’78 International Scout II – Part 4a Fuel and Air Delivery

In carburetor, international harvester, project truck, scout on January 11, 2015 at 5:09 am

Let me start this episode by saying that when I began this next project I knew nothing about carburetors.  I now know slightly more but still very little.

At some point this truck has to pass California emissions testing.  On a side note you can look up the emissions test results for any car or truck in California as long as you know the license plate number or VIN.  License plates do change on occasion so the VIN is the better option.  My truck has failed many more emissions tests than it has passed.  At one point it even failed due to suspected tampering of emissions equipment.  On average it probably fails twice before passing each time it was required. It did pass the emissions test that was required to sell it (to me) after only one fail.  So that’s a positive I guess.  I removed a Crane multi-spark ignition from the Scout and replaced it with an OE style distributor.  I now have a tachometer that works but from an emissions stand point this is a step backwards.  The multiple sparks of the Crane help burn more fuel so that your vehicle runs cleaner and makes a little more power. Essentially I am saying that I have my work cut out for me.

The Scout idled at about 2200 rpm and you could smell that it was burning rich (to much fuel for the amount of air).  I cracked open the shop manuals and discovered that the truck was supposed to idle at about 650 to 675 rpm (and red-line was about 3800).  2200 was WAY to high.  It did mean that you could just lift off the clutch without having to worry about giving it any gas regardless of what gear you were in though.  So there is that.  Anyway, I needed to adjust it down.  I didn’t know how to do that but I opened the manual and learned just enough to be dangerous.  I discovered that there is a curb idle speed, a fast idle speed, and a high idle speed.  One is supposed to be in neutral after the car has warmed up, one is in gear but not moving, and one is at start up with a cold engine.  There were a lot of diagrams that didn’t mean much to me but I did find a couple of screws that were labeled idle adjust, one for each barrel (it is a two barrel carburetor).  It turns out that these are the air/fuel mixture adjustment screws rather than an idle speed adjustment screw but I didn’t know that at the time.  Adjusting them does change the idle speed as it changes the amount of fuel that gets injected into the incoming air stream.  I was able to get the idle speed down to about 1500 but any lower than that and it would die on me.

I did a little more reading and discovered that fuel leaves some deposits behind when it evaporates and those deposits can clog up the inner workings of a carburetor.  My truck ran until I replaced the distributor.  Then it sat for two years.  Deposits were a strong possibility.  I decided that I would take the carburetor apart and clean it up.  I took a few photos of everything as it was so that I would be able to put it back together.

Scout Old Carb (4) Scout Old Carb (5)

As it turns out there a few problems that you can see right away.  I didn’t know about them at the time or at least didn’t realize their importance.  The first you can see in the second photo.  There is a rectangular box about half way up the side of the carburetor.  That box has a vacuum sensor in it.  You can see it in the photo.  It is a small silvery circle in the right side of the box.  That box is supposed to have a cork gasket and cover over it.  The second problem is the decaying rubber vacuum plug that you can see just under the box.  It is in bad enough shape that it leaks air.  The third problem is the port next to it.  This to run a line up to the air filter box that sits on top of the carb.  Mine doesn’t actually use this so it should also be capped.  You can also get a sense of how dirty it is.  Apparently the guy who owned it before me does a lot of wood working as I found just about all the exterior nooks and crannies stuffed full of sawdust.

I just did the bare minimum of disassembly.  I didn’t have a rebuild kit and didn’t want to pay for one if I could avoid it.  Mostly I just wanted to get access to the fuel bowl and clean the ports leading in and out of it.  I figured that would be the prime location for deposits left by evaporation.  I did my cleaning, put it back together, and reinstalled it on the Scout.  I was able to get the idle rpm down to about 1300.  I needed to be at half that.  This was the point that I decided I needed a rebuild kit.  Of course nobody had one in stock so I had to order one.

In the mean time I had a couple of other small projects to take car of.  The first was bolting down the drivers seat.  It had a couple of bolts in on the right side but none on the left side.  So when I made a u-turn at the end of the block the night before the seat tipped over.  Not exactly safe.  The second project was seat belts.  I had discovered that I did in fact have seat belts for the Scout.  I didn’t think I did, but I found some in amongst the box of spare parts.   I had one for the driver and the both belts for the back seat.  I got those installed and bolted down the seat.  I also ordered some gaskets, pig tails (the socket and wiring), and a lens for the side marker lights.

A couple days later I had the rebuild kit.  I took the carburetor of the engine again and started to disassemble it.    I discovered that it badly needed to be rebuilt.  Here are the photos.

Scout Old Carb (3) Scout Old Carb (2) Scout Old Carb (1)

You can see in the first photo just how bad that gasket is.  And because it is so bad water has gotten into the carb and rusted the butterfly valves.  I didn’t take it apart farther than this.  I didn’t need too. That was enough to discover that the rebuild kit was not the correct one.  It seems that parts stores have retroactively decided that 78 and earlier Scouts used a Holley 2345 carburetor even though it was used until 1979.  My Scout came with a Holley 2110c.  The gaskets are completely different.  Some of the smaller o-rings will work but that is about all.  I did a little more reading and determined that nobody really sells rebuild kits for my carb.  One poster on an International Harvester forum said that you now need 3 different kits to get all the stuff you need to rebuild a 21xx series carburetor.  I said to heck with that, returned the rebuild kit, and ordered a complete rebuilt carburetor.  The new carb was supposed to be completely set up so that you just had to install it, hook up the throttle and choke linkages and start the truck.  Idle, choke, and throttle mixture where supposed to be adjusted at the factory.


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