carb, runs better than a raggedy stock
- Better gas mileage (most likely with the 32/36 - so long as you don't have a lead foot but there are reports of slightly better mileage with the 34/34 too.)
- More power (how much is hotly debated)
- Relatively easy and cheap to re-jet to adapt to higher elevations vs. nearly impossible rejet of the Aisan. I think almost everyone at 5000' elevation or more would do better with a properly-jetted Weber.
- You replace the gangly air cleaner with a much more compact one
- Most of the 32/36 Webers conversion kits include a 2 piece adapter plate that is notorious for leaking (but Summit Racing sells a one-piece adapter)
- In some cases you have to go through a painful period of finding the right size jets and tuning it properly
- Some people have trouble with flooding - solution seems to be adjusting the fuel bowl float height.
- Some people claim the stock fuel pump has too much pressure and that makes the weber run rich, and therefore the solution is to buy an electric fuel pump and fuel pressure regulator, obviously adding to the $$ and hassle. Other people say the stock pump works fine.
- Some people report it doesn't do well on inclines, especially on side hills. Other owners report it works fine on hills.
Some Weber links (by the way if you decide to try a Weber conversion I've read not such good things about jtoutfitters.com (on ebay as joetlc):
89 Pick Up - Life Of Carb??
22r Aftermarket Carbs
A one-piece adapter for the 32/36:
Seems like it might be worth giving the Aisan rebuild a try. At lower elevations the Webers don't seem to offer that much over a properly functioning Aisan.
Hope you'll keep us posted on your progress.